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/Analysis/AssumptionCache.h"
15#include "llvm/Analysis/InstructionSimplify.h"
16#include "llvm/Analysis/LazyBlockFrequencyInfo.h"
17#include "llvm/Analysis/LoopInfo.h"
18#include "llvm/Analysis/LoopPass.h"
19#include "llvm/Analysis/MemorySSA.h"
20#include "llvm/Analysis/MemorySSAUpdater.h"
21#include "llvm/Analysis/ScalarEvolution.h"
22#include "llvm/Analysis/TargetTransformInfo.h"
23#include "llvm/InitializePasses.h"
24#include "llvm/Support/CommandLine.h"
25#include "llvm/Transforms/Scalar.h"
26#include "llvm/Transforms/Utils/LoopRotationUtils.h"
27#include "llvm/Transforms/Utils/LoopUtils.h"
28#include <optional>
29using namespace llvm;
30
31#define DEBUG_TYPE "loop-rotate"
32
33static cl::opt<unsigned> DefaultRotationThreshold(
34 "rotation-max-header-size", cl::init(Val: 16), cl::Hidden,
35 cl::desc("The default maximum header size for automatic loop rotation"));
36
37static cl::opt<bool> PrepareForLTOOption(
38 "rotation-prepare-for-lto", cl::init(Val: false), cl::Hidden,
39 cl::desc("Run loop-rotation in the prepare-for-lto stage. This option "
40 "should be used for testing only."));
41
42LoopRotatePass::LoopRotatePass(bool EnableHeaderDuplication, bool PrepareForLTO)
43 : EnableHeaderDuplication(EnableHeaderDuplication),
44 PrepareForLTO(PrepareForLTO) {}
45
46void LoopRotatePass::printPipeline(
47 raw_ostream &OS, function_ref<StringRef(StringRef)> MapClassName2PassName) {
48 static_cast<PassInfoMixin<LoopRotatePass> *>(this)->printPipeline(
49 OS, MapClassName2PassName);
50 OS << "<";
51 if (!EnableHeaderDuplication)
52 OS << "no-";
53 OS << "header-duplication;";
54
55 if (!PrepareForLTO)
56 OS << "no-";
57 OS << "prepare-for-lto";
58 OS << ">";
59}
60
61PreservedAnalyses LoopRotatePass::run(Loop &L, LoopAnalysisManager &AM,
62 LoopStandardAnalysisResults &AR,
63 LPMUpdater &) {
64 // Vectorization requires loop-rotation. Use default threshold for loops the
65 // user explicitly marked for vectorization, even when header duplication is
66 // disabled.
67 int Threshold =
68 (EnableHeaderDuplication && !L.getHeader()->getParent()->hasMinSize()) ||
69 hasVectorizeTransformation(L: &L) == TM_ForcedByUser
70 ? DefaultRotationThreshold
71 : 0;
72 const DataLayout &DL = L.getHeader()->getDataLayout();
73 const SimplifyQuery SQ = getBestSimplifyQuery(AR, DL);
74
75 std::optional<MemorySSAUpdater> MSSAU;
76 if (AR.MSSA)
77 MSSAU = MemorySSAUpdater(AR.MSSA);
78 bool Changed = LoopRotation(L: &L, LI: &AR.LI, TTI: &AR.TTI, AC: &AR.AC, DT: &AR.DT, SE: &AR.SE,
79 MSSAU: MSSAU ? &*MSSAU : nullptr, SQ, RotationOnly: false, Threshold,
80 IsUtilMode: false, PrepareForLTO: PrepareForLTO || PrepareForLTOOption);
81
82 if (!Changed)
83 return PreservedAnalyses::all();
84
85 if (AR.MSSA && VerifyMemorySSA)
86 AR.MSSA->verifyMemorySSA();
87
88 auto PA = getLoopPassPreservedAnalyses();
89 if (AR.MSSA)
90 PA.preserve<MemorySSAAnalysis>();
91 return PA;
92}
93