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