diff options
Diffstat (limited to 'gnu/llvm/lib/Transforms/Scalar/GVNHoist.cpp')
| -rw-r--r-- | gnu/llvm/lib/Transforms/Scalar/GVNHoist.cpp | 802 |
1 files changed, 482 insertions, 320 deletions
diff --git a/gnu/llvm/lib/Transforms/Scalar/GVNHoist.cpp b/gnu/llvm/lib/Transforms/Scalar/GVNHoist.cpp index 29de792bd24..026fab5dbd3 100644 --- a/gnu/llvm/lib/Transforms/Scalar/GVNHoist.cpp +++ b/gnu/llvm/lib/Transforms/Scalar/GVNHoist.cpp @@ -13,44 +13,72 @@ // 1. To reduce the code size. // 2. In some cases reduce critical path (by exposing more ILP). // +// The algorithm factors out the reachability of values such that multiple +// queries to find reachability of values are fast. This is based on finding the +// ANTIC points in the CFG which do not change during hoisting. The ANTIC points +// are basically the dominance-frontiers in the inverse graph. So we introduce a +// data structure (CHI nodes) to keep track of values flowing out of a basic +// block. We only do this for values with multiple occurrences in the function +// as they are the potential hoistable candidates. This approach allows us to +// hoist instructions to a basic block with more than two successors, as well as +// deal with infinite loops in a trivial way. +// +// Limitations: This pass does not hoist fully redundant expressions because +// they are already handled by GVN-PRE. It is advisable to run gvn-hoist before +// and after gvn-pre because gvn-pre creates opportunities for more instructions +// to be hoisted. +// // Hoisting may affect the performance in some cases. To mitigate that, hoisting // is disabled in the following cases. // 1. Scalars across calls. // 2. geps when corresponding load/store cannot be hoisted. -// -// TODO: Hoist from >2 successors. Currently GVNHoist will not hoist stores -// in this case because it works on two instructions at a time. -// entry: -// switch i32 %c1, label %exit1 [ -// i32 0, label %sw0 -// i32 1, label %sw1 -// ] -// -// sw0: -// store i32 1, i32* @G -// br label %exit -// -// sw1: -// store i32 1, i32* @G -// br label %exit -// -// exit1: -// store i32 1, i32* @G -// ret void -// exit: -// ret void //===----------------------------------------------------------------------===// #include "llvm/ADT/DenseMap.h" +#include "llvm/ADT/DenseSet.h" +#include "llvm/ADT/STLExtras.h" #include "llvm/ADT/SmallPtrSet.h" +#include "llvm/ADT/SmallVector.h" #include "llvm/ADT/Statistic.h" +#include "llvm/ADT/iterator_range.h" +#include "llvm/Analysis/AliasAnalysis.h" #include "llvm/Analysis/GlobalsModRef.h" +#include "llvm/Analysis/IteratedDominanceFrontier.h" +#include "llvm/Analysis/MemoryDependenceAnalysis.h" #include "llvm/Analysis/MemorySSA.h" #include "llvm/Analysis/MemorySSAUpdater.h" +#include "llvm/Analysis/PostDominators.h" #include "llvm/Analysis/ValueTracking.h" +#include "llvm/IR/Argument.h" +#include "llvm/IR/BasicBlock.h" +#include "llvm/IR/CFG.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/Intrinsics.h" +#include "llvm/IR/LLVMContext.h" +#include "llvm/IR/PassManager.h" +#include "llvm/IR/Use.h" +#include "llvm/IR/User.h" +#include "llvm/IR/Value.h" +#include "llvm/Pass.h" +#include "llvm/Support/Casting.h" +#include "llvm/Support/CommandLine.h" +#include "llvm/Support/Debug.h" +#include "llvm/Support/raw_ostream.h" #include "llvm/Transforms/Scalar.h" #include "llvm/Transforms/Scalar/GVN.h" #include "llvm/Transforms/Utils/Local.h" +#include <algorithm> +#include <cassert> +#include <iterator> +#include <memory> +#include <utility> +#include <vector> using namespace llvm; @@ -69,6 +97,7 @@ static cl::opt<int> MaxHoistedThreshold("gvn-max-hoisted", cl::Hidden, cl::init(-1), cl::desc("Max number of instructions to hoist " "(default unlimited = -1)")); + static cl::opt<int> MaxNumberOfBBSInPath( "gvn-hoist-max-bbs", cl::Hidden, cl::init(4), cl::desc("Max number of basic blocks on the path between " @@ -86,34 +115,50 @@ static cl::opt<int> namespace llvm { -// Provides a sorting function based on the execution order of two instructions. -struct SortByDFSIn { -private: - DenseMap<const Value *, unsigned> &DFSNumber; +using BBSideEffectsSet = DenseMap<const BasicBlock *, bool>; +using SmallVecInsn = SmallVector<Instruction *, 4>; +using SmallVecImplInsn = SmallVectorImpl<Instruction *>; -public: - SortByDFSIn(DenseMap<const Value *, unsigned> &D) : DFSNumber(D) {} - - // Returns true when A executes before B. - bool operator()(const Instruction *A, const Instruction *B) const { - const BasicBlock *BA = A->getParent(); - const BasicBlock *BB = B->getParent(); - unsigned ADFS, BDFS; - if (BA == BB) { - ADFS = DFSNumber.lookup(A); - BDFS = DFSNumber.lookup(B); - } else { - ADFS = DFSNumber.lookup(BA); - BDFS = DFSNumber.lookup(BB); - } - assert(ADFS && BDFS); - return ADFS < BDFS; - } -}; +// Each element of a hoisting list contains the basic block where to hoist and +// a list of instructions to be hoisted. +using HoistingPointInfo = std::pair<BasicBlock *, SmallVecInsn>; + +using HoistingPointList = SmallVector<HoistingPointInfo, 4>; // A map from a pair of VNs to all the instructions with those VNs. -typedef DenseMap<std::pair<unsigned, unsigned>, SmallVector<Instruction *, 4>> - VNtoInsns; +using VNType = std::pair<unsigned, unsigned>; + +using VNtoInsns = DenseMap<VNType, SmallVector<Instruction *, 4>>; + +// CHI keeps information about values flowing out of a basic block. It is +// similar to PHI but in the inverse graph, and used for outgoing values on each +// edge. For conciseness, it is computed only for instructions with multiple +// occurrences in the CFG because they are the only hoistable candidates. +// A (CHI[{V, B, I1}, {V, C, I2}] +// / \ +// / \ +// B(I1) C (I2) +// The Value number for both I1 and I2 is V, the CHI node will save the +// instruction as well as the edge where the value is flowing to. +struct CHIArg { + VNType VN; + + // Edge destination (shows the direction of flow), may not be where the I is. + BasicBlock *Dest; + + // The instruction (VN) which uses the values flowing out of CHI. + Instruction *I; + + bool operator==(const CHIArg &A) { return VN == A.VN; } + bool operator!=(const CHIArg &A) { return !(*this == A); } +}; + +using CHIIt = SmallVectorImpl<CHIArg>::iterator; +using CHIArgs = iterator_range<CHIIt>; +using OutValuesType = DenseMap<BasicBlock *, SmallVector<CHIArg, 2>>; +using InValuesType = + DenseMap<BasicBlock *, SmallVector<std::pair<VNType, Instruction *>, 2>>; + // An invalid value number Used when inserting a single value number into // VNtoInsns. enum : unsigned { InvalidVN = ~2U }; @@ -192,16 +237,10 @@ public: } const VNtoInsns &getScalarVNTable() const { return VNtoCallsScalars; } - const VNtoInsns &getLoadVNTable() const { return VNtoCallsLoads; } - const VNtoInsns &getStoreVNTable() const { return VNtoCallsStores; } }; -typedef DenseMap<const BasicBlock *, bool> BBSideEffectsSet; -typedef SmallVector<Instruction *, 4> SmallVecInsn; -typedef SmallVectorImpl<Instruction *> SmallVecImplInsn; - static void combineKnownMetadata(Instruction *ReplInst, Instruction *I) { static const unsigned KnownIDs[] = { LLVMContext::MD_tbaa, LLVMContext::MD_alias_scope, @@ -216,15 +255,13 @@ static void combineKnownMetadata(Instruction *ReplInst, Instruction *I) { // cases reduce critical path (by exposing more ILP). class GVNHoist { public: - GVNHoist(DominatorTree *DT, AliasAnalysis *AA, MemoryDependenceResults *MD, - MemorySSA *MSSA) - : DT(DT), AA(AA), MD(MD), MSSA(MSSA), - MSSAUpdater(make_unique<MemorySSAUpdater>(MSSA)), - HoistingGeps(false), - HoistedCtr(0) - { } + GVNHoist(DominatorTree *DT, PostDominatorTree *PDT, AliasAnalysis *AA, + MemoryDependenceResults *MD, MemorySSA *MSSA) + : DT(DT), PDT(PDT), AA(AA), MD(MD), MSSA(MSSA), + MSSAUpdater(llvm::make_unique<MemorySSAUpdater>(MSSA)) {} bool run(Function &F) { + NumFuncArgs = F.arg_size(); VN.setDomTree(DT); VN.setAliasAnalysis(AA); VN.setMemDep(MD); @@ -241,7 +278,7 @@ public: int ChainLength = 0; // FIXME: use lazy evaluation of VN to avoid the fix-point computation. - while (1) { + while (true) { if (MaxChainLength != -1 && ++ChainLength >= MaxChainLength) return Res; @@ -261,18 +298,48 @@ public: return Res; } + // Copied from NewGVN.cpp + // This function provides global ranking of operations so that we can place + // them in a canonical order. Note that rank alone is not necessarily enough + // for a complete ordering, as constants all have the same rank. However, + // generally, we will simplify an operation with all constants so that it + // doesn't matter what order they appear in. + unsigned int rank(const Value *V) const { + // Prefer constants to undef to anything else + // Undef is a constant, have to check it first. + // Prefer smaller constants to constantexprs + if (isa<ConstantExpr>(V)) + return 2; + if (isa<UndefValue>(V)) + return 1; + if (isa<Constant>(V)) + return 0; + else if (auto *A = dyn_cast<Argument>(V)) + return 3 + A->getArgNo(); + + // Need to shift the instruction DFS by number of arguments + 3 to account + // for the constant and argument ranking above. + auto Result = DFSNumber.lookup(V); + if (Result > 0) + return 4 + NumFuncArgs + Result; + // Unreachable or something else, just return a really large number. + return ~0; + } + private: GVN::ValueTable VN; DominatorTree *DT; + PostDominatorTree *PDT; AliasAnalysis *AA; MemoryDependenceResults *MD; MemorySSA *MSSA; std::unique_ptr<MemorySSAUpdater> MSSAUpdater; - const bool HoistingGeps; DenseMap<const Value *, unsigned> DFSNumber; BBSideEffectsSet BBSideEffects; - DenseSet<const BasicBlock*> HoistBarrier; - int HoistedCtr; + DenseSet<const BasicBlock *> HoistBarrier; + SmallVector<BasicBlock *, 32> IDFBlocks; + unsigned NumFuncArgs; + const bool HoistingGeps = false; enum InsKind { Unknown, Scalar, Load, Store }; @@ -305,45 +372,7 @@ private: return false; } - // Return true when all paths from HoistBB to the end of the function pass - // through one of the blocks in WL. - bool hoistingFromAllPaths(const BasicBlock *HoistBB, - SmallPtrSetImpl<const BasicBlock *> &WL) { - - // Copy WL as the loop will remove elements from it. - SmallPtrSet<const BasicBlock *, 2> WorkList(WL.begin(), WL.end()); - - for (auto It = df_begin(HoistBB), E = df_end(HoistBB); It != E;) { - // There exists a path from HoistBB to the exit of the function if we are - // still iterating in DF traversal and we removed all instructions from - // the work list. - if (WorkList.empty()) - return false; - - const BasicBlock *BB = *It; - if (WorkList.erase(BB)) { - // Stop DFS traversal when BB is in the work list. - It.skipChildren(); - continue; - } - - // We reached the leaf Basic Block => not all paths have this instruction. - if (!BB->getTerminator()->getNumSuccessors()) - return false; - - // When reaching the back-edge of a loop, there may be a path through the - // loop that does not pass through B or C before exiting the loop. - if (successorDominate(BB, HoistBB)) - return false; - - // Increment DFS traversal when not skipping children. - ++It; - } - - return true; - } - - /* Return true when I1 appears before I2 in the instructions of BB. */ + // Return true when I1 appears before I2 in the instructions of BB. bool firstInBB(const Instruction *I1, const Instruction *I2) { assert(I1->getParent() == I2->getParent()); unsigned I1DFS = DFSNumber.lookup(I1); @@ -387,6 +416,25 @@ private: return false; } + bool hasEHhelper(const BasicBlock *BB, const BasicBlock *SrcBB, + int &NBBsOnAllPaths) { + // Stop walk once the limit is reached. + if (NBBsOnAllPaths == 0) + return true; + + // Impossible to hoist with exceptions on the path. + if (hasEH(BB)) + return true; + + // No such instruction after HoistBarrier in a basic block was + // selected for hoisting so instructions selected within basic block with + // a hoist barrier can be hoisted. + if ((BB != SrcBB) && HoistBarrier.count(BB)) + return true; + + return false; + } + // Return true when there are exception handling or loads of memory Def // between Def and NewPt. This function is only called for stores: Def is // the MemoryDef of the store to be hoisted. @@ -414,18 +462,7 @@ private: continue; } - // Stop walk once the limit is reached. - if (NBBsOnAllPaths == 0) - return true; - - // Impossible to hoist with exceptions on the path. - if (hasEH(BB)) - return true; - - // No such instruction after HoistBarrier in a basic block was - // selected for hoisting so instructions selected within basic block with - // a hoist barrier can be hoisted. - if ((BB != OldBB) && HoistBarrier.count(BB)) + if (hasEHhelper(BB, OldBB, NBBsOnAllPaths)) return true; // Check that we do not move a store past loads. @@ -463,18 +500,7 @@ private: continue; } - // Stop walk once the limit is reached. - if (NBBsOnAllPaths == 0) - return true; - - // Impossible to hoist with exceptions on the path. - if (hasEH(BB)) - return true; - - // No such instruction after HoistBarrier in a basic block was - // selected for hoisting so instructions selected within basic block with - // a hoist barrier can be hoisted. - if ((BB != SrcBB) && HoistBarrier.count(BB)) + if (hasEHhelper(BB, SrcBB, NBBsOnAllPaths)) return true; // -1 is unlimited number of blocks on all paths. @@ -491,7 +517,6 @@ private: // to NewPt. bool safeToHoistLdSt(const Instruction *NewPt, const Instruction *OldPt, MemoryUseOrDef *U, InsKind K, int &NBBsOnAllPaths) { - // In place hoisting is safe. if (NewPt == OldPt) return true; @@ -533,141 +558,258 @@ private: // Return true when it is safe to hoist scalar instructions from all blocks in // WL to HoistBB. - bool safeToHoistScalar(const BasicBlock *HoistBB, - SmallPtrSetImpl<const BasicBlock *> &WL, + bool safeToHoistScalar(const BasicBlock *HoistBB, const BasicBlock *BB, int &NBBsOnAllPaths) { - // Check that the hoisted expression is needed on all paths. - if (!hoistingFromAllPaths(HoistBB, WL)) - return false; + return !hasEHOnPath(HoistBB, BB, NBBsOnAllPaths); + } - for (const BasicBlock *BB : WL) - if (hasEHOnPath(HoistBB, BB, NBBsOnAllPaths)) + // In the