1 //===- MachineBranchProbabilityInfo.cpp - Machine Branch Probability Info -===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This analysis uses probability info stored in Machine Basic Blocks.
12 //===----------------------------------------------------------------------===//
14 #include "llvm/Instructions.h"
15 #include "llvm/CodeGen/MachineBranchProbabilityInfo.h"
16 #include "llvm/CodeGen/MachineBasicBlock.h"
17 #include "llvm/Support/Debug.h"
18 #include "llvm/Support/raw_ostream.h"
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)
27 char MachineBranchProbabilityInfo::ID = 0;
29 uint32_t MachineBranchProbabilityInfo::
30 getSumForBlock(MachineBasicBlock *MBB) const {
33 for (MachineBasicBlock::const_succ_iterator I = MBB->succ_begin(),
34 E = MBB->succ_end(); I != E; ++I) {
35 MachineBasicBlock *Succ = *I;
36 uint32_t Weight = getEdgeWeight(MBB, Succ);
37 uint32_t PrevSum = Sum;
40 assert(Sum > PrevSum); (void) PrevSum;
47 MachineBranchProbabilityInfo::getEdgeWeight(MachineBasicBlock *Src,
48 MachineBasicBlock *Dst) const {
49 uint32_t Weight = Src->getSuccWeight(Dst);
51 return DEFAULT_WEIGHT;
55 bool MachineBranchProbabilityInfo::isEdgeHot(MachineBasicBlock *Src,
56 MachineBasicBlock *Dst) const {
57 // Hot probability is at least 4/5 = 80%
58 // FIXME: Compare against a static "hot" BranchProbability.
59 return getEdgeProbability(Src, Dst) > BranchProbability(4, 5);
63 MachineBranchProbabilityInfo::getHotSucc(MachineBasicBlock *MBB) const {
65 uint32_t MaxWeight = 0;
66 MachineBasicBlock *MaxSucc = 0;
68 for (MachineBasicBlock::const_succ_iterator I = MBB->succ_begin(),
69 E = MBB->succ_end(); I != E; ++I) {
70 MachineBasicBlock *Succ = *I;
71 uint32_t Weight = getEdgeWeight(MBB, Succ);
72 uint32_t PrevSum = Sum;
75 assert(Sum > PrevSum); (void) PrevSum;
77 if (Weight > MaxWeight) {
83 if (BranchProbability(MaxWeight, Sum) >= BranchProbability(4, 5))
90 MachineBranchProbabilityInfo::getEdgeProbability(MachineBasicBlock *Src,
91 MachineBasicBlock *Dst) const {
92 uint32_t N = getEdgeWeight(Src, Dst);
93 uint32_t D = getSumForBlock(Src);
95 return BranchProbability(N, D);
98 raw_ostream &MachineBranchProbabilityInfo::
99 printEdgeProbability(raw_ostream &OS, MachineBasicBlock *Src,
100 MachineBasicBlock *Dst) const {
102 const BranchProbability Prob = getEdgeProbability(Src, Dst);
103 OS << "edge MBB#" << Src->getNumber() << " -> MBB#" << Dst->getNumber()
104 << " probability is " << Prob
105 << (isEdgeHot(Src, Dst) ? " [HOT edge]\n" : "\n");