mirror of
https://github.com/c64scene-ar/llvm-6502.git
synced 2024-08-30 21:29:28 +00:00
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@64888 91177308-0d34-0410-b5e6-96231b3b80d8
134 lines
4.1 KiB
C++
134 lines
4.1 KiB
C++
//===- DCE.cpp - Code to perform dead code elimination --------------------===//
|
|
//
|
|
// The LLVM Compiler Infrastructure
|
|
//
|
|
// This file is distributed under the University of Illinois Open Source
|
|
// License. See LICENSE.TXT for details.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
//
|
|
// This file implements dead inst elimination and dead code elimination.
|
|
//
|
|
// Dead Inst Elimination performs a single pass over the function removing
|
|
// instructions that are obviously dead. Dead Code Elimination is similar, but
|
|
// it rechecks instructions that were used by removed instructions to see if
|
|
// they are newly dead.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
#define DEBUG_TYPE "dce"
|
|
#include "llvm/Transforms/Scalar.h"
|
|
#include "llvm/Transforms/Utils/Local.h"
|
|
#include "llvm/Instruction.h"
|
|
#include "llvm/Pass.h"
|
|
#include "llvm/Support/Compiler.h"
|
|
#include "llvm/Support/InstIterator.h"
|
|
#include "llvm/ADT/Statistic.h"
|
|
#include <set>
|
|
using namespace llvm;
|
|
|
|
STATISTIC(DIEEliminated, "Number of insts removed by DIE pass");
|
|
STATISTIC(DCEEliminated, "Number of insts removed");
|
|
|
|
namespace {
|
|
//===--------------------------------------------------------------------===//
|
|
// DeadInstElimination pass implementation
|
|
//
|
|
struct VISIBILITY_HIDDEN DeadInstElimination : public BasicBlockPass {
|
|
static char ID; // Pass identification, replacement for typeid
|
|
DeadInstElimination() : BasicBlockPass(&ID) {}
|
|
virtual bool runOnBasicBlock(BasicBlock &BB) {
|
|
bool Changed = false;
|
|
for (BasicBlock::iterator DI = BB.begin(); DI != BB.end(); ) {
|
|
Instruction *Inst = DI++;
|
|
if (isInstructionTriviallyDead(Inst)) {
|
|
Inst->eraseFromParent();
|
|
Changed = true;
|
|
++DIEEliminated;
|
|
}
|
|
}
|
|
return Changed;
|
|
}
|
|
|
|
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
|
|
AU.setPreservesCFG();
|
|
}
|
|
};
|
|
}
|
|
|
|
char DeadInstElimination::ID = 0;
|
|
static RegisterPass<DeadInstElimination>
|
|
X("die", "Dead Instruction Elimination");
|
|
|
|
Pass *llvm::createDeadInstEliminationPass() {
|
|
return new DeadInstElimination();
|
|
}
|
|
|
|
|
|
namespace {
|
|
//===--------------------------------------------------------------------===//
|
|
// DeadCodeElimination pass implementation
|
|
//
|
|
struct DCE : public FunctionPass {
|
|
static char ID; // Pass identification, replacement for typeid
|
|
DCE() : FunctionPass(&ID) {}
|
|
|
|
virtual bool runOnFunction(Function &F);
|
|
|
|
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
|
|
AU.setPreservesCFG();
|
|
}
|
|
};
|
|
}
|
|
|
|
char DCE::ID = 0;
|
|
static RegisterPass<DCE> Y("dce", "Dead Code Elimination");
|
|
|
|
bool DCE::runOnFunction(Function &F) {
|
|
// Start out with all of the instructions in the worklist...
|
|
std::vector<Instruction*> WorkList;
|
|
for (inst_iterator i = inst_begin(F), e = inst_end(F); i != e; ++i)
|
|
WorkList.push_back(&*i);
|
|
|
|
// Loop over the worklist finding instructions that are dead. If they are
|
|
// dead make them drop all of their uses, making other instructions
|
|
// potentially dead, and work until the worklist is empty.
|
|
//
|
|
bool MadeChange = false;
|
|
while (!WorkList.empty()) {
|
|
Instruction *I = WorkList.back();
|
|
WorkList.pop_back();
|
|
|
|
if (isInstructionTriviallyDead(I)) { // If the instruction is dead.
|
|
// Loop over all of the values that the instruction uses, if there are
|
|
// instructions being used, add them to the worklist, because they might
|
|
// go dead after this one is removed.
|
|
//
|
|
for (User::op_iterator OI = I->op_begin(), E = I->op_end(); OI != E; ++OI)
|
|
if (Instruction *Used = dyn_cast<Instruction>(*OI))
|
|
WorkList.push_back(Used);
|
|
|
|
// Remove the instruction.
|
|
I->eraseFromParent();
|
|
|
|
// Remove the instruction from the worklist if it still exists in it.
|
|
for (std::vector<Instruction*>::iterator WI = WorkList.begin();
|
|
WI != WorkList.end(); ) {
|
|
if (*WI == I)
|
|
WI = WorkList.erase(WI);
|
|
else
|
|
++WI;
|
|
}
|
|
|
|
MadeChange = true;
|
|
++DCEEliminated;
|
|
}
|
|
}
|
|
return MadeChange;
|
|
}
|
|
|
|
FunctionPass *llvm::createDeadCodeEliminationPass() {
|
|
return new DCE();
|
|
}
|
|
|