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Diffstat (limited to 'gnu/llvm/lib/Transforms/Scalar/MergeICmps.cpp')
| -rw-r--r-- | gnu/llvm/lib/Transforms/Scalar/MergeICmps.cpp | 870 |
1 files changed, 0 insertions, 870 deletions
diff --git a/gnu/llvm/lib/Transforms/Scalar/MergeICmps.cpp b/gnu/llvm/lib/Transforms/Scalar/MergeICmps.cpp deleted file mode 100644 index a24fee54949..00000000000 --- a/gnu/llvm/lib/Transforms/Scalar/MergeICmps.cpp +++ /dev/null @@ -1,870 +0,0 @@ -//===- MergeICmps.cpp - Optimize chains of integer comparisons ------------===// -// -// The LLVM Compiler Infrastructure -// -// This file is distributed under the University of Illinois Open Source -// License. See LICENSE.TXT for details. -// -//===----------------------------------------------------------------------===// -// -// This pass turns chains of integer comparisons into memcmp (the memcmp is -// later typically inlined as a chain of efficient hardware comparisons). This -// typically benefits c++ member or nonmember operator==(). -// -// The basic idea is to replace a longer chain of integer comparisons loaded -// from contiguous memory locations into a shorter chain of larger integer -// comparisons. Benefits are double: -// - There are less jumps, and therefore less opportunities for mispredictions -// and I-cache misses. -// - Code size is smaller, both because jumps are removed and because the -// encoding of a 2*n byte compare is smaller than that of two n-byte -// compares. -// -// Example: -// -// struct S { -// int a; -// char b; -// char c; -// uint16_t d; -// bool operator==(const S& o) const { -// return a == o.a && b == o.b && c == o.c && d == o.d; -// } -// }; -// -// Is optimized as : -// -// bool S::operator==(const S& o) const { -// return memcmp(this, &o, 8) == 0; -// } -// -// Which will later be expanded (ExpandMemCmp) as a single 8-bytes icmp. -// -//===----------------------------------------------------------------------===// - -#include "llvm/Analysis/Loads.h" -#include "llvm/Analysis/TargetLibraryInfo.h" -#include "llvm/Analysis/TargetTransformInfo.h" -#include "llvm/IR/Function.h" -#include "llvm/IR/IRBuilder.h" -#include "llvm/Pass.h" -#include "llvm/Transforms/Scalar.h" -#include "llvm/Transforms/Utils/BuildLibCalls.h" -#include <algorithm> -#include <numeric> -#include <utility> -#include <vector> - -using namespace llvm; - -namespace { - -#define DEBUG_TYPE "mergeicmps" - -// Returns true if the instruction is a simple load or a simple store -static bool isSimpleLoadOrStore(const Instruction *I) { - if (const LoadInst *LI = dyn_cast<LoadInst>(I)) - return LI->isSimple(); - if (const StoreInst *SI = dyn_cast<StoreInst>(I)) - return SI->isSimple(); - return false; -} - -// A BCE atom "Binary Compare Expression Atom" represents an integer load -// that is a constant offset from a base value, e.g. `a` or `o.c` in the example -// at the top. -struct BCEAtom { - BCEAtom() = default; - BCEAtom(GetElementPtrInst *GEP, LoadInst *LoadI, int BaseId, APInt Offset) - : GEP(GEP), LoadI(LoadI), BaseId(BaseId), Offset(Offset) {} - - // We want to order BCEAtoms by (Base, Offset). However we cannot use - // the pointer values for Base because these are non-deterministic. - // To make sure that the sort order is stable, we first assign to each atom - // base value an index based on its order of appearance in the chain of - // comparisons. We call this index `BaseOrdering`. For example, for: - // b[3] == c[2] && a[1] == d[1] && b[4] == c[3] - // | block 1 | | block 2 | | block 3 | - // b gets assigned index 0 and a index 1, because b appears as LHS in block 1, - // which is before block 2. - // We then sort by (BaseOrdering[LHS.Base()], LHS.Offset), which is stable. - bool operator<(const BCEAtom &O) const { - return BaseId != O.BaseId ? BaseId < O.BaseId : Offset.slt(O.Offset); - } - - GetElementPtrInst *GEP = nullptr; - LoadInst *LoadI = nullptr; - unsigned BaseId = 0; - APInt Offset; -}; - -// A class that assigns increasing ids to values in the order in which they are -// seen. See comment in `BCEAtom::operator<()``. -class BaseIdentifier { -public: - // Returns the id for value `Base`, after assigning one if `Base` has not been - // seen before. - int getBaseId(const Value *Base) { - assert(Base && "invalid base"); - const auto Insertion = BaseToIndex.try_emplace(Base, Order); - if (Insertion.second) - ++Order; - return Insertion.first->second; - } - -private: - unsigned Order = 1; - DenseMap<const Value*, int> BaseToIndex; -}; - -// If this value is a load from a constant offset w.r.t. a base address, and -// there are no other users of the load or address, returns the base address and -// the offset. -BCEAtom visitICmpLoadOperand(Value *const Val, BaseIdentifier &BaseId) { - auto *const LoadI = dyn_cast<LoadInst>(Val); - if (!LoadI) - return {}; - LLVM_DEBUG(dbgs() << "load\n"); - if (LoadI->isUsedOutsideOfBlock(LoadI->getParent())) { - LLVM_DEBUG(dbgs() << "used outside of block\n"); - return {}; - } - // Do not optimize atomic loads to non-atomic memcmp - if (!LoadI->isSimple()) { - LLVM_DEBUG(dbgs() << "volatile or atomic\n"); - return {}; - } - Value *const Addr = LoadI->getOperand(0); - auto *const GEP = dyn_cast<GetElementPtrInst>(Addr); - if (!GEP) - return {}; - LLVM_DEBUG(dbgs() << "GEP\n"); - if (GEP->isUsedOutsideOfBlock(LoadI->getParent())) { - LLVM_DEBUG(dbgs() << "used outside of block\n"); - return {}; - } - const auto &DL = GEP->getModule()->getDataLayout(); - if (!isDereferenceablePointer(GEP, DL)) { - LLVM_DEBUG(dbgs() << "not dereferenceable\n"); - // We need to make sure that we can do comparison in any order, so we - // require memory to be unconditionnally dereferencable. - return {}; - } - APInt Offset = APInt(DL.getPointerTypeSizeInBits(GEP->getType()), 0); - if (!GEP->accumulateConstantOffset(DL, Offset)) - return {}; - return BCEAtom(GEP, LoadI, BaseId.getBaseId(GEP->getPointerOperand()), - Offset); -} - -// A basic block with a comparison between two BCE atoms, e.g. `a == o.a` in the -// example at the top. -// The block might do extra work besides the atom comparison, in which case -// doesOtherWork() returns true. Under some conditions, the block can be -// split into the atom comparison part and the "other work" part -// (see canSplit()). -// Note: the terminology is misleading: the comparison is symmetric, so there -// is no real {l/r}hs. What we want though is to have the same base on the -// left (resp. right), so that we can detect consecutive loads. To ensure this -// we put the smallest atom on the left. -class BCECmpBlock { - public: - BCECmpBlock() {} - - BCECmpBlock(BCEAtom L, BCEAtom R, int SizeBits) - : Lhs_(L), Rhs_(R), SizeBits_(SizeBits) { - if (Rhs_ < Lhs_) std::swap(Rhs_, Lhs_); - } - - bool IsValid() const { return Lhs_.BaseId != 0 && Rhs_.BaseId != 0; } - - // Assert the block is consistent: If valid, it should also have - // non-null members besides Lhs_ and Rhs_. - void AssertConsistent() const { - if (IsValid()) { - assert(BB); - assert(CmpI); - assert(BranchI); - } - } - - const BCEAtom &Lhs() const { return Lhs_; } - const BCEAtom &Rhs() const { return Rhs_; } - int SizeBits() const { return SizeBits_; } - - // Returns true if the block does other works besides comparison. - bool doesOtherWork() const; - - // Returns true if the non-BCE-cmp instructions can be separated from BCE-cmp - // instructions in the block. - bool canSplit(AliasAnalysis *AA) const; - - // Return true if this all the relevant instructions in the BCE-cmp-block can - // be sunk below this instruction. By doing this, we know we can separate the - // BCE-cmp-block instructions from the non-BCE-cmp-block instructions in the - // block. - bool canSinkBCECmpInst(const Instruction *, DenseSet<Instruction *> &, - AliasAnalysis *AA) const; - - // We can separate the BCE-cmp-block instructions and the non-BCE-cmp-block - // instructions. Split the old block and move all non-BCE-cmp-insts into the - // new parent block. - void split(BasicBlock *NewParent, AliasAnalysis *AA) const; - - // The basic block where this comparison happens. - BasicBlock *BB = nullptr; - // The ICMP for this comparison. - ICmpInst *CmpI = nullptr; - // The terminating branch. - BranchInst *BranchI = nullptr; - // The block requires splitting. - bool RequireSplit = false; - -private: - BCEAtom Lhs_; - BCEAtom Rhs_; - int SizeBits_ = 0; -}; - -bool BCECmpBlock::canSinkBCECmpInst(const Instruction *Inst, - DenseSet<Instruction *> &BlockInsts, - AliasAnalysis *AA) const { - // If this instruction has side effects and its in middle of the BCE cmp block - // instructions, then bail for now. - if (Inst->mayHaveSideEffects()) { - // Bail if this is not a simple load or store - if (!isSimpleLoadOrStore(Inst)) - return false; - // Disallow stores that might alias the BCE operands - MemoryLocation LLoc = MemoryLocation::get(Lhs_.LoadI); - MemoryLocation RLoc = MemoryLocation::get(Rhs_.LoadI); - if (isModSet(AA->getModRefInfo(Inst, LLoc)) || - isModSet(AA->getModRefInfo(Inst, RLoc))) - return false; - } - // Make sure this instruction does not use any of the BCE cmp block - // instructions as operand. - for (auto BI : BlockInsts) { - if (is_contained(Inst->operands(), BI)) - return false; - } - return true; -} - -void BCECmpBlock::split(BasicBlock *NewParent, AliasAnalysis *AA) const { - DenseSet<Instruction *> BlockInsts( - {Lhs_.GEP, Rhs_.GEP, Lhs_.LoadI, Rhs_.LoadI, CmpI, BranchI}); - llvm::SmallVector<Instruction *, 4> OtherInsts; - for (Instruction &Inst : *BB) { - if (BlockInsts.count(&Inst)) - continue; - assert(canSinkBCECmpInst(&Inst, BlockInsts, AA) && - "Split unsplittable block"); - // This is a non-BCE-cmp-block instruction. And it can be separated - // from the BCE-cmp-block instruction. - OtherInsts.push_back(&Inst); - } - - // Do the actual spliting. - for (Instruction *Inst : reverse(OtherInsts)) { - Inst->moveBefore(&*NewParent->begin()); - } -} - -bool BCECmpBlock::canSplit(AliasAnalysis *AA) const { - DenseSet<Instruction *> BlockInsts( - {Lhs_.GEP, Rhs_.GEP, Lhs_.LoadI, Rhs_.LoadI, CmpI, BranchI}); - for (Instruction &Inst : *BB) { - if (!BlockInsts.count(&Inst)) { - if (!canSinkBCECmpInst(&Inst, BlockInsts, AA)) - return false; - } - } - return true; -} - -bool BCECmpBlock::doesOtherWork() const { - AssertConsistent(); - // All the instructions we care about in the BCE cmp block. - DenseSet<Instruction *> BlockInsts( - {Lhs_.GEP, Rhs_.GEP, Lhs_.LoadI, Rhs_.LoadI, CmpI, BranchI}); - // TODO(courbet): Can we allow some other things ? This is very conservative. - // We might be able to get away with anything does not have any side - // effects outside of the basic block. - // Note: The GEPs and/or loads are not necessarily in the same block. - for (const Instruction &Inst : *BB) { - if (!BlockInsts.count(&Inst)) - return true; - } - return false; -} - -// Visit the given comparison. If this is a comparison between two valid -// BCE atoms, returns the comparison. -BCECmpBlock visitICmp(const ICmpInst *const CmpI, - const ICmpInst::Predicate ExpectedPredicate, - BaseIdentifier &BaseId) { - // The comparison can only be used once: - // - For intermediate blocks, as a branch condition. - // - For the final block, as an incoming value for the Phi. - // If there are any other uses of the comparison, we cannot merge it with - // other comparisons as we would create an orphan use of the value. - if (!CmpI->hasOneUse()) { - LLVM_DEBUG(dbgs() << "cmp has several uses\n"); - return {}; - } - if (CmpI->getPredicate() != ExpectedPredicate) - return {}; - LLVM_DEBUG(dbgs() << "cmp " - << (ExpectedPredicate == ICmpInst::ICMP_EQ ? "eq" : "ne") - << "\n"); - auto Lhs = visitICmpLoadOperand(CmpI->getOperand(0), BaseId); - if (!Lhs.BaseId) - return {}; - auto Rhs = visitICmpLoadOperand(CmpI->getOperand(1), BaseId); - if (!Rhs.BaseId) - return {}; - const auto &DL = CmpI->getModule()->getDataLayout(); - return BCECmpBlock(std::move(Lhs), std::move(Rhs), - DL.getTypeSizeInBits(CmpI->getOperand(0)->getType())); -} - -// Visit the given comparison block. If this is a comparison between two valid -// BCE atoms, returns the comparison. -BCECmpBlock visitCmpBlock(Value *const Val, BasicBlock *const Block, - const BasicBlock *const PhiBlock, - BaseIdentifier &BaseId) { - if (Block->empty()) return {}; - auto *const BranchI = dyn_cast<BranchInst>(Block->getTerminator()); - if (!BranchI) return {}; - LLVM_DEBUG(dbgs() << "branch\n"); - if (BranchI->isUnconditional()) { - // In this case, we expect an incoming value which is the result of the - // comparison. This is the last link in the chain of comparisons (note - // that this does not mean that this is the last incoming value, blocks - // can be reordered). - auto *const CmpI = dyn_cast<ICmpInst>(Val); - if (!CmpI) return {}; - LLVM_DEBUG(dbgs() << "icmp\n"); - auto Result = visitICmp(CmpI, ICmpInst::ICMP_EQ, BaseId); - Result.CmpI = CmpI; - Result.BranchI = BranchI; - return Result; - } else { - // In this case, we expect a constant incoming value (the comparison is - // chained). - const auto *const Const = dyn_cast<ConstantInt>(Val); - LLVM_DEBUG(dbgs() << "const\n"); - if (!Const->isZero()) return {}; - LLVM_DEBUG(dbgs() << "false\n"); - auto *const CmpI = dyn_cast<ICmpInst>(BranchI->getCondition()); - if (!CmpI) return {}; - LLVM_DEBUG(dbgs() << "icmp\n"); - assert(BranchI->getNumSuccessors() == 2 && "expecting a cond branch"); - BasicBlock *const FalseBlock = BranchI->getSuccessor(1); - auto Result = visitICmp( - CmpI, FalseBlock == PhiBlock ? ICmpInst::ICMP_EQ : ICmpInst::ICMP_NE, - BaseId); - Result.CmpI = CmpI; - Result.BranchI = BranchI; - return Result; - } - return {}; -} - -static inline void enqueueBlock(std::vector<BCECmpBlock> &Comparisons, - BCECmpBlock &Comparison) { - LLVM_DEBUG(dbgs() << "Block '" << Comparison.BB->getName() - << "': Found cmp of " << Comparison.SizeBits() - << " bits between " << Comparison.Lhs().BaseId << " + " - << Comparison.Lhs().Offset << " and " - << Comparison.Rhs().BaseId << " + " - << Comparison.Rhs().Offset << "\n"); - LLVM_DEBUG(dbgs() << "\n"); - Comparisons.push_back(Comparison); -} - -// A chain of comparisons. -class BCECmpChain { - public: - BCECmpChain(const std::vector<BasicBlock *> &Blocks, PHINode &Phi, - AliasAnalysis *AA); - - int size() const { return Comparisons_.size(); } - -#ifdef MERGEICMPS_DOT_ON - void dump() const; -#endif // MERGEICMPS_DOT_ON - - bool simplify(const TargetLibraryInfo *const TLI, AliasAnalysis *AA); - - private: - static bool IsContiguous(const BCECmpBlock &First, - const BCECmpBlock &Second) { - return First.Lhs().BaseId == Second.Lhs().BaseId && - First.Rhs().BaseId == Second.Rhs().BaseId && - First.Lhs().Offset + First.SizeBits() / 8 == Second.Lhs().Offset && - First.Rhs().Offset + First.SizeBits() / 8 == Second.Rhs().Offset; - } - - // Merges the given comparison blocks into one memcmp block and update - // branches. Comparisons are assumed to be continguous. If NextBBInChain is - // null, the merged block will link to the phi block. - void mergeComparisons(ArrayRef<BCECmpBlock> Comparisons, - BasicBlock *const NextBBInChain, PHINode &Phi, - const TargetLibraryInfo *const TLI, AliasAnalysis *AA); - - PHINode &Phi_; - std::vector<BCECmpBlock> Comparisons_; - // The original entry block (before sorting); - BasicBlock *EntryBlock_; -}; - -BCECmpChain::BCECmpChain(const std::vector<BasicBlock *> &Blocks, PHINode &Phi, - AliasAnalysis *AA) - : Phi_(Phi) { - assert(!Blocks.empty() && "a chain should have at least one block"); - // Now look inside blocks to check for BCE comparisons. - std::vector<BCECmpBlock> Comparisons; - BaseIdentifier BaseId; - for (size_t BlockIdx = 0; BlockIdx < Blocks.size(); ++BlockIdx) { - BasicBlock *const Block = Blocks[BlockIdx]; - assert(Block && "invalid block"); - BCECmpBlock Comparison = visitCmpBlock(Phi.getIncomingValueForBlock(Block), - Block, Phi.getParent(), BaseId); - Comparison.BB = Block; - if (!Comparison.IsValid()) { - LLVM_DEBUG(dbgs() << "chain with invalid BCECmpBlock, no merge.