inverse CFG, the dominance frontier of basic block (BB) is the + // point where ANTIC needs to be computed for instructions which are going + // to be hoisted. Since this point does not change during gvn-hoist, + // we compute it only once (on demand). + // The ides is inspired from: + // "Partial Redundancy Elimination in SSA Form" + // ROBERT KENNEDY, SUN CHAN, SHIN-MING LIU, RAYMOND LO, PENG TU and FRED CHOW + // They use similar idea in the forward graph to to find fully redundant and + // partially redundant expressions, here it is used in the inverse graph to + // find fully anticipable instructions at merge point (post-dominator in + // the inverse CFG). + // Returns the edge via which an instruction in BB will get the values from. + + // Returns true when the values are flowing out to each edge. + bool valueAnticipable(CHIArgs C, TerminatorInst *TI) const { + if (TI->getNumSuccessors() > (unsigned)std::distance(C.begin(), C.end())) + return false; // Not enough args in this CHI. + + for (auto CHI : C) { + BasicBlock *Dest = CHI.Dest; + // Find if all the edges have values flowing out of BB. + bool Found = llvm::any_of(TI->successors(), [Dest](const BasicBlock *BB) { + return BB == Dest; }); + if (!Found) return false; - + } return true; } - // Each element of a hoisting list contains the basic block where to hoist and - // a list of instructions to be hoisted. - typedef std::pair<BasicBlock *, SmallVecInsn> HoistingPointInfo; - typedef SmallVector<HoistingPointInfo, 4> HoistingPointList; - - // Partition InstructionsToHoist into a set of candidates which can share a - // common hoisting point. The partitions are collected in HPL. IsScalar is - // true when the instructions in InstructionsToHoist are scalars. IsLoad is - // true when the InstructionsToHoist are loads, false when they are stores. - void partitionCandidates(SmallVecImplInsn &InstructionsToHoist, - HoistingPointList &HPL, InsKind K) { - // No need to sort for two instructions. - if (InstructionsToHoist.size() > 2) { - SortByDFSIn Pred(DFSNumber); - std::sort(InstructionsToHoist.begin(), InstructionsToHoist.end(), Pred); - } - + // Check if it is safe to hoist values tracked by CHI in the range + // [Begin, End) and accumulate them in Safe. + void checkSafety(CHIArgs C, BasicBlock *BB, InsKind K, + SmallVectorImpl<CHIArg> &Safe) { int NumBBsOnAllPaths = MaxNumberOfBBSInPath; - - SmallVecImplInsn::iterator II = InstructionsToHoist.begin(); - SmallVecImplInsn::iterator Start = II; - Instruction *HoistPt = *II; - BasicBlock *HoistBB = HoistPt->getParent(); - MemoryUseOrDef *UD; - if (K != InsKind::Scalar) - UD = MSSA->getMemoryAccess(HoistPt); - - for (++II; II != InstructionsToHoist.end(); ++II) { - Instruction *Insn = *II; - BasicBlock *BB = Insn->getParent(); - BasicBlock *NewHoistBB; - Instruction *NewHoistPt; - - if (BB == HoistBB) { // Both are in the same Basic Block. - NewHoistBB = HoistBB; - NewHoistPt = firstInBB(Insn, HoistPt) ? Insn : HoistPt; + for (auto CHI : C) { + Instruction *Insn = CHI.I; + if (!Insn) // No instruction was inserted in this CHI. + continue; + if (K == InsKind::Scalar) { + if (safeToHoistScalar(BB, Insn->getParent(), NumBBsOnAllPaths)) + Safe.push_back(CHI); } else { - // If the hoisting point contains one of the instructions, - // then hoist there, otherwise hoist before the terminator. - NewHoistBB = DT->findNearestCommonDominator(HoistBB, BB); - if (NewHoistBB == BB) - NewHoistPt = Insn; - else if (NewHoistBB == HoistBB) - NewHoistPt = HoistPt; - else - NewHoistPt = NewHoistBB->getTerminator(); + MemoryUseOrDef *UD = MSSA->getMemoryAccess(Insn); + if (safeToHoistLdSt(BB->getTerminator(), Insn, UD, K, NumBBsOnAllPaths)) + Safe.push_back(CHI); } + } + } - SmallPtrSet<const BasicBlock *, 2> WL; - WL.insert(HoistBB); - WL.insert(BB); + using RenameStackType = DenseMap<VNType, SmallVector<Instruction *, 2>>; + + // Push all the VNs corresponding to BB into RenameStack. + void fillRenameStack(BasicBlock *BB, InValuesType &ValueBBs, + RenameStackType &RenameStack) { + auto it1 = ValueBBs.find(BB); + if (it1 != ValueBBs.end()) { + // Iterate in reverse order to keep lower ranked values on the top. + for (std::pair<VNType, Instruction *> &VI : reverse(it1->second)) { + // Get the value of instruction I + DEBUG(dbgs() << "\nPushing on stack: " << *VI.second); + RenameStack[VI.first].push_back(VI.second); + } + } + } - if (K == InsKind::Scalar) { - if (safeToHoistScalar(NewHoistBB, WL, NumBBsOnAllPaths)) { - // Extend HoistPt to NewHoistPt. - HoistPt = NewHoistPt; - HoistBB = NewHoistBB; - continue; - } - } else { - // When NewBB already contains an instruction to be hoisted, the - // expression is