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Diffstat (limited to 'gnu/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp')
| -rw-r--r-- | gnu/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp | 2959 |
1 files changed, 0 insertions, 2959 deletions
diff --git a/gnu/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp b/gnu/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp deleted file mode 100644 index 5a67178cef3..00000000000 --- a/gnu/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp +++ /dev/null @@ -1,2959 +0,0 @@ -///===- SimpleLoopUnswitch.cpp - Hoist loop-invariant control flow ---------===// -// -// The LLVM Compiler Infrastructure -// -// This file is distributed under the University of Illinois Open Source -// License. See LICENSE.TXT for details. -// -//===----------------------------------------------------------------------===// - -#include "llvm/Transforms/Scalar/SimpleLoopUnswitch.h" -#include "llvm/ADT/DenseMap.h" -#include "llvm/ADT/STLExtras.h" -#include "llvm/ADT/Sequence.h" -#include "llvm/ADT/SetVector.h" -#include "llvm/ADT/SmallPtrSet.h" -#include "llvm/ADT/SmallVector.h" -#include "llvm/ADT/Statistic.h" -#include "llvm/ADT/Twine.h" -#include "llvm/Analysis/AssumptionCache.h" -#include "llvm/Analysis/CFG.h" -#include "llvm/Analysis/CodeMetrics.h" -#include "llvm/Analysis/GuardUtils.h" -#include "llvm/Analysis/InstructionSimplify.h" -#include "llvm/Analysis/LoopAnalysisManager.h" -#include "llvm/Analysis/LoopInfo.h" -#include "llvm/Analysis/LoopIterator.h" -#include "llvm/Analysis/LoopPass.h" -#include "llvm/Analysis/MemorySSA.h" -#include "llvm/Analysis/MemorySSAUpdater.h" -#include "llvm/Analysis/Utils/Local.h" -#include "llvm/IR/BasicBlock.h" -#include "llvm/IR/Constant.h" -#include "llvm/IR/Constants.h" -#include "llvm/IR/Dominators.h" -#include "llvm/IR/Function.h" -#include "llvm/IR/InstrTypes.h" -#include "llvm/IR/Instruction.h" -#include "llvm/IR/Instructions.h" -#include "llvm/IR/IntrinsicInst.h" -#include "llvm/IR/Use.h" -#include "llvm/IR/Value.h" -#include "llvm/Pass.h" -#include "llvm/Support/Casting.h" -#include "llvm/Support/Debug.h" -#include "llvm/Support/ErrorHandling.h" -#include "llvm/Support/GenericDomTree.h" -#include "llvm/Support/raw_ostream.h" -#include "llvm/Transforms/Scalar/SimpleLoopUnswitch.h" -#include "llvm/Transforms/Utils/BasicBlockUtils.h" -#include "llvm/Transforms/Utils/Cloning.h" -#include "llvm/Transforms/Utils/LoopUtils.h" -#include "llvm/Transforms/Utils/ValueMapper.h" -#include <algorithm> -#include <cassert> -#include <iterator> -#include <numeric> -#include <utility> - -#define DEBUG_TYPE "simple-loop-unswitch" - -using namespace llvm; - -STATISTIC(NumBranches, "Number of branches unswitched"); -STATISTIC(NumSwitches, "Number of switches unswitched"); -STATISTIC(NumGuards, "Number of guards turned into branches for unswitching"); -STATISTIC(NumTrivial, "Number of unswitches that are trivial"); -STATISTIC( - NumCostMultiplierSkipped, - "Number of unswitch candidates that had their cost multiplier skipped"); - -static cl::opt<bool> EnableNonTrivialUnswitch( - "enable-nontrivial-unswitch", cl::init(false), cl::Hidden, - cl::desc("Forcibly enables non-trivial loop unswitching rather than " - "following the configuration passed into the pass.")); - -static cl::opt<int> - UnswitchThreshold("unswitch-threshold", cl::init(50), cl::Hidden, - cl::desc("The cost threshold for unswitching a loop.")); - -static cl::opt<bool> EnableUnswitchCostMultiplier( - "enable-unswitch-cost-multiplier", cl::init(true), cl::Hidden, - cl::desc("Enable unswitch cost multiplier that prohibits exponential " - "explosion in nontrivial unswitch.")); -static cl::opt<int> UnswitchSiblingsToplevelDiv( - "unswitch-siblings-toplevel-div", cl::init(2), cl::Hidden, - cl::desc("Toplevel siblings divisor for cost multiplier.")); -static cl::opt<int> UnswitchNumInitialUnscaledCandidates( - "unswitch-num-initial-unscaled-candidates", cl::init(8), cl::Hidden, - cl::desc("Number of unswitch candidates that are ignored when calculating " - "cost multiplier.")); -static cl::opt<bool> UnswitchGuards( - "simple-loop-unswitch-guards", cl::init(true), cl::Hidden, - cl::desc("If enabled, simple loop unswitching will also consider " - "llvm.experimental.guard intrinsics as unswitch candidates.")); - -/// Collect all of the loop invariant input values transitively used by the -/// homogeneous instruction graph from a given root. -/// -/// This essentially walks from a root recursively through loop variant operands -/// which have the exact same opcode and finds all inputs which are loop -/// invariant. For some operations these can be re-associated and unswitched out -/// of the loop entirely. -static TinyPtrVector<Value *> -collectHomogenousInstGraphLoopInvariants(Loop &L, Instruction &Root, - LoopInfo &LI) { - assert(!L.isLoopInvariant(&Root) && - "Only need to walk the graph if root itself is not invariant."); - TinyPtrVector<Value *> Invariants; - - // Build a worklist and recurse through operators collecting invariants. - SmallVector<Instruction *, 4> Worklist; - SmallPtrSet<Instruction *, 8> Visited; - Worklist.push_back(&Root); - Visited.insert(&Root); - do { - Instruction &I = *Worklist.pop_back_val(); - for (Value *OpV : I.operand_values()) { - // Skip constants as unswitching isn't interesting for them. - if (isa<Constant>(OpV)) - continue; - - // Add it to our result if loop invariant. - if (L.isLoopInvariant(OpV)) { - Invariants.push_back(OpV); - continue; - } - - // If not an instruction with the same opcode, nothing we can do. - Instruction *OpI = dyn_cast<Instruction>(OpV); - if (!OpI || OpI->getOpcode() != Root.getOpcode()) - continue; - - // Visit this operand. - if (Visited.insert(OpI).second) - Worklist.push_back(OpI); - } - } while (!Worklist.empty()); - - return Invariants; -} - -static void replaceLoopInvariantUses(Loop &L, Value *Invariant, - Constant &Replacement) { - assert(!isa<Constant>(Invariant) && "Why are we unswitching on a constant?"); - - // Replace uses of LIC in the loop with the given constant. - for (auto UI = Invariant->use_begin(), UE = Invariant->use_end(); UI != UE;) { - // Grab the use and walk past it so we can clobber it in the use list. - Use *U = &*UI++; - Instruction *UserI = dyn_cast<Instruction>(U->getUser()); - - // Replace this use within the loop body. - if (UserI && L.contains(UserI)) - U->set(&Replacement); - } -} - -/// Check that all the LCSSA PHI nodes in the loop exit block have trivial -/// incoming values along this edge. -static bool areLoopExitPHIsLoopInvariant(Loop &L, BasicBlock &ExitingBB, - BasicBlock &ExitBB) { - for (Instruction &I : ExitBB) { - auto *PN = dyn_cast<PHINode>(&I); - if (!PN) - // No more PHIs to check. - return true; - - // If the incoming value for this edge isn't loop invariant the unswitch - // won't be trivial. - if (!L.isLoopInvariant(PN->getIncomingValueForBlock(&ExitingBB))) - return false; - } - llvm_unreachable("Basic blocks should never be empty!"); -} - -/// Insert code to test a set of loop invariant values, and conditionally branch -/// on them. -static void buildPartialUnswitchConditionalBranch(BasicBlock &BB, - ArrayRef<Value *> Invariants, - bool Direction, - BasicBlock &UnswitchedSucc, - BasicBlock &NormalSucc) { - IRBuilder<> IRB(&BB); - Value *Cond = Invariants.front(); - for (Value *Invariant : - make_range(std::next(Invariants.begin()), Invariants.end())) - if (Direction) - Cond = IRB.CreateOr(Cond, Invariant); - else - Cond = IRB.CreateAnd(Cond, Invariant); - - IRB.CreateCondBr(Cond, Direction ? &UnswitchedSucc : &NormalSucc, - Direction ? &NormalSucc : &UnswitchedSucc); -} - -/// Rewrite the PHI nodes in an unswitched loop exit basic block. -/// -/// Requires that the loop exit and unswitched basic block are the same, and -/// that the exiting block was a unique predecessor of that block. Rewrites the -/// PHI nodes in that block such that what were LCSSA PHI nodes become trivial -/// PHI nodes from the old preheader that now contains the unswitched -/// terminator. -static void rewritePHINodesForUnswitchedExitBlock(BasicBlock &UnswitchedBB, - BasicBlock &OldExitingBB, - BasicBlock &OldPH) { - for (PHINode &PN : UnswitchedBB.phis()) { - // When the loop exit is directly unswitched we just need to update the - // incoming basic block. We loop to handle weird cases with repeated - // incoming blocks, but expect to typically only have one operand here. - for (auto i : seq<int>(0, PN.getNumOperands())) { - assert(PN.getIncomingBlock(i) == &OldExitingBB && - "Found incoming block different from unique predecessor!"); - PN.setIncomingBlock(i, &OldPH); - } - } -} - -/// Rewrite the PHI nodes in the loop exit basic block and the split off -/// unswitched block. -/// -/// Because the exit block remains an exit from the loop, this rewrites the -/// LCSSA PHI nodes in it to remove the unswitched edge and introduces PHI -/// nodes into the unswitched basic block to select between the value in the -/// old preheader and the loop exit. -static void rewritePHINodesForExitAndUnswitchedBlocks(BasicBlock &ExitBB, - BasicBlock &UnswitchedBB, - BasicBlock &OldExitingBB, - BasicBlock &OldPH, - bool FullUnswitch) { - assert(&ExitBB != &UnswitchedBB && - "Must have different loop exit and unswitched blocks!"); - Instruction *InsertPt = &*UnswitchedBB.begin(); - for (PHINode &PN : ExitBB.phis()) { - auto *NewPN = PHINode::Create(PN.getType(), /*NumReservedValues*/ 2, - PN.getName() + ".split", InsertPt); - - // Walk backwards over the old PHI node's inputs to minimize the cost of - // removing each one. We have to do this weird loop manually so that we - // create the same number of new incoming edges in the new PHI as we expect - // each case-based edge to be included in the unswitched switch in some - // cases. - // FIXME: This is really, really gross. It would be much cleaner if LLVM - // allowed us to create a single entry for a predecessor block without - // having separate entries for each "edge" even though these edges are - // required to produce identical results. - for (int i = PN.getNumIncomingValues() - 1; i >= 0; --i) { - if (PN.getIncomingBlock(i) != &OldExitingBB) - continue; - - Value *Incoming = PN.getIncomingValue(i); - if (FullUnswitch) - // No more edge from the old exiting block to the exit block. - PN.removeIncomingValue(i); - - NewPN->addIncoming(Incoming, &OldPH); - } - - // Now replace the old PHI with the new one and wire the old one in as an - // input to the new one. - PN.replaceAllUsesWith(NewPN); - NewPN->addIncoming(&PN, &ExitBB); - } -} - -/// Hoist the current loop up to the innermost loop containing a remaining exit. -/// -/// Because we've removed an exit from the loop, we may have changed the set of -/// loops reachable and need to move the current loop up the loop nest or even -/// to an entirely separate nest. -static void hoistLoopToNewParent(Loop &L, BasicBlock &Preheader, - DominatorTree &DT, LoopInfo &LI) { - // If the loop is already at the top level, we can't hoist it anywhere. - Loop *OldParentL = L.getParentLoop(); - if (!OldParentL) - return; - - SmallVector<BasicBlock *, 4> Exits; - L.getExitBlocks(Exits); - Loop *NewParentL = nullptr; - for (auto *ExitBB : Exits) - if (Loop *ExitL = LI.getLoopFor(ExitBB)) - if (!NewParentL || NewParentL->contains(ExitL)) - NewParentL = ExitL; - - if (NewParentL == OldParentL) - return; - - // The new parent loop (if different) should always contain the old one. - if (NewParentL) - assert(NewParentL->contains(OldParentL) && - "Can only hoist this loop up the nest!"); - - // The preheader will need to move with the body of this loop. However, - // because it isn't in this loop we also need to update the primary loop map. - assert(OldParentL == LI.getLoopFor(&Preheader) && - "Parent loop of this loop should contain this loop's preheader!"); - LI.changeLoopFor(&Preheader, NewParentL); - - // Remove this loop from its old parent. - OldParentL->removeChildLoop(&L); - - // Add the loop either to the new parent or as a top-level loop. - if (NewParentL) - NewParentL->addChildLoop(&L); - else - LI.addTopLevelLoop(&L); - - // Remove this loops blocks from the old parent and every other loop up the - // nest until reaching the new parent. Also update all of these - // no-longer-containing loops to reflect the nesting change. - for (Loop *OldContainingL = OldParentL; OldContainingL != NewParentL; - OldContainingL = OldContainingL->getParentLoop()) { - llvm::erase_if(OldContainingL->getBlocksVector(), - [&](const BasicBlock *BB) { - return BB == &Preheader || L.contains(BB); - }); - - OldContainingL->getBlocksSet().erase(&Preheader); - for (BasicBlock *BB : L.blocks()) - OldContainingL->getBlocksSet().erase(BB); - - // Because we just hoisted a loop out of this one, we have essentially - // created new exit paths from it. That means we need to form LCSSA PHI - // nodes for values used in the no-longer-nested loop. - formLCSSA(*OldContainingL, DT, &LI, nullptr); - - // We shouldn't need to form dedicated exits because the exit introduced - // here is the (just split by unswitching) preheader. However, after trivial - // unswitching it is possible to get new non-dedicated exits out of parent - // loop so let's conservatively form dedicated exit blocks and figure out - // if we can optimize later. - formDedicatedExitBlocks(OldContainingL, &DT, &LI, /*PreserveLCSSA*/ true); - } -} - -/// Unswitch a trivial branch if the condition is loop invariant. -/// -/// This routine should only be called when loop code leading to the branch has -/// been validated as trivial (no side effects). This routine checks if the -/// condition is invariant and one of the successors is a loop exit. This -/// allows us to unswitch without duplicating the loop, making it trivial. -/// -/// If this routine fails to unswitch the branch it returns false. -/// -/// If the branch can be unswitched, this routine splits the preheader and -/// hoists the branch above that split. Preserves loop simplified form -/// (splitting the exit block as necessary). It simplifies the branch within -/// the loop to an unconditional branch but doesn't remove it entirely. Further -/// cleanup can be done with some simplify-cfg like pass. -/// -/// If `SE` is not null, it will be updated based on the potential loop SCEVs -/// invalidated by this. -static bool unswitchTrivialBranch(Loop &L, BranchInst &BI, DominatorTree &DT, - LoopInfo &LI, ScalarEvolution *SE, - MemorySSAUpdater *MSSAU) { - assert(BI.isConditional() && "Can only unswitch a conditional branch!"); - LLVM_DEBUG(dbgs() << " Trying to unswitch branch: " << BI << "\n"); - - // The