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 #include "llvm/Transforms/Scalar.h"
15 #include "llvm/ADT/STLExtras.h"
16 #include "llvm/ADT/Statistic.h"
17 #include "llvm/Analysis/AssumptionCache.h"
18 #include "llvm/Analysis/InstructionSimplify.h"
19 #include "llvm/Analysis/LoopInfo.h"
20 #include "llvm/Analysis/LoopPass.h"
21 #include "llvm/IR/DataLayout.h"
22 #include "llvm/IR/Dominators.h"
23 #include "llvm/IR/Instructions.h"
24 #include "llvm/Support/Debug.h"
25 #include "llvm/Analysis/TargetLibraryInfo.h"
26 #include "llvm/Transforms/Utils/Local.h"
29 #define DEBUG_TYPE "loop-instsimplify"
31 STATISTIC(NumSimplified, "Number of redundant instructions simplified");
34 class LoopInstSimplify : public LoopPass {
36 static char ID; // Pass ID, replacement for typeid
37 LoopInstSimplify() : LoopPass(ID) {
38 initializeLoopInstSimplifyPass(*PassRegistry::getPassRegistry());
41 bool runOnLoop(Loop*, LPPassManager&) override;
43 void getAnalysisUsage(AnalysisUsage &AU) const override {
45 AU.addRequired<AssumptionCacheTracker>();
46 AU.addRequired<LoopInfo>();
47 AU.addRequiredID(LoopSimplifyID);
48 AU.addPreservedID(LoopSimplifyID);
49 AU.addPreservedID(LCSSAID);
50 AU.addPreserved("scalar-evolution");
51 AU.addRequired<TargetLibraryInfo>();
56 char LoopInstSimplify::ID = 0;
57 INITIALIZE_PASS_BEGIN(LoopInstSimplify, "loop-instsimplify",
58 "Simplify instructions in loops", false, false)
59 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
60 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo)
61 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
62 INITIALIZE_PASS_DEPENDENCY(LoopInfo)
63 INITIALIZE_PASS_DEPENDENCY(LCSSA)
64 INITIALIZE_PASS_END(LoopInstSimplify, "loop-instsimplify",
65 "Simplify instructions in loops", false, false)
67 Pass *llvm::createLoopInstSimplifyPass() {
68 return new LoopInstSimplify();
71 bool LoopInstSimplify::runOnLoop(Loop *L, LPPassManager &LPM) {
72 if (skipOptnoneFunction(L))
75 DominatorTreeWrapperPass *DTWP =
76 getAnalysisIfAvailable<DominatorTreeWrapperPass>();
77 DominatorTree *DT = DTWP ? &DTWP->getDomTree() : nullptr;
78 LoopInfo *LI = &getAnalysis<LoopInfo>();
79 DataLayoutPass *DLP = getAnalysisIfAvailable<DataLayoutPass>();
80 const DataLayout *DL = DLP ? &DLP->getDataLayout() : nullptr;
81 const TargetLibraryInfo *TLI = &getAnalysis<TargetLibraryInfo>();
82 auto &AC = getAnalysis<AssumptionCacheTracker>().getAssumptionCache(
83 *L->getHeader()->getParent());
85 SmallVector<BasicBlock*, 8> ExitBlocks;
86 L->getUniqueExitBlocks(ExitBlocks);
87 array_pod_sort(ExitBlocks.begin(), ExitBlocks.end());
89 SmallPtrSet<const Instruction*, 8> S1, S2, *ToSimplify = &S1, *Next = &S2;
91 // The bit we are stealing from the pointer represents whether this basic
92 // block is the header of a subloop, in which case we only process its phis.
93 typedef PointerIntPair<BasicBlock*, 1> WorklistItem;
94 SmallVector<WorklistItem, 16> VisitStack;
95 SmallPtrSet<BasicBlock*, 32> Visited;
100 LocalChanged = false;
105 VisitStack.push_back(WorklistItem(L->getHeader(), false));
107 while (!VisitStack.empty()) {
108 WorklistItem Item = VisitStack.pop_back_val();
109 BasicBlock *BB = Item.getPointer();
110 bool IsSubloopHeader = Item.getInt();
112 // Simplify instructions in the current basic block.
113 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE;) {
114 Instruction *I = BI++;
116 // The first time through the loop ToSimplify is empty and we try to
117 // simplify all instructions. On later iterations ToSimplify is not
118 // empty and we only bother simplifying instructions that are in it.
119 if (!ToSimplify->empty() && !ToSimplify->count(I))
122 // Don't bother simplifying unused instructions.
123 if (!I->use_empty()) {
124 Value *V = SimplifyInstruction(I, DL, TLI, DT, &AC);
125 if (V && LI->replacementPreservesLCSSAForm(I, V)) {
126 // Mark all uses for resimplification next time round the loop.
127 for (User *U : I->users())
128 Next->insert(cast<Instruction>(U));
130 I->replaceAllUsesWith(V);
135 bool res = RecursivelyDeleteTriviallyDeadInstructions(I, TLI);
137 // RecursivelyDeleteTriviallyDeadInstruction can remove
138 // more than one instruction, so simply incrementing the
139 // iterator does not work. When instructions get deleted
140 // re-iterate instead.
141 BI = BB->begin(); BE = BB->end();
145 if (IsSubloopHeader && !isa<PHINode>(I))
149 // Add all successors to the worklist, except for loop exit blocks and the
150 // bodies of subloops. We visit the headers of loops so that we can process
151 // their phis, but we contract the rest of the subloop body and only follow
152 // edges leading back to the original loop.
153 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE;
155 BasicBlock *SuccBB = *SI;
156 if (!Visited.insert(SuccBB).second)
159 const Loop *SuccLoop = LI->getLoopFor(SuccBB);
160 if (SuccLoop && SuccLoop->getHeader() == SuccBB
161 && L->contains(SuccLoop)) {
162 VisitStack.push_back(WorklistItem(SuccBB, true));
164 SmallVector<BasicBlock*, 8> SubLoopExitBlocks;
165 SuccLoop->getExitBlocks(SubLoopExitBlocks);
167 for (unsigned i = 0; i < SubLoopExitBlocks.size(); ++i) {
168 BasicBlock *ExitBB = SubLoopExitBlocks[i];
169 if (LI->getLoopFor(ExitBB) == L && Visited.insert(ExitBB).second)
170 VisitStack.push_back(WorklistItem(ExitBB, false));
176 bool IsExitBlock = std::binary_search(ExitBlocks.begin(),
177 ExitBlocks.end(), SuccBB);
181 VisitStack.push_back(WorklistItem(SuccBB, false));
185 // Place the list of instructions to simplify on the next loop iteration
187 std::swap(ToSimplify, Next);
190 Changed |= LocalChanged;
191 } while (LocalChanged);