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//===------ SimplifyInstructions.cpp - Remove redundant instructions ------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This is a utility pass used for testing the InstructionSimplify analysis.
// The analysis is applied to every instruction, and if it simplifies then the
// instruction is replaced by the simplification. If you are looking for a pass
// that performs serious instruction folding, use the instcombine pass instead.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "instsimplify"
#include "llvm/Function.h"
#include "llvm/Pass.h"
#include "llvm/Type.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Utils/Local.h"
using namespace llvm;
STATISTIC(NumSimplified, "Number of redundant instructions removed");
namespace {
struct InstSimplifier : public FunctionPass {
static char ID; // Pass identification, replacement for typeid
InstSimplifier() : FunctionPass(ID) {
initializeInstSimplifierPass(*PassRegistry::getPassRegistry());
}
void getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesCFG();
}
/// runOnFunction - Remove instructions that simplify.
bool runOnFunction(Function &F) {
const TargetData *TD = getAnalysisIfAvailable<TargetData>();
const DominatorTree *DT = getAnalysisIfAvailable<DominatorTree>();
bool Changed = false;
// Add all interesting instructions to the worklist.
std::set<Instruction*> Worklist;
for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE;) {
Instruction *I = BI++;
// Zap any dead instructions.
if (isInstructionTriviallyDead(I)) {
I->eraseFromParent();
Changed = true;
continue;
}
// Add all others to the worklist.
Worklist.insert(I);
}
// Simplify everything in the worklist until the cows come home.
while (!Worklist.empty()) {
Instruction *I = *Worklist.begin();
Worklist.erase(Worklist.begin());
Value *V = SimplifyInstruction(I, TD, DT);
if (!V) continue;
// This instruction simplifies! Replace it with its simplification and
// add all uses to the worklist, since they may now simplify.
I->replaceAllUsesWith(V);
for (Value::use_iterator UI = I->use_begin(), UE = I->use_end();
UI != UE; ++UI)
// In unreachable code an instruction can use itself, in which case
// don't add it to the worklist since we are about to erase it.
if (*UI != I) Worklist.insert(cast<Instruction>(*UI));
if (isInstructionTriviallyDead(I))
I->eraseFromParent();
++NumSimplified;
Changed = true;
}
return Changed;
}
};
}
char InstSimplifier::ID = 0;
INITIALIZE_PASS(InstSimplifier, "instsimplify", "Remove redundant instructions",
false, false)
char &llvm::InstructionSimplifierID = InstSimplifier::ID;
// Public interface to the simplify instructions pass.
FunctionPass *llvm::createInstructionSimplifierPass() {
return new InstSimplifier();
}
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