\n"); - return; - } - if (Comparison.doesOtherWork()) { - LLVM_DEBUG(dbgs() << "block '" << Comparison.BB->getName() - << "' does extra work besides compare\n"); - if (Comparisons.empty()) { - // This is the initial block in the chain, in case this block does other - // work, we can try to split the block and move the irrelevant - // instructions to the predecessor. - // - // If this is not the initial block in the chain, splitting it wont - // work. - // - // As once split, there will still be instructions before the BCE cmp - // instructions that do other work in program order, i.e. within the - // chain before sorting. Unless we can abort the chain at this point - // and start anew. - // - // NOTE: we only handle block with single predecessor for now. - if (Comparison.canSplit(AA)) { - LLVM_DEBUG(dbgs() - << "Split initial block '" << Comparison.BB->getName() - << "' that does extra work besides compare\n"); - Comparison.RequireSplit = true; - enqueueBlock(Comparisons, Comparison); - } else { - LLVM_DEBUG(dbgs() - << "ignoring initial block '" << Comparison.BB->getName() - << "' that does extra work besides compare\n"); - } - continue; - } - // TODO(courbet): Right now we abort the whole chain. We could be - // merging only the blocks that don't do other work and resume the - // chain from there. For example: - // if (a[0] == b[0]) { // bb1 - // if (a[1] == b[1]) { // bb2 - // some_value = 3; //bb3 - // if (a[2] == b[2]) { //bb3 - // do a ton of stuff //bb4 - // } - // } - // } - // - // This is: - // - // bb1 --eq--> bb2 --eq--> bb3* -eq--> bb4 --+ - // \ \ \ \ - // ne ne ne \ - // \ \ \ v - // +------------+-----------+----------> bb_phi - // - // We can only merge the first two comparisons, because bb3* does - // "other work" (setting some_value to 3). - // We could still merge bb1 and bb2 though. - return; - } - enqueueBlock(Comparisons, Comparison); - } - - // It is possible we have no suitable comparison to merge. - if (Comparisons.empty()) { - LLVM_DEBUG(dbgs() << "chain with no BCE basic blocks, no merge\n"); - return; - } - EntryBlock_ = Comparisons[0].BB; - Comparisons_ = std::move(Comparisons); -#ifdef MERGEICMPS_DOT_ON - errs() << "BEFORE REORDERING:\n\n"; - dump(); -#endif // MERGEICMPS_DOT_ON - // Reorder blocks by LHS. We can do that without changing the - // semantics because we are only accessing dereferencable memory. - llvm::sort(Comparisons_, - [](const BCECmpBlock &LhsBlock, const BCECmpBlock &RhsBlock) { - return LhsBlock.Lhs() < RhsBlock.Lhs(); - }); -#ifdef MERGEICMPS_DOT_ON - errs() << "AFTER REORDERING:\n\n"; - dump(); -#endif // MERGEICMPS_DOT_ON -} - -#ifdef MERGEICMPS_DOT_ON -void BCECmpChain::dump() const { - errs() << "digraph dag {\n"; - errs() << " graph [bgcolor=transparent];\n"; - errs() << " node [color=black,style=filled,fillcolor=lightyellow];\n"; - errs() << " edge [color=black];\n"; - for (size_t I = 0; I < Comparisons_.size(); ++I) { - const auto &Comparison = Comparisons_[I]; - errs() << " \"" << I << "\" [label=\"%" - << Comparison.Lhs().Base()->getName() << " + " - << Comparison.Lhs().Offset << " == %" - << Comparison.Rhs().Base()->getName() << " + " - << Comparison.Rhs().Offset << " (" << (Comparison.SizeBits() / 8) - << " bytes)\"];\n"; - const Value *const Val = Phi_.getIncomingValueForBlock(Comparison.BB); - if (I > 0) errs() << " \"" << (I - 1) << "\" -> \"" << I << "\";\n"; - errs() << " \"" << I << "\" -> \"Phi\" [label=\"" << *Val << "\"];\n"; - } - errs() << " \"Phi\" [label=\"Phi\"];\n"; - errs() << "}\n\n"; -} -#endif // MERGEICMPS_DOT_ON - -bool BCECmpChain::simplify(const TargetLibraryInfo *const TLI, - AliasAnalysis *AA) { - // First pass to check if there is at least one merge. If not, we don't do - // anything and we keep analysis passes intact. - { - bool AtLeastOneMerged = false; - for (size_t I = 1; I < Comparisons_.size(); ++I) { - if (IsContiguous(Comparisons_[I - 1], Comparisons_[I])) { - AtLeastOneMerged = true; - break; - } - } - if (!AtLeastOneMerged) return false; - } - - // Remove phi references to comparison blocks, they will be rebuilt as we - // merge the blocks. - for (const auto &Comparison : Comparisons_) { - Phi_.removeIncomingValue(Comparison.BB, false); - } - - // If entry block is part of the chain, we need to make the first block - // of the chain the new entry block of the function. - BasicBlock *Entry = &Comparisons_[0].BB->getParent()->getEntryBlock(); - for (size_t I = 1; I < Comparisons_.size(); ++I) { - if (Entry == Comparisons_[I].BB) { - BasicBlock *NEntryBB = BasicBlock::Create(Entry->getContext(), "", - Entry->getParent(), Entry); - BranchInst::Create(Entry, NEntryBB); - break; - } - } - - // Point the predecessors of the chain to the first comparison block (which is - // the new entry point) and update the entry block of the chain. - if (EntryBlock_ != Comparisons_[0].BB) { - EntryBlock_->replaceAllUsesWith(Comparisons_[0].BB); - EntryBlock_ = Comparisons_[0].BB; - } - - // Effectively merge blocks. - int NumMerged = 1; - for (size_t I = 1; I < Comparisons_.size(); ++I) { - if (IsContiguous(Comparisons_[I - 1], Comparisons_[I])) { - ++NumMerged; - } else { - // Merge all previous comparisons and start a new merge block. - mergeComparisons( - makeArrayRef(Comparisons_).slice(I - NumMerged, NumMerged), - Comparisons_[I].BB, Phi_, TLI, AA); - NumMerged = 1; - } - } - mergeComparisons(makeArrayRef(Comparisons_) - .slice(Comparisons_.size() - NumMerged, NumMerged), - nullptr, Phi_, TLI, AA); - - return true; -} - -void BCECmpChain::mergeComparisons(ArrayRef<BCECmpBlock> Comparisons, - BasicBlock *const NextBBInChain, - PHINode &Phi, - const TargetLibraryInfo *const TLI, - AliasAnalysis *AA) { - assert(!Comparisons.empty()); - const auto &FirstComparison = *Comparisons.begin(); - BasicBlock *const BB = FirstComparison.BB; - LLVMContext &Context = BB->getContext(); - - if (Comparisons.size() >= 2) { - // If there is one block that requires splitting, we do it now, i.e. - // just before we know we will collapse the chain. The instructions - // can be executed before any of the instructions in the chain. - auto C = std::find_if(Comparisons.begin(), Comparisons.end(), - [](const BCECmpBlock &B) { return B.RequireSplit; }); - if (C != Comparisons.end()) - C->split(EntryBlock_, AA); - - LLVM_DEBUG(dbgs() << "Merging " << Comparisons.size() << " comparisons\n"); - const auto TotalSize = - std::accumulate(Comparisons.begin(), Comparisons.end(), 0, - [](int Size, const BCECmpBlock &C) { - return Size + C.SizeBits(); - }) / - 8; - - // Incoming edges do not need to be updated, and both GEPs are already - // computing the right address, we just need to: - // - replace the two loads and the icmp with the memcmp - // - update the branch - // - update the incoming values in the phi. - FirstComparison.BranchI->eraseFromParent(); - FirstComparison.CmpI->eraseFromParent(); - FirstComparison.Lhs().LoadI->eraseFromParent(); - FirstComparison.Rhs().LoadI->eraseFromParent(); - - IRBuilder<> Builder(BB); - const auto &DL = Phi.getModule()->getDataLayout(); - Value *const MemCmpCall = emitMemCmp( - FirstComparison.Lhs().GEP, FirstComparison.Rhs().GEP, - ConstantInt::get(DL.getIntPtrType(Context), TotalSize), - Builder, DL, TLI); - Value *const MemCmpIsZero = Builder.CreateICmpEQ( - MemCmpCall, ConstantInt::get(Type::getInt32Ty(Context), 