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 
19 using namespace llvm;
20 
21 INITIALIZE_PASS_BEGIN(MachineBranchProbabilityInfo, "machine-branch-prob",
22                       "Machine Branch Probability Analysis", false, true)
23 INITIALIZE_PASS_END(MachineBranchProbabilityInfo, "machine-branch-prob",
24                     "Machine Branch Probability Analysis", false, true)
25 
26 namespace llvm {
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 } // namespace llvm
39 
40 char MachineBranchProbabilityInfo::ID = 0;
41 
42 MachineBranchProbabilityInfo::MachineBranchProbabilityInfo()
43     : ImmutablePass(ID) {
44   PassRegistry &Registry = *PassRegistry::getPassRegistry();
45   initializeMachineBranchProbabilityInfoPass(Registry);
46 }
47 
48 void MachineBranchProbabilityInfo::anchor() {}
49 
50 BranchProbability MachineBranchProbabilityInfo::getEdgeProbability(
51     const MachineBasicBlock *Src,
52     MachineBasicBlock::const_succ_iterator Dst) const {
53   return Src->getSuccProbability(Dst);
54 }
55 
56 BranchProbability MachineBranchProbabilityInfo::getEdgeProbability(
57     const MachineBasicBlock *Src, const MachineBasicBlock *Dst) const {
58   // This is a linear search. Try to use the const_succ_iterator version when
59   // possible.
60   return getEdgeProbability(Src, find(Src->successors(), Dst));
61 }
62 
63 bool MachineBranchProbabilityInfo::isEdgeHot(
64     const MachineBasicBlock *Src, const MachineBasicBlock *Dst) const {
65   BranchProbability HotProb(StaticLikelyProb, 100);
66   return getEdgeProbability(Src, Dst) > HotProb;
67 }
68 
69 raw_ostream &MachineBranchProbabilityInfo::printEdgeProbability(
70     raw_ostream &OS, const MachineBasicBlock *Src,
71     const MachineBasicBlock *Dst) const {
72 
73   const BranchProbability Prob = getEdgeProbability(Src, Dst);
74   OS << "edge " << printMBBReference(*Src) << " -> " << printMBBReference(*Dst)
75      << " probability is " << Prob
76      << (isEdgeHot(Src, Dst) ? " [HOT edge]\n" : "\n");
77 
78   return OS;
79 }
80