needed on all paths. - // Check that the hoisted expression is needed on all paths: it is - // unsafe to hoist loads to a place where there may be a path not - // loading from the same address: for instance there may be a branch on - // which the address of the load may not be initialized. - if ((HoistBB == NewHoistBB || BB == NewHoistBB || - hoistingFromAllPaths(NewHoistBB, WL)) && - // Also check that it is safe to move the load or store from HoistPt - // to NewHoistPt, and from Insn to NewHoistPt. - safeToHoistLdSt(NewHoistPt, HoistPt, UD, K, NumBBsOnAllPaths) && - safeToHoistLdSt(NewHoistPt, Insn, MSSA->getMemoryAccess(Insn), - K, NumBBsOnAllPaths)) { - // Extend HoistPt to NewHoistPt. - HoistPt = NewHoistPt; - HoistBB = NewHoistBB; - continue; - } + void fillChiArgs(BasicBlock *BB, OutValuesType &CHIBBs, + RenameStackType &RenameStack) { + // For each *predecessor* (because Post-DOM) of BB check if it has a CHI + for (auto Pred : predecessors(BB)) { + auto P = CHIBBs.find(Pred); + if (P == CHIBBs.end()) { + continue; } + DEBUG(dbgs() << "\nLooking at CHIs in: " << Pred->getName();); + // A CHI is found (BB -> Pred is an edge in the CFG) + // Pop the stack until Top(V) = Ve. + auto &VCHI = P->second; + for (auto It = VCHI.begin(), E = VCHI.end(); It != E;) { + CHIArg &C = *It; + if (!C.Dest) { + auto si = RenameStack.find(C.VN); + // The Basic Block where CHI is must dominate the value we want to + // track in a CHI. In the PDom walk, there can be values in the + // stack which are not control dependent e.g., nested loop. + if (si != RenameStack.end() && si->second.size() && + DT->properlyDominates(Pred, si->second.back()->getParent())) { + C.Dest = BB; // Assign the edge + C.I = si->second.pop_back_val(); // Assign the argument + DEBUG(dbgs() << "\nCHI Inserted in BB: " << C.Dest->getName() + << *C.I << ", VN: " << C.VN.first << ", " + << C.VN.second); + } + // Move to next CHI of a different value + It = std::find_if(It, VCHI.end(), + [It](CHIArg &A) { return A != *It; }); + } else + ++It; + } + } + } + + // Walk the post-dominator tree top-down and use a stack for each value to + // store the last value you see. When you hit a CHI from a given edge, the + // value to use as the argument is at the top of the stack, add the value to + // CHI and pop. + void insertCHI(InValuesType &ValueBBs, OutValuesType &CHIBBs) { + auto Root = PDT->getNode(nullptr); + if (!Root) + return; + // Depth first walk on PDom tree to fill the CHIargs at each PDF. + RenameStackType RenameStack; + for (auto Node : depth_first(Root)) { + BasicBlock *BB = Node->getBlock(); + if (!BB) + continue; + + // Collect all values in BB and push to stack. + fillRenameStack(BB, ValueBBs, RenameStack); - // At this point it is not safe to extend the current hoisting to - // NewHoistPt: save the hoisting list so far. - if (std::distance(Start, II) > 1) - HPL.push_back({HoistBB, SmallVecInsn(Start, II)}); - - // Start over from BB. - Start = II; - if (K != InsKind::Scalar) - UD = MSSA->getMemoryAccess(*Start); - HoistPt = Insn; - HoistBB = BB; - NumBBsOnAllPaths = MaxNumberOfBBSInPath; + // Fill outgoing values in each CHI corresponding to BB. + fillChiArgs(BB, CHIBBs, RenameStack); } + } + + // Walk all the CHI-nodes to find ones which have a empty-entry and remove + // them Then collect all the instructions which are safe to hoist and see if + // they form a list of anticipable values. OutValues contains CHIs + // corresponding to each basic block. + void findHoistableCandidates(OutValuesType &CHIBBs, InsKind K, + HoistingPointList &HPL) { + auto cmpVN = [](const CHIArg &A, const CHIArg &B) { return A.VN < B.VN; }; + + // CHIArgs now have the outgoing values, so check for anticipability and + // accumulate hoistable candidates in HPL. + for (std::pair<BasicBlock *, SmallVector<CHIArg, 2>> &A : CHIBBs) { + BasicBlock *BB = A.first; + SmallVectorImpl<CHIArg> &CHIs = A.second; + // Vector of PHIs contains PHIs for different instructions. + // Sort the args according to their VNs, such that identical + // instructions are together. + std::stable_sort(CHIs.begin(), CHIs.end(), cmpVN); + auto TI = BB->getTerminator(); + auto B = CHIs.begin(); + // [PreIt, PHIIt) form a range of CHIs which have identical VNs. + auto PHIIt = std::find_if(CHIs.begin(), CHIs.end(), + [B](CHIArg &A) { return A != *B; }); + auto PrevIt = CHIs.begin(); + while (PrevIt != PHIIt) { + // Collect values which satisfy safety checks. + SmallVector<CHIArg, 2> Safe; + // We check for safety first because there might be multiple values in + // the same path, some of which are not safe to be hoisted, but overall + // each edge has at least one value which can be