0)); - - // Add a branch to the next basic block in the chain. - if (NextBBInChain) { - Builder.CreateCondBr(MemCmpIsZero, NextBBInChain, Phi.getParent()); - Phi.addIncoming(ConstantInt::getFalse(Context), BB); - } else { - Builder.CreateBr(Phi.getParent()); - Phi.addIncoming(MemCmpIsZero, BB); - } - - // Delete merged blocks. - for (size_t I = 1; I < Comparisons.size(); ++I) { - BasicBlock *CBB = Comparisons[I].BB; - CBB->replaceAllUsesWith(BB); - CBB->eraseFromParent(); - } - } else { - assert(Comparisons.size() == 1); - // There are no blocks to merge, but we still need to update the branches. - LLVM_DEBUG(dbgs() << "Only one comparison, updating branches\n"); - if (NextBBInChain) { - if (FirstComparison.BranchI->isConditional()) { - LLVM_DEBUG(dbgs() << "conditional -> conditional\n"); - // Just update the "true" target, the "false" target should already be - // the phi block. - assert(FirstComparison.BranchI->getSuccessor(1) == Phi.getParent()); - FirstComparison.BranchI->setSuccessor(0, NextBBInChain); - Phi.addIncoming(ConstantInt::getFalse(Context), BB); - } else { - LLVM_DEBUG(dbgs() << "unconditional -> conditional\n"); - // Replace the unconditional branch by a conditional one. - FirstComparison.BranchI->eraseFromParent(); - IRBuilder<> Builder(BB); - Builder.CreateCondBr(FirstComparison.CmpI, NextBBInChain, - Phi.getParent()); - Phi.addIncoming(FirstComparison.CmpI, BB); - } - } else { - if (FirstComparison.BranchI->isConditional()) { - LLVM_DEBUG(dbgs() << "conditional -> unconditional\n"); - // Replace the conditional branch by an unconditional one. - FirstComparison.BranchI->eraseFromParent(); - IRBuilder<> Builder(BB); - Builder.CreateBr(Phi.getParent()); - Phi.addIncoming(FirstComparison.CmpI, BB); - } else { - LLVM_DEBUG(dbgs() << "unconditional -> unconditional\n"); - Phi.addIncoming(FirstComparison.CmpI, BB); - } - } - } -} - -std::vector<BasicBlock *> getOrderedBlocks(PHINode &Phi, - BasicBlock *const LastBlock, - int NumBlocks) { - // Walk up from the last block to find other blocks. - std::vector<BasicBlock *> Blocks(NumBlocks); - assert(LastBlock && "invalid last block"); - BasicBlock *CurBlock = LastBlock; - for (int BlockIndex = NumBlocks - 1; BlockIndex > 0; --BlockIndex) { - if (CurBlock->hasAddressTaken()) { - // Somebody is jumping to the block through an address, all bets are - // off. - LLVM_DEBUG(dbgs() << "skip: block " << BlockIndex - << " has its address taken\n"); - return {}; - } - Blocks[BlockIndex] = CurBlock; - auto *SinglePredecessor = CurBlock->getSinglePredecessor(); - if (!SinglePredecessor) { - // The block has two or more predecessors. - LLVM_DEBUG(dbgs() << "skip: block " << BlockIndex - << " has two or more predecessors\n"); - return {}; - } - if (Phi.getBasicBlockIndex(SinglePredecessor) < 0) { - // The block does not link back to the phi. - LLVM_DEBUG(dbgs() << "skip: block " << BlockIndex - << " does not link back to the phi\n"); - return {}; - } - CurBlock = SinglePredecessor; - } - Blocks[0] = CurBlock; - return Blocks; -} - -bool processPhi(PHINode &Phi, const TargetLibraryInfo *const TLI, - AliasAnalysis *AA) { - LLVM_DEBUG(dbgs() << "processPhi()\n"); - if (Phi.getNumIncomingValues() <= 1) { - LLVM_DEBUG(dbgs() << "skip: only one incoming value in phi\n"); - return false; - } - // We are looking for something that has the following structure: - // bb1 --eq--> bb2 --eq--> bb3 --eq--> bb4 --+ - // \ \ \ \ - // ne ne ne \ - // \ \ \ v - // +------------+-----------+----------> bb_phi - // - // - The last basic block (bb4 here) must branch unconditionally to bb_phi. - // It's the only block that contributes a non-constant value to the Phi. - // - All other blocks (b1, b2, b3) must have exactly two successors, one of - // them being the phi block. - // - All intermediate blocks (bb2, bb3) must have only one predecessor. - // - Blocks cannot do other work besides the comparison, see