mirror of
https://github.com/c64scene-ar/llvm-6502.git
synced 2024-12-21 00:32:23 +00:00
a806a87e29
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@51680 91177308-0d34-0410-b5e6-96231b3b80d8
93 lines
3.0 KiB
C++
93 lines
3.0 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 the Aggressive Dead Code Elimination pass. This pass
|
|
// optimistically assumes that all instructions are dead until proven otherwise,
|
|
// allowing it to eliminate dead computations that other DCE passes do not
|
|
// catch, particularly involving loop computations.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
#define DEBUG_TYPE "adce"
|
|
#include "llvm/Transforms/Scalar.h"
|
|
#include "llvm/Instructions.h"
|
|
#include "llvm/Pass.h"
|
|
#include "llvm/Support/Compiler.h"
|
|
#include "llvm/Support/InstIterator.h"
|
|
#include "llvm/ADT/Statistic.h"
|
|
#include "llvm/ADT/SmallPtrSet.h"
|
|
|
|
using namespace llvm;
|
|
|
|
STATISTIC(NumRemoved, "Number of instructions removed");
|
|
|
|
namespace {
|
|
struct VISIBILITY_HIDDEN ADCE : public FunctionPass {
|
|
static char ID; // Pass identification, replacement for typeid
|
|
ADCE() : FunctionPass((intptr_t)&ID) {}
|
|
|
|
virtual bool runOnFunction(Function& F);
|
|
|
|
virtual void getAnalysisUsage(AnalysisUsage& AU) const {
|
|
AU.setPreservesCFG();
|
|
}
|
|
|
|
};
|
|
}
|
|
|
|
char ADCE::ID = 0;
|
|
static RegisterPass<ADCE> X("adce", "Aggressive Dead Code Elimination");
|
|
|
|
bool ADCE::runOnFunction(Function& F) {
|
|
SmallPtrSet<Instruction*, 32> alive;
|
|
std::vector<Instruction*> worklist;
|
|
|
|
// Collect the set of "root" instructions that are known live.
|
|
for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
|
|
if (isa<TerminatorInst>(I.getInstructionIterator()) ||
|
|
I->mayWriteToMemory()) {
|
|
alive.insert(I.getInstructionIterator());
|
|
worklist.push_back(I.getInstructionIterator());
|
|
}
|
|
|
|
// Propagate liveness backwards to operands.
|
|
while (!worklist.empty()) {
|
|
Instruction* curr = worklist.back();
|
|
worklist.pop_back();
|
|
|
|
for (Instruction::op_iterator OI = curr->op_begin(), OE = curr->op_end();
|
|
OI != OE; ++OI)
|
|
if (Instruction* Inst = dyn_cast<Instruction>(OI))
|
|
if (alive.insert(Inst))
|
|
worklist.push_back(Inst);
|
|
}
|
|
|
|
// The inverse of the live set is the dead set. These are those instructions
|
|
// which have no side effects and do not influence the control flow or return
|
|
// value of the function, and may therefore be deleted safely.
|
|
SmallPtrSet<Instruction*, 32> dead;
|
|
for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
|
|
if (!alive.count(I.getInstructionIterator())) {
|
|
dead.insert(I.getInstructionIterator());
|
|
I->dropAllReferences();
|
|
}
|
|
|
|
for (SmallPtrSet<Instruction*, 32>::iterator I = dead.begin(),
|
|
E = dead.end(); I != E; ++I) {
|
|
NumRemoved++;
|
|
(*I)->eraseFromParent();
|
|
}
|
|
|
|
return !dead.empty();
|
|
}
|
|
|
|
FunctionPass *llvm::createAggressiveDCEPass() {
|
|
return new ADCE();
|
|
}
|