| //===------- VectorCombine.cpp - Optimize partial vector operations -------===// |
| // |
| // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| // See https://llvm.org/LICENSE.txt for license information. |
| // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This pass optimizes scalar/vector interactions using target cost models. The |
| // transforms implemented here may not fit in traditional loop-based or SLP |
| // vectorization passes. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "llvm/Transforms/Vectorize/VectorCombine.h" |
| #include "llvm/ADT/Statistic.h" |
| #include "llvm/Analysis/GlobalsModRef.h" |
| #include "llvm/Analysis/TargetTransformInfo.h" |
| #include "llvm/Analysis/ValueTracking.h" |
| #include "llvm/IR/Dominators.h" |
| #include "llvm/IR/Function.h" |
| #include "llvm/IR/IRBuilder.h" |
| #include "llvm/IR/PatternMatch.h" |
| #include "llvm/InitializePasses.h" |
| #include "llvm/Pass.h" |
| #include "llvm/Transforms/Vectorize.h" |
| #include "llvm/Transforms/Utils/Local.h" |
| |
| using namespace llvm; |
| using namespace llvm::PatternMatch; |
| |
| #define DEBUG_TYPE "vector-combine" |
| STATISTIC(NumVecCmp, "Number of vector compares formed"); |
| STATISTIC(NumVecBO, "Number of vector binops formed"); |
| |
| /// Compare the relative costs of extracts followed by scalar operation vs. |
| /// vector operation followed by extract: |
| /// opcode (extelt V0, C), (extelt V1, C) --> extelt (opcode V0, V1), C |
| /// Unless the vector op is much more expensive than the scalar op, this |
| /// eliminates an extract. |
| static bool isExtractExtractCheap(Instruction *Ext0, Instruction *Ext1, |
| unsigned Opcode, |
| const TargetTransformInfo &TTI) { |
| assert(Ext0->getOperand(1) == Ext1->getOperand(1) && |
| isa<ConstantInt>(Ext0->getOperand(1)) && |
| "Expected same constant extract index"); |
| |
| Type *ScalarTy = Ext0->getType(); |
| Type *VecTy = Ext0->getOperand(0)->getType(); |
| int ScalarOpCost, VectorOpCost; |
| |
| // Get cost estimates for scalar and vector versions of the operation. |
| bool IsBinOp = Instruction::isBinaryOp(Opcode); |
| if (IsBinOp) { |
| ScalarOpCost = TTI.getArithmeticInstrCost(Opcode, ScalarTy); |
| VectorOpCost = TTI.getArithmeticInstrCost(Opcode, VecTy); |
| } else { |
| assert((Opcode == Instruction::ICmp || Opcode == Instruction::FCmp) && |
| "Expected a compare"); |
| ScalarOpCost = TTI.getCmpSelInstrCost(Opcode, ScalarTy, |
| CmpInst::makeCmpResultType(ScalarTy)); |
| VectorOpCost = TTI.getCmpSelInstrCost(Opcode, VecTy, |
| CmpInst::makeCmpResultType(VecTy)); |
| } |
| |
| // Get cost estimate for the extract element. This cost will factor into |
| // both sequences. |
| unsigned ExtIndex = cast<ConstantInt>(Ext0->getOperand(1))->getZExtValue(); |
| int ExtractCost = TTI.getVectorInstrCost(Instruction::ExtractElement, |
| VecTy, ExtIndex); |
| |
| // Extra uses of the extracts mean that we include those costs in the |
| // vector total because those instructions will not be eliminated. |
| int OldCost, NewCost; |
| if (Ext0->getOperand(0) == Ext1->getOperand(0)) { |
| // Handle a special case. If the 2 operands are identical, adjust the |
| // formulas to account for that. The extra use charge allows for either the |
| // CSE'd pattern or an unoptimized form with identical values: |
| // opcode (extelt V, C), (extelt V, C) --> extelt (opcode V, V), C |
