llvm/lib/CodeGen/MachineBranchProbabilityInfo.cpp

   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 }