139 lines · cpp
1//===- HexagonOptimizeSZextends.cpp - Remove unnecessary argument extends -===//2//3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.4// See https://llvm.org/LICENSE.txt for license information.5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception6//7//===----------------------------------------------------------------------===//8//9// Pass that removes sign extends for function parameters. These parameters10// are already sign extended by the caller per Hexagon's ABI11//12//===----------------------------------------------------------------------===//13 14#include "Hexagon.h"15#include "llvm/CodeGen/StackProtector.h"16#include "llvm/CodeGen/ValueTypes.h"17#include "llvm/IR/Function.h"18#include "llvm/IR/Instructions.h"19#include "llvm/IR/IntrinsicInst.h"20#include "llvm/IR/IntrinsicsHexagon.h"21#include "llvm/Pass.h"22#include "llvm/Transforms/Scalar.h"23 24using namespace llvm;25 26namespace {27 struct HexagonOptimizeSZextends : public FunctionPass {28 public:29 static char ID;30 HexagonOptimizeSZextends() : FunctionPass(ID) {}31 bool runOnFunction(Function &F) override;32 33 StringRef getPassName() const override { return "Remove sign extends"; }34 35 void getAnalysisUsage(AnalysisUsage &AU) const override {36 AU.addPreserved<StackProtector>();37 FunctionPass::getAnalysisUsage(AU);38 }39 40 bool intrinsicAlreadySextended(Intrinsic::ID IntID);41 };42}43 44char HexagonOptimizeSZextends::ID = 0;45 46INITIALIZE_PASS(HexagonOptimizeSZextends, "reargs",47 "Remove Sign and Zero Extends for Args", false, false)48 49bool HexagonOptimizeSZextends::intrinsicAlreadySextended(Intrinsic::ID IntID) {50 switch(IntID) {51 case llvm::Intrinsic::hexagon_A2_addh_l16_sat_ll:52 return true;53 default:54 break;55 }56 return false;57}58 59bool HexagonOptimizeSZextends::runOnFunction(Function &F) {60 if (skipFunction(F))61 return false;62 63 unsigned Idx = 0;64 // Try to optimize sign extends in formal parameters. It's relying on65 // callee already sign extending the values. I'm not sure if our ABI66 // requires callee to sign extend though.67 for (auto &Arg : F.args()) {68 if (F.getAttributes().hasParamAttr(Idx, Attribute::SExt)) {69 if (!isa<PointerType>(Arg.getType())) {70 for (Use &U : llvm::make_early_inc_range(Arg.uses())) {71 if (isa<SExtInst>(U)) {72 Instruction* Use = cast<Instruction>(U);73 SExtInst* SI = new SExtInst(&Arg, Use->getType());74 assert (EVT::getEVT(SI->getType()) ==75 (EVT::getEVT(Use->getType())));76 Use->replaceAllUsesWith(SI);77 BasicBlock::iterator First = F.getEntryBlock().begin();78 SI->insertBefore(First);79 Use->eraseFromParent();80 }81 }82 }83 }84 ++Idx;85 }86 87 // Try to remove redundant sext operations on Hexagon. The hardware88 // already sign extends many 16 bit intrinsic operations to 32 bits.89 // For example:90 // %34 = tail call i32 @llvm.hexagon.A2.addh.l16.sat.ll(i32 %x, i32 %y)91 // %sext233 = shl i32 %34, 1692 // %conv52 = ashr exact i32 %sext233, 1693 for (auto &B : F) {94 for (auto &I : B) {95 // Look for arithmetic shift right by 16.96 BinaryOperator *Ashr = dyn_cast<BinaryOperator>(&I);97 if (!(Ashr && Ashr->getOpcode() == Instruction::AShr))98 continue;99 Value *AshrOp1 = Ashr->getOperand(1);100 ConstantInt *C = dyn_cast<ConstantInt>(AshrOp1);101 // Right shifted by 16.102 if (!(C && C->getSExtValue() == 16))103 continue;104 105 // The first operand of Ashr comes from logical shift left.106 Instruction *Shl = dyn_cast<Instruction>(Ashr->getOperand(0));107 if (!(Shl && Shl->getOpcode() == Instruction::Shl))108 continue;109 Value *Intr = Shl->getOperand(0);110 Value *ShlOp1 = Shl->getOperand(1);111 C = dyn_cast<ConstantInt>(ShlOp1);112 // Left shifted by 16.113 if (!(C && C->getSExtValue() == 16))114 continue;115 116 // The first operand of Shl comes from an intrinsic.117 if (IntrinsicInst *I = dyn_cast<IntrinsicInst>(Intr)) {118 if (!intrinsicAlreadySextended(I->getIntrinsicID()))119 continue;120 // All is well. Replace all uses of AShr with I.121 for (auto UI = Ashr->user_begin(), UE = Ashr->user_end();122 UI != UE; ++UI) {123 const Use &TheUse = UI.getUse();124 if (Instruction *J = dyn_cast<Instruction>(TheUse.getUser())) {125 J->replaceUsesOfWith(Ashr, I);126 }127 }128 }129 }130 }131 132 return true;133}134 135 136FunctionPass *llvm::createHexagonOptimizeSZextends() {137 return new HexagonOptimizeSZextends();138}139