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/IR/Instructions.h"
16 #include "llvm/InitializePasses.h"
17 #include "llvm/Support/CommandLine.h"
18 #include "llvm/Support/Debug.h"
19 #include "llvm/Support/raw_ostream.h"
20
21 using namespace llvm;
22
23 INITIALIZE_PASS_BEGIN(MachineBranchProbabilityInfo, "machine-branch-prob",
24 "Machine Branch Probability Analysis", false, true)
25 INITIALIZE_PASS_END(MachineBranchProbabilityInfo, "machine-branch-prob",
26 "Machine Branch Probability Analysis", false, true)
27
28 namespace llvm {
29 cl::opt<unsigned>
30 StaticLikelyProb("static-likely-prob",
31 cl::desc("branch probability threshold in percentage"
32 "to be considered very likely"),
33 cl::init(80), cl::Hidden);
34
35 cl::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(51), cl::Hidden);
40 } // namespace llvm
41
42 char MachineBranchProbabilityInfo::ID = 0;
43
MachineBranchProbabilityInfo()44 MachineBranchProbabilityInfo::MachineBranchProbabilityInfo()
45 : ImmutablePass(ID) {
46 PassRegistry &Registry = *PassRegistry::getPassRegistry();
47 initializeMachineBranchProbabilityInfoPass(Registry);
48 }
49
anchor()50 void MachineBranchProbabilityInfo::anchor() {}
51
getEdgeProbability(const MachineBasicBlock * Src,MachineBasicBlock::const_succ_iterator Dst) const52 BranchProbability MachineBranchProbabilityInfo::getEdgeProbability(
53 const MachineBasicBlock *Src,
54 MachineBasicBlock::const_succ_iterator Dst) const {
55 return Src->getSuccProbability(Dst);
56 }
57
getEdgeProbability(const MachineBasicBlock * Src,const MachineBasicBlock * Dst) const58 BranchProbability MachineBranchProbabilityInfo::getEdgeProbability(
59 const MachineBasicBlock *Src, const MachineBasicBlock *Dst) const {
60 // This is a linear search. Try to use the const_succ_iterator version when
61 // possible.
62 return getEdgeProbability(Src, find(Src->successors(), Dst));
63 }
64
isEdgeHot(const MachineBasicBlock * Src,const MachineBasicBlock * Dst) const65 bool MachineBranchProbabilityInfo::isEdgeHot(
66 const MachineBasicBlock *Src, const MachineBasicBlock *Dst) const {
67 BranchProbability HotProb(StaticLikelyProb, 100);
68 return getEdgeProbability(Src, Dst) > HotProb;
69 }
70
71 MachineBasicBlock *
getHotSucc(MachineBasicBlock * MBB) const72 MachineBranchProbabilityInfo::getHotSucc(MachineBasicBlock *MBB) const {
73 auto MaxProb = BranchProbability::getZero();
74 MachineBasicBlock *MaxSucc = nullptr;
75 for (MachineBasicBlock::const_succ_iterator I = MBB->succ_begin(),
76 E = MBB->succ_end(); I != E; ++I) {
77 auto Prob = getEdgeProbability(MBB, I);
78 if (Prob > MaxProb) {
79 MaxProb = Prob;
80 MaxSucc = *I;
81 }
82 }
83
84 BranchProbability HotProb(StaticLikelyProb, 100);
85 if (getEdgeProbability(MBB, MaxSucc) >= HotProb)
86 return MaxSucc;
87
88 return nullptr;
89 }
90
printEdgeProbability(raw_ostream & OS,const MachineBasicBlock * Src,const MachineBasicBlock * Dst) const91 raw_ostream &MachineBranchProbabilityInfo::printEdgeProbability(
92 raw_ostream &OS, const MachineBasicBlock *Src,
93 const MachineBasicBlock *Dst) const {
94
95 const BranchProbability Prob = getEdgeProbability(Src, Dst);
96 OS << "edge " << printMBBReference(*Src) << " -> " << printMBBReference(*Dst)
97 << " probability is " << Prob
98 << (isEdgeHot(Src, Dst) ? " [HOT edge]\n" : "\n");
99
100 return OS;
101 }
102