1 //===- LoopRotation.cpp - Loop Rotation Pass ------------------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file implements Loop Rotation Pass.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #include "llvm/Transforms/Scalar/LoopRotation.h"
14 #include "llvm/ADT/Statistic.h"
15 #include "llvm/Analysis/InstructionSimplify.h"
16 #include "llvm/Analysis/LoopPass.h"
17 #include "llvm/Analysis/MemorySSA.h"
18 #include "llvm/Analysis/MemorySSAUpdater.h"
19 #include "llvm/Analysis/ScalarEvolution.h"
20 #include "llvm/Analysis/TargetTransformInfo.h"
21 #include "llvm/InitializePasses.h"
22 #include "llvm/Support/CommandLine.h"
23 #include "llvm/Support/Debug.h"
24 #include "llvm/Transforms/Scalar.h"
25 #include "llvm/Transforms/Scalar/LoopPassManager.h"
26 #include "llvm/Transforms/Utils/LoopRotationUtils.h"
27 #include "llvm/Transforms/Utils/LoopUtils.h"
28 using namespace llvm;
29 
30 #define DEBUG_TYPE "loop-rotate"
31 
32 static cl::opt<unsigned> DefaultRotationThreshold(
33     "rotation-max-header-size", cl::init(16), cl::Hidden,
34     cl::desc("The default maximum header size for automatic loop rotation"));
35 
36 LoopRotatePass::LoopRotatePass(bool EnableHeaderDuplication)
37     : EnableHeaderDuplication(EnableHeaderDuplication) {}
38 
39 PreservedAnalyses LoopRotatePass::run(Loop &L, LoopAnalysisManager &AM,
40                                       LoopStandardAnalysisResults &AR,
41                                       LPMUpdater &) {
42   // Vectorization requires loop-rotation. Use default threshold for loops the
43   // user explicitly marked for vectorization, even when header duplication is
44   // disabled.
45   int Threshold = EnableHeaderDuplication ||
46                           hasVectorizeTransformation(&L) == TM_ForcedByUser
47                       ? DefaultRotationThreshold
48                       : 0;
49   const DataLayout &DL = L.getHeader()->getModule()->getDataLayout();
50   const SimplifyQuery SQ = getBestSimplifyQuery(AR, DL);
51 
52   Optional<MemorySSAUpdater> MSSAU;
53   if (AR.MSSA)
54     MSSAU = MemorySSAUpdater(AR.MSSA);
55   bool Changed = LoopRotation(&L, &AR.LI, &AR.TTI, &AR.AC, &AR.DT, &AR.SE,
56                               MSSAU.hasValue() ? MSSAU.getPointer() : nullptr,
57                               SQ, false, Threshold, false);
58 
59   if (!Changed)
60     return PreservedAnalyses::all();
61 
62   if (AR.MSSA && VerifyMemorySSA)
63     AR.MSSA->verifyMemorySSA();
64 
65   auto PA = getLoopPassPreservedAnalyses();
66   if (AR.MSSA)
67     PA.preserve<MemorySSAAnalysis>();
68   return PA;
69 }
70 
71 namespace {
72 
73 class LoopRotateLegacyPass : public LoopPass {
74   unsigned MaxHeaderSize;
75 
76 public:
77   static char ID; // Pass ID, replacement for typeid
78   LoopRotateLegacyPass(int SpecifiedMaxHeaderSize = -1) : LoopPass(ID) {
79     initializeLoopRotateLegacyPassPass(*PassRegistry::getPassRegistry());
80     if (SpecifiedMaxHeaderSize == -1)
81       MaxHeaderSize = DefaultRotationThreshold;
82     else
83       MaxHeaderSize = unsigned(SpecifiedMaxHeaderSize);
84   }
85 
86   // LCSSA form makes instruction renaming easier.
87   void getAnalysisUsage(AnalysisUsage &AU) const override {
88     AU.addRequired<AssumptionCacheTracker>();
89     AU.addRequired<TargetTransformInfoWrapperPass>();
90     if (EnableMSSALoopDependency)
91       AU.addPreserved<MemorySSAWrapperPass>();
92     getLoopAnalysisUsage(AU);
93   }
94 
95   bool runOnLoop(Loop *L, LPPassManager &LPM) override {
96     if (skipLoop(L))
97       return false;
98     Function &F = *L->getHeader()->getParent();
99 
100     auto *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
101     const auto *TTI = &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
102     auto *AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
103     auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
104     auto &SE = getAnalysis<ScalarEvolutionWrapperPass>().getSE();
105     const SimplifyQuery SQ = getBestSimplifyQuery(*this, F);
106     Optional<MemorySSAUpdater> MSSAU;
107     if (EnableMSSALoopDependency) {
108       // Not requiring MemorySSA and getting it only if available will split
109       // the loop pass pipeline when LoopRotate is being run first.
110       auto *MSSAA = getAnalysisIfAvailable<MemorySSAWrapperPass>();
111       if (MSSAA)
112         MSSAU = MemorySSAUpdater(&MSSAA->getMSSA());
113     }
114     // Vectorization requires loop-rotation. Use default threshold for loops the
115     // user explicitly marked for vectorization, even when header duplication is
116     // disabled.
117     int Threshold = hasVectorizeTransformation(L) == TM_ForcedByUser
118                         ? DefaultRotationThreshold
119                         : MaxHeaderSize;
120 
121     return LoopRotation(L, LI, TTI, AC, &DT, &SE,
122                         MSSAU.hasValue() ? MSSAU.getPointer() : nullptr, SQ,
123                         false, Threshold, false);
124   }
125 };
126 } // end namespace
127 
128 char LoopRotateLegacyPass::ID = 0;
129 INITIALIZE_PASS_BEGIN(LoopRotateLegacyPass, "loop-rotate", "Rotate Loops",
130                       false, false)
131 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
132 INITIALIZE_PASS_DEPENDENCY(LoopPass)
133 INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
134 INITIALIZE_PASS_DEPENDENCY(MemorySSAWrapperPass)
135 INITIALIZE_PASS_END(LoopRotateLegacyPass, "loop-rotate", "Rotate Loops", false,
136                     false)
137 
138 Pass *llvm::createLoopRotatePass(int MaxHeaderSize) {
139   return new LoopRotateLegacyPass(MaxHeaderSize);
140 }
141