1 //===- LoopInstSimplify.cpp - Loop Instruction Simplification Pass --------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This pass performs lightweight instruction simplification on loop bodies.
12 //===----------------------------------------------------------------------===//
14 #define DEBUG_TYPE "loop-instsimplify"
15 #include "llvm/Analysis/Dominators.h"
16 #include "llvm/Analysis/InstructionSimplify.h"
17 #include "llvm/Analysis/LoopInfo.h"
18 #include "llvm/Analysis/LoopPass.h"
19 #include "llvm/Support/Debug.h"
20 #include "llvm/Target/TargetData.h"
21 #include "llvm/Transforms/Scalar.h"
22 #include "llvm/Transforms/Utils/Local.h"
23 #include "llvm/ADT/Statistic.h"
26 STATISTIC(NumSimplified, "Number of redundant instructions simplified");
29 class LoopInstSimplify : public LoopPass {
31 static char ID; // Pass ID, replacement for typeid
32 LoopInstSimplify() : LoopPass(ID) {
33 initializeLoopInstSimplifyPass(*PassRegistry::getPassRegistry());
36 bool runOnLoop(Loop*, LPPassManager&);
38 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
40 AU.addRequired<LoopInfo>();
41 AU.addRequiredID(LoopSimplifyID);
42 AU.addPreservedID(LCSSAID);
47 char LoopInstSimplify::ID = 0;
48 INITIALIZE_PASS_BEGIN(LoopInstSimplify, "loop-instsimplify",
49 "Simplify instructions in loops", false, false)
50 INITIALIZE_PASS_DEPENDENCY(DominatorTree)
51 INITIALIZE_PASS_DEPENDENCY(LoopInfo)
52 INITIALIZE_PASS_DEPENDENCY(LCSSA)
53 INITIALIZE_PASS_END(LoopInstSimplify, "loop-instsimplify",
54 "Simplify instructions in loops", false, false)
56 Pass* llvm::createLoopInstSimplifyPass() {
57 return new LoopInstSimplify();
60 bool LoopInstSimplify::runOnLoop(Loop *L, LPPassManager &LPM) {
61 DominatorTree *DT = getAnalysisIfAvailable<DominatorTree>();
62 LoopInfo *LI = &getAnalysis<LoopInfo>();
63 const TargetData *TD = getAnalysisIfAvailable<TargetData>();
65 SmallVector<BasicBlock*, 8> ExitBlocks;
66 L->getUniqueExitBlocks(ExitBlocks);
67 array_pod_sort(ExitBlocks.begin(), ExitBlocks.end());
69 SmallPtrSet<const Instruction*, 8> S1, S2, *ToSimplify = &S1, *Next = &S2;
71 SmallVector<BasicBlock*, 16> VisitStack;
72 SmallPtrSet<BasicBlock*, 32> Visited;
82 VisitStack.push_back(L->getHeader());
84 while (!VisitStack.empty()) {
85 BasicBlock *BB = VisitStack.back();
86 VisitStack.pop_back();
88 // Simplify instructions in the current basic block.
89 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE;) {
90 Instruction *I = BI++;
92 // The first time through the loop ToSimplify is empty and we try to
93 // simplify all instructions. On later iterations ToSimplify is not
94 // empty and we only bother simplifying instructions that are in it.
95 if (!ToSimplify->empty() && !ToSimplify->count(I))
98 // Don't bother simplifying unused instructions.
99 if (!I->use_empty()) {
100 Value *V = SimplifyInstruction(I, TD, DT);
101 if (V && LI->replacementPreservesLCSSAForm(I, V)) {
102 // Mark all uses for resimplification next time round the loop.
103 for (Value::use_iterator UI = I->use_begin(), UE = I->use_end();
105 Next->insert(cast<Instruction>(*UI));
107 I->replaceAllUsesWith(V);
112 LocalChanged |= RecursivelyDeleteTriviallyDeadInstructions(I);
115 // Add all successors to the worklist, except for loop exit blocks.
116 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE;
118 BasicBlock *SuccBB = *SI;
119 bool IsExitBlock = std::binary_search(ExitBlocks.begin(),
120 ExitBlocks.end(), SuccBB);
121 if (!IsExitBlock && Visited.insert(SuccBB))
122 VisitStack.push_back(SuccBB);
126 // Place the list of instructions to simplify on the next loop iteration
128 std::swap(ToSimplify, Next);
131 Changed |= LocalChanged;
132 } while (LocalChanged);