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//===- LoopInstSimplify.cpp - Loop Instruction Simplification Pass --------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This pass performs lightweight instruction simplification on loop bodies.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "loop-instsimplify"
#include "llvm/Analysis/LoopPass.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"
#include "llvm/ADT/Statistic.h"
using namespace llvm;
STATISTIC(NumSimplified, "Number of redundant instructions simplified");
namespace {
class LoopInstSimplify : public LoopPass {
public:
static char ID; // Pass ID, replacement for typeid
LoopInstSimplify() : LoopPass(ID) {
initializeLoopInstSimplifyPass(*PassRegistry::getPassRegistry());
}
bool runOnLoop(Loop*, LPPassManager&);
virtual void getAnalysisUsage(AnalysisUsage& AU) const {
AU.setPreservesCFG();
AU.addRequired<DominatorTree>();
AU.addPreserved<DominatorTree>();
AU.addRequired<LoopInfo>();
AU.addPreserved<LoopInfo>();
AU.addPreservedID(LCSSAID);
}
};
}
char LoopInstSimplify::ID = 0;
INITIALIZE_PASS_BEGIN(LoopInstSimplify, "loop-instsimplify",
"Simplify instructions in loops", false, false)
INITIALIZE_PASS_DEPENDENCY(DominatorTree)
INITIALIZE_PASS_DEPENDENCY(LoopInfo)
INITIALIZE_PASS_DEPENDENCY(LCSSA)
INITIALIZE_PASS_END(LoopInstSimplify, "loop-instsimplify",
"Simplify instructions in loops", false, false)
Pass* llvm::createLoopInstSimplifyPass() {
return new LoopInstSimplify();
}
bool LoopInstSimplify::runOnLoop(Loop* L, LPPassManager& LPM) {
DominatorTree* DT = &getAnalysis<DominatorTree>();
const LoopInfo* LI = &getAnalysis<LoopInfo>();
const TargetData* TD = getAnalysisIfAvailable<TargetData>();
bool Changed = false;
bool LocalChanged;
do {
LocalChanged = false;
SmallPtrSet<BasicBlock*, 32> Visited;
SmallVector<BasicBlock*, 32> VisitStack;
VisitStack.push_back(L->getHeader());
while (!VisitStack.empty()) {
BasicBlock* BB = VisitStack.back();
VisitStack.pop_back();
if (Visited.count(BB))
continue;
Visited.insert(BB);
for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE;) {
Instruction* I = BI++;
// Don't bother simplifying unused instructions.
if (!I->use_empty()) {
if (Value* V = SimplifyInstruction(I, TD, DT)) {
I->replaceAllUsesWith(V);
LocalChanged = true;
++NumSimplified;
}
}
LocalChanged |= RecursivelyDeleteTriviallyDeadInstructions(I);
}
Changed |= LocalChanged;
DomTreeNode* Node = DT->getNode(BB);
const std::vector<DomTreeNode*>& Children = Node->getChildren();
for (unsigned i = 0; i < Children.size(); ++i) {
// Only visit children that are in the same loop.
BasicBlock* ChildBB = Children[i]->getBlock();
if (!Visited.count(ChildBB) && LI->getLoopFor(ChildBB) == L)
VisitStack.push_back(ChildBB);
}
}
} while (LocalChanged);
// Nothing that SimplifyInstruction() does should invalidate LCSSA form.
assert(L->isLCSSAForm(*DT));
return Changed;
}