hoisted, making the + // value anticipable along that path. + checkSafety(make_range(PrevIt, PHIIt), BB, K, Safe); + + // List of safe values should be anticipable at TI. + if (valueAnticipable(make_range(Safe.begin(), Safe.end()), TI)) { + HPL.push_back({BB, SmallVecInsn()}); + SmallVecInsn &V = HPL.back().second; + for (auto B : Safe) + V.push_back(B.I); + } - // Save the last partition. - if (std::distance(Start, II) > 1) - HPL.push_back({HoistBB, SmallVecInsn(Start, II)}); + // Check other VNs + PrevIt = PHIIt; + PHIIt = std::find_if(PrevIt, CHIs.end(), + [PrevIt](CHIArg &A) { return A != *PrevIt; }); + } + } } - // Initialize HPL from Map. + // Compute insertion points for each values which can be fully anticipated at + // a dominator. HPL contains all such values. void computeInsertionPoints(const VNtoInsns &Map, HoistingPointList &HPL, InsKind K) { + // Sort VNs based on their rankings + std::vector<VNType> Ranks; for (const auto &Entry : Map) { - if (MaxHoistedThreshold != -1 && ++HoistedCtr > MaxHoistedThreshold) - return; + Ranks.push_back(Entry.first); + } - const SmallVecInsn &V = Entry.second; + // TODO: Remove fully-redundant expressions. + // Get instruction from the Map, assume that all the Instructions + // with same VNs have same rank (this is an approximation). + std::sort(Ranks.begin(), Ranks.end(), + [this, &Map](const VNType &r1, const VNType &r2) { + return (rank(*Map.lookup(r1).begin()) < + rank(*Map.lookup(r2).begin())); + }); + + // - Sort VNs according to their rank, and start with lowest ranked VN + // - Take a VN and for each instruction with same VN + // - Find the dominance frontier in the inverse graph (PDF) + // - Insert the chi-node at PDF + // - Remove the chi-nodes with missing entries + // - Remove values from CHI-nodes which do not truly flow out, e.g., + // modified along the path. + // - Collect the remaining values that are still anticipable + SmallVector<BasicBlock *, 2> IDFBlocks; + ReverseIDFCalculator IDFs(*PDT); + OutValuesType OutValue; + InValuesType InValue; + for (const auto &R : Ranks) { + const SmallVecInsn &V = Map.lookup(R); if (V.size() < 2) continue; - - // Compute the insertion point and the list of expressions to be hoisted. - SmallVecInsn InstructionsToHoist; - for (auto I : V) - // We don't need to check for hoist-barriers here because if - // I->getParent() is a barrier then I precedes the barrier. - if (!hasEH(I->getParent())) - InstructionsToHoist.push_back(I); - - if (!InstructionsToHoist.empty()) - partitionCandidates(InstructionsToHoist, HPL, K); + const VNType &VN = R; + SmallPtrSet<BasicBlock *, 2> VNBlocks; + for (auto &I : V) { + BasicBlock *BBI = I->getParent(); + if (!hasEH(BBI)) + VNBlocks.insert(BBI); + } + // Compute the Post Dominance Frontiers of each basic block + // The dominance frontier of a live block X in the reverse + // control graph is the set of blocks upon which X is control + // dependent. The following sequence computes the set of blocks + // which currently have dead terminators that are control + // dependence sources of a block which is in NewLiveBlocks. + IDFs.setDefiningBlocks(VNBlocks); + IDFs.calculate(IDFBlocks); + + // Make a map of BB vs instructions to be hoisted. + for (unsigned i = 0; i < V.size(); ++i) { + InValue[V[i]->getParent()].push_back(std::make_pair(VN, V[i])); + } + // Insert empty CHI node for this VN. This is used to factor out + // basic blocks where the ANTIC can potentially change. + for (auto IDFB : IDFBlocks) { // TODO: Prune out useless CHI insertions. + for (unsigned i = 0; i < V.size(); ++i) { + CHIArg C = {VN, nullptr, nullptr}; + // Ignore spurious PDFs. + if (DT->properlyDominates(IDFB, V[i]->getParent())) { + OutValue[IDFB].push_back(C); + DEBUG(dbgs() << "\nInsertion a CHI for BB: " << IDFB->getName() + << ", for Insn: " << *V[i]); + } + } + } } + + // Insert CHI args at each PDF to iterate on factored graph of + // control dependence. + insertCHI(InValue, OutValue); + // Using the CHI args inserted at each PDF, find fully anticipable values. + findHoistableCandidates(OutValue, K, HPL); } // Return true when all operands of Instr are available at insertion point @@ -714,7 +856,6 @@ private: Instruction *ClonedGep = Gep->clone(); for (unsigned i = 0, e = Gep->getNumOperands(); i != e; ++i) if (Instruction *Op = dyn_cast<Instruction>(Gep->getOperand(i))) { - // Check whether the operand is already available. if (DT->dominates(Op->getParent(), HoistPt)) continue; @@ -748,6 +889,88 @@ private: Repl->replaceUsesOfWith(Gep, ClonedGep); } + void updateAlignment(Instruction *I, Instruction *Repl) { + if (auto *ReplacementLoad = dyn_cast<LoadInst>(Repl)) { + ReplacementLoad->setAlignment( + std::min(ReplacementLoad->getAlignment(), + cast<LoadInst>(I)->getAlignment())); + ++NumLoadsRemoved; + } else if (auto *ReplacementStore = dyn_cast<StoreInst>(Repl)) { + ReplacementStore->setAlignment( + std::min(ReplacementStore->getAlignment(), + cast<StoreInst>(I)->getAlignment())); + ++NumStoresRemoved; + } else if (auto *ReplacementAlloca = dyn_cast<AllocaInst>(Repl)) { + ReplacementAlloca->setAlignment( + std::max(ReplacementAlloca->getAlignment(), + cast<AllocaInst>(I)->getAlignment())); + } else if (isa<CallInst>(Repl)) { + ++NumCallsRemoved; + } + } + + // Remove all the instructions in Candidates and replace their usage with Repl. + // Returns the number of instructions removed. + unsigned rauw(const SmallVecInsn &Candidates, Instruction *Repl, + MemoryUseOrDef *NewMemAcc) { + unsigned NR = 0; + for (Instruction *I : Candidates) { + if (I != Repl) { + ++NR; + updateAlignment(I, Repl); + if (NewMemAcc) { + // Update the uses of the old MSSA access with NewMemAcc. + MemoryAccess *OldMA = MSSA->getMemoryAccess(I); + OldMA->replaceAllUsesWith(NewMemAcc); + MSSAUpdater->removeMemoryAccess(OldMA); + } + + Repl->andIRFlags(I); + combineKnownMetadata(Repl, I); + I->replaceAllUsesWith(Repl); + // Also invalidate the Alias Analysis cache. + MD->removeInstruction(I); + I->eraseFromParent(); + } + } + return NR; + } + + // Replace all Memory PHI usage with NewMemAcc. + void raMPHIuw(MemoryUseOrDef *NewMemAcc) { + SmallPtrSet<MemoryPhi *, 4> UsePhis; + for (User *U : NewMemAcc->users()) + if (MemoryPhi *Phi = dyn_cast<MemoryPhi>(U)) + UsePhis.insert(Phi); + + for (MemoryPhi *Phi : UsePhis) { + auto In = Phi->incoming_values(); + if (llvm::all_of(In, [&](Use &U) { return U == NewMemAcc; })) { + Phi->replaceAllUsesWith(NewMemAcc); + MSSAUpdater->removeMemoryAccess(Phi); + } + } + } + + // Remove all other instructions and replace them with Repl. + unsigned removeAndReplace(const SmallVecInsn &Candidates, Instruction *Repl, + BasicBlock *DestBB, bool MoveAccess) { + MemoryUseOrDef *NewMemAcc = MSSA->getMemoryAccess(Repl); + if (MoveAccess && NewMemAcc) { + // The definition of this ld/st will not change: ld/st hoisting is + // legal when the ld/st is not moved past its current definition. + MSSAUpdater->moveToPlace(NewMemAcc, DestBB, MemorySSA::End); + } + + // Replace all other instructions with Repl with memory access NewMemAcc. + unsigned NR = rauw(Candidates, Repl, NewMemAcc); + + // Remove MemorySSA phi nodes with the same arguments. + if (NewMemAcc) + raMPHIuw(NewMemAcc); + return NR; + } + // In the case Repl is a load or a store, we make all their GEPs // available: GEPs are not hoisted by default to avoid the address // computations to be hoisted without the associated load or store. @@ -789,11 +1012,11 @@ private: for (const HoistingPointInfo &HP : HPL) { // Find out whether we already have one of the instructions in HoistPt, // in which case we do not have to move it. - BasicBlock *HoistPt = HP.first; + BasicBlock *DestBB = HP.first; const SmallVecInsn &InstructionsToHoist = HP.second; Instruction *Repl = nullptr; for (Instruction *I : InstructionsToHoist) - if (I->getParent() == HoistPt) + if (I->getParent() == DestBB) // If there are two instructions in HoistPt to be hoisted in place: // update Repl to be the first one, such that we can rename the uses // of the second based on the first. @@ -805,7 +1028,7 @@ private: bool MoveAccess = true; if (Repl) { // Repl is already in HoistPt: it remains in place. - assert(allOperandsAvailable(Repl, HoistPt) && + assert(allOperandsAvailable(Repl, DestBB) && "instruction depends on operands that are not available"); MoveAccess = false; } else { @@ -816,40 +1039,26 @@ private: // We can move Repl in HoistPt only when all operands are available. // The order in which hoistings are done may influence the availability // of operands. - if (!allOperandsAvailable(Repl, HoistPt)) { - + if (!allOperandsAvailable(Repl, DestBB)) { // When HoistingGeps there is nothing more we can do to make the // operands available: just continue. if (HoistingGeps) continue; // When not HoistingGeps we need to copy the GEPs. - if (!makeGepOperandsAvailable(Repl, HoistPt, InstructionsToHoist)) + if (!makeGepOperandsAvailable(Repl, DestBB, InstructionsToHoist)) continue; } // Move the instruction at the end of HoistPt. - Instruction *Last = HoistPt->getTerminator(); + Instruction *Last = DestBB->getTerminator(); MD->removeInstruction(Repl); Repl->moveBefore(Last); DFSNumber[Repl] = DFSNumber[Last]++; } - MemoryAccess *NewMemAcc = MSSA->getMemoryAccess(Repl); - - if (MoveAccess) { - if (MemoryUseOrDef *OldMemAcc = - dyn_cast_or_null<MemoryUseOrDef>(NewMemAcc)) { - // The