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      1 //===- HexagonOptimizeSZextends.cpp - Remove unnecessary argument extends -===//
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is distributed under the University of Illinois Open Source
      6 // License. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 //
     10 // Pass that removes sign extends for function parameters. These parameters
     11 // are already sign extended by the caller per Hexagon's ABI
     12 //
     13 //===----------------------------------------------------------------------===//
     14 
     15 #include "llvm/CodeGen/MachineFunctionAnalysis.h"
     16 #include "llvm/CodeGen/StackProtector.h"
     17 #include "llvm/IR/Function.h"
     18 #include "llvm/IR/Instructions.h"
     19 #include "llvm/IR/IntrinsicInst.h"
     20 #include "llvm/Pass.h"
     21 #include "llvm/Transforms/Scalar.h"
     22 
     23 #include "Hexagon.h"
     24 
     25 using namespace llvm;
     26 
     27 namespace llvm {
     28   FunctionPass *createHexagonOptimizeSZextends();
     29   void initializeHexagonOptimizeSZextendsPass(PassRegistry&);
     30 }
     31 
     32 namespace {
     33   struct HexagonOptimizeSZextends : public FunctionPass {
     34   public:
     35     static char ID;
     36     HexagonOptimizeSZextends() : FunctionPass(ID) {
     37       initializeHexagonOptimizeSZextendsPass(*PassRegistry::getPassRegistry());
     38     }
     39     bool runOnFunction(Function &F) override;
     40 
     41     const char *getPassName() const override {
     42       return "Remove sign extends";
     43     }
     44 
     45     void getAnalysisUsage(AnalysisUsage &AU) const override {
     46       AU.addRequired<MachineFunctionAnalysis>();
     47       AU.addPreserved<MachineFunctionAnalysis>();
     48       AU.addPreserved<StackProtector>();
     49       FunctionPass::getAnalysisUsage(AU);
     50     }
     51 
     52     bool intrinsicAlreadySextended(Intrinsic::ID IntID);
     53   };
     54 }
     55 
     56 char HexagonOptimizeSZextends::ID = 0;
     57 
     58 INITIALIZE_PASS(HexagonOptimizeSZextends, "reargs",
     59                 "Remove Sign and Zero Extends for Args", false, false)
     60 
     61 bool HexagonOptimizeSZextends::intrinsicAlreadySextended(Intrinsic::ID IntID) {
     62   switch(IntID) {
     63     case llvm::Intrinsic::hexagon_A2_addh_l16_sat_ll:
     64       return true;
     65     default:
     66       break;
     67   }
     68   return false;
     69 }
     70 
     71 bool HexagonOptimizeSZextends::runOnFunction(Function &F) {
     72   unsigned Idx = 1;
     73   // Try to optimize sign extends in formal parameters. It's relying on
     74   // callee already sign extending the values. I'm not sure if our ABI
     75   // requires callee to sign extend though.
     76   for (auto &Arg : F.args()) {
     77     if (F.getAttributes().hasAttribute(Idx, Attribute::SExt)) {
     78       if (!isa<PointerType>(Arg.getType())) {
     79         for (auto UI = Arg.use_begin(); UI != Arg.use_end();) {
     80           if (isa<SExtInst>(*UI)) {
     81             Instruction* Use = cast<Instruction>(*UI);
     82             SExtInst* SI = new SExtInst(&Arg, Use->getType());
     83             assert (EVT::getEVT(SI->getType()) ==
     84                     (EVT::getEVT(Use->getType())));
     85             ++UI;
     86             Use->replaceAllUsesWith(SI);
     87             Instruction* First = &F.getEntryBlock().front();
     88             SI->insertBefore(First);
     89             Use->eraseFromParent();
     90           } else {
     91             ++UI;
     92           }
     93         }
     94       }
     95     }
     96     ++Idx;
     97   }
     98 
     99   // Try to remove redundant sext operations on Hexagon. The hardware
    100   // already sign extends many 16 bit intrinsic operations to 32 bits.
    101   // For example:
    102   // %34 = tail call i32 @llvm.hexagon.A2.addh.l16.sat.ll(i32 %x, i32 %y)
    103   // %sext233 = shl i32 %34, 16
    104   // %conv52 = ashr exact i32 %sext233, 16
    105   for (auto &B : F) {
    106     for (auto &I : B) {
    107       // Look for arithmetic shift right by 16.
    108       BinaryOperator *Ashr = dyn_cast<BinaryOperator>(&I);
    109       if (!(Ashr && Ashr->getOpcode() == Instruction::AShr))
    110         continue;
    111       Value *AshrOp1 = Ashr->getOperand(1);
    112       ConstantInt *C = dyn_cast<ConstantInt>(AshrOp1);
    113       // Right shifted by 16.
    114       if (!(C && C->getSExtValue() == 16))
    115         continue;
    116 
    117       // The first operand of Ashr comes from logical shift left.
    118       Instruction *Shl = dyn_cast<Instruction>(Ashr->getOperand(0));
    119       if (!(Shl && Shl->getOpcode() == Instruction::Shl))
    120         continue;
    121       Value *Intr = Shl->getOperand(0);
    122       Value *ShlOp1 = Shl->getOperand(1);
    123       C = dyn_cast<ConstantInt>(ShlOp1);
    124       // Left shifted by 16.
    125       if (!(C && C->getSExtValue() == 16))
    126         continue;
    127 
    128       // The first operand of Shl comes from an intrinsic.
    129       if (IntrinsicInst *I = dyn_cast<IntrinsicInst>(Intr)) {
    130         if (!intrinsicAlreadySextended(I->getIntrinsicID()))
    131           continue;
    132         // All is well. Replace all uses of AShr with I.
    133         for (auto UI = Ashr->user_begin(), UE = Ashr->user_end();
    134              UI != UE; ++UI) {
    135           const Use &TheUse = UI.getUse();
    136           if (Instruction *J = dyn_cast<Instruction>(TheUse.getUser())) {
    137             J->replaceUsesOfWith(Ashr, I);
    138           }
    139         }
    140       }
    141     }
    142   }
    143 
    144   return true;
    145 }
    146 
    147 
    148 FunctionPass *llvm::createHexagonOptimizeSZextends() {
    149   return new HexagonOptimizeSZextends();
    150 }
    151