1 //===- MachineBranchProbabilityInfo.cpp - Machine Branch Probability Info -===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This analysis uses probability info stored in Machine Basic Blocks.
11 //
12 //===----------------------------------------------------------------------===//
13
14 #include "llvm/CodeGen/MachineBranchProbabilityInfo.h"
15 #include "llvm/CodeGen/MachineBasicBlock.h"
16 #include "llvm/IR/Instructions.h"
17 #include "llvm/Support/Debug.h"
18 #include "llvm/Support/raw_ostream.h"
19
20 using namespace llvm;
21
22 INITIALIZE_PASS_BEGIN(MachineBranchProbabilityInfo, "machine-branch-prob",
23 "Machine Branch Probability Analysis", false, true)
24 INITIALIZE_PASS_END(MachineBranchProbabilityInfo, "machine-branch-prob",
25 "Machine Branch Probability Analysis", false, true)
26
27 cl::opt<unsigned>
28 StaticLikelyProb("static-likely-prob",
29 cl::desc("branch probability threshold in percentage"
30 "to be considered very likely"),
31 cl::init(80), cl::Hidden);
32
33 cl::opt<unsigned> ProfileLikelyProb(
34 "profile-likely-prob",
35 cl::desc("branch probability threshold in percentage to be considered"
36 " very likely when profile is available"),
37 cl::init(51), cl::Hidden);
38
39 char MachineBranchProbabilityInfo::ID = 0;
40
anchor()41 void MachineBranchProbabilityInfo::anchor() {}
42
getEdgeProbability(const MachineBasicBlock * Src,MachineBasicBlock::const_succ_iterator Dst) const43 BranchProbability MachineBranchProbabilityInfo::getEdgeProbability(
44 const MachineBasicBlock *Src,
45 MachineBasicBlock::const_succ_iterator Dst) const {
46 return Src->getSuccProbability(Dst);
47 }
48
getEdgeProbability(const MachineBasicBlock * Src,const MachineBasicBlock * Dst) const49 BranchProbability MachineBranchProbabilityInfo::getEdgeProbability(
50 const MachineBasicBlock *Src, const MachineBasicBlock *Dst) const {
51 // This is a linear search. Try to use the const_succ_iterator version when
52 // possible.
53 return getEdgeProbability(Src, find(Src->successors(), Dst));
54 }
55
isEdgeHot(const MachineBasicBlock * Src,const MachineBasicBlock * Dst) const56 bool MachineBranchProbabilityInfo::isEdgeHot(
57 const MachineBasicBlock *Src, const MachineBasicBlock *Dst) const {
58 BranchProbability HotProb(StaticLikelyProb, 100);
59 return getEdgeProbability(Src, Dst) > HotProb;
60 }
61
62 MachineBasicBlock *
getHotSucc(MachineBasicBlock * MBB) const63 MachineBranchProbabilityInfo::getHotSucc(MachineBasicBlock *MBB) const {
64 auto MaxProb = BranchProbability::getZero();
65 MachineBasicBlock *MaxSucc = nullptr;
66 for (MachineBasicBlock::const_succ_iterator I = MBB->succ_begin(),
67 E = MBB->succ_end(); I != E; ++I) {
68 auto Prob = getEdgeProbability(MBB, I);
69 if (Prob > MaxProb) {
70 MaxProb = Prob;
71 MaxSucc = *I;
72 }
73 }
74
75 BranchProbability HotProb(StaticLikelyProb, 100);
76 if (getEdgeProbability(MBB, MaxSucc) >= HotProb)
77 return MaxSucc;
78
79 return nullptr;
80 }
81
printEdgeProbability(raw_ostream & OS,const MachineBasicBlock * Src,const MachineBasicBlock * Dst) const82 raw_ostream &MachineBranchProbabilityInfo::printEdgeProbability(
83 raw_ostream &OS, const MachineBasicBlock *Src,
84 const MachineBasicBlock *Dst) const {
85
86 const BranchProbability Prob = getEdgeProbability(Src, Dst);
87 OS << "edge " << printMBBReference(*Src) << " -> " << printMBBReference(*Dst)
88 << " probability is " << Prob
89 << (isEdgeHot(Src, Dst) ? " [HOT edge]\n" : "\n");
90
91 return OS;
92 }
93