loop invariant values that we want to unswitch. - TinyPtrVector<Value *> Invariants; - - // When true, we're fully unswitching the branch rather than just unswitching - // some input conditions to the branch. - bool FullUnswitch = false; - - if (L.isLoopInvariant(BI.getCondition())) { - Invariants.push_back(BI.getCondition()); - FullUnswitch = true; - } else { - if (auto *CondInst = dyn_cast<Instruction>(BI.getCondition())) - Invariants = collectHomogenousInstGraphLoopInvariants(L, *CondInst, LI); - if (Invariants.empty()) - // Couldn't find invariant inputs! - return false; - } - - // Check that one of the branch's successors exits, and which one. - bool ExitDirection = true; - int LoopExitSuccIdx = 0; - auto *LoopExitBB = BI.getSuccessor(0); - if (L.contains(LoopExitBB)) { - ExitDirection = false; - LoopExitSuccIdx = 1; - LoopExitBB = BI.getSuccessor(1); - if (L.contains(LoopExitBB)) - return false; - } - auto *ContinueBB = BI.getSuccessor(1 - LoopExitSuccIdx); - auto *ParentBB = BI.getParent(); - if (!areLoopExitPHIsLoopInvariant(L, *ParentBB, *LoopExitBB)) - return false; - - // When unswitching only part of the branch's condition, we need the exit - // block to be reached directly from the partially unswitched input. This can - // be done when the exit block is along the true edge and the branch condition - // is a graph of `or` operations, or the exit block is along the false edge - // and the condition is a graph of `and` operations. - if (!FullUnswitch) { - if (ExitDirection) { - if (cast<Instruction>(BI.getCondition())->getOpcode() != Instruction::Or) - return false; - } else { - if (cast<Instruction>(BI.getCondition())->getOpcode() != Instruction::And) - return false; - } - } - - LLVM_DEBUG({ - dbgs() << " unswitching trivial invariant conditions for: " << BI - << "\n"; - for (Value *Invariant : Invariants) { - dbgs() << " " << *Invariant << " == true"; - if (Invariant != Invariants.back()) - dbgs() << " ||"; - dbgs() << "\n"; - } - }); - - // If we have scalar evolutions, we need to invalidate them including this - // loop and the loop containing the exit block. - if (SE) { - if (Loop *ExitL = LI.getLoopFor(LoopExitBB)) - SE->forgetLoop(ExitL); - else - // Forget the entire nest as this exits the entire nest. - SE->forgetTopmostLoop(&L); - } - - if (MSSAU && VerifyMemorySSA) - MSSAU->getMemorySSA()->verifyMemorySSA(); - - // Split the preheader, so that we know that there is a safe place to insert - // the conditional branch. We will change the preheader to have a conditional - // branch on LoopCond. - BasicBlock *OldPH = L.getLoopPreheader(); - BasicBlock *NewPH = SplitEdge(OldPH, L.getHeader(), &DT, &LI, MSSAU); - - // Now that we have a place to insert the conditional branch, create a place - // to branch to: this is the exit block out of the loop that we are - // unswitching. We need to split this if there are other loop predecessors. - // Because the loop is in simplified form, *any* other predecessor is enough. - BasicBlock *UnswitchedBB; - if (FullUnswitch && LoopExitBB->getUniquePredecessor()) { - assert(LoopExitBB->getUniquePredecessor() == BI.getParent() && - "A branch's parent isn't a predecessor!"); - UnswitchedBB = LoopExitBB; - } else { - UnswitchedBB = - SplitBlock(LoopExitBB, &LoopExitBB->front(), &DT, &LI, MSSAU); - } - - if (MSSAU && VerifyMemorySSA) - MSSAU->getMemorySSA()->verifyMemorySSA(); - - // Actually move the invariant uses into the unswitched position. If possible, - // we do this by moving the instructions, but when doing partial unswitching - // we do it by building a new merge of the values in the unswitched position. - OldPH->getTerminator()->eraseFromParent(); - if (FullUnswitch) { - // If fully unswitching, we can use the existing branch instruction. - // Splice it into the old PH to gate reaching the new preheader and re-point - // its successors. - OldPH->getInstList().splice(OldPH->end(), BI.getParent()->getInstList(), - BI); - if (MSSAU) { - // Temporarily clone the terminator, to make MSSA update cheaper by - // separating "insert edge" updates from "remove edge" ones. - ParentBB->getInstList().push_back(BI.clone()); - } else { - // Create a new unconditional branch that will continue the loop as a new - // terminator. - BranchInst::Create(ContinueBB, ParentBB); - } - BI.setSuccessor(LoopExitSuccIdx, UnswitchedBB); - BI.setSuccessor(1 - LoopExitSuccIdx, NewPH); - } else { - // Only unswitching a subset of inputs to the condition, so we will need to - // build a new branch that merges the invariant inputs. - if (ExitDirection) - assert(cast<Instruction>(BI.getCondition())->getOpcode() == - Instruction::Or && - "Must have an `or` of `i1`s for the condition!"); - else - assert(cast<Instruction>(BI.getCondition())->getOpcode() == - Instruction::And && - "Must have an `and` of `i1`s for the condition!"); - buildPartialUnswitchConditionalBranch(*OldPH, Invariants, ExitDirection, - *UnswitchedBB, *NewPH); - } - - // Update the dominator tree with the added edge. - DT.insertEdge(OldPH, UnswitchedBB); - - // After the dominator tree was updated with the added edge, update MemorySSA - // if available. - if (MSSAU) { - SmallVector<CFGUpdate, 1> Updates; - Updates.push_back({cfg::UpdateKind::Insert, OldPH, UnswitchedBB}); - MSSAU->applyInsertUpdates(Updates, DT); - } - - // Finish updating dominator tree and memory ssa for full unswitch. - if (FullUnswitch) { - if (MSSAU) { - // Remove the cloned branch instruction. - ParentBB->getTerminator()->eraseFromParent(); - // Create unconditional branch now. - BranchInst::Create(ContinueBB, ParentBB); - MSSAU->removeEdge(ParentBB, LoopExitBB); - } - DT.deleteEdge(ParentBB, LoopExitBB); - } - - if (MSSAU && VerifyMemorySSA) - MSSAU->getMemorySSA()->verifyMemorySSA(); - - // Rewrite the relevant PHI nodes. - if (UnswitchedBB == LoopExitBB) - rewritePHINodesForUnswitchedExitBlock(*UnswitchedBB, *ParentBB, *OldPH); - else - rewritePHINodesForExitAndUnswitchedBlocks(*LoopExitBB, *UnswitchedBB, - *ParentBB, *OldPH, FullUnswitch); - - // The constant we can replace all of our invariants with inside the loop - // body. If any of the invariants have a value other than this the loop won't - // be entered. - ConstantInt *Replacement = ExitDirection - ? ConstantInt::getFalse(BI.getContext()) - : ConstantInt::getTrue(BI.getContext()); - - // Since this is an i1 condition we can also trivially replace uses of it - // within the loop with a constant. - for (Value *Invariant : Invariants) - replaceLoopInvariantUses(L, Invariant, *Replacement); - - // If this was full unswitching, we may have changed the nesting relationship - // for this loop so hoist it to its correct parent if needed. - if (FullUnswitch) - hoistLoopToNewParent(L, *NewPH, DT, LI); - - LLVM_DEBUG(dbgs() << " done: unswitching trivial branch...\n"); - ++NumTrivial; - ++NumBranches; - return true; -} - -/// Unswitch a trivial switch if the condition is loop invariant. -/// -/// This routine should only be called when loop code leading to the switch has -/// been validated as trivial (no side effects). This routine checks if the -/// condition is invariant and that at least one of the successors is a loop -/// exit. This allows us to unswitch without duplicating the loop, making it -/// trivial. -/// -/// If this routine fails to unswitch the switch it returns false. -/// -/// If the switch can be unswitched, this routine splits the preheader and -/// copies the switch above that split. If the default case is one of the -/// exiting cases, it copies the non-exiting cases and points them at the new -/// preheader. If the default case is not exiting, it copies the exiting cases -/// and points the default at the preheader. It preserves loop simplified form -/// (splitting the exit blocks as necessary). It simplifies the switch within -/// the loop by removing now-dead cases. If the default case is one of those -/// unswitched, it replaces its destination with a new basic block containing -/// only unreachable. Such basic blocks, while technically loop exits, are not -/// considered for unswitching so this is a stable transform and the same -/// switch will not be revisited. If after unswitching there is only a single -/// in-loop successor, the switch is further simplified to an unconditional -/// branch. Still more cleanup can be done with some simplify-cfg like pass. -/// -/// If `SE` is not null, it will be updated based on the potential loop SCEVs -/// invalidated by this. -static bool unswitchTrivialSwitch(Loop &L, SwitchInst &SI, DominatorTree &DT, - LoopInfo &LI, ScalarEvolution *SE, - MemorySSAUpdater *MSSAU) { - LLVM_DEBUG(dbgs() << " Trying to unswitch switch: " << SI << "\n"); - Value *LoopCond = SI.getCondition(); - - // If this isn't switching on an invariant condition, we can't unswitch it. - if (!L.isLoopInvariant(LoopCond)) - return false; - - auto *ParentBB = SI.getParent(); - - SmallVector<int, 4> ExitCaseIndices; - for (auto Case : SI.cases()) { - auto *SuccBB = Case.getCaseSuccessor(); - if (!L.contains(SuccBB) && - areLoopExitPHIsLoopInvariant(L, *ParentBB, *SuccBB)) - ExitCaseIndices.push_back(Case.getCaseIndex()); - } - BasicBlock *DefaultExitBB = nullptr; - if (!L.contains(SI.getDefaultDest()) && - areLoopExitPHIsLoopInvariant(L, *ParentBB, *SI.getDefaultDest()) && - !isa<UnreachableInst>(SI.getDefaultDest()->getTerminator())) - DefaultExitBB = SI.getDefaultDest(); - else if (ExitCaseIndices.empty()) - return false; - - LLVM_DEBUG(dbgs() << " unswitching trivial switch...\n"); - - if (MSSAU && VerifyMemorySSA) - MSSAU->getMemorySSA()->verifyMemorySSA(); - - // We may need to invalidate SCEVs for the outermost loop reached by any of - // the exits. - Loop *OuterL = &L; - - if (DefaultExitBB) { - // Clear out the default destination temporarily to allow accurate - // predecessor lists to be examined below. - SI.setDefaultDest(nullptr); - // Check the loop containing this exit. - Loop *ExitL = LI.getLoopFor(DefaultExitBB); - if (!ExitL || ExitL->contains(OuterL)) - OuterL = ExitL; - } - - // Store the exit cases into a separate data structure and remove them from - // the switch. - SmallVector<std::pair<ConstantInt *, BasicBlock *>, 4> ExitCases; - ExitCases.reserve(ExitCaseIndices.size()); - // We walk the case indices backwards so that we remove the last case first - // and don't disrupt the earlier indices. - for (unsigned Index : reverse(ExitCaseIndices)) { - auto CaseI = SI.case_begin() + Index; - // Compute the outer loop from this exit. - Loop *ExitL = LI.getLoopFor(CaseI->getCaseSuccessor()); - if (!ExitL || ExitL->contains(OuterL)) - OuterL = ExitL; - // Save the value of this case. - ExitCases.push_back({CaseI->getCaseValue(), CaseI->getCaseSuccessor()}); - // Delete the unswitched cases. - SI.removeCase(CaseI); - } - - if (SE) { - if (OuterL) - SE->forgetLoop(OuterL); - else - SE->forgetTopmostLoop(&L); - } - - // Check if after this all of the remaining cases point at the same - // successor. - BasicBlock *CommonSuccBB = nullptr; - if (SI.getNumCases() > 0 && - std::all_of(std::next(SI.case_begin()), SI.case_end(), - [&SI](const SwitchInst::CaseHandle &Case) { - return Case.getCaseSuccessor() == - SI.case_begin()->getCaseSuccessor(); - })) - CommonSuccBB = SI.case_begin()->getCaseSuccessor(); - if (!DefaultExitBB) { - // If we're not unswitching the default, we need it to match any cases to - // have a common successor or if we have no cases it is the common - // successor. - if (SI.getNumCases() == 0) - CommonSuccBB = SI.getDefaultDest(); - else if (SI.getDefaultDest() != CommonSuccBB) - CommonSuccBB = nullptr; - } - - // Split the preheader, so that we know that there is a safe place to insert - // the switch. - BasicBlock *OldPH = L.getLoopPreheader(); - BasicBlock *NewPH = SplitEdge(OldPH, L.getHeader(), &DT, &LI, MSSAU); - OldPH->getTerminator()->eraseFromParent(); - - // Now add the unswitched switch. - auto *NewSI = SwitchInst::Create(LoopCond, NewPH, ExitCases.size(), OldPH); - - // Rewrite the IR for the unswitched basic blocks. This requires two steps. - // First, we split any exit blocks with remaining in-loop predecessors. Then - // we update the PHIs in one of two ways depending on if there was a split. - // We walk in reverse so that we split in the same order as the cases - // appeared. This is purely for convenience of reading the resulting IR, but - // it doesn't cost anything really. - SmallPtrSet<BasicBlock *, 2> UnswitchedExitBBs; - SmallDenseMap<BasicBlock *, BasicBlock *, 2> SplitExitBBMap; - // Handle the default exit if necessary. - // FIXME: It'd be great if we could merge this with the loop below but LLVM's - // ranges aren't quite powerful enough yet. - if (DefaultExitBB) { - if (pred_empty(DefaultExitBB)) { - UnswitchedExitBBs.insert(DefaultExitBB); - rewritePHINodesForUnswitchedExitBlock(*DefaultExitBB, *ParentBB, *OldPH); - } else { - auto *SplitBB = - SplitBlock(DefaultExitBB, &DefaultExitBB->front(), &DT, &LI, MSSAU); - rewritePHINodesForExitAndUnswitchedBlocks(*DefaultExitBB, *SplitBB, - *ParentBB, *OldPH, - /*FullUnswitch*/ true); - DefaultExitBB = SplitExitBBMap[DefaultExitBB] = SplitBB; - } - } - // Note that we must use a reference in the for loop so that we update the - // container. - for (auto &CasePair : reverse(ExitCases)) { - // Grab a reference to the exit block in the pair so that we can update it. - BasicBlock *ExitBB = CasePair.second; - - // If this case is the last edge into the exit block, we can simply reuse it - // as it will no longer be a loop exit. No mapping necessary. - if (pred_empty(ExitBB)) { - // Only rewrite once. - if (UnswitchedExitBBs.insert(ExitBB).second) - rewritePHINodesForUnswitchedExitBlock(*ExitBB, *ParentBB, *OldPH); - continue; - } - - // Otherwise we need to split the exit block so that we retain an exit - // block from the loop and a target for the unswitched condition. - BasicBlock *&SplitExitBB = SplitExitBBMap[ExitBB]; - if (!SplitExitBB) { - // If this is the first time we see this, do the split and remember it. - SplitExitBB = SplitBlock(ExitBB, &ExitBB->front(), &DT, &LI, MSSAU); - rewritePHINodesForExitAndUnswitchedBlocks(*ExitBB, *SplitExitBB, - *ParentBB, *OldPH, - /*FullUnswitch*/ true); - } - // Update the case pair to point to the split block. - CasePair.second = SplitExitBB; - } - - // Now add the unswitched cases. We do this in reverse order as we built them - // in reverse order. - for (auto CasePair : reverse(ExitCases)) { - ConstantInt *CaseVal = CasePair.first; - BasicBlock *UnswitchedBB = CasePair.second; - - NewSI->addCase(CaseVal, UnswitchedBB); - } - - // If the default was unswitched, re-point it and add explicit cases