1 //===- LoopRotation.cpp - Loop Rotation 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 Loop Rotation Pass.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "llvm/Transforms/Scalar/LoopRotation.h"
15 #include "llvm/ADT/Statistic.h"
16 #include "llvm/Analysis/InstructionSimplify.h"
17 #include "llvm/Analysis/LoopPass.h"
18 #include "llvm/Analysis/MemorySSA.h"
19 #include "llvm/Analysis/MemorySSAUpdater.h"
20 #include "llvm/Analysis/ScalarEvolution.h"
21 #include "llvm/Analysis/TargetTransformInfo.h"
22 #include "llvm/Support/Debug.h"
23 #include "llvm/Transforms/Scalar.h"
24 #include "llvm/Transforms/Scalar/LoopPassManager.h"
25 #include "llvm/Transforms/Utils/LoopRotationUtils.h"
26 #include "llvm/Transforms/Utils/LoopUtils.h"
27 using namespace llvm;
28 
29 #define DEBUG_TYPE "loop-rotate"
30 
31 static cl::opt<unsigned> DefaultRotationThreshold(
32     "rotation-max-header-size", cl::init(16), cl::Hidden,
33     cl::desc("The default maximum header size for automatic loop rotation"));
34 
35 LoopRotatePass::LoopRotatePass(bool EnableHeaderDuplication)
36     : EnableHeaderDuplication(EnableHeaderDuplication) {}
37 
38 PreservedAnalyses LoopRotatePass::run(Loop &L, LoopAnalysisManager &AM,
39                                       LoopStandardAnalysisResults &AR,
40                                       LPMUpdater &) {
41   int Threshold = EnableHeaderDuplication ? DefaultRotationThreshold : 0;
42   const DataLayout &DL = L.getHeader()->getModule()->getDataLayout();
43   const SimplifyQuery SQ = getBestSimplifyQuery(AR, DL);
44 
45   Optional<MemorySSAUpdater> MSSAU;
46   if (AR.MSSA)
47     MSSAU = MemorySSAUpdater(AR.MSSA);
48   bool Changed = LoopRotation(&L, &AR.LI, &AR.TTI, &AR.AC, &AR.DT, &AR.SE,
49                               MSSAU.hasValue() ? MSSAU.getPointer() : nullptr,
50                               SQ, false, Threshold, false);
51 
52   if (!Changed)
53     return PreservedAnalyses::all();
54 
55   if (AR.MSSA && VerifyMemorySSA)
56     AR.MSSA->verifyMemorySSA();
57 
58   return getLoopPassPreservedAnalyses();
59 }
60 
61 namespace {
62 
63 class LoopRotateLegacyPass : public LoopPass {
64   unsigned MaxHeaderSize;
65 
66 public:
67   static char ID; // Pass ID, replacement for typeid
68   LoopRotateLegacyPass(int SpecifiedMaxHeaderSize = -1) : LoopPass(ID) {
69     initializeLoopRotateLegacyPassPass(*PassRegistry::getPassRegistry());
70     if (SpecifiedMaxHeaderSize == -1)
71       MaxHeaderSize = DefaultRotationThreshold;
72     else
73       MaxHeaderSize = unsigned(SpecifiedMaxHeaderSize);
74   }
75 
76   // LCSSA form makes instruction renaming easier.
77   void getAnalysisUsage(AnalysisUsage &AU) const override {
78     AU.addRequired<AssumptionCacheTracker>();
79     AU.addRequired<TargetTransformInfoWrapperPass>();
80     if (EnableMSSALoopDependency) {
81       AU.addRequired<MemorySSAWrapperPass>();
82       AU.addPreserved<MemorySSAWrapperPass>();
83     }
84     getLoopAnalysisUsage(AU);
85   }
86 
87   bool runOnLoop(Loop *L, LPPassManager &LPM) override {
88     if (skipLoop(L))
89       return false;
90     Function &F = *L->getHeader()->getParent();
91 
92     auto *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
93     const auto *TTI = &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
94     auto *AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
95     auto *DTWP = getAnalysisIfAvailable<DominatorTreeWrapperPass>();
96     auto *DT = DTWP ? &DTWP->getDomTree() : nullptr;
97     auto *SEWP = getAnalysisIfAvailable<ScalarEvolutionWrapperPass>();
98     auto *SE = SEWP ? &SEWP->getSE() : nullptr;
99     const SimplifyQuery SQ = getBestSimplifyQuery(*this, F);
100     Optional<MemorySSAUpdater> MSSAU;
101     if (EnableMSSALoopDependency) {
102       MemorySSA *MSSA = &getAnalysis<MemorySSAWrapperPass>().getMSSA();
103       MSSAU = MemorySSAUpdater(MSSA);
104     }
105     return LoopRotation(L, LI, TTI, AC, DT, SE,
106                         MSSAU.hasValue() ? MSSAU.getPointer() : nullptr, SQ,
107                         false, MaxHeaderSize, false);
108   }
109 };
110 }
111 
112 char LoopRotateLegacyPass::ID = 0;
113 INITIALIZE_PASS_BEGIN(LoopRotateLegacyPass, "loop-rotate", "Rotate Loops",
114                       false, false)
115 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
116 INITIALIZE_PASS_DEPENDENCY(LoopPass)
117 INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
118 INITIALIZE_PASS_DEPENDENCY(MemorySSAWrapperPass)
119 INITIALIZE_PASS_END(LoopRotateLegacyPass, "loop-rotate", "Rotate Loops", false,
120                     false)
121 
122 Pass *llvm::createLoopRotatePass(int MaxHeaderSize) {
123   return new LoopRotateLegacyPass(MaxHeaderSize);
124 }
125