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 char MachineBranchProbabilityInfo::ID = 0;
28
anchor()29 void MachineBranchProbabilityInfo::anchor() { }
30
getEdgeProbability(const MachineBasicBlock * Src,MachineBasicBlock::const_succ_iterator Dst) const31 BranchProbability MachineBranchProbabilityInfo::getEdgeProbability(
32 const MachineBasicBlock *Src,
33 MachineBasicBlock::const_succ_iterator Dst) const {
34 return Src->getSuccProbability(Dst);
35 }
36
getEdgeProbability(const MachineBasicBlock * Src,const MachineBasicBlock * Dst) const37 BranchProbability MachineBranchProbabilityInfo::getEdgeProbability(
38 const MachineBasicBlock *Src, const MachineBasicBlock *Dst) const {
39 // This is a linear search. Try to use the const_succ_iterator version when
40 // possible.
41 return getEdgeProbability(Src,
42 std::find(Src->succ_begin(), Src->succ_end(), Dst));
43 }
44
45 bool
isEdgeHot(const MachineBasicBlock * Src,const MachineBasicBlock * Dst) const46 MachineBranchProbabilityInfo::isEdgeHot(const MachineBasicBlock *Src,
47 const MachineBasicBlock *Dst) const {
48 // Hot probability is at least 4/5 = 80%
49 static BranchProbability HotProb(4, 5);
50 return getEdgeProbability(Src, Dst) > HotProb;
51 }
52
53 MachineBasicBlock *
getHotSucc(MachineBasicBlock * MBB) const54 MachineBranchProbabilityInfo::getHotSucc(MachineBasicBlock *MBB) const {
55 auto MaxProb = BranchProbability::getZero();
56 MachineBasicBlock *MaxSucc = nullptr;
57 for (MachineBasicBlock::const_succ_iterator I = MBB->succ_begin(),
58 E = MBB->succ_end(); I != E; ++I) {
59 auto Prob = getEdgeProbability(MBB, I);
60 if (Prob > MaxProb) {
61 MaxProb = Prob;
62 MaxSucc = *I;
63 }
64 }
65
66 static BranchProbability HotProb(4, 5);
67 if (getEdgeProbability(MBB, MaxSucc) >= HotProb)
68 return MaxSucc;
69
70 return nullptr;
71 }
72
printEdgeProbability(raw_ostream & OS,const MachineBasicBlock * Src,const MachineBasicBlock * Dst) const73 raw_ostream &MachineBranchProbabilityInfo::printEdgeProbability(
74 raw_ostream &OS, const MachineBasicBlock *Src,
75 const MachineBasicBlock *Dst) const {
76
77 const BranchProbability Prob = getEdgeProbability(Src, Dst);
78 OS << "edge MBB#" << Src->getNumber() << " -> MBB#" << Dst->getNumber()
79 << " probability is " << Prob
80 << (isEdgeHot(Src, Dst) ? " [HOT edge]\n" : "\n");
81
82 return OS;
83 }
84