definition of this ld/st will not change: ld/st hoisting is - // legal when the ld/st is not moved past its current definition. - MemoryAccess *Def = OldMemAcc->getDefiningAccess(); - NewMemAcc = - MSSAUpdater->createMemoryAccessInBB(Repl, Def, HoistPt, MemorySSA::End); - OldMemAcc->replaceAllUsesWith(NewMemAcc); - MSSAUpdater->removeMemoryAccess(OldMemAcc); - } - } + NR += removeAndReplace(InstructionsToHoist, Repl, DestBB, MoveAccess); if (isa<LoadInst>(Repl)) ++NL; @@ -859,59 +1068,6 @@ private: ++NC; else // Scalar ++NI; - - // Remove and rename all other instructions. - for (Instruction *I : InstructionsToHoist) - if (I != Repl) { - ++NR; - if (auto *ReplacementLoad = dyn_cast<LoadInst>(Repl)) { - ReplacementLoad->setAlignment( - std::min(ReplacementLoad->getAlignment(), - cast<LoadInst>(I)->getAlignment())); - ++NumLoadsRemoved; - } else if (auto *ReplacementStore = dyn_cast<StoreInst>(Repl)) { - ReplacementStore->setAlignment( - std::min(ReplacementStore->getAlignment(), - cast<StoreInst>(I)->getAlignment())); - ++NumStoresRemoved; - } else if (auto *ReplacementAlloca = dyn_cast<AllocaInst>(Repl)) { - ReplacementAlloca->setAlignment( - std::max(ReplacementAlloca->getAlignment(), - cast<AllocaInst>(I)->getAlignment())); - } else if (isa<CallInst>(Repl)) { - ++NumCallsRemoved; - } - - if (NewMemAcc) { - // Update the uses of the old MSSA access with NewMemAcc. - MemoryAccess *OldMA = MSSA->getMemoryAccess(I); - OldMA->replaceAllUsesWith(NewMemAcc); - MSSAUpdater->removeMemoryAccess(OldMA); - } - - Repl->andIRFlags(I); - combineKnownMetadata(Repl, I); - I->replaceAllUsesWith(Repl); - // Also invalidate the Alias Analysis cache. - MD->removeInstruction(I); - I->eraseFromParent(); - } - - // Remove MemorySSA phi nodes with the same arguments. - if (NewMemAcc) { - SmallPtrSet<MemoryPhi *, 4> UsePhis; - for (User *U : NewMemAcc->users()) - if (MemoryPhi *Phi = dyn_cast<MemoryPhi>(U)) - UsePhis.insert(Phi); - - for (auto *Phi : UsePhis) { - auto In = Phi->incoming_values(); - if (all_of(In, [&](Use &U) { return U == NewMemAcc; })) { - Phi->replaceAllUsesWith(NewMemAcc); - MSSAUpdater->removeMemoryAccess(Phi); - } - } - } } NumHoisted += NL + NS + NC + NI; @@ -935,8 +1091,8 @@ private: // If I1 cannot guarantee progress, subsequent instructions // in BB cannot be hoisted anyways. if (!isGuaranteedToTransferExecutionToSuccessor(&I1)) { - HoistBarrier.insert(BB); - break; + HoistBarrier.insert(BB); + break; } // Only hoist the first instructions in BB up to MaxDepthInBB. Hoisting // deeper may increase the register pressure and compilation time. @@ -954,7 +1110,8 @@ private: else if (auto *Call = dyn_cast<CallInst>(&I1)) { if (auto *Intr = dyn_cast<IntrinsicInst>(Call)) { if (isa<DbgInfoIntrinsic>(Intr) || - Intr->getIntrinsicID() == Intrinsic::assume) + Intr->getIntrinsicID() == Intrinsic::assume || + Intr->getIntrinsicID() == Intrinsic::sideeffect) continue; } if (Call->mayHaveSideEffects()) @@ -996,16 +1153,18 @@ public: if (skipFunction(F)) return false; auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree(); + auto &PDT = getAnalysis<PostDominatorTreeWrapperPass>().getPostDomTree(); auto &AA = getAnalysis<AAResultsWrapperPass>().getAAResults(); auto &MD = getAnalysis<MemoryDependenceWrapperPass>().getMemDep(); auto &MSSA = getAnalysis<MemorySSAWrapperPass>().getMSSA(); - GVNHoist G(&DT, &AA, &MD, &MSSA); + GVNHoist G(&DT, &PDT, &AA, &MD, &MSSA); return G.run(F); } void getAnalysisUsage(AnalysisUsage &AU) const override { AU.addRequired<DominatorTreeWrapperPass>(); + AU.addRequired<PostDominatorTreeWrapperPass>(); AU.addRequired<AAResultsWrapperPass>(); AU.addRequired<MemoryDependenceWrapperPass>(); AU.addRequired<MemorySSAWrapperPass>(); @@ -1014,14 +1173,16 @@ public: AU.addPreserved<GlobalsAAWrapperPass>(); } }; -} // namespace + +} // end namespace llvm PreservedAnalyses GVNHoistPass::run(Function &F, FunctionAnalysisManager &AM) { DominatorTree &DT = AM.getResult<DominatorTreeAnalysis>(F); + PostDominatorTree &PDT = AM.getResult<PostDominatorTreeAnalysis>(F); AliasAnalysis &AA = AM.getResult<AAManager>(F); MemoryDependenceResults &MD = AM.getResult<MemoryDependenceAnalysis>(F); MemorySSA &MSSA = AM.getResult<MemorySSAAnalysis>(F).getMSSA(); - GVNHoist G(&DT, &AA, &MD, &MSSA); + GVNHoist G(&DT, &PDT, &AA, &MD, &MSSA); if (!G.run(F)) return PreservedAnalyses::all(); @@ -1033,6 +1194,7 @@ PreservedAnalyses GVNHoistPass::run(Function &F, FunctionAnalysisManager &AM) { } char GVNHoistLegacyPass::ID = 0; + INITIALIZE_PASS_BEGIN(GVNHoistLegacyPass, "gvn-hoist", "Early GVN Hoisting of Expressions", false, false) INITIALIZE_PASS_DEPENDENCY(MemoryDependenceWrapperPass) |