| bool HasUseTax = Ext0 == Ext1 ? !Ext0->hasNUses(2) |
| : !Ext0->hasOneUse() || !Ext1->hasOneUse(); |
| OldCost = ExtractCost + ScalarOpCost; |
| NewCost = VectorOpCost + ExtractCost + HasUseTax * ExtractCost; |
| } else { |
| // Handle the general case. Each extract is actually a different value: |
| // opcode (extelt V0, C), (extelt V1, C) --> extelt (opcode V0, V1), C |
| OldCost = 2 * ExtractCost + ScalarOpCost; |
| NewCost = VectorOpCost + ExtractCost + !Ext0->hasOneUse() * ExtractCost + |
| !Ext1->hasOneUse() * ExtractCost; |
| } |
| // TODO: The cost comparison should not differ based on opcode. Either we |
| // want to be uniformly more or less aggressive in deciding if a vector |
| // operation should replace the scalar operation. |
| return IsBinOp ? OldCost <= NewCost : OldCost < NewCost; |
| } |
| |
| /// Try to reduce extract element costs by converting scalar compares to vector |
| /// compares followed by extract. |
| /// cmp (ext0 V0, C), (ext1 V1, C) |
| static void foldExtExtCmp(Instruction *Ext0, Instruction *Ext1, |
| Instruction &I, const TargetTransformInfo &TTI) { |
| assert(isa<CmpInst>(&I) && "Expected a compare"); |
| |
| // cmp Pred (extelt V0, C), (extelt V1, C) --> extelt (cmp Pred V0, V1), C |
| ++NumVecCmp; |
| IRBuilder<> Builder(&I); |
| CmpInst::Predicate Pred = cast<CmpInst>(&I)->getPredicate(); |
| Value *V0 = Ext0->getOperand(0), *V1 = Ext1->getOperand(0); |
| Value *VecCmp = |
| Ext0->getType()->isFloatingPointTy() ? Builder.CreateFCmp(Pred, V0, V1) |
| : Builder.CreateICmp(Pred, V0, V1); |
| Value *Extract = Builder.CreateExtractElement(VecCmp, Ext0->getOperand(1)); |
| I.replaceAllUsesWith(Extract); |
| } |
| |
| /// Try to reduce extract element costs by converting scalar binops to vector |
| /// binops followed by extract. |
| /// bo (ext0 V0, C), (ext1 V1, C) |
| static void foldExtExtBinop(Instruction *Ext0, Instruction *Ext1, |
| Instruction &I, const TargetTransformInfo &TTI) { |
| assert(isa<BinaryOperator>(&I) && "Expected a binary operator"); |
| |
| // bo (extelt V0, C), (extelt V1, C) --> extelt (bo V0, V1), C |
| ++NumVecBO; |
| IRBuilder<> Builder(&I); |
| Value *V0 = Ext0->getOperand(0), *V1 = Ext1->getOperand(0); |
| Value *VecBO = |
| Builder.CreateBinOp(cast<BinaryOperator>(&I)->getOpcode(), V0, V1); |
| |
| // All IR flags are safe to back-propagate because any potential poison |
| // created in unused vector elements is discarded by the extract. |
| if (auto *VecBOInst = dyn_cast<Instruction>(VecBO)) |
| VecBOInst->copyIRFlags(&I); |
| |
| Value *Extract = Builder.CreateExtractElement(VecBO, Ext0->getOperand(1)); |
| I.replaceAllUsesWith(Extract); |
| } |
| |
| /// Match an instruction with extracted vector operands. |
| static bool foldExtractExtract(Instruction &I, const TargetTransformInfo &TTI) { |
| // It is not safe to transform things like div, urem, etc. because we may |
| // create undefined behavior when executing those on unknown vector elements. |
| if (!isSafeToSpeculativelyExecute(&I)) |
| return false; |
| |
| Instruction *Ext0, *Ext1; |
| CmpInst::Predicate Pred = CmpInst::BAD_ICMP_PREDICATE; |
| if (!match(&I, m_Cmp(Pred, m_Instruction(Ext0), m_Instruction(Ext1))) && |
| !match(&I, m_BinOp(m_Instruction(Ext0), m_Instruction(Ext1)))) |
| return false; |
| |
| Value *V0, *V1; |
| uint64_t C0, C1; |
