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