1//===- MachineBranchProbabilityInfo.cpp - Machine Branch Probability Info -===//
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 analysis uses probability info stored in Machine Basic Blocks.
10//
11//===----------------------------------------------------------------------===//
12
13#include "llvm/CodeGen/MachineBranchProbabilityInfo.h"
14#include "llvm/CodeGen/MachineBasicBlock.h"
15#include "llvm/InitializePasses.h"
16#include "llvm/Support/CommandLine.h"
17#include "llvm/Support/raw_ostream.h"
18
19using namespace llvm;
20
21INITIALIZE_PASS_BEGIN(MachineBranchProbabilityInfoWrapperPass,
22 "machine-branch-prob",
23 "Machine Branch Probability Analysis", false, true)
24INITIALIZE_PASS_END(MachineBranchProbabilityInfoWrapperPass,
25 "machine-branch-prob",
26 "Machine Branch Probability Analysis", false, true)
27
28namespace llvm {
29cl::opt<unsigned>
30 StaticLikelyProb("static-likely-prob",
31 cl::desc("branch probability threshold in percentage"
32 " to be considered very likely"),
33 cl::init(Val: 80), cl::Hidden);
34
35cl::opt<unsigned> ProfileLikelyProb(
36 "profile-likely-prob",
37 cl::desc("branch probability threshold in percentage to be considered"
38 " very likely when profile is available"),
39 cl::init(Val: 51), cl::Hidden);
40} // namespace llvm
41
42MachineBranchProbabilityAnalysis::Result
43MachineBranchProbabilityAnalysis::run(MachineFunction &,
44 MachineFunctionAnalysisManager &) {
45 return MachineBranchProbabilityInfo();
46}
47
48PreservedAnalyses
49MachineBranchProbabilityPrinterPass::run(MachineFunction &MF,
50 MachineFunctionAnalysisManager &MFAM) {
51 OS << "Printing analysis 'Machine Branch Probability Analysis' for machine "
52 "function '"
53 << MF.getName() << "':\n";
54 auto &MBPI = MFAM.getResult<MachineBranchProbabilityAnalysis>(IR&: MF);
55 for (const MachineBasicBlock &MBB : MF) {
56 for (const MachineBasicBlock *Succ : MBB.successors())
57 MBPI.printEdgeProbability(OS&: OS << " ", Src: &MBB, Dst: Succ);
58 }
59 return PreservedAnalyses::all();
60}
61
62char MachineBranchProbabilityInfoWrapperPass::ID = 0;
63
64MachineBranchProbabilityInfoWrapperPass::
65 MachineBranchProbabilityInfoWrapperPass()
66 : ImmutablePass(ID) {
67 PassRegistry &Registry = *PassRegistry::getPassRegistry();
68 initializeMachineBranchProbabilityInfoWrapperPassPass(Registry);
69}
70
71void MachineBranchProbabilityInfoWrapperPass::anchor() {}
72
73AnalysisKey MachineBranchProbabilityAnalysis::Key;
74
75bool MachineBranchProbabilityInfo::invalidate(
76 MachineFunction &, const PreservedAnalyses &PA,
77 MachineFunctionAnalysisManager::Invalidator &) {
78 auto PAC = PA.getChecker<MachineBranchProbabilityAnalysis>();
79 return !PAC.preservedWhenStateless();
80}
81
82BranchProbability MachineBranchProbabilityInfo::getEdgeProbability(
83 const MachineBasicBlock *Src,
84 MachineBasicBlock::const_succ_iterator Dst) const {
85 return Src->getSuccProbability(Succ: Dst);
86}
87
88BranchProbability MachineBranchProbabilityInfo::getEdgeProbability(
89 const MachineBasicBlock *Src, const MachineBasicBlock *Dst) const {
90 // This is a linear search. Try to use the const_succ_iterator version when
91 // possible.
92 return getEdgeProbability(Src, Dst: find(Range: Src->successors(), Val: Dst));
93}
94
95bool MachineBranchProbabilityInfo::isEdgeHot(
96 const MachineBasicBlock *Src, const MachineBasicBlock *Dst) const {
97 BranchProbability HotProb(StaticLikelyProb, 100);
98 return getEdgeProbability(Src, Dst) > HotProb;
99}
100
101raw_ostream &MachineBranchProbabilityInfo::printEdgeProbability(
102 raw_ostream &OS, const MachineBasicBlock *Src,
103 const MachineBasicBlock *Dst) const {
104
105 const BranchProbability Prob = getEdgeProbability(Src, Dst);
106 OS << "edge " << printMBBReference(MBB: *Src) << " -> " << printMBBReference(MBB: *Dst)
107 << " probability is " << Prob
108 << (isEdgeHot(Src, Dst) ? " [HOT edge]\n" : "\n");
109
110 return OS;
111}
112