| if (!match(Ext0, m_ExtractElement(m_Value(V0), m_ConstantInt(C0))) || |
| !match(Ext1, m_ExtractElement(m_Value(V1), m_ConstantInt(C1))) || |
| V0->getType() != V1->getType()) |
| return false; |
| |
| // TODO: Handle C0 != C1 by shuffling 1 of the operands. |
| if (C0 != C1) |
| return false; |
| |
| if (isExtractExtractCheap(Ext0, Ext1, I.getOpcode(), TTI)) |
| return false; |
| |
| if (Pred != CmpInst::BAD_ICMP_PREDICATE) |
| foldExtExtCmp(Ext0, Ext1, I, TTI); |
| else |
| foldExtExtBinop(Ext0, Ext1, I, TTI); |
| |
| return true; |
| } |
| |
| /// This is the entry point for all transforms. Pass manager differences are |
| /// handled in the callers of this function. |
| static bool runImpl(Function &F, const TargetTransformInfo &TTI, |
| const DominatorTree &DT) { |
| bool MadeChange = false; |
| for (BasicBlock &BB : F) { |
| // Ignore unreachable basic blocks. |
| if (!DT.isReachableFromEntry(&BB)) |
| continue; |
| // Do not delete instructions under here and invalidate the iterator. |
| // Walk the block backwards for efficiency. We're matching a chain of |
| // use->defs, so we're more likely to succeed by starting from the bottom. |
| // TODO: It could be more efficient to remove dead instructions |
| // iteratively in this loop rather than waiting until the end. |
| for (Instruction &I : make_range(BB.rbegin(), BB.rend())) |
| MadeChange |= foldExtractExtract(I, TTI); |
| } |
| |
| // We're done with transforms, so remove dead instructions. |
| if (MadeChange) |
| for (BasicBlock &BB : F) |
| SimplifyInstructionsInBlock(&BB); |
| |
| return MadeChange; |
| } |
| |
| // Pass manager boilerplate below here. |
| |
| namespace { |
| class VectorCombineLegacyPass : public FunctionPass { |
| public: |
| static char ID; |
| VectorCombineLegacyPass() : FunctionPass(ID) { |
| initializeVectorCombineLegacyPassPass(*PassRegistry::getPassRegistry()); |
| } |
| |
| void getAnalysisUsage(AnalysisUsage &AU) const override { |
| AU.addRequired<DominatorTreeWrapperPass>(); |
| AU.addRequired<TargetTransformInfoWrapperPass>(); |
| AU.setPreservesCFG(); |
| AU.addPreserved<DominatorTreeWrapperPass>(); |
| AU.addPreserved<GlobalsAAWrapperPass>(); |
| FunctionPass::getAnalysisUsage(AU); |
| } |
| |
| bool runOnFunction(Function &F) override { |
| if (skipFunction(F)) |
| return false; |
| auto &TTI = getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F); |
| auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree(); |
| return runImpl(F, TTI, DT); |
| } |
| }; |
| } // namespace |
| |
| char VectorCombineLegacyPass::ID = 0; |
| INITIALIZE_PASS_BEGIN(VectorCombineLegacyPass, "vector-combine", |
| "Optimize scalar/vector ops", false, |
| false) |
| INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass) |
| INITIALIZE_PASS_END(VectorCombineLegacyPass, "vector-combine", |
| "Optimize scalar/vector ops", false, false) |
| Pass *llvm::createVectorCombinePass() { |
| return new VectorCombineLegacyPass(); |
| } |
| |
| PreservedAnalyses VectorCombinePass::run(Function &F, |
| FunctionAnalysisManager &FAM) { |
| TargetTransformInfo &TTI = FAM.getResult<TargetIRAnalysis>(F); |
| DominatorTree &DT = FAM.getResult<DominatorTreeAnalysis>(F); |
| if (!runImpl(F, TTI, DT)) |
| return PreservedAnalyses::all(); |
| PreservedAnalyses PA; |
| PA.preserveSet<CFGAnalyses>(); |
| PA.preserve<GlobalsAA>(); |
| return PA; |
| } |