for - // entering the loop. - if (DefaultExitBB) { - NewSI->setDefaultDest(DefaultExitBB); - - // We removed all the exit cases, so we just copy the cases to the - // unswitched switch. - for (auto Case : SI.cases()) - NewSI->addCase(Case.getCaseValue(), NewPH); - } - - // If we ended up with a common successor for every path through the switch - // after unswitching, rewrite it to an unconditional branch to make it easy - // to recognize. Otherwise we potentially have to recognize the default case - // pointing at unreachable and other complexity. - if (CommonSuccBB) { - BasicBlock *BB = SI.getParent(); - // We may have had multiple edges to this common successor block, so remove - // them as predecessors. We skip the first one, either the default or the - // actual first case. - bool SkippedFirst = DefaultExitBB == nullptr; - for (auto Case : SI.cases()) { - assert(Case.getCaseSuccessor() == CommonSuccBB && - "Non-common successor!"); - (void)Case; - if (!SkippedFirst) { - SkippedFirst = true; - continue; - } - CommonSuccBB->removePredecessor(BB, - /*DontDeleteUselessPHIs*/ true); - } - // Now nuke the switch and replace it with a direct branch. - SI.eraseFromParent(); - BranchInst::Create(CommonSuccBB, BB); - } else if (DefaultExitBB) { - assert(SI.getNumCases() > 0 && - "If we had no cases we'd have a common successor!"); - // Move the last case to the default successor. This is valid as if the - // default got unswitched it cannot be reached. This has the advantage of - // being simple and keeping the number of edges from this switch to - // successors the same, and avoiding any PHI update complexity. - auto LastCaseI = std::prev(SI.case_end()); - SI.setDefaultDest(LastCaseI->getCaseSuccessor()); - SI.removeCase(LastCaseI); - } - - // Walk the unswitched exit blocks and the unswitched split blocks and update - // the dominator tree based on the CFG edits. While we are walking unordered - // containers here, the API for applyUpdates takes an unordered list of - // updates and requires them to not contain duplicates. - SmallVector<DominatorTree::UpdateType, 4> DTUpdates; - for (auto *UnswitchedExitBB : UnswitchedExitBBs) { - DTUpdates.push_back({DT.Delete, ParentBB, UnswitchedExitBB}); - DTUpdates.push_back({DT.Insert, OldPH, UnswitchedExitBB}); - } - for (auto SplitUnswitchedPair : SplitExitBBMap) { - auto *UnswitchedBB = SplitUnswitchedPair.second; - DTUpdates.push_back({DT.Delete, ParentBB, UnswitchedBB}); - DTUpdates.push_back({DT.Insert, OldPH, UnswitchedBB}); - } - DT.applyUpdates(DTUpdates); - - if (MSSAU) { - MSSAU->applyUpdates(DTUpdates, DT); - if (VerifyMemorySSA) - MSSAU->getMemorySSA()->verifyMemorySSA(); - } - - assert(DT.verify(DominatorTree::VerificationLevel::Fast)); - - // We may have changed the nesting relationship for this loop so hoist it to - // its correct parent if needed. - hoistLoopToNewParent(L, *NewPH, DT, LI); - - ++NumTrivial; - ++NumSwitches; - LLVM_DEBUG(dbgs() << " done: unswitching trivial switch...\n"); - return true; -} - -/// This routine scans the loop to find a branch or switch which occurs before -/// any side effects occur. These can potentially be unswitched without -/// duplicating the loop. If a branch or switch is successfully unswitched the -/// scanning continues to see if subsequent branches or switches have become -/// trivial. Once all trivial candidates have been unswitched, this routine -/// returns. -/// -/// The return value indicates whether anything was unswitched (and therefore -/// changed). -/// -/// If `SE` is not null, it will be updated based on the potential loop SCEVs -/// invalidated by this. -static bool unswitchAllTrivialConditions(Loop &L, DominatorTree &DT, - LoopInfo &LI, ScalarEvolution *SE, - MemorySSAUpdater *MSSAU) { - bool Changed = false; - - // If loop header has only one reachable successor we should keep looking for - // trivial condition candidates in the successor as well. An alternative is - // to constant fold conditions and merge successors into loop header (then we - // only need to check header's terminator). The reason for not doing this in - // LoopUnswitch pass is that it could potentially break LoopPassManager's - // invariants. Folding dead branches could either eliminate the current loop - // or make other loops unreachable. LCSSA form might also not be preserved - // after deleting branches. The following code keeps traversing loop header's - // successors until it finds the trivial condition candidate (condition that - // is not a constant). Since unswitching generates branches with constant - // conditions, this scenario could be very common in practice. - BasicBlock *CurrentBB = L.getHeader(); - SmallPtrSet<BasicBlock *, 8> Visited; - Visited.insert(CurrentBB); - do { - // Check if there are any side-effecting instructions (e.g. stores, calls, - // volatile loads) in the part of the loop that the code *would* execute - // without unswitching. - if (llvm::any_of(*CurrentBB, - [](Instruction &I) { return I.mayHaveSideEffects(); })) - return Changed; - - Instruction *CurrentTerm = CurrentBB->getTerminator(); - - if (auto *SI = dyn_cast<SwitchInst>(CurrentTerm)) { - // Don't bother trying to unswitch past a switch with a constant - // condition. This should be removed prior to running this pass by - // simplify-cfg. - if (isa<Constant>(SI->getCondition())) - return Changed; - - if (!unswitchTrivialSwitch(L, *SI, DT, LI, SE, MSSAU)) - // Couldn't unswitch this one so we're done. - return Changed; - - // Mark that we managed to unswitch something. - Changed = true; - - // If unswitching turned the terminator into an unconditional branch then - // we can continue. The unswitching logic specifically works to fold any - // cases it can into an unconditional branch to make it easier to - // recognize here. - auto *BI = dyn_cast<BranchInst>(CurrentBB->getTerminator()); - if (!BI || BI->isConditional()) - return Changed; - - CurrentBB = BI->getSuccessor(0); - continue; - } - - auto *BI = dyn_cast<BranchInst>(CurrentTerm); - if (!BI) - // We do not understand other terminator instructions. - return Changed; - - // Don't bother trying to unswitch past an unconditional branch or a branch - // with a constant value. These should be removed by simplify-cfg prior to - // running this pass. - if (!BI->isConditional() || isa<Constant>(BI->getCondition())) - return Changed; - - // Found a trivial condition candidate: non-foldable conditional branch. If - // we fail to unswitch this, we can't do anything else that is trivial. - if (!unswitchTrivialBranch(L, *BI, DT, LI, SE, MSSAU)) - return Changed; - - // Mark that we managed to unswitch something. - Changed = true; - - // If we only unswitched some of the conditions feeding the branch, we won't - // have collapsed it to a single successor. - BI = cast<BranchInst>(CurrentBB->getTerminator()); - if (BI->isConditional()) - return Changed; - - // Follow the newly unconditional branch into its successor. - CurrentBB = BI->getSuccessor(0); - - // When continuing, if we exit the loop or reach a previous visited block, - // then we can not reach any trivial condition candidates (unfoldable - // branch instructions or switch instructions) and no unswitch can happen. - } while (L.contains(CurrentBB) && Visited.insert(CurrentBB).second); - - return Changed; -} - -/// Build the cloned blocks for an unswitched copy of the given loop. -/// -/// The cloned blocks are inserted before the loop preheader (`LoopPH`) and -/// after the split block (`SplitBB`) that will be used to select between the -/// cloned and original loop. -/// -/// This routine handles cloning all of the necessary loop blocks and exit -/// blocks including rewriting their instructions and the relevant PHI nodes. -/// Any loop blocks or exit blocks which are dominated by a different successor -/// than the one for this clone of the loop blocks can be trivially skipped. We -/// use the `DominatingSucc` map to determine whether a block satisfies that -/// property with a simple map lookup. -/// -/// It also correctly creates the unconditional branch in the cloned -/// unswitched parent block to only point at the unswitched successor. -/// -/// This does not handle most of the necessary updates to `LoopInfo`. Only exit -/// block splitting is correctly reflected in `LoopInfo`, essentially all of -/// the cloned blocks (and their loops) are left without full `LoopInfo` -/// updates. This also doesn't fully update `DominatorTree`. It adds the cloned -/// blocks to them but doesn't create the cloned `DominatorTree` structure and -/// instead the caller must recompute an accurate DT. It *does* correctly -/// update the `AssumptionCache` provided in `AC`. -static BasicBlock *buildClonedLoopBlocks( - Loop &L, BasicBlock *LoopPH, BasicBlock *SplitBB, - ArrayRef<BasicBlock *> ExitBlocks, BasicBlock *ParentBB, - BasicBlock *UnswitchedSuccBB, BasicBlock *ContinueSuccBB, - const SmallDenseMap<BasicBlock *, BasicBlock *, 16> &DominatingSucc, - ValueToValueMapTy &VMap, - SmallVectorImpl<DominatorTree::UpdateType> &DTUpdates, AssumptionCache &AC, - DominatorTree &DT, LoopInfo &LI, MemorySSAUpdater *MSSAU) { - SmallVector<BasicBlock *, 4> NewBlocks; - NewBlocks.reserve(L.getNumBlocks() + ExitBlocks.size()); - - // We will need to clone a bunch of blocks, wrap up the clone operation in - // a helper. - auto CloneBlock = [&](BasicBlock *OldBB) { - // Clone the basic block and insert it before the new preheader. - BasicBlock *NewBB = CloneBasicBlock(OldBB, VMap, ".us", OldBB->getParent()); - NewBB->moveBefore(LoopPH); - - // Record this block and the mapping. - NewBlocks.push_back(NewBB); - VMap[OldBB] = NewBB; - - return NewBB; - }; - - // We skip cloning blocks when they have a dominating succ that is not the - // succ we are cloning for. - auto SkipBlock = [&](BasicBlock *BB) { - auto It = DominatingSucc.find(BB); - return It != DominatingSucc.end() && It->second != UnswitchedSuccBB; - }; - - // First, clone the preheader. - auto *ClonedPH = CloneBlock(LoopPH); - - // Then clone all the loop blocks, skipping the ones that aren't necessary. - for (auto *LoopBB : L.blocks()) - if (!SkipBlock(LoopBB)) - CloneBlock(LoopBB); - - // Split all the loop exit edges so that when we clone the exit blocks, if - // any of the exit blocks are *also* a preheader for some other loop, we - // don't create multiple predecessors entering the loop header. - for (auto *ExitBB : ExitBlocks) { - if (SkipBlock(ExitBB)) - continue; - - // When we are going to clone an exit, we don't need to clone all the - // instructions in the exit block and we want to ensure we have an easy - // place to merge the CFG, so split the exit first. This is always safe to - // do because there cannot be any non-loop predecessors of a loop exit in - // loop simplified form. - auto *MergeBB = SplitBlock(ExitBB, &ExitBB->front(), &DT, &LI, MSSAU); - - // Rearrange the names to make it easier to write test cases by having the - // exit block carry the suffix rather than the merge block carrying the - // suffix. - MergeBB->takeName(ExitBB); - ExitBB->setName(Twine(MergeBB->getName()) + ".split"); - - // Now clone the original exit block. - auto *ClonedExitBB = CloneBlock(ExitBB); - assert(ClonedExitBB->getTerminator()->getNumSuccessors() == 1 && - "Exit block should have been split to have one successor!"); - assert(ClonedExitBB->getTerminator()->getSuccessor(0) == MergeBB && - "Cloned exit block has the wrong successor!"); - - // Remap any cloned instructions and create a merge phi node for them. - for (auto ZippedInsts : llvm::zip_first( - llvm::make_range(ExitBB->begin(), std::prev(ExitBB->end())), - llvm::make_range(ClonedExitBB->begin(), - std::prev(ClonedExitBB->end())))) { - Instruction &I = std::get<0>(ZippedInsts); - Instruction &ClonedI = std::get<1>(ZippedInsts); - - // The only instructions in the exit block should be PHI nodes and - // potentially a landing pad. - assert( - (isa<PHINode>(I) || isa<LandingPadInst>(I) || isa<CatchPadInst>(I)) && - "Bad instruction in exit block!"); - // We should have a value map between the instruction and its clone. - assert(VMap.lookup(&I) == &ClonedI && "Mismatch in the value map!"); - - auto *MergePN = - PHINode::Create(I.getType(), /*NumReservedValues*/ 2, ".us-phi", - &*MergeBB->getFirstInsertionPt()); - I.replaceAllUsesWith(MergePN); - MergePN->addIncoming(&I, ExitBB); - MergePN->addIncoming(&ClonedI, ClonedExitBB); - } - } - - // Rewrite the instructions in the cloned blocks to refer to the instructions - // in the cloned blocks. We have to do this as a second pass so that we have - // everything available. Also, we have inserted new instructions which may - // include assume intrinsics, so we update the assumption cache while - // processing this. - for (auto *ClonedBB : NewBlocks) - for (Instruction &I : *ClonedBB) { - RemapInstruction(&I, VMap, - RF_NoModuleLevelChanges | RF_IgnoreMissingLocals); - if (auto *II = dyn_cast<IntrinsicInst>(&I)) - if (II->getIntrinsicID() == Intrinsic::assume) - AC.registerAssumption(II); - } - - // Update any PHI nodes in the cloned successors of the skipped blocks to not - // have spurious incoming values. - for (auto *LoopBB : L.blocks()) - if (SkipBlock(LoopBB)) - for (auto *SuccBB : successors(LoopBB)) - if (auto *ClonedSuccBB = cast_or_null<BasicBlock>(VMap.lookup(SuccBB))) - for (PHINode &PN : ClonedSuccBB->phis()) - PN.removeIncomingValue(LoopBB, /*DeletePHIIfEmpty*/ false); - - // Remove the cloned parent as a predecessor of any successor we ended up - // cloning other than the unswitched one. - auto *ClonedParentBB = cast<BasicBlock>(VMap.lookup(ParentBB)); - for (auto *SuccBB : successors(ParentBB)) { - if (SuccBB == UnswitchedSuccBB) - continue; - - auto *ClonedSuccBB = cast_or_null<BasicBlock>(VMap.lookup(SuccBB)); - if (!ClonedSuccBB) - continue; - - ClonedSuccBB->removePredecessor(ClonedParentBB, - /*DontDeleteUselessPHIs*/ true); - } - - // Replace the cloned branch with an unconditional branch to the cloned - // unswitched successor. - auto *ClonedSuccBB = cast<BasicBlock>(VMap.lookup(UnswitchedSuccBB)); - ClonedParentBB->getTerminator()->eraseFromParent(); - BranchInst::Create(ClonedSuccBB, ClonedParentBB); - - // If there are duplicate entries in the PHI nodes because of multiple edges - // to the unswitched successor, we need to nuke all but one as we replaced it - // with a direct branch. - for (PHINode &PN : ClonedSuccBB->phis()) { - bool Found = false; - // Loop over the incoming operands backwards so we can easily delete as we - // go without invalidating the index. - for (int i = PN.getNumOperands() - 1; i >= 0; --i) { - if (PN.getIncomingBlock(i) != ClonedParentBB) - continue; - if (!Found) { - Found = true; - continue; - } - PN.removeIncomingValue(i, /*DeletePHIIfEmpty*/ false); - } - } - - // Record the domtree updates for the new blocks. - SmallPtrSet<BasicBlock *, 4> SuccSet; - for (auto *ClonedBB : NewBlocks) { - for (auto *SuccBB : successors(ClonedBB)) - if (SuccSet.insert(SuccBB).second) - DTUpdates.push_back({DominatorTree::Insert, ClonedBB, SuccBB}); - SuccSet.clear(); - } - - return ClonedPH; -} - -/// Recursively clone the specified loop and all of its children. -/// -/// The target parent loop for the clone should be provided, or can be null if -/// the clone is a top-level loop. While cloning, all the blocks are mapped -/// with the provided value map. The entire original loop must be present in -/// the value map. The cloned loop is returned. -static Loop *cloneLoopNest(Loop &OrigRootL, Loop *RootParentL, - const ValueToValueMapTy &VMap, LoopInfo &LI) { - auto AddClonedBlocksToLoop = [&](Loop &OrigL, Loop &ClonedL) { - assert(ClonedL.getBlocks().empty() && "Must start with an empty loop!"); - ClonedL.reserveBlocks(OrigL.getNumBlocks()); - for (auto *BB : OrigL.blocks()) { - auto *ClonedBB = cast<BasicBlock>(VMap.lookup(BB)); - ClonedL.addBlockEntry(ClonedBB); - if (LI.getLoopFor(BB) == &OrigL) - LI.changeLoopFor(ClonedBB, &ClonedL); - } - }; - - // We specially handle the first loop because it may get cloned into - // a different parent and because we most commonly are cloning leaf loops. - Loop *ClonedRootL = LI.AllocateLoop(); - if (RootParentL) - RootParentL->addChildLoop(ClonedRootL); - else - LI.addTopLevelLoop(ClonedRootL); - AddClonedBlocksToLoop(OrigRootL, *ClonedRootL); - - if (OrigRootL.empty()) - return ClonedRootL; - - // If we have a nest, we can quickly clone the entire loop nest using an - // iterative approach because it is a tree. We keep the cloned parent in the - // data structure to avoid repeatedly querying through a map to find it. - SmallVector<std::pair<Loop *, Loop *>, 16> LoopsToClone; - // Build up the loops to clone in reverse order as we'll clone them from the - // back. - for (Loop *ChildL : llvm::reverse(OrigRootL)) - LoopsToClone.push_back({ClonedRootL, ChildL}); - do { - Loop *ClonedParentL, *L; - std::tie(ClonedParentL, L) = LoopsToClone.pop_back_val(); - Loop *ClonedL = LI.AllocateLoop(); - ClonedParentL->addChildLoop(ClonedL); - AddClonedBlocksToLoop(*L, *ClonedL); - for (Loop *ChildL : llvm::reverse(*L)) - LoopsToClone.push_back({ClonedL, ChildL}); - } while (!LoopsToClone.empty()); - - return ClonedRootL; -} - -/// Build the cloned loops of an original loop from unswitching. -/// -/// Because unswitching simplifies the CFG of the loop, this isn't a trivial -/// operation. We need to re-verify that there even is a loop (as the backedge -/// may not have been cloned), and even if there are remaining backedges the -/// backedge set may be different. However, we know that each child loop is -/// undisturbed, we only need to find where to place each child loop within -/// either any parent loop or within a cloned version of the original loop. -/// -/// Because child loops may end up cloned outside of any cloned version of the -/// original loop, multiple cloned sibling loops may be created. All of them -/// are returned so that the newly introduced loop nest roots can be -/// identified. -static void buildClonedLoops(Loop &OrigL, ArrayRef<BasicBlock *> ExitBlocks, - const ValueToValueMapTy &VMap, LoopInfo &LI, - SmallVectorImpl<Loop *> &NonChildClonedLoops) { - Loop *ClonedL = nullptr; - - auto *OrigPH = OrigL.getLoopPreheader(); - auto *OrigHeader = OrigL.getHeader(); - - auto *ClonedPH = cast<BasicBlock>(VMap.lookup(OrigPH)); - auto *ClonedHeader = cast<BasicBlock>(VMap.lookup(OrigHeader)); - - // We need to know the loops of the cloned exit blocks to even compute the - // accurate parent loop. If we only clone exits to some parent of the - // original parent, we want to clone into that outer loop. We also keep track - // of the loops that our cloned exit blocks participate in. - Loop *ParentL = nullptr; - SmallVector<BasicBlock *, 4> ClonedExitsInLoops; - SmallDenseMap<BasicBlock *, Loop *, 16> ExitLoopMap; - ClonedExitsInLoops.reserve(ExitBlocks.size()); - for (auto *ExitBB : ExitBlocks) - if (auto *ClonedExitBB = cast_or_null<BasicBlock>(VMap.lookup(ExitBB))) - if (Loop *ExitL = LI.getLoopFor(ExitBB)) { - ExitLoopMap[ClonedExitBB] = ExitL; - ClonedExitsInLoops.push_back(ClonedExitBB); - if (!ParentL || (ParentL != ExitL && ParentL->contains(ExitL))) - ParentL = ExitL; - } - assert((!ParentL || ParentL == OrigL.getParentLoop() || - ParentL->contains(OrigL.getParentLoop())) && - "The computed parent loop should always contain (or be) the parent of " - "the original loop."); - - // We build the set of blocks dominated by the cloned header from the set of - // cloned blocks out of the original loop. While not all of these will - // necessarily be in the cloned loop, it is enough to establish that they - // aren't in unreachable cycles, etc. - SmallSetVector<BasicBlock *, 16> ClonedLoopBlocks; - for (auto *BB : OrigL.blocks()) - if (auto *ClonedBB = cast_or_null<BasicBlock>(VMap.lookup(BB))) - ClonedLoopBlocks.insert(ClonedBB); - - // Rebuild the set of blocks that will end up in the cloned loop. We may have - // skipped cloning some region of this loop which can in turn skip some of - // the backedges so we have to rebuild the blocks in the loop based on the - // backedges that remain after cloning. - SmallVector<BasicBlock *, 16> Worklist; - SmallPtrSet<BasicBlock *, 16> BlocksInClonedLoop; - for (auto *Pred : predecessors(ClonedHeader)) { - // The only possible non-loop header predecessor is the preheader because - // we know we cloned the loop in simplified form. - if (Pred == ClonedPH) - continue; - - // Because the loop was in simplified form, the only non-loop predecessor - // should be the preheader. - assert(ClonedLoopBlocks.count(Pred) && "Found a predecessor of the loop " - "header other than the preheader " - "that is not part of the loop!"); - - // Insert this block into the loop set and on the first visit (and if it - // isn't the header we're currently walking) put it into the worklist to - // recurse through. - if (BlocksInClonedLoop.insert(Pred).second && Pred != ClonedHeader) - Worklist.push_back(Pred); - } - - // If we had any backedges then there *is* a cloned loop. Put the header into - // the loop set and then walk the worklist backwards to find all the blocks - // that remain within the loop after cloning. - if (!BlocksInClonedLoop.empty()) { - BlocksInClonedLoop.insert(ClonedHeader); - - while (!Worklist.empty()) { - BasicBlock *BB = Worklist.pop_back_val(); - assert(BlocksInClonedLoop.count(BB) && - "Didn't put block into the loop set!"); - - // Insert any predecessors that are in the possible set into the cloned - // set, and if the insert is successful, add them to the worklist. Note - // that we filter on the blocks that are definitely reachable via the - // backedge to the loop header so we may prune out dead code within the - // cloned loop. - for (auto *Pred : predecessors(BB)) - if (ClonedLoopBlocks.count(Pred) && - BlocksInClonedLoop.insert(Pred).second) - Worklist.push_back(Pred); - } - - ClonedL = LI.AllocateLoop(); - if (ParentL) { - ParentL->addBasicBlockToLoop(ClonedPH, LI); - ParentL->addChildLoop(ClonedL); - } else { - LI.addTopLevelLoop(ClonedL); - } - NonChildClonedLoops.push_back(ClonedL); - - ClonedL->reserveBlocks(BlocksInClonedLoop.size()); - // We don't want to just add the cloned loop blocks based on how we - // discovered them. The original order of blocks was carefully built in - // a way that doesn't rely on predecessor ordering. Rather than re-invent - // that logic, we just re-walk the original blocks (and those of the child - // loops) and filter them as we add them into the cloned loop. - for (auto *BB : OrigL.blocks()) { - auto *ClonedBB = cast_or_null<BasicBlock>(VMap.lookup(BB)); - if (!ClonedBB || !BlocksInClonedLoop.count(ClonedBB)) - continue; - - // Directly add the blocks that are only in this loop. - if (LI.getLoopFor(BB) == &OrigL) { - ClonedL->addBasicBlockToLoop(ClonedBB, LI); - continue; - } - - // We want to manually add it to this loop and parents. - // Registering it with LoopInfo will happen when we clone the top - // loop for this block. - for (Loop *PL = ClonedL; PL; PL = PL->getParentLoop()) - PL->addBlockEntry(ClonedBB); - } - - // Now add each child loop whose header remains within the cloned loop. All - // of the blocks within the loop must satisfy the same constraints as the - // header so once we pass the header checks we can just clone the entire - // child loop nest. - for (Loop *ChildL : OrigL) { - auto *ClonedChildHeader = - cast_or_null<BasicBlock>(VMap.lookup(ChildL->getHeader())); - if (!ClonedChildHeader || !BlocksInClonedLoop.count(ClonedChildHeader)) - continue; - -#ifndef NDEBUG - // We should never have a cloned child loop header but fail to have - // all of the blocks for that child loop. - for (auto *ChildLoopBB : ChildL->blocks()) - assert(BlocksInClonedLoop.count( - cast<BasicBlock>(VMap.lookup(ChildLoopBB))) && - "Child cloned loop has a header within the cloned outer " - "loop but not all of its blocks!"); -#endif - - cloneLoopNest(*ChildL, ClonedL, VMap, LI); - } - } - - // Now that we've handled all the components of the original loop that were - // cloned into a new loop, we still need to handle anything from the original - // loop that wasn't in a cloned loop. - - // Figure out what blocks are left to place within any loop nest containing - // the unswitched loop. If we never formed a loop, the cloned PH is one of - // them. - SmallPtrSet<BasicBlock *, 16> UnloopedBlockSet; - if (BlocksInClonedLoop.empty()) - UnloopedBlockSet.insert(ClonedPH); - for (auto *ClonedBB : ClonedLoopBlocks) - if (!BlocksInClonedLoop.count(ClonedBB)) - UnloopedBlockSet.insert(ClonedBB); - - // Copy the cloned exits and sort them in ascending loop depth, we'll work - // backwards across these to process them inside out. The order shouldn't - // matter as we're just trying to build up the map from inside-out; we use - // the map in a more stably ordered way below. - auto OrderedClonedExitsInLoops = ClonedExitsInLoops; - llvm::sort(OrderedClonedExitsInLoops, [&](BasicBlock *LHS, BasicBlock *RHS) { - return ExitLoopMap.lookup(LHS)->getLoopDepth() < - ExitLoopMap.lookup(RHS)->getLoopDepth(); - }); - - // Populate the existing ExitLoopMap with everything reachable from each - // exit, starting from the inner most exit. - while (!UnloopedBlockSet.empty() && !OrderedClonedExitsInLoops.empty()) { - assert(Worklist.empty() && "Didn't clear worklist!"); - - BasicBlock *ExitBB = OrderedClonedExitsInLoops.pop_back_val(); - Loop *ExitL = ExitLoopMap.lookup(ExitBB); - - // Walk the CFG back until we hit the cloned PH adding everything reachable - // and in the unlooped set to this exit block's loop. - Worklist.push_back(ExitBB); - do { - BasicBlock *BB = Worklist.pop_back_val(); - // We can stop recursing at the cloned preheader (if we get there). - if (BB == ClonedPH) - continue; - - for (BasicBlock *PredBB : predecessors(BB)) { - // If this pred has already been moved to our set or is part of some - // (inner) loop, no update needed. - if (!UnloopedBlockSet.erase(PredBB)) { - assert( - (BlocksInClonedLoop.count(PredBB) || ExitLoopMap.count(PredBB)) && - "Predecessor not mapped to a loop!"); - continue; - } - - // We just insert into the loop set here. We'll add these blocks to the - // exit loop after we build up the set in an order that doesn't rely on - // predecessor order (which in turn relies on use list order). - bool Inserted = ExitLoopMap.insert({PredBB, ExitL}).second; - (void)Inserted; - assert(Inserted && "Should only visit an unlooped block once!"); - - // And recurse through to its predecessors. - Worklist.push_back(PredBB); - } - } while (!Worklist.empty()); - } - - // Now that the ExitLoopMap gives as mapping for all the non-looping cloned - // blocks to their outer loops, walk the cloned blocks and the cloned exits - // in their original order adding them to the correct loop. - - // We need a stable insertion order. We use the order of the original loop - // order and map into the correct parent loop. - for (auto *BB : llvm::concat<BasicBlock *const>( - makeArrayRef(ClonedPH), ClonedLoopBlocks, ClonedExitsInLoops)) - if (Loop *OuterL = ExitLoopMap.lookup(BB)) - OuterL->addBasicBlockToLoop(BB, LI); - -#ifndef NDEBUG - for (auto &BBAndL : ExitLoopMap) { - auto *BB = BBAndL.first; - auto *OuterL = BBAndL.second; - assert(LI.getLoopFor(BB) == OuterL && - "Failed to put all blocks into outer loops!"); - } -#endif - - // Now that all the blocks are placed into the correct containing loop in the - // absence of child loops, find all the potentially cloned child loops and - // clone them into whatever outer loop we placed their header into. - for (Loop *ChildL : OrigL) { - auto *ClonedChildHeader = - cast_or_null<BasicBlock>(VMap.lookup(ChildL->getHeader())); - if (!ClonedChildHeader || BlocksInClonedLoop.count(ClonedChildHeader)) - continue; - -#ifndef NDEBUG - for (auto *ChildLoopBB : ChildL->blocks()) - assert(VMap.count(ChildLoopBB) && - "Cloned a child loop header but not all of that loops blocks!"); -#endif - - NonChildClonedLoops.push_back(cloneLoopNest( - *ChildL, ExitLoopMap.lookup(ClonedChildHeader), VMap, LI)); - } -} - -static void -deleteDeadClonedBlocks(Loop &L, ArrayRef<BasicBlock *> ExitBlocks, - ArrayRef<std::unique_ptr<ValueToValueMapTy>> VMaps, - DominatorTree &DT, MemorySSAUpdater *MSSAU) { - // Find all the dead clones, and remove them from their successors. - SmallVector<BasicBlock *, 16> DeadBlocks; - for (BasicBlock *BB : llvm::concat<BasicBlock *const>(L.blocks(), ExitBlocks)) - for (auto &VMap : VMaps) - if (BasicBlock *ClonedBB = cast_or_null<BasicBlock>(VMap->lookup(BB))) - if (!DT.isReachableFromEntry(ClonedBB)) { - for (BasicBlock *SuccBB : successors(ClonedBB)) - SuccBB->removePredecessor(ClonedBB); - DeadBlocks.push_back(ClonedBB); - } - - // Remove all MemorySSA in the dead blocks - if (MSSAU) { - SmallPtrSet<BasicBlock *, 16> DeadBlockSet(DeadBlocks.begin(), - DeadBlocks.end()); - MSSAU->removeBlocks(DeadBlockSet); - } - - // Drop any remaining references to break cycles. - for (BasicBlock *BB : DeadBlocks) - BB->dropAllReferences(); - // Erase them from the IR. - for (BasicBlock *BB : DeadBlocks) - BB->eraseFromParent(); -} - -static void deleteDeadBlocksFromLoop(Loop &L, - SmallVectorImpl<BasicBlock *> &ExitBlocks, - DominatorTree &DT, LoopInfo &LI, - MemorySSAUpdater *MSSAU) { - // Find all the dead blocks tied to this loop, and remove them from their - // successors. - SmallPtrSet<BasicBlock *, 16> DeadBlockSet; - - // Start with loop/exit blocks and get a transitive closure of reachable dead - // blocks. - SmallVector<BasicBlock *, 16> DeathCandidates(ExitBlocks.begin(), - ExitBlocks.end()); - DeathCandidates.append(L.blocks().begin(), L.blocks().end()); - while (!DeathCandidates.empty()) { - auto *BB = DeathCandidates.pop_back_val(); - if (!DeadBlockSet.count(BB) && !DT.isReachableFromEntry(BB)) { - for (BasicBlock *SuccBB : successors(BB)) { - SuccBB->removePredecessor(BB); - DeathCandidates.push_back(SuccBB); - } - DeadBlockSet.insert(BB); - } - } - - // Remove all MemorySSA in the dead blocks - if (MSSAU) - MSSAU->removeBlocks(DeadBlockSet); - - // Filter out the dead blocks from the exit blocks list so that it can be - // used in the caller. - llvm::erase_if(ExitBlocks, - [&](BasicBlock *BB) { return DeadBlockSet.count(BB); }); - - // Walk from this loop up through its parents removing all of the dead blocks. - for (Loop *ParentL = &L; ParentL; ParentL = ParentL->getParentLoop()) { - for (auto *BB : DeadBlockSet) - ParentL->getBlocksSet().erase(BB); - llvm::erase_if(ParentL->getBlocksVector(), - [&](BasicBlock *BB) { return DeadBlockSet.count(BB); }); - } - - // Now delete the dead child loops. This raw delete will clear them - // recursively. - llvm::erase_if(L.getSubLoopsVector(), [&](Loop *ChildL) { - if (!DeadBlockSet.count(ChildL->getHeader())) - return false; - - assert(llvm::all_of(ChildL->blocks(), - [&](BasicBlock *ChildBB) { - return DeadBlockSet.count(ChildBB); - }) && - "If the child loop header is dead all blocks in the child loop must " - "be dead as well!"); - LI.destroy(ChildL); - return true; - }); - - // Remove the loop mappings for the dead blocks and drop all the references - // from these blocks to others to handle cyclic references as we start - // deleting the blocks themselves. - for (auto *BB : DeadBlockSet) { - // Check that the dominator tree has already been updated. - assert(!DT.getNode(BB) && "Should already have cleared domtree!"); - LI.changeLoopFor(BB, nullptr); - BB->dropAllReferences(); - } - - // Actually delete the blocks now that they've been fully unhooked from the - // IR. - for (auto *BB : DeadBlockSet) - BB->eraseFromParent(); -} - -/// Recompute the set of blocks in a loop after unswitching. -/// -/// This walks from the original headers predecessors to rebuild the loop. We -/// take advantage of the fact that new blocks can't have been added, and so we -/// filter by the original loop's blocks. This also handles potentially -/// unreachable code that we don't want to explore but might be found examining -/// the predecessors of the header. -/// -/// If the original loop is no longer a loop, this will return an empty set. If -/// it remains a loop, all the blocks within it will be added to the set -/// (including those blocks in inner loops). -static SmallPtrSet<const BasicBlock *, 16> recomputeLoopBlockSet(Loop &L, - LoopInfo &LI) { - SmallPtrSet<const BasicBlock *, 16> LoopBlockSet; - - auto *PH = L.getLoopPreheader(); - auto *Header = L.getHeader(); - - // A worklist to use while walking backwards from the header. - SmallVector<BasicBlock *, 16> Worklist; - - // First walk the predecessors of the header to find the backedges. This will - // form the basis of our walk. - for (auto *Pred : predecessors(Header)) { - // Skip the preheader. - if (Pred == PH) - continue; - - // Because the loop was in simplified form, the only non-loop predecessor - // is the preheader. - assert(L.contains(Pred) && "Found a predecessor of the loop header other " - "than the preheader that is not part of the " - "loop!"); - - // Insert this block into the loop set and on the first visit and, if it - // isn't the header we're currently walking, put it into the worklist to - // recurse through. - if (LoopBlockSet.insert(Pred).second && Pred != Header) - Worklist.push_back(Pred); - } - - // If no backedges were found, we're done. - if (LoopBlockSet.empty()) - return LoopBlockSet; - - // We found backedges, recurse through them to identify the loop blocks. - while (!Worklist.empty()) { - BasicBlock *BB = Worklist.pop_back_val(); - assert(LoopBlockSet.count(BB) && "Didn't put block into the loop set!"); - - // No need to walk past the header. - if (BB == Header) - continue; - - // Because we know the inner loop structure remains valid we can use the - // loop structure to jump immediately across the entire nested loop. - // Further, because it is in loop simplified form, we can directly jump - // to its preheader afterward. - if (Loop *InnerL = LI.getLoopFor(BB)) - if (InnerL != &L) { - assert(L.contains(InnerL) && - "Should not reach a loop *outside* this loop!"); - // The preheader is the only possible predecessor of the loop so - // insert it into the set and check whether it was already handled. - auto *InnerPH = InnerL->getLoopPreheader(); - assert(L.contains(InnerPH) && "Cannot contain an inner loop block " - "but not contain the inner loop " - "preheader!"); - if (!LoopBlockSet.insert(InnerPH).second) - // The only way to reach the preheader is through the loop body - // itself so if it has been visited the loop is already handled. - continue; - - // Insert all of the blocks (other than those already present) into - // the loop set. We expect at least the block that led us to find the - // inner loop to be in the block set, but we may also have other loop - // blocks if they were already enqueued as predecessors of some other - // outer loop block. - for (auto *InnerBB : InnerL->blocks()) { - if (InnerBB == BB) { - assert(LoopBlockSet.count(InnerBB) && - "Block should already be in the set!"); - continue; - } - - LoopBlockSet.insert(InnerBB); - } - - // Add the preheader to the worklist so we will continue past the - // loop body. - Worklist.push_back(InnerPH); - continue; - } - - // Insert any predecessors that were in the original loop into the new - // set, and if the insert is successful, add them to the worklist. - for (auto *Pred : predecessors(BB)) - if (L.contains(Pred) && LoopBlockSet.insert(Pred).second) - Worklist.push_back(Pred); - } - - assert(LoopBlockSet.count(Header) && "Cannot fail to add the header!"); - - // We've found all the blocks participating in the loop, return our completed - // set. - return LoopBlockSet; -} - -/// Rebuild a loop after unswitching removes some subset of blocks and edges. -/// -/// The removal may have removed some child loops entirely but cannot have -/// disturbed any remaining child loops. However, they may need to be hoisted -/// to the parent loop (or to be top-level loops). The original loop may be -/// completely removed. -/// -/// The sibling loops resulting from this update are returned. If the original -/// loop remains a valid loop, it will be the first entry in this list with all -/// of the newly sibling loops following it. -/// -/// Returns true if the loop remains a loop after unswitching, and false if it -/// is no longer a loop after unswitching (and should not continue to be -/// referenced). -static bool rebuildLoopAfterUnswitch(Loop &L, ArrayRef<BasicBlock *> ExitBlocks, - LoopInfo &LI, - SmallVectorImpl<Loop *> &HoistedLoops) { - auto *PH = L.getLoopPreheader(); - - // Compute the actual parent loop from the exit blocks. Because we may have - // pruned some exits the loop may be different from the original parent. - Loop *ParentL = nullptr; - SmallVector<Loop *, 4> ExitLoops; - SmallVector<BasicBlock *, 4> ExitsInLoops; - ExitsInLoops.reserve(ExitBlocks.size()); - for (auto *ExitBB : ExitBlocks) - if (Loop *ExitL = LI.getLoopFor(ExitBB)) { - ExitLoops.push_back(ExitL); - ExitsInLoops.push_back(ExitBB); - if (!ParentL || (ParentL != ExitL && ParentL->contains(ExitL))) - ParentL = ExitL; - } - - // Recompute the blocks participating in this loop. This may be empty if it - // is no longer a loop. - auto LoopBlockSet = recomputeLoopBlockSet(L, LI); - - // If we still have a loop, we need to re-set the loop's parent as the exit - // block set changing may have moved it within the loop nest. Note that this - // can only happen when this loop has a parent as it can only hoist the loop - // *up* the nest. - if (!LoopBlockSet.empty() && L.getParentLoop() != ParentL) { - // Remove this loop's (original) blocks from all of the intervening loops. - for (Loop *IL = L.getParentLoop(); IL != ParentL; - IL = IL->getParentLoop()) { - IL->getBlocksSet().erase(PH); - for (auto *BB : L.blocks()) - IL->getBlocksSet().erase(BB); - llvm::erase_if(IL->getBlocksVector(), [&](BasicBlock *BB) { - return BB == PH || L.contains(BB); - }); - } - - LI.changeLoopFor(PH, ParentL); - L.getParentLoop()->removeChildLoop(&L); - if (ParentL) - ParentL->addChildLoop(&L); - else - LI.addTopLevelLoop(&L); - } - - // Now we update all the blocks which are no longer within the loop. - auto &Blocks = L.getBlocksVector(); - auto BlocksSplitI = - LoopBlockSet.empty() - ? Blocks.begin() - : std::stable_partition( - Blocks.begin(), Blocks.end(), - [&](BasicBlock *BB) { return LoopBlockSet.count(BB); }); - - // Before we erase the list of unlooped blocks, build a set of them. - SmallPtrSet<BasicBlock *, 16> UnloopedBlocks(BlocksSplitI, Blocks.end()); - if (LoopBlockSet.empty()) - UnloopedBlocks.insert(PH); - - // Now erase these blocks from the loop. - for (auto *BB : make_range(BlocksSplitI, Blocks.end())) - L.getBlocksSet().erase(BB); - Blocks.erase(BlocksSplitI, Blocks.end()); - - // Sort the exits in ascending loop depth, we'll work backwards across these - // to process them inside out. - std::stable_sort(ExitsInLoops.begin(), ExitsInLoops.end(), - [&](BasicBlock *LHS, BasicBlock *RHS) { - return LI.getLoopDepth(LHS) < LI.getLoopDepth(RHS); - }); - - // We'll build up a set for each exit loop. - SmallPtrSet<BasicBlock *, 16> NewExitLoopBlocks; - Loop *PrevExitL = L.getParentLoop(); // The deepest possible exit loop. - - auto RemoveUnloopedBlocksFromLoop = - [](Loop &L, SmallPtrSetImpl<BasicBlock *> &UnloopedBlocks) { - for (auto *BB : UnloopedBlocks) - L.getBlocksSet().erase(BB); - llvm::erase_if(L.getBlocksVector(), [&](BasicBlock *BB) { - return UnloopedBlocks.count(BB); - }); - }; - - SmallVector<BasicBlock *, 16> Worklist; - while (!UnloopedBlocks.empty() && !ExitsInLoops.empty()) { - assert(Worklist.empty() && "Didn't clear worklist!"); - assert(NewExitLoopBlocks.empty() && "Didn't clear loop set!"); - - // Grab the next exit block, in decreasing loop depth order. - BasicBlock *ExitBB = ExitsInLoops.pop_back_val(); - Loop &ExitL = *LI.getLoopFor(ExitBB); - assert(ExitL.contains(&L) && "Exit loop must contain the inner loop!"); - - // Erase all of the unlooped blocks from the loops between the previous - // exit loop and this exit loop. This works because the ExitInLoops list is - // sorted in increasing order of loop depth and thus we visit loops in - // decreasing order of loop depth. - for (; PrevExitL != &ExitL; PrevExitL = PrevExitL->getParentLoop()) - RemoveUnloopedBlocksFromLoop(*PrevExitL, UnloopedBlocks); - - // Walk the CFG back until we hit the cloned PH adding everything reachable - // and in the unlooped set to this exit block's loop. - Worklist.push_back(ExitBB); - do { - BasicBlock *BB = Worklist.pop_back_val(); - // We can stop recursing at the cloned preheader (if we get there). - if (BB == PH) - continue; - - for (BasicBlock *PredBB : predecessors(BB)) { - // If this pred has already been moved to our set or is part of some - // (inner) loop, no update needed. - if (!UnloopedBlocks.erase(PredBB)) { - assert((NewExitLoopBlocks.count(PredBB) || - ExitL.contains(LI.getLoopFor(PredBB))) && - "Predecessor not in a nested loop (or already visited)!"); - continue; - } - - // We just insert into the loop set here. We'll add these blocks to the - // exit loop after we build up the set in a deterministic order rather - // than the predecessor-influenced visit order. - bool Inserted = NewExitLoopBlocks.insert(PredBB).second; - (void)Inserted; - assert(Inserted && "Should only visit an unlooped block once!"); - - // And recurse through to its predecessors. - Worklist.push_back(PredBB); - } - } while (!Worklist.empty()); - - // If blocks in this exit loop were directly part of the original loop (as - // opposed to a child loop) update the map to point to this exit loop. This - // just updates a map and so the fact that the order is unstable is fine. - for (auto *BB : NewExitLoopBlocks) - if (Loop *BBL = LI.getLoopFor(BB)) - if (BBL == &L || !L.contains(BBL)) - LI.changeLoopFor(BB, &ExitL); - - // We will remove the remaining unlooped blocks from this loop in the next - // iteration or below. - NewExitLoopBlocks.clear(); - } - - // Any remaining unlooped blocks are no longer part of any loop unless they - // are part of some child loop. - for (; PrevExitL; PrevExitL = PrevExitL->getParentLoop()) - RemoveUnloopedBlocksFromLoop(*PrevExitL, UnloopedBlocks); - for (auto *BB : UnloopedBlocks) - if (Loop *BBL = LI.getLoopFor(BB)) - if (BBL == &L || !L.contains(BBL)) - LI.changeLoopFor(BB, nullptr); - - // Sink all the child loops whose headers are no longer in the loop set to - // the parent (or to be top level loops). We reach into the loop and directly - // update its subloop vector to make this batch update efficient. - auto &SubLoops = L.getSubLoopsVector(); - auto SubLoopsSplitI = - LoopBlockSet.empty() - ? SubLoops.begin() - : std::stable_partition( - SubLoops.begin(), SubLoops.end(), [&](Loop *SubL) { - return LoopBlockSet.count(SubL->getHeader()); - }); - for (auto *HoistedL : make_range(SubLoopsSplitI, SubLoops.end())) { - HoistedLoops.push_back(HoistedL); - HoistedL->setParentLoop(nullptr); - - // To compute the new parent of this hoisted loop we look at where we - // placed the preheader above. We can't lookup the header itself because we - // retained the mapping from the header to the hoisted loop. But the - // preheader and header should have the exact same new parent computed - // based on the set of exit blocks from the original loop as the preheader - // is a predecessor of the header and so reached in the reverse walk. And - // because the loops were all in simplified form the preheader of the - // hoisted loop can't be part of some *other* loop. - if (auto *NewParentL = LI.getLoopFor(HoistedL->getLoopPreheader())) - NewParentL->addChildLoop(HoistedL); - else - LI.addTopLevelLoop(HoistedL); - } - SubLoops.erase(SubLoopsSplitI, SubLoops.end()); - - // Actually delete the loop if nothing remained within it. - if (Blocks.empty()) { - assert(SubLoops.empty() && - "Failed