1 //===- bolt/Passes/LoopInversionPass.cpp ----------------------------------===//
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 the LoopInversionPass class.
10 //
11 //===----------------------------------------------------------------------===//
12
13 #include "bolt/Passes/LoopInversionPass.h"
14 #include "bolt/Core/ParallelUtilities.h"
15
16 using namespace llvm;
17
18 namespace opts {
19 extern cl::OptionCategory BoltCategory;
20
21 extern cl::opt<bolt::ReorderBasicBlocks::LayoutType> ReorderBlocks;
22
23 static cl::opt<bool> LoopReorder(
24 "loop-inversion-opt",
25 cl::desc("reorder unconditional jump instructions in loops optimization"),
26 cl::init(true), cl::cat(BoltCategory), cl::ReallyHidden);
27 } // namespace opts
28
29 namespace llvm {
30 namespace bolt {
31
runOnFunction(BinaryFunction & BF)32 bool LoopInversionPass::runOnFunction(BinaryFunction &BF) {
33 bool IsChanged = false;
34 if (BF.getLayout().block_size() < 3 || !BF.hasValidProfile())
35 return false;
36
37 BF.getLayout().updateLayoutIndices();
38 for (BinaryBasicBlock *BB : BF.getLayout().blocks()) {
39 if (BB->succ_size() != 1 || BB->pred_size() != 1)
40 continue;
41
42 BinaryBasicBlock *SuccBB = *BB->succ_begin();
43 BinaryBasicBlock *PredBB = *BB->pred_begin();
44 const unsigned BBIndex = BB->getLayoutIndex();
45 const unsigned SuccBBIndex = SuccBB->getLayoutIndex();
46 if (SuccBB == PredBB && BB != SuccBB && BBIndex != 0 && SuccBBIndex != 0 &&
47 SuccBB->succ_size() == 2 &&
48 BB->getFragmentNum() == SuccBB->getFragmentNum()) {
49 // Get the second successor (after loop BB)
50 BinaryBasicBlock *SecondSucc = nullptr;
51 for (BinaryBasicBlock *Succ : SuccBB->successors()) {
52 if (Succ != &*BB) {
53 SecondSucc = Succ;
54 break;
55 }
56 }
57
58 assert(SecondSucc != nullptr && "Unable to find a second BB successor");
59 const uint64_t LoopCount = SuccBB->getBranchInfo(*BB).Count;
60 const uint64_t ExitCount = SuccBB->getBranchInfo(*SecondSucc).Count;
61
62 if (LoopCount < ExitCount) {
63 if (BBIndex > SuccBBIndex)
64 continue;
65 } else if (BBIndex < SuccBBIndex) {
66 continue;
67 }
68
69 IsChanged = true;
70 BB->setLayoutIndex(SuccBBIndex);
71 SuccBB->setLayoutIndex(BBIndex);
72 }
73 }
74
75 if (IsChanged) {
76 BinaryFunction::BasicBlockOrderType NewOrder(BF.getLayout().block_begin(),
77 BF.getLayout().block_end());
78 llvm::sort(NewOrder, [&](BinaryBasicBlock *BB1, BinaryBasicBlock *BB2) {
79 return BB1->getLayoutIndex() < BB2->getLayoutIndex();
80 });
81 BF.getLayout().update(NewOrder);
82 }
83
84 return IsChanged;
85 }
86
runOnFunctions(BinaryContext & BC)87 Error LoopInversionPass::runOnFunctions(BinaryContext &BC) {
88 std::atomic<uint64_t> ModifiedFuncCount{0};
89 if (opts::ReorderBlocks == ReorderBasicBlocks::LT_NONE ||
90 opts::LoopReorder == false)
91 return Error::success();
92
93 ParallelUtilities::WorkFuncTy WorkFun = [&](BinaryFunction &BF) {
94 if (runOnFunction(BF))
95 ++ModifiedFuncCount;
96 };
97
98 ParallelUtilities::PredicateTy SkipFunc = [&](const BinaryFunction &BF) {
99 return !shouldOptimize(BF);
100 };
101
102 ParallelUtilities::runOnEachFunction(
103 BC, ParallelUtilities::SchedulingPolicy::SP_TRIVIAL, WorkFun, SkipFunc,
104 "LoopInversionPass");
105
106 BC.outs() << "BOLT-INFO: " << ModifiedFuncCount
107 << " Functions were reordered by LoopInversionPass\n";
108 return Error::success();
109 }
110
111 } // end namespace bolt
112 } // end namespace llvm
113