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/Instructions.h"
16 #include "llvm/Analysis/Dominators.h"
17 #include "llvm/Analysis/InstructionSimplify.h"
18 #include "llvm/Analysis/LoopInfo.h"
19 #include "llvm/Analysis/LoopPass.h"
20 #include "llvm/Support/Debug.h"
21 #include "llvm/Target/TargetData.h"
22 #include "llvm/Transforms/Scalar.h"
23 #include "llvm/Transforms/Utils/Local.h"
24 #include "llvm/ADT/Statistic.h"
27 STATISTIC(NumSimplified, "Number of redundant instructions simplified");
30 class LoopInstSimplify : public LoopPass {
32 static char ID; // Pass ID, replacement for typeid
33 LoopInstSimplify() : LoopPass(ID) {
34 initializeLoopInstSimplifyPass(*PassRegistry::getPassRegistry());
37 bool runOnLoop(Loop*, LPPassManager&);
39 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
41 AU.addRequired<LoopInfo>();
42 AU.addRequiredID(LoopSimplifyID);
43 AU.addPreservedID(LCSSAID);
48 char LoopInstSimplify::ID = 0;
49 INITIALIZE_PASS_BEGIN(LoopInstSimplify, "loop-instsimplify",
50 "Simplify instructions in loops", false, false)
51 INITIALIZE_PASS_DEPENDENCY(DominatorTree)
52 INITIALIZE_PASS_DEPENDENCY(LoopInfo)
53 INITIALIZE_PASS_DEPENDENCY(LCSSA)
54 INITIALIZE_PASS_END(LoopInstSimplify, "loop-instsimplify",
55 "Simplify instructions in loops", false, false)
57 Pass *llvm::createLoopInstSimplifyPass() {
58 return new LoopInstSimplify();
61 bool LoopInstSimplify::runOnLoop(Loop *L, LPPassManager &LPM) {
62 DominatorTree *DT = getAnalysisIfAvailable<DominatorTree>();
63 LoopInfo *LI = &getAnalysis<LoopInfo>();
64 const TargetData *TD = getAnalysisIfAvailable<TargetData>();
66 SmallVector<BasicBlock*, 8> ExitBlocks;
67 L->getUniqueExitBlocks(ExitBlocks);
68 array_pod_sort(ExitBlocks.begin(), ExitBlocks.end());
70 SmallPtrSet<const Instruction*, 8> S1, S2, *ToSimplify = &S1, *Next = &S2;
72 // The bit we are stealing from the pointer represents whether this basic
73 // block is the header of a subloop, in which case we only process its phis.
74 typedef PointerIntPair<BasicBlock*, 1> WorklistItem;
75 SmallVector<WorklistItem, 16> VisitStack;
76 SmallPtrSet<BasicBlock*, 32> Visited;
86 VisitStack.push_back(WorklistItem(L->getHeader(), false));
88 while (!VisitStack.empty()) {
89 WorklistItem Item = VisitStack.pop_back_val();
90 BasicBlock *BB = Item.getPointer();
91 bool IsSubloopHeader = Item.getInt();
93 // Simplify instructions in the current basic block.
94 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE;) {
95 Instruction *I = BI++;
97 // The first time through the loop ToSimplify is empty and we try to
98 // simplify all instructions. On later iterations ToSimplify is not
99 // empty and we only bother simplifying instructions that are in it.
100 if (!ToSimplify->empty() && !ToSimplify->count(I))
103 // Don't bother simplifying unused instructions.
104 if (!I->use_empty()) {
105 Value *V = SimplifyInstruction(I, TD, DT);
106 if (V && LI->replacementPreservesLCSSAForm(I, V)) {
107 // Mark all uses for resimplification next time round the loop.
108 for (Value::use_iterator UI = I->use_begin(), UE = I->use_end();
110 Next->insert(cast<Instruction>(*UI));
112 I->replaceAllUsesWith(V);
117 LocalChanged |= RecursivelyDeleteTriviallyDeadInstructions(I);
119 if (IsSubloopHeader && !isa<PHINode>(I))
123 // Add all successors to the worklist, except for loop exit blocks and the
124 // bodies of subloops. We visit the headers of loops so that we can process
125 // their phis, but we contract the rest of the subloop body and only follow
126 // edges leading back to the original loop.
127 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE;
129 BasicBlock *SuccBB = *SI;
130 if (!Visited.insert(SuccBB))
133 const Loop *SuccLoop = LI->getLoopFor(SuccBB);
134 if (SuccLoop && SuccLoop->getHeader() == SuccBB
135 && L->contains(SuccLoop)) {
136 VisitStack.push_back(WorklistItem(SuccBB, true));
138 SmallVector<BasicBlock*, 8> SubLoopExitBlocks;
139 SuccLoop->getExitBlocks(SubLoopExitBlocks);
141 for (unsigned i = 0; i < SubLoopExitBlocks.size(); ++i) {
142 BasicBlock *ExitBB = SubLoopExitBlocks[i];
143 if (LI->getLoopFor(ExitBB) == L && Visited.insert(ExitBB))
144 VisitStack.push_back(WorklistItem(ExitBB, false));
150 bool IsExitBlock = std::binary_search(ExitBlocks.begin(),
151 ExitBlocks.end(), SuccBB);
155 VisitStack.push_back(WorklistItem(SuccBB, false));
159 // Place the list of instructions to simplify on the next loop iteration
161 std::swap(ToSimplify, Next);
164 Changed |= LocalChanged;
165 } while (LocalChanged);