1 //===--------- LoopSimplifyCFG.cpp - Loop CFG Simplification Pass ---------===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
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.
14 //
15 //===----------------------------------------------------------------------===//
16
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.h"
34 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
35 #include "llvm/Transforms/Utils/Local.h"
36 #include "llvm/Transforms/Utils/LoopUtils.h"
37 using namespace llvm;
38
39 #define DEBUG_TYPE "loop-simplifycfg"
40
simplifyLoopCFG(Loop & L,DominatorTree & DT,LoopInfo & LI,ScalarEvolution & SE)41 static bool simplifyLoopCFG(Loop &L, DominatorTree &DT, LoopInfo &LI,
42 ScalarEvolution &SE) {
43 bool Changed = false;
44 // Copy blocks into a temporary array to avoid iterator invalidation issues
45 // as we remove them.
46 SmallVector<WeakTrackingVH, 16> Blocks(L.blocks());
47
48 for (auto &Block : Blocks) {
49 // Attempt to merge blocks in the trivial case. Don't modify blocks which
50 // belong to other loops.
51 BasicBlock *Succ = cast_or_null<BasicBlock>(Block);
52 if (!Succ)
53 continue;
54
55 BasicBlock *Pred = Succ->getSinglePredecessor();
56 if (!Pred || !Pred->getSingleSuccessor() || LI.getLoopFor(Pred) != &L)
57 continue;
58
59 // Merge Succ into Pred and delete it.
60 MergeBlockIntoPredecessor(Succ, &DT, &LI);
61
62 SE.forgetLoop(&L);
63 Changed = true;
64 }
65
66 return Changed;
67 }
68
run(Loop & L,LoopAnalysisManager & AM,LoopStandardAnalysisResults & AR,LPMUpdater &)69 PreservedAnalyses LoopSimplifyCFGPass::run(Loop &L, LoopAnalysisManager &AM,
70 LoopStandardAnalysisResults &AR,
71 LPMUpdater &) {
72 if (!simplifyLoopCFG(L, AR.DT, AR.LI, AR.SE))
73 return PreservedAnalyses::all();
74
75 return getLoopPassPreservedAnalyses();
76 }
77
78 namespace {
79 class LoopSimplifyCFGLegacyPass : public LoopPass {
80 public:
81 static char ID; // Pass ID, replacement for typeid
LoopSimplifyCFGLegacyPass()82 LoopSimplifyCFGLegacyPass() : LoopPass(ID) {
83 initializeLoopSimplifyCFGLegacyPassPass(*PassRegistry::getPassRegistry());
84 }
85
runOnLoop(Loop * L,LPPassManager &)86 bool runOnLoop(Loop *L, LPPassManager &) override {
87 if (skipLoop(L))
88 return false;
89
90 DominatorTree &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
91 LoopInfo &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
92 ScalarEvolution &SE = getAnalysis<ScalarEvolutionWrapperPass>().getSE();
93 return simplifyLoopCFG(*L, DT, LI, SE);
94 }
95
getAnalysisUsage(AnalysisUsage & AU) const96 void getAnalysisUsage(AnalysisUsage &AU) const override {
97 AU.addPreserved<DependenceAnalysisWrapperPass>();
98 getLoopAnalysisUsage(AU);
99 }
100 };
101 }
102
103 char LoopSimplifyCFGLegacyPass::ID = 0;
104 INITIALIZE_PASS_BEGIN(LoopSimplifyCFGLegacyPass, "loop-simplifycfg",
105 "Simplify loop CFG", false, false)
INITIALIZE_PASS_DEPENDENCY(LoopPass)106 INITIALIZE_PASS_DEPENDENCY(LoopPass)
107 INITIALIZE_PASS_END(LoopSimplifyCFGLegacyPass, "loop-simplifycfg",
108 "Simplify loop CFG", false, false)
109
110 Pass *llvm::createLoopSimplifyCFGPass() {
111 return new LoopSimplifyCFGLegacyPass();
112 }
113