1 //===--------- LoopSimplifyCFG.cpp - Loop CFG 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 file implements the Loop SimplifyCFG Pass. This pass is responsible for
11 // basic loop CFG cleanup, primarily to assist other loop passes. If you
12 // encounter a noncanonical CFG construct that causes another loop pass to
13 // perform suboptimally, this is the place to fix it up.
15 //===----------------------------------------------------------------------===//
17 #include "llvm/Transforms/Scalar/LoopSimplifyCFG.h"
18 #include "llvm/ADT/SmallVector.h"
19 #include "llvm/ADT/Statistic.h"
20 #include "llvm/Analysis/AliasAnalysis.h"
21 #include "llvm/Analysis/AssumptionCache.h"
22 #include "llvm/Analysis/BasicAliasAnalysis.h"
23 #include "llvm/Analysis/DependenceAnalysis.h"
24 #include "llvm/Analysis/GlobalsModRef.h"
25 #include "llvm/Analysis/LoopInfo.h"
26 #include "llvm/Analysis/LoopPass.h"
27 #include "llvm/Analysis/ScalarEvolution.h"
28 #include "llvm/Analysis/ScalarEvolutionAliasAnalysis.h"
29 #include "llvm/Analysis/TargetTransformInfo.h"
30 #include "llvm/IR/Dominators.h"
31 #include "llvm/Transforms/Scalar.h"
32 #include "llvm/Transforms/Scalar/LoopPassManager.h"
33 #include "llvm/Transforms/Utils/Local.h"
34 #include "llvm/Transforms/Utils/LoopUtils.h"
37 #define DEBUG_TYPE "loop-simplifycfg"
39 static bool simplifyLoopCFG(Loop &L, DominatorTree &DT, LoopInfo &LI) {
41 // Copy blocks into a temporary array to avoid iterator invalidation issues
43 SmallVector<WeakVH, 16> Blocks(L.blocks());
45 for (auto &Block : Blocks) {
46 // Attempt to merge blocks in the trivial case. Don't modify blocks which
47 // belong to other loops.
48 BasicBlock *Succ = cast_or_null<BasicBlock>(Block);
52 BasicBlock *Pred = Succ->getSinglePredecessor();
53 if (!Pred || !Pred->getSingleSuccessor() || LI.getLoopFor(Pred) != &L)
56 // Pred is going to disappear, so we need to update the loop info.
57 if (L.getHeader() == Pred)
60 MergeBasicBlockIntoOnlyPred(Succ, &DT);
67 PreservedAnalyses LoopSimplifyCFGPass::run(Loop &L, LoopAnalysisManager &AM,
68 LoopStandardAnalysisResults &AR,
70 if (!simplifyLoopCFG(L, AR.DT, AR.LI))
71 return PreservedAnalyses::all();
72 return getLoopPassPreservedAnalyses();
76 class LoopSimplifyCFGLegacyPass : public LoopPass {
78 static char ID; // Pass ID, replacement for typeid
79 LoopSimplifyCFGLegacyPass() : LoopPass(ID) {
80 initializeLoopSimplifyCFGLegacyPassPass(*PassRegistry::getPassRegistry());
83 bool runOnLoop(Loop *L, LPPassManager &) override {
87 DominatorTree &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
88 LoopInfo &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
89 return simplifyLoopCFG(*L, DT, LI);
92 void getAnalysisUsage(AnalysisUsage &AU) const override {
93 AU.addPreserved<DependenceAnalysisWrapperPass>();
94 getLoopAnalysisUsage(AU);
99 char LoopSimplifyCFGLegacyPass::ID = 0;
100 INITIALIZE_PASS_BEGIN(LoopSimplifyCFGLegacyPass, "loop-simplifycfg",
101 "Simplify loop CFG", false, false)
102 INITIALIZE_PASS_DEPENDENCY(LoopPass)
103 INITIALIZE_PASS_END(LoopSimplifyCFGLegacyPass, "loop-simplifycfg",
104 "Simplify loop CFG", false, false)
106 Pass *llvm::createLoopSimplifyCFGPass() {
107 return new LoopSimplifyCFGLegacyPass();