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//===- HexagonOptimizeSZextends.cpp - Remove unnecessary argument extends -===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// Pass that removes sign extends for function parameters. These parameters
// are already sign extended by the caller per Hexagon's ABI
//
//===----------------------------------------------------------------------===//
#include "llvm/CodeGen/StackProtector.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/IntrinsicsHexagon.h"
#include "llvm/Pass.h"
#include "llvm/Transforms/Scalar.h"
#include "Hexagon.h"
using namespace llvm;
namespace llvm {
FunctionPass *createHexagonOptimizeSZextends();
void initializeHexagonOptimizeSZextendsPass(PassRegistry&);
}
namespace {
struct HexagonOptimizeSZextends : public FunctionPass {
public:
static char ID;
HexagonOptimizeSZextends() : FunctionPass(ID) {
initializeHexagonOptimizeSZextendsPass(*PassRegistry::getPassRegistry());
}
bool runOnFunction(Function &F) override;
StringRef getPassName() const override { return "Remove sign extends"; }
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addPreserved<StackProtector>();
FunctionPass::getAnalysisUsage(AU);
}
bool intrinsicAlreadySextended(Intrinsic::ID IntID);
};
}
char HexagonOptimizeSZextends::ID = 0;
INITIALIZE_PASS(HexagonOptimizeSZextends, "reargs",
"Remove Sign and Zero Extends for Args", false, false)
bool HexagonOptimizeSZextends::intrinsicAlreadySextended(Intrinsic::ID IntID) {
switch(IntID) {
case llvm::Intrinsic::hexagon_A2_addh_l16_sat_ll:
return true;
default:
break;
}
return false;
}
bool HexagonOptimizeSZextends::runOnFunction(Function &F) {
if (skipFunction(F))
return false;
unsigned Idx = 1;
// Try to optimize sign extends in formal parameters. It's relying on
// callee already sign extending the values. I'm not sure if our ABI
// requires callee to sign extend though.
for (auto &Arg : F.args()) {
if (F.getAttributes().hasAttribute(Idx, Attribute::SExt)) {
if (!isa<PointerType>(Arg.getType())) {
for (auto UI = Arg.use_begin(); UI != Arg.use_end();) {
if (isa<SExtInst>(*UI)) {
Instruction* Use = cast<Instruction>(*UI);
SExtInst* SI = new SExtInst(&Arg, Use->getType());
assert (EVT::getEVT(SI->getType()) ==
(EVT::getEVT(Use->getType())));
++UI;
Use->replaceAllUsesWith(SI);
Instruction* First = &F.getEntryBlock().front();
SI->insertBefore(First);
Use->eraseFromParent();
} else {
++UI;
}
}
}
}
++Idx;
}
// Try to remove redundant sext operations on Hexagon. The hardware
// already sign extends many 16 bit intrinsic operations to 32 bits.
// For example:
// %34 = tail call i32 @llvm.hexagon.A2.addh.l16.sat.ll(i32 %x, i32 %y)
// %sext233 = shl i32 %34, 16
// %conv52 = ashr exact i32 %sext233, 16
for (auto &B : F) {
for (auto &I : B) {
// Look for arithmetic shift right by 16.
BinaryOperator *Ashr = dyn_cast<BinaryOperator>(&I);
if (!(Ashr && Ashr->getOpcode() == Instruction::AShr))
continue;
Value *AshrOp1 = Ashr->getOperand(1);
ConstantInt *C = dyn_cast<ConstantInt>(AshrOp1);
// Right shifted by 16.
if (!(C && C->getSExtValue() == 16))
continue;
// The first operand of Ashr comes from logical shift left.
Instruction *Shl = dyn_cast<Instruction>(Ashr->getOperand(0));
if (!(Shl && Shl->getOpcode() == Instruction::Shl))
continue;
Value *Intr = Shl->getOperand(0);
Value *ShlOp1 = Shl->getOperand(1);
C = dyn_cast<ConstantInt>(ShlOp1);
// Left shifted by 16.
if (!(C && C->getSExtValue() == 16))
continue;
// The first operand of Shl comes from an intrinsic.
if (IntrinsicInst *I = dyn_cast<IntrinsicInst>(Intr)) {
if (!intrinsicAlreadySextended(I->getIntrinsicID()))
continue;
// All is well. Replace all uses of AShr with I.
for (auto UI = Ashr->user_begin(), UE = Ashr->user_end();
UI != UE; ++UI) {
const Use &TheUse = UI.getUse();
if (Instruction *J = dyn_cast<Instruction>(TheUse.getUser())) {
J->replaceUsesOfWith(Ashr, I);
}
}
}
}
}
return true;
}
FunctionPass *llvm::createHexagonOptimizeSZextends() {
return new HexagonOptimizeSZextends();
}
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