doesOtherWork() - - // The blocks are not necessarily ordered in the phi, so we start from the - // last block and reconstruct the order. - BasicBlock *LastBlock = nullptr; - for (unsigned I = 0; I < Phi.getNumIncomingValues(); ++I) { - if (isa<ConstantInt>(Phi.getIncomingValue(I))) continue; - if (LastBlock) { - // There are several non-constant values. - LLVM_DEBUG(dbgs() << "skip: several non-constant values\n"); - return false; - } - if (!isa<ICmpInst>(Phi.getIncomingValue(I)) || - cast<ICmpInst>(Phi.getIncomingValue(I))->getParent() != - Phi.getIncomingBlock(I)) { - // Non-constant incoming value is not from a cmp instruction or not - // produced by the last block. We could end up processing the value - // producing block more than once. - // - // This is an uncommon case, so we bail. - LLVM_DEBUG( - dbgs() - << "skip: non-constant value not from cmp or not from last block.\n"); - return false; - } - LastBlock = Phi.getIncomingBlock(I); - } - if (!LastBlock) { - // There is no non-constant block. - LLVM_DEBUG(dbgs() << "skip: no non-constant block\n"); - return false; - } - if (LastBlock->getSingleSuccessor() != Phi.getParent()) { - LLVM_DEBUG(dbgs() << "skip: last block non-phi successor\n"); - return false; - } - - const auto Blocks = - getOrderedBlocks(Phi, LastBlock, Phi.getNumIncomingValues()); - if (Blocks.empty()) return false; - BCECmpChain CmpChain(Blocks, Phi, AA); - - if (CmpChain.size() < 2) { - LLVM_DEBUG(dbgs() << "skip: only one compare block\n"); - return false; - } - - return CmpChain.simplify(TLI, AA); -} - -class MergeICmps : public FunctionPass { - public: - static char ID; - - MergeICmps() : FunctionPass(ID) { - initializeMergeICmpsPass(*PassRegistry::getPassRegistry()); - } - - bool runOnFunction(Function &F) override { - if (skipFunction(F)) return false; - const auto &TLI = getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(); - const auto &TTI = getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F); - AliasAnalysis *AA = &getAnalysis<AAResultsWrapperPass>().getAAResults(); - auto PA = runImpl(F, &TLI, &TTI, AA); - return !PA.areAllPreserved(); - } - - private: - void getAnalysisUsage(AnalysisUsage &AU) const override { - AU.addRequired<TargetLibraryInfoWrapperPass>(); - AU.addRequired<TargetTransformInfoWrapperPass>(); - AU.addRequired<AAResultsWrapperPass>(); - } - - PreservedAnalyses runImpl(Function &F, const TargetLibraryInfo *TLI, - const TargetTransformInfo *TTI, AliasAnalysis *AA); -}; - -PreservedAnalyses MergeICmps::runImpl(Function &F, const TargetLibraryInfo *TLI, - const TargetTransformInfo *TTI, - AliasAnalysis *AA) { - LLVM_DEBUG(dbgs() << "MergeICmpsPass: " << F.getName() << "\n"); - - // We only try merging comparisons if the target wants to expand memcmp later. - // The rationale is to avoid turning small chains into memcmp calls. - if (!TTI->enableMemCmpExpansion(true)) return PreservedAnalyses::all(); - - // If we don't have memcmp avaiable we can't emit calls to it. - if (!TLI->has(LibFunc_memcmp)) - return PreservedAnalyses::all(); - - bool MadeChange = false; - - for (auto BBIt = ++F.begin(); BBIt != F.end(); ++BBIt) { - // A Phi operation is always first in a basic block. - if (auto *const Phi = dyn_cast<PHINode>(&*BBIt->begin())) - MadeChange |= processPhi(*Phi, TLI, AA); - } - - if (MadeChange) return PreservedAnalyses::none(); - return PreservedAnalyses::all(); -} - -} // namespace - -char MergeICmps::ID = 0; -INITIALIZE_PASS_BEGIN(MergeICmps, "mergeicmps", - "Merge contiguous icmps into a memcmp", false, false) -INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass) -INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass) -INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass) -INITIALIZE_PASS_END(MergeICmps, "mergeicmps", - "Merge contiguous icmps into a memcmp", false, false) - -Pass *llvm::createMergeICmpsPass() { return new MergeICmps(); } |