to remove all subloops from the original loop!"); - if (Loop *ParentL = L.getParentLoop()) - ParentL->removeChildLoop(llvm::find(*ParentL, &L)); - else - LI.removeLoop(llvm::find(LI, &L)); - LI.destroy(&L); - return false; - } - - return true; -} - -/// Helper to visit a dominator subtree, invoking a callable on each node. -/// -/// Returning false at any point will stop walking past that node of the tree. -template <typename CallableT> -void visitDomSubTree(DominatorTree &DT, BasicBlock *BB, CallableT Callable) { - SmallVector<DomTreeNode *, 4> DomWorklist; - DomWorklist.push_back(DT[BB]); -#ifndef NDEBUG - SmallPtrSet<DomTreeNode *, 4> Visited; - Visited.insert(DT[BB]); -#endif - do { - DomTreeNode *N = DomWorklist.pop_back_val(); - - // Visit this node. - if (!Callable(N->getBlock())) - continue; - - // Accumulate the child nodes. - for (DomTreeNode *ChildN : *N) { - assert(Visited.insert(ChildN).second && - "Cannot visit a node twice when walking a tree!"); - DomWorklist.push_back(ChildN); - } - } while (!DomWorklist.empty()); -} - -static void unswitchNontrivialInvariants( - Loop &L, Instruction &TI, ArrayRef<Value *> Invariants, - SmallVectorImpl<BasicBlock *> &ExitBlocks, DominatorTree &DT, LoopInfo &LI, - AssumptionCache &AC, function_ref<void(bool, ArrayRef<Loop *>)> UnswitchCB, - ScalarEvolution *SE, MemorySSAUpdater *MSSAU) { - auto *ParentBB = TI.getParent(); - BranchInst *BI = dyn_cast<BranchInst>(&TI); - SwitchInst *SI = BI ? nullptr : cast<SwitchInst>(&TI); - - // We can only unswitch switches, conditional branches with an invariant - // condition, or combining invariant conditions with an instruction. - assert((SI || BI->isConditional()) && - "Can only unswitch switches and conditional branch!"); - bool FullUnswitch = SI || BI->getCondition() == Invariants[0]; - if (FullUnswitch) - assert(Invariants.size() == 1 && - "Cannot have other invariants with full unswitching!"); - else - assert(isa<Instruction>(BI->getCondition()) && - "Partial unswitching requires an instruction as the condition!"); - - if (MSSAU && VerifyMemorySSA) - MSSAU->getMemorySSA()->verifyMemorySSA(); - - // Constant and BBs tracking the cloned and continuing successor. When we are - // unswitching the entire condition, this can just be trivially chosen to - // unswitch towards `true`. However, when we are unswitching a set of - // invariants combined with `and` or `or`, the combining operation determines - // the best direction to unswitch: we want to unswitch the direction that will - // collapse the branch. - bool Direction = true; - int ClonedSucc = 0; - if (!FullUnswitch) { - if (cast<Instruction>(BI->getCondition())->getOpcode() != Instruction::Or) { - assert(cast<Instruction>(BI->getCondition())->getOpcode() == - Instruction::And && - "Only `or` and `and` instructions can combine invariants being " - "unswitched."); - Direction = false; - ClonedSucc = 1; - } - } - - BasicBlock *RetainedSuccBB = - BI ? BI->getSuccessor(1 - ClonedSucc) : SI->getDefaultDest(); - SmallSetVector<BasicBlock *, 4> UnswitchedSuccBBs; - if (BI) - UnswitchedSuccBBs.insert(BI->getSuccessor(ClonedSucc)); - else - for (auto Case : SI->cases()) - if (Case.getCaseSuccessor() != RetainedSuccBB) - UnswitchedSuccBBs.insert(Case.getCaseSuccessor()); - - assert(!UnswitchedSuccBBs.count(RetainedSuccBB) && - "Should not unswitch the same successor we are retaining!"); - - // The branch should be in this exact loop. Any inner loop's invariant branch - // should be handled by unswitching that inner loop. The caller of this - // routine should filter out any candidates that remain (but were skipped for - // whatever reason). - assert(LI.getLoopFor(ParentBB) == &L && "Branch in an inner loop!"); - - // Compute the parent loop now before we start hacking on things. - Loop *ParentL = L.getParentLoop(); - // Get blocks in RPO order for MSSA update, before changing the CFG. - LoopBlocksRPO LBRPO(&L); - if (MSSAU) - LBRPO.perform(&LI); - - // Compute the outer-most loop containing one of our exit blocks. This is the - // furthest up our loopnest which can be mutated, which we will use below to - // update things. - Loop *OuterExitL = &L; - for (auto *ExitBB : ExitBlocks) { - Loop *NewOuterExitL = LI.getLoopFor(ExitBB); - if (!NewOuterExitL) { - // We exited the entire nest with this block, so we're done. - OuterExitL = nullptr; - break; - } - if (NewOuterExitL != OuterExitL && NewOuterExitL->contains(OuterExitL)) - OuterExitL = NewOuterExitL; - } - - // At this point, we're definitely going to unswitch something so invalidate - // any cached information in ScalarEvolution for the outer most loop - // containing an exit block and all nested loops. - if (SE) { - if (OuterExitL) - SE->forgetLoop(OuterExitL); - else - SE->forgetTopmostLoop(&L); - } - - // If the edge from this terminator to a successor dominates that successor, - // store a map from each block in its dominator subtree to it. This lets us - // tell when cloning for a particular successor if a block is dominated by - // some *other* successor with a single data structure. We use this to - // significantly reduce cloning. - SmallDenseMap<BasicBlock *, BasicBlock *, 16> DominatingSucc; - for (auto *SuccBB : llvm::concat<BasicBlock *const>( - makeArrayRef(RetainedSuccBB), UnswitchedSuccBBs)) - if (SuccBB->getUniquePredecessor() || - llvm::all_of(predecessors(SuccBB), [&](BasicBlock *PredBB) { - return PredBB == ParentBB || DT.dominates(SuccBB, PredBB); - })) - visitDomSubTree(DT, SuccBB, [&](BasicBlock *BB) { - DominatingSucc[BB] = SuccBB; - return true; - }); - - // Split the preheader, so that we know that there is a safe place to insert - // the conditional branch. We will change the preheader to have a conditional - // branch on LoopCond. The original preheader will become the split point - // between the unswitched versions, and we will have a new preheader for the - // original loop. - BasicBlock *SplitBB = L.getLoopPreheader(); - BasicBlock *LoopPH = SplitEdge(SplitBB, L.getHeader(), &DT, &LI, MSSAU); - - // Keep track of the dominator tree updates needed. - SmallVector<DominatorTree::UpdateType, 4> DTUpdates; - - // Clone the loop for each unswitched successor. - SmallVector<std::unique_ptr<ValueToValueMapTy>, 4> VMaps; - VMaps.reserve(UnswitchedSuccBBs.size()); - SmallDenseMap<BasicBlock *, BasicBlock *, 4> ClonedPHs; - for (auto *SuccBB : UnswitchedSuccBBs) { - VMaps.emplace_back(new ValueToValueMapTy()); - ClonedPHs[SuccBB] = buildClonedLoopBlocks( - L, LoopPH, SplitBB, ExitBlocks, ParentBB, SuccBB, RetainedSuccBB, - DominatingSucc, *VMaps.back(), DTUpdates, AC, DT, LI, MSSAU); - } - - // The stitching of the branched code back together depends on whether we're - // doing full unswitching or not with the exception that we always want to - // nuke the initial terminator placed in the split block. - SplitBB->getTerminator()->eraseFromParent(); - if (FullUnswitch) { - // Splice the terminator from the original loop and rewrite its - // successors. - SplitBB->getInstList().splice(SplitBB->end(), ParentBB->getInstList(), TI); - - // Keep a clone of the terminator for MSSA updates. - Instruction *NewTI = TI.clone(); - ParentBB->getInstList().push_back(NewTI); - - // First wire up the moved terminator to the preheaders. - if (BI) { - BasicBlock *ClonedPH = ClonedPHs.begin()->second; - BI->setSuccessor(ClonedSucc, ClonedPH); - BI->setSuccessor(1 - ClonedSucc, LoopPH); - DTUpdates.push_back({DominatorTree::Insert, SplitBB, ClonedPH}); - } else { - assert(SI && "Must either be a branch or switch!"); - - // Walk the cases and directly update their successors. - assert(SI->getDefaultDest() == RetainedSuccBB && - "Not retaining default successor!"); - SI->setDefaultDest(LoopPH); - for (auto &Case : SI->cases()) - if (Case.getCaseSuccessor() == RetainedSuccBB) - Case.setSuccessor(LoopPH); - else - Case.setSuccessor(ClonedPHs.find(Case.getCaseSuccessor())->second); - - // We need to use the set to populate domtree updates as even when there - // are multiple cases pointing at the same successor we only want to - // remove and insert one edge in the domtree. - for (BasicBlock *SuccBB : UnswitchedSuccBBs) - DTUpdates.push_back( - {DominatorTree::Insert, SplitBB, ClonedPHs.find(SuccBB)->second}); - } - - if (MSSAU) { - DT.applyUpdates(DTUpdates); - DTUpdates.clear(); - - // Remove all but one edge to the retained block and all unswitched - // blocks. This is to avoid having duplicate entries in the cloned Phis, - // when we know we only keep a single edge for each case. - MSSAU->removeDuplicatePhiEdgesBetween(ParentBB, RetainedSuccBB); - for (BasicBlock *SuccBB : UnswitchedSuccBBs) - MSSAU->removeDuplicatePhiEdgesBetween(ParentBB, SuccBB); - - for (auto &VMap : VMaps) - MSSAU->updateForClonedLoop(LBRPO, ExitBlocks, *VMap, - /*IgnoreIncomingWithNoClones=*/true); - MSSAU->updateExitBlocksForClonedLoop(ExitBlocks, VMaps, DT); - - // Remove all edges to unswitched blocks. - for (BasicBlock *SuccBB : UnswitchedSuccBBs) - MSSAU->removeEdge(ParentBB, SuccBB); - } - - // Now unhook the successor relationship as we'll be replacing - // the terminator with a direct branch. This is much simpler for branches - // than switches so we handle those first. - if (BI) { - // Remove the parent as a predecessor of the unswitched successor. - assert(UnswitchedSuccBBs.size() == 1 && - "Only one possible unswitched block for a branch!"); - BasicBlock *UnswitchedSuccBB = *UnswitchedSuccBBs.begin(); - UnswitchedSuccBB->removePredecessor(ParentBB, - /*DontDeleteUselessPHIs*/ true); - DTUpdates.push_back({DominatorTree::Delete, ParentBB, UnswitchedSuccBB}); - } else { - // Note that we actually want to remove the parent block as a predecessor - // of *every* case successor. The case successor is either unswitched, - // completely eliminating an edge from the parent to that successor, or it - // is a duplicate edge to the retained successor as the retained successor - // is always the default successor and as we'll replace this with a direct - // branch we no longer need the duplicate entries in the PHI nodes. - SwitchInst *NewSI = cast<SwitchInst>(NewTI); - assert(NewSI->getDefaultDest() == RetainedSuccBB && - "Not retaining default successor!"); - for (auto &Case : NewSI->cases()) - Case.getCaseSuccessor()->removePredecessor( - ParentBB, - /*DontDeleteUselessPHIs*/ true); - - // We need to use the set to populate domtree updates as even when there - // are multiple cases pointing at the same successor we only want to - // remove and insert one edge in the domtree. - for (BasicBlock *SuccBB : UnswitchedSuccBBs) - DTUpdates.push_back({DominatorTree::Delete, ParentBB, SuccBB}); - } - - // After MSSAU update, remove the cloned terminator instruction NewTI. - ParentBB->getTerminator()->eraseFromParent(); - - // Create a new unconditional branch to the continuing block (as opposed to - // the one cloned). - BranchInst::Create(RetainedSuccBB, ParentBB); - } else { - assert(BI && "Only branches have partial unswitching."); - assert(UnswitchedSuccBBs.size() == 1 && - "Only one possible unswitched block for a branch!"); - BasicBlock *ClonedPH = ClonedPHs.begin()->second; - // When doing a partial unswitch, we have to do a bit more work to build up - // the branch in the split block. - buildPartialUnswitchConditionalBranch(*SplitBB, Invariants, Direction, - *ClonedPH, *LoopPH); - DTUpdates.push_back({DominatorTree::Insert, SplitBB, ClonedPH}); - } - - // Apply the updates accumulated above to get an up-to-date dominator tree. - DT.applyUpdates(DTUpdates); - if (!FullUnswitch && MSSAU) { - // Update MSSA for partial unswitch, after DT update. - SmallVector<CFGUpdate, 1> Updates; - Updates.push_back( - {cfg::UpdateKind::Insert, SplitBB, ClonedPHs.begin()->second}); - MSSAU->applyInsertUpdates(Updates, DT); - } - - // Now that we have an accurate dominator tree, first delete the dead cloned - // blocks so that we can accurately build any cloned loops. It is important to - // not delete the blocks from the original loop yet because we still want to - // reference the original loop to understand the cloned loop's structure. - deleteDeadClonedBlocks(L, ExitBlocks, VMaps, DT, MSSAU); - - // Build the cloned loop structure itself. This may be substantially - // different from the original structure due to the simplified CFG. This also - // handles inserting all the cloned blocks into the correct loops. - SmallVector<Loop *, 4> NonChildClonedLoops; - for (std::unique_ptr<ValueToValueMapTy> &VMap : VMaps) - buildClonedLoops(L, ExitBlocks, *VMap, LI, NonChildClonedLoops); - - // Now that our cloned loops have been built, we can update the original loop. - // First we delete the dead blocks from it and then we rebuild the loop - // structure taking these deletions into account. - deleteDeadBlocksFromLoop(L, ExitBlocks, DT, LI, MSSAU); - - if (MSSAU && VerifyMemorySSA) - MSSAU->getMemorySSA()->verifyMemorySSA(); - - SmallVector<Loop *, 4> HoistedLoops; - bool IsStillLoop = rebuildLoopAfterUnswitch(L, ExitBlocks, LI, HoistedLoops); - - if (MSSAU && VerifyMemorySSA) - MSSAU->getMemorySSA()->verifyMemorySSA(); - - // This transformation has a high risk of corrupting the dominator tree, and - // the below steps to rebuild loop structures will result in hard to debug - // errors in that case so verify that the dominator tree is sane first. - // FIXME: Remove this when the bugs stop showing up and rely on existing - // verification steps. - assert(DT.verify(DominatorTree::VerificationLevel::Fast)); - - if (BI) { - // If we unswitched a branch which collapses the condition to a known - // constant we want to replace all the uses of the invariants within both - // the original and cloned blocks. We do this here so that we can use the - // now updated dominator tree to identify which side the users are on. - assert(UnswitchedSuccBBs.size() == 1 && - "Only one possible unswitched block for a branch!"); - BasicBlock *ClonedPH = ClonedPHs.begin()->second; - - // When considering multiple partially-unswitched invariants - // we cant just go replace them with constants in both branches. - // - // For 'AND' we infer that true branch ("continue") means true - // for each invariant operand. - // For 'OR' we can infer that false branch ("continue") means false - // for each invariant operand. - // So it happens that for multiple-partial case we dont replace - // in the unswitched branch. - bool ReplaceUnswitched = FullUnswitch || (Invariants.size() == 1); - - ConstantInt *UnswitchedReplacement = - Direction ? ConstantInt::getTrue(BI->getContext()) - : ConstantInt::getFalse(BI->getContext()); - ConstantInt *ContinueReplacement = - Direction ? ConstantInt::getFalse(BI->getContext()) - : ConstantInt::getTrue(BI->getContext()); - for (Value *Invariant : Invariants) - for (auto UI = Invariant->use_begin(), UE = Invariant->use_end(); - UI != UE;) { - // Grab the use and walk past it so we can clobber it in the use list. - Use *U = &*UI++; - Instruction *UserI = dyn_cast<Instruction>(U->getUser()); - if (!UserI) - continue; - - // Replace it with the 'continue' side if in the main loop body, and the - // unswitched if in the cloned blocks. - if (DT.dominates(LoopPH, UserI->getParent())) - U->set(ContinueReplacement); - else if (ReplaceUnswitched && - DT.dominates(ClonedPH, UserI->getParent())) - U->set(UnswitchedReplacement); - } - } - - // We can change which blocks are exit blocks of all the cloned sibling - // loops, the current loop, and any parent loops which shared exit blocks - // with the current loop. As a consequence, we need to re-form LCSSA for - // them. But we shouldn't need to re-form LCSSA for any child loops. - // FIXME: This could be made more efficient by tracking which exit blocks are - // new, and focusing on them, but that isn't likely to be necessary. - // - // In order to reasonably rebuild LCSSA we need to walk inside-out across the - // loop nest and update every loop that could have had its exits changed. We - // also need to cover any intervening loops. We add all of these loops to - // a list and sort them by loop depth to achieve this without updating - // unnecessary loops. - auto UpdateLoop = [&](Loop &UpdateL) { -#ifndef NDEBUG - UpdateL.verifyLoop(); - for (Loop *ChildL : UpdateL) { - ChildL->verifyLoop(); - assert(ChildL->isRecursivelyLCSSAForm(DT, LI) && - "Perturbed a child loop's LCSSA form!"); - } -#endif - // First build LCSSA for this loop so that we can preserve it when - // forming dedicated exits. We don't want to perturb some other loop's - // LCSSA while doing that CFG edit. - formLCSSA(UpdateL, DT, &LI, nullptr); - - // For loops reached by this loop's original exit blocks we may - // introduced new, non-dedicated exits. At least try to re-form dedicated - // exits for these loops. This may fail if they couldn't have dedicated - // exits to start with. - formDedicatedExitBlocks(&UpdateL, &DT, &LI, /*PreserveLCSSA*/ true); - }; - - // For non-child cloned loops and hoisted loops, we just need to update LCSSA - // and we can do it in any order as they don't nest relative to each other. - // - // Also check if any of the loops we have updated have become top-level loops - // as that will necessitate widening the outer loop scope. - for (Loop *UpdatedL : - llvm::concat<Loop *>(NonChildClonedLoops, HoistedLoops)) { - UpdateLoop(*UpdatedL); - if (!UpdatedL->getParentLoop()) - OuterExitL = nullptr; - } - if (IsStillLoop) { - UpdateLoop(L); - if (!L.getParentLoop()) - OuterExitL = nullptr; - } - - // If the original loop had exit blocks, walk up through the outer most loop - // of those exit blocks to update LCSSA and form updated dedicated exits. - if (OuterExitL != &L) - for (Loop *OuterL = ParentL; OuterL != OuterExitL; - OuterL = OuterL->getParentLoop()) - UpdateLoop(*OuterL); - -#ifndef NDEBUG - // Verify the entire loop structure to catch any incorrect updates before we - // progress in the pass pipeline. - LI.verify(DT); -#endif - - // Now that we've unswitched something, make callbacks to report the changes. - // For that we need to merge together the updated loops and the cloned loops - // and check whether the original loop survived. - SmallVector<Loop *, 4> SibLoops; - for (Loop *UpdatedL : llvm::concat<Loop *>(NonChildClonedLoops, HoistedLoops)) - if (UpdatedL->getParentLoop() == ParentL) - SibLoops.push_back(UpdatedL); - UnswitchCB(IsStillLoop, SibLoops); - - if (MSSAU && VerifyMemorySSA) - MSSAU->getMemorySSA()->verifyMemorySSA(); - - if (BI) - ++NumBranches; - else - ++NumSwitches; -} - -/// Recursively compute the cost of a dominator subtree based on the per-block -/// cost map provided. -/// -/// The recursive computation is memozied into the provided DT-indexed cost map -/// to allow querying it for most nodes in the domtree without it becoming -/// quadratic. -static int -computeDomSubtreeCost(DomTreeNode &N, - const SmallDenseMap<BasicBlock *, int, 4> &BBCostMap, - SmallDenseMap<DomTreeNode *, int, 4> &DTCostMap) { - // Don't accumulate cost (or recurse through) blocks not in our block cost - // map and thus not part of the duplication cost being considered. - auto BBCostIt = BBCostMap.find(N.getBlock()); - if (BBCostIt == BBCostMap.end()) - return 0; - - // Lookup this node to see if we already computed its cost. - auto DTCostIt = DTCostMap.find(&N); - if (DTCostIt != DTCostMap.end()) - return DTCostIt->second; - - // If not, we have to compute it. We can't use insert above and update - // because computing the cost may insert more things into the map. - int Cost = std::accumulate( - N.begin(), N.end(), BBCostIt->second, [&](int Sum, DomTreeNode *ChildN) { - return Sum + computeDomSubtreeCost(*ChildN, BBCostMap, DTCostMap); - }); - bool Inserted = DTCostMap.insert({&N, Cost}).second; - (void)Inserted; - assert(Inserted && "Should not insert a node while visiting children!"); - return Cost; -} - -/// Turns a llvm.experimental.guard intrinsic into implicit control flow branch, -/// making the following replacement: -/// -/// --code before guard-- -/// call void (i1, ...) @llvm.experimental.guard(i1 %cond) [ "deopt"() ] -/// --code after guard-- -/// -/// into -/// -/// --code before guard-- -/// br i1 %cond, label %guarded, label %deopt -/// -/// guarded: -/// --code after guard-- -/// -/// deopt: -/// call void (i1, ...) @llvm.experimental.guard(i1 false) [ "deopt"() ] -/// unreachable -/// -/// It also makes all relevant DT and LI updates, so that all structures are in -/// valid state after this transform. -static BranchInst * -turnGuardIntoBranch(IntrinsicInst *GI, Loop &L, - SmallVectorImpl<BasicBlock *> &ExitBlocks, - DominatorTree &DT, LoopInfo &LI, MemorySSAUpdater *MSSAU) { - SmallVector<DominatorTree::UpdateType, 4> DTUpdates; - LLVM_DEBUG(dbgs() << "Turning " << *GI << " into a branch.\n"); - BasicBlock *CheckBB = GI->getParent(); - - if (MSSAU && VerifyMemorySSA) - MSSAU->getMemorySSA()->verifyMemorySSA(); - - // Remove all CheckBB's successors from DomTree. A block can be seen among - // successors more than once, but for DomTree it should be added only once. - SmallPtrSet<BasicBlock *, 4> Successors; - for (auto *Succ : successors(CheckBB)) - if (Successors.insert(Succ).second) - DTUpdates.push_back({DominatorTree::Delete, CheckBB, Succ}); - - Instruction *DeoptBlockTerm = - SplitBlockAndInsertIfThen(GI->getArgOperand(0), GI, true); - BranchInst *CheckBI = cast<BranchInst>(CheckBB->getTerminator()); - // SplitBlockAndInsertIfThen inserts control flow that branches to - // DeoptBlockTerm if the condition is true. We want the opposite. - CheckBI->swapSuccessors(); - - BasicBlock *GuardedBlock = CheckBI->getSuccessor(0); - GuardedBlock->setName("guarded"); - CheckBI->getSuccessor(1)->setName("deopt"); - BasicBlock *DeoptBlock = CheckBI->getSuccessor(1); - - // We now have a new exit block. - ExitBlocks.push_back(CheckBI->getSuccessor(1)); - - if (MSSAU) - MSSAU->moveAllAfterSpliceBlocks(CheckBB, GuardedBlock, GI); - - GI->moveBefore(DeoptBlockTerm); - GI->setArgOperand(0, ConstantInt::getFalse(GI->getContext())); - - // Add new successors of CheckBB into DomTree. - for (auto *Succ : successors(CheckBB)) - DTUpdates.push_back({DominatorTree::Insert, CheckBB, Succ}); - - // Now the blocks that used to be CheckBB's successors are GuardedBlock's - // successors. - for (auto *Succ : Successors) - DTUpdates.push_back({DominatorTree::Insert, GuardedBlock, Succ}); - - // Make proper changes to DT. - DT.applyUpdates(DTUpdates); - // Inform LI of a new loop block. - L.addBasicBlockToLoop(GuardedBlock, LI); - - if (MSSAU) { - MemoryDef *MD = cast<MemoryDef>(MSSAU->getMemorySSA()->getMemoryAccess(GI)); - MSSAU->moveToPlace(MD, DeoptBlock, MemorySSA::End); - if (VerifyMemorySSA) - MSSAU->getMemorySSA()->verifyMemorySSA(); - } - - ++NumGuards; - return CheckBI; -} - -/// Cost multiplier is a way to limit potentially exponential behavior -/// of loop-unswitch. Cost is multipied in proportion of 2^number of unswitch -/// candidates available. Also accounting for the number of "sibling" loops with -/// the idea to account for previous unswitches that already happened on this -/// cluster of loops. There was an attempt to keep this formula simple, -/// just enough to limit the worst case behavior. Even if it is not that simple -/// now it is still not an attempt to provide a detailed heuristic size -/// prediction. -/// -/// TODO: Make a proper accounting of "explosion" effect for all kinds of -/// unswitch candidates, making adequate predictions instead of wild guesses. -/// That requires knowing not just the number of "remaining" candidates but -/// also costs of unswitching for each of these candidates. -static int calculateUnswitchCostMultiplier( - Instruction &TI, Loop &L, LoopInfo &LI, DominatorTree &DT, - ArrayRef<std::pair<Instruction *, TinyPtrVector<Value *>>> - UnswitchCandidates) { - - // Guards and other exiting conditions do not contribute to exponential - // explosion as soon as they dominate the latch (otherwise there might be - // another path to the latch remaining that does not allow to eliminate the - // loop copy on unswitch). - BasicBlock *Latch = L.getLoopLatch(); - BasicBlock *CondBlock = TI.getParent(); - if (DT.dominates(CondBlock, Latch) && - (isGuard(&TI) || - llvm::count_if(successors(&TI), [&L](BasicBlock *SuccBB) { - return L.contains(SuccBB); - }) <= 1)) { - NumCostMultiplierSkipped++; - return 1; - } - - auto *ParentL = L.getParentLoop(); - int SiblingsCount = (ParentL ? ParentL->getSubLoopsVector().size() - : std::distance(LI.begin(), LI.end())); - // Count amount of clones that all the candidates might cause during - // unswitching. Branch/guard counts as 1, switch counts as log2 of its cases. - int UnswitchedClones = 0; - for (auto Candidate : UnswitchCandidates) { - Instruction *CI = Candidate.first; - BasicBlock *CondBlock = CI->getParent(); - bool SkipExitingSuccessors = DT.dominates(CondBlock, Latch); - if (isGuard(CI)) { - if (!SkipExitingSuccessors) - UnswitchedClones++; - continue; - } - int NonExitingSuccessors = llvm::count_if( - successors(CondBlock), [SkipExitingSuccessors, &L](BasicBlock *SuccBB) { - return !SkipExitingSuccessors || L.contains(SuccBB); - }); - UnswitchedClones += Log2_32(NonExitingSuccessors); - } - - // Ignore up to the "unscaled candidates" number of unswitch candidates - // when calculating the power-of-two scaling of the cost. The main idea - // with this control is to allow a small number of unswitches to happen - // and rely more on siblings multiplier (see below) when the number - // of candidates is small. - unsigned ClonesPower = - std::max(UnswitchedClones - (int)UnswitchNumInitialUnscaledCandidates, 0); - - // Allowing top-level loops to spread a bit more than nested ones. - int SiblingsMultiplier = - std::max((ParentL ? SiblingsCount - : SiblingsCount / (int)UnswitchSiblingsToplevelDiv), - 1); - // Compute the cost multiplier in a way that won't overflow by saturating - // at an upper bound. - int CostMultiplier; - if (ClonesPower > Log2_32(UnswitchThreshold) || - SiblingsMultiplier > UnswitchThreshold) - CostMultiplier = UnswitchThreshold; - else - CostMultiplier = std::min(SiblingsMultiplier * (1 << ClonesPower), - (int)UnswitchThreshold); - - LLVM_DEBUG(dbgs() << " Computed multiplier " << CostMultiplier - << " (siblings " << SiblingsMultiplier << " * clones " - << (1 << ClonesPower) << ")" - << " for unswitch candidate: " << TI << "\n"); - return CostMultiplier; -} - -static bool -unswitchBestCondition(Loop &L, DominatorTree &DT, LoopInfo &LI, - AssumptionCache &AC, TargetTransformInfo &TTI, - function_ref<void(bool, ArrayRef<Loop *>)> UnswitchCB, - ScalarEvolution *SE, MemorySSAUpdater *MSSAU) { - // Collect all invariant conditions within this loop (as opposed to an inner - // loop which would be handled when visiting that inner loop). - SmallVector<std::pair<Instruction *, TinyPtrVector<Value *>>, 4> - UnswitchCandidates; - - // Whether or not we should also collect guards in the loop. - bool CollectGuards = false; - if (UnswitchGuards) { - auto *GuardDecl = L.getHeader()->getParent()->getParent()->getFunction( - Intrinsic::getName(Intrinsic::experimental_guard)); - if (GuardDecl && !GuardDecl->use_empty()) - CollectGuards = true; - } - - for (auto *BB : L.blocks()) { - if (LI.getLoopFor(BB) != &L) - continue; - - if (CollectGuards) - for (auto &I : *BB) - if (isGuard(&I)) { - auto *Cond = cast<IntrinsicInst>(&I)->getArgOperand(0); - // TODO: Support AND, OR conditions and partial unswitching. - if (!isa<Constant>(Cond) && L.isLoopInvariant(Cond)) - UnswitchCandidates.push_back({&I, {Cond}}); - } - - if (auto *SI = dyn_cast<SwitchInst>(BB->getTerminator())) { - // We can only consider fully loop-invariant switch conditions as we need - // to completely eliminate the switch after unswitching. - if (!isa<Constant>(SI->getCondition()) && - L.isLoopInvariant(SI->getCondition())) - UnswitchCandidates.push_back({SI, {SI->getCondition()}}); - continue; - } - - auto *BI = dyn_cast<BranchInst>(BB->getTerminator()); - if (!BI || !BI->isConditional() || isa<Constant>(BI->getCondition()) || - BI->getSuccessor(0) == BI->getSuccessor(1)) - continue; - - if (L.isLoopInvariant(BI->getCondition())) { - UnswitchCandidates.push_back({BI, {BI->getCondition()}}); - continue; - } - - Instruction &CondI = *cast<Instruction>(BI->getCondition()); - if (CondI.getOpcode() != Instruction::And && - CondI.getOpcode() != Instruction::Or) - continue; - - TinyPtrVector<Value *> Invariants = - collectHomogenousInstGraphLoopInvariants(L, CondI, LI); - if (Invariants.empty()) - continue; - - UnswitchCandidates.push_back({BI, std::move(Invariants)}); - } - - // If we didn't find any candidates, we're done. - if (UnswitchCandidates.empty()) - return false; - - // Check if there are irreducible CFG cycles in this loop. If so, we cannot - // easily unswitch non-trivial edges out of the loop. Doing so might turn the - // irreducible control flow into reducible control flow and introduce new - // loops "out of thin air". If we ever discover important use cases for doing - // this, we can add support to loop unswitch, but it is a lot of complexity - // for what seems little or no real world benefit. - LoopBlocksRPO RPOT(&L); - RPOT.perform(&LI); - if (containsIrreducibleCFG<const BasicBlock *>(RPOT, LI)) - return false; - - SmallVector<BasicBlock *, 4> ExitBlocks; - L.getUniqueExitBlocks(ExitBlocks); - - // We cannot unswitch if exit blocks contain a cleanuppad instruction as we - // don't know how to split those exit blocks. - // FIXME: We should teach SplitBlock to handle this and remove this - // restriction. - for (auto *ExitBB : ExitBlocks) - if (isa<CleanupPadInst>(ExitBB->getFirstNonPHI())) { - dbgs() << "Cannot unswitch because of cleanuppad in exit block\n"; - return false; - } - - LLVM_DEBUG( - dbgs() << "Considering " << UnswitchCandidates.size() - << " non-trivial loop invariant conditions for unswitching.