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//===- CodeGenLICM.cpp - LICM a function for code generation --------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This function performs late LICM, hoisting constants out of loops that
// are not valid immediates. It should not be followed by instcombine,
// because instcombine would quickly stuff the constants back into the loop.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "codegen-licm"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Instructions.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/LLVMContext.h"
#include "llvm/Analysis/LoopPass.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/ADT/DenseMap.h"
using namespace llvm;
namespace {
class CodeGenLICM : public LoopPass {
virtual bool runOnLoop(Loop *L, LPPassManager &LPM);
virtual void getAnalysisUsage(AnalysisUsage &AU) const;
public:
static char ID; // Pass identification, replacement for typeid
explicit CodeGenLICM() : LoopPass(&ID) {}
};
}
char CodeGenLICM::ID = 0;
static RegisterPass<CodeGenLICM> X("codegen-licm",
"hoist constants out of loops");
Pass *llvm::createCodeGenLICMPass() {
return new CodeGenLICM();
}
bool CodeGenLICM::runOnLoop(Loop *L, LPPassManager &) {
bool Changed = false;
// Only visit outermost loops.
if (L->getParentLoop()) return Changed;
Instruction *PreheaderTerm = L->getLoopPreheader()->getTerminator();
DenseMap<Constant *, BitCastInst *> HoistedConstants;
for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
I != E; ++I) {
BasicBlock *BB = *I;
for (BasicBlock::iterator BBI = BB->begin(), BBE = BB->end();
BBI != BBE; ++BBI) {
Instruction *I = BBI;
// TODO: For now, skip all intrinsic instructions, because some of them
// can require their operands to be constants, and we don't want to
// break that.
if (isa<IntrinsicInst>(I))
continue;
// LLVM represents fneg as -0.0-x; don't hoist the -0.0 out.
if (BinaryOperator::isFNeg(I) ||
BinaryOperator::isNeg(I) ||
BinaryOperator::isNot(I))
continue;
for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
// Don't hoist out switch case constants.
if (isa<SwitchInst>(I) && i == 1)
break;
// Don't hoist out shuffle masks.
if (isa<ShuffleVectorInst>(I) && i == 2)
break;
Value *Op = I->getOperand(i);
Constant *C = dyn_cast<Constant>(Op);
if (!C) continue;
// TODO: Ask the target which constants are legal. This would allow
// us to add support for hoisting ConstantInts and GlobalValues too.
if (isa<ConstantFP>(C) ||
isa<ConstantVector>(C) ||
isa<ConstantAggregateZero>(C)) {
BitCastInst *&BC = HoistedConstants[C];
if (!BC)
BC = new BitCastInst(C, C->getType(), "hoist", PreheaderTerm);
I->setOperand(i, BC);
Changed = true;
}
}
}
}
return Changed;
}
void CodeGenLICM::getAnalysisUsage(AnalysisUsage &AU) const {
// This pass preserves just about everything. List some popular things here.
AU.setPreservesCFG();
AU.addPreservedID(LoopSimplifyID);
AU.addPreserved<LoopInfo>();
AU.addPreserved<AliasAnalysis>();
AU.addPreserved("scalar-evolution");
AU.addPreserved("iv-users");
AU.addPreserved("lda");
AU.addPreserved("live-values");
// Hoisting requires a loop preheader.
AU.addRequiredID(LoopSimplifyID);
}
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