\n"); - - // Given that unswitching these terminators will require duplicating parts of - // the loop, so we need to be able to model that cost. Compute the ephemeral - // values and set up a data structure to hold per-BB costs. We cache each - // block's cost so that we don't recompute this when considering different - // subsets of the loop for duplication during unswitching. - SmallPtrSet<const Value *, 4> EphValues; - CodeMetrics::collectEphemeralValues(&L, &AC, EphValues); - SmallDenseMap<BasicBlock *, int, 4> BBCostMap; - - // Compute the cost of each block, as well as the total loop cost. Also, bail - // out if we see instructions which are incompatible with loop unswitching - // (convergent, noduplicate, or cross-basic-block tokens). - // FIXME: We might be able to safely handle some of these in non-duplicated - // regions. - int LoopCost = 0; - for (auto *BB : L.blocks()) { - int Cost = 0; - for (auto &I : *BB) { - if (EphValues.count(&I)) - continue; - - if (I.getType()->isTokenTy() && I.isUsedOutsideOfBlock(BB)) - return false; - if (auto CS = CallSite(&I)) - if (CS.isConvergent() || CS.cannotDuplicate()) - return false; - - Cost += TTI.getUserCost(&I); - } - assert(Cost >= 0 && "Must not have negative costs!"); - LoopCost += Cost; - assert(LoopCost >= 0 && "Must not have negative loop costs!"); - BBCostMap[BB] = Cost; - } - LLVM_DEBUG(dbgs() << " Total loop cost: " << LoopCost << "\n"); - - // Now we find the best candidate by searching for the one with the following - // properties in order: - // - // 1) An unswitching cost below the threshold - // 2) The smallest number of duplicated unswitch candidates (to avoid - // creating redundant subsequent unswitching) - // 3) The smallest cost after unswitching. - // - // We prioritize reducing fanout of unswitch candidates provided the cost - // remains below the threshold because this has a multiplicative effect. - // - // This requires memoizing each dominator subtree to avoid redundant work. - // - // FIXME: Need to actually do the number of candidates part above. - SmallDenseMap<DomTreeNode *, int, 4> DTCostMap; - // Given a terminator which might be unswitched, computes the non-duplicated - // cost for that terminator. - auto ComputeUnswitchedCost = [&](Instruction &TI, bool FullUnswitch) { - BasicBlock &BB = *TI.getParent(); - SmallPtrSet<BasicBlock *, 4> Visited; - - int Cost = LoopCost; - for (BasicBlock *SuccBB : successors(&BB)) { - // Don't count successors more than once. - if (!Visited.insert(SuccBB).second) - continue; - - // If this is a partial unswitch candidate, then it must be a conditional - // branch with a condition of either `or` or `and`. In that case, one of - // the successors is necessarily duplicated, so don't even try to remove - // its cost. - if (!FullUnswitch) { - auto &BI = cast<BranchInst>(TI); - if (cast<Instruction>(BI.getCondition())->getOpcode() == - Instruction::And) { - if (SuccBB == BI.getSuccessor(1)) - continue; - } else { - assert(cast<Instruction>(BI.getCondition())->getOpcode() == - Instruction::Or && - "Only `and` and `or` conditions can result in a partial " - "unswitch!"); - if (SuccBB == BI.getSuccessor(0)) - continue; - } - } - - // This successor's domtree will not need to be duplicated after - // unswitching if the edge to the successor dominates it (and thus the - // entire tree). This essentially means there is no other path into this - // subtree and so it will end up live in only one clone of the loop. - if (SuccBB->getUniquePredecessor() || - llvm::all_of(predecessors(SuccBB), [&](BasicBlock *PredBB) { - return PredBB == &BB || DT.dominates(SuccBB, PredBB); - })) { - Cost -= computeDomSubtreeCost(*DT[SuccBB], BBCostMap, DTCostMap); - assert(Cost >= 0 && - "Non-duplicated cost should never exceed total loop cost!"); - } - } - - // Now scale the cost by the number of unique successors minus one. We - // subtract one because there is already at least one copy of the entire - // loop. This is computing the new cost of unswitching a condition. - // Note that guards always have 2 unique successors that are implicit and - // will be materialized if we decide to unswitch it. - int SuccessorsCount = isGuard(&TI) ? 2 : Visited.size(); - assert(SuccessorsCount > 1 && - "Cannot unswitch a condition without multiple distinct successors!"); - return Cost * (SuccessorsCount - 1); - }; - Instruction *BestUnswitchTI = nullptr; - int BestUnswitchCost; - ArrayRef<Value *> BestUnswitchInvariants; - for (auto &TerminatorAndInvariants : UnswitchCandidates) { - Instruction &TI = *TerminatorAndInvariants.first; - ArrayRef<Value *> Invariants = TerminatorAndInvariants.second; - BranchInst *BI = dyn_cast<BranchInst>(&TI); - int CandidateCost = ComputeUnswitchedCost( - TI, /*FullUnswitch*/ !BI || (Invariants.size() == 1 && - Invariants[0] == BI->getCondition())); - // Calculate cost multiplier which is a tool to limit potentially - // exponential behavior of loop-unswitch. - if (EnableUnswitchCostMultiplier) { - int CostMultiplier = - calculateUnswitchCostMultiplier(TI, L, LI, DT, UnswitchCandidates); - assert( - (CostMultiplier > 0 && CostMultiplier <= UnswitchThreshold) && - "cost multiplier needs to be in the range of 1..UnswitchThreshold"); - CandidateCost *= CostMultiplier; - LLVM_DEBUG(dbgs() << " Computed cost of " << CandidateCost - << " (multiplier: " << CostMultiplier << ")" - << " for unswitch candidate: " << TI << "\n"); - } else { - LLVM_DEBUG(dbgs() << " Computed cost of " << CandidateCost - << " for unswitch candidate: " << TI << "\n"); - } - - if (!BestUnswitchTI || CandidateCost < BestUnswitchCost) { - BestUnswitchTI = &TI; - BestUnswitchCost = CandidateCost; - BestUnswitchInvariants = Invariants; - } - } - - if (BestUnswitchCost >= UnswitchThreshold) { - LLVM_DEBUG(dbgs() << "Cannot unswitch, lowest cost found: " - << BestUnswitchCost << "\n"); - return false; - } - - // If the best candidate is a guard, turn it into a branch. - if (isGuard(BestUnswitchTI)) - BestUnswitchTI = turnGuardIntoBranch(cast<IntrinsicInst>(BestUnswitchTI), L, - ExitBlocks, DT, LI, MSSAU); - - LLVM_DEBUG(dbgs() << " Unswitching non-trivial (cost = " - << BestUnswitchCost << ") terminator: " << *BestUnswitchTI - << "\n"); - unswitchNontrivialInvariants(L, *BestUnswitchTI, BestUnswitchInvariants, - ExitBlocks, DT, LI, AC, UnswitchCB, SE, MSSAU); - return true; -} - -/// Unswitch control flow predicated on loop invariant conditions. -/// -/// This first hoists all branches or switches which are trivial (IE, do not -/// require duplicating any part of the loop) out of the loop body. It then -/// looks at other loop invariant control flows and tries to unswitch those as -/// well by cloning the loop if the result is small enough. -/// -/// The `DT`, `LI`, `AC`, `TTI` parameters are required analyses that are also -/// updated based on the unswitch. -/// The `MSSA` analysis is also updated if valid (i.e. its use is enabled). -/// -/// If either `NonTrivial` is true or the flag `EnableNonTrivialUnswitch` is -/// true, we will attempt to do non-trivial unswitching as well as trivial -/// unswitching. -/// -/// The `UnswitchCB` callback provided will be run after unswitching is -/// complete, with the first parameter set to `true` if the provided loop -/// remains a loop, and a list of new sibling loops created. -/// -/// If `SE` is non-null, we will update that analysis based on the unswitching -/// done. -static bool unswitchLoop(Loop &L, DominatorTree &DT, LoopInfo &LI, - AssumptionCache &AC, TargetTransformInfo &TTI, - bool NonTrivial, - function_ref<void(bool, ArrayRef<Loop *>)> UnswitchCB, - ScalarEvolution *SE, MemorySSAUpdater *MSSAU) { - assert(L.isRecursivelyLCSSAForm(DT, LI) && - "Loops must be in LCSSA form before unswitching."); - bool Changed = false; - - // Must be in loop simplified form: we need a preheader and dedicated exits. - if (!L.isLoopSimplifyForm()) - return false; - - // Try trivial unswitch first before loop over other basic blocks in the loop. - if (unswitchAllTrivialConditions(L, DT, LI, SE, MSSAU)) { - // If we unswitched successfully we will want to clean up the loop before - // processing it further so just mark it as unswitched and return. - UnswitchCB(/*CurrentLoopValid*/ true, {}); - return true; - } - - // If we're not doing non-trivial unswitching, we're done. We both accept - // a parameter but also check a local flag that can be used for testing - // a debugging. - if (!NonTrivial && !EnableNonTrivialUnswitch) - return false; - - // For non-trivial unswitching, because it often creates new loops, we rely on - // the pass manager to iterate on the loops rather than trying to immediately - // reach a fixed point. There is no substantial advantage to iterating - // internally, and if any of the new loops are simplified enough to contain - // trivial unswitching we want to prefer those. - - // Try to unswitch the best invariant condition. We prefer this full unswitch to - // a partial unswitch when possible below the threshold. - if (unswitchBestCondition(L, DT, LI, AC, TTI, UnswitchCB, SE, MSSAU)) - return true; - - // No other opportunities to unswitch. - return Changed; -} - -PreservedAnalyses SimpleLoopUnswitchPass::run(Loop &L, LoopAnalysisManager &AM, - LoopStandardAnalysisResults &AR, - LPMUpdater &U) { - Function &F = *L.getHeader()->getParent(); - (void)F; - - LLVM_DEBUG(dbgs() << "Unswitching loop in " << F.getName() << ": " << L - << "\n"); - - // Save the current loop name in a variable so that we can report it even - // after it has been deleted. - std::string LoopName = L.getName(); - - auto UnswitchCB = [&L, &U, &LoopName](bool CurrentLoopValid, - ArrayRef<Loop *> NewLoops) { - // If we did a non-trivial unswitch, we have added new (cloned) loops. - if (!NewLoops.empty()) - U.addSiblingLoops(NewLoops); - - // If the current loop remains valid, we should revisit it to catch any - // other unswitch opportunities. Otherwise, we need to mark it as deleted. - if (CurrentLoopValid) - U.revisitCurrentLoop(); - else - U.markLoopAsDeleted(L, LoopName); - }; - - Optional<MemorySSAUpdater> MSSAU; - if (AR.MSSA) { - MSSAU = MemorySSAUpdater(AR.MSSA); - if (VerifyMemorySSA) - AR.MSSA->verifyMemorySSA(); - } - if (!unswitchLoop(L, AR.DT, AR.LI, AR.AC, AR.TTI, NonTrivial, UnswitchCB, - &AR.SE, MSSAU.hasValue() ? MSSAU.getPointer() : nullptr)) - return PreservedAnalyses::all(); - - if (AR.MSSA && VerifyMemorySSA) - AR.MSSA->verifyMemorySSA(); - - // Historically this pass has had issues with the dominator tree so verify it - // in asserts builds. - assert(AR.DT.verify(DominatorTree::VerificationLevel::Fast)); - return getLoopPassPreservedAnalyses(); -} - -namespace { - -class SimpleLoopUnswitchLegacyPass : public LoopPass { - bool NonTrivial; - -public: - static char ID; // Pass ID, replacement for typeid - - explicit SimpleLoopUnswitchLegacyPass(bool NonTrivial = false) - : LoopPass(ID), NonTrivial(NonTrivial) { - initializeSimpleLoopUnswitchLegacyPassPass( - *PassRegistry::getPassRegistry()); - } - - bool runOnLoop(Loop *L, LPPassManager &LPM) override; - - void getAnalysisUsage(AnalysisUsage &AU) const override { - AU.addRequired<AssumptionCacheTracker>(); - AU.addRequired<TargetTransformInfoWrapperPass>(); - if (EnableMSSALoopDependency) { - AU.addRequired<MemorySSAWrapperPass>(); - AU.addPreserved<MemorySSAWrapperPass>(); - } - getLoopAnalysisUsage(AU); - } -}; - -} // end anonymous namespace - -bool SimpleLoopUnswitchLegacyPass::runOnLoop(Loop *L, LPPassManager &LPM) { - if (skipLoop(L)) - return false; - - Function &F = *L->getHeader()->getParent(); - - LLVM_DEBUG(dbgs() << "Unswitching loop in " << F.getName() << ": " << *L - << "\n"); - - auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree(); - auto &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo(); - auto &AC = getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F); - auto &TTI = getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F); - MemorySSA *MSSA = nullptr; - Optional<MemorySSAUpdater> MSSAU; - if (EnableMSSALoopDependency) { - MSSA = &getAnalysis<MemorySSAWrapperPass>().getMSSA(); - MSSAU = MemorySSAUpdater(MSSA); - } - - auto *SEWP = getAnalysisIfAvailable<ScalarEvolutionWrapperPass>(); - auto *SE = SEWP ? &SEWP->getSE() : nullptr; - - auto UnswitchCB = [&L, &LPM](bool CurrentLoopValid, - ArrayRef<Loop *> NewLoops) { - // If we did a non-trivial unswitch, we have added new (cloned) loops. - for (auto *NewL : NewLoops) - LPM.addLoop(*NewL); - - // If the current loop remains valid, re-add it to the queue. This is - // a little wasteful as we'll finish processing the current loop as well, - // but it is the best we can do in the old PM. - if (CurrentLoopValid) - LPM.addLoop(*L); - else - LPM.markLoopAsDeleted(*L); - }; - - if (MSSA && VerifyMemorySSA) - MSSA->verifyMemorySSA(); - - bool Changed = unswitchLoop(*L, DT, LI, AC, TTI, NonTrivial, UnswitchCB, SE, - MSSAU.hasValue() ? MSSAU.getPointer() : nullptr); - - if (MSSA && VerifyMemorySSA) - MSSA->verifyMemorySSA(); - - // If anything was unswitched, also clear any cached information about this - // loop. - LPM.deleteSimpleAnalysisLoop(L); - - // Historically this pass has had issues with the dominator tree so verify it - // in asserts builds. - assert(DT.verify(DominatorTree::VerificationLevel::Fast)); - - return Changed; -} - -char SimpleLoopUnswitchLegacyPass::ID = 0; -INITIALIZE_PASS_BEGIN(SimpleLoopUnswitchLegacyPass, "simple-loop-unswitch", - "Simple unswitch loops", false, false) -INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker) -INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass) -INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass) -INITIALIZE_PASS_DEPENDENCY(LoopPass) -INITIALIZE_PASS_DEPENDENCY(MemorySSAWrapperPass) -INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass) -INITIALIZE_PASS_END(SimpleLoopUnswitchLegacyPass, "simple-loop-unswitch", - "Simple unswitch loops", false, false) - -Pass *llvm::createSimpleLoopUnswitchLegacyPass(bool NonTrivial) { - return new SimpleLoopUnswitchLegacyPass(NonTrivial); -} |