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 uint32_t Weight = getEdgeWeight(Src, Dst);
59 uint32_t Sum = getSumForBlock(Src);
61 // FIXME: Implement BranchProbability::compare then change this code to
62 // compare this BranchProbability against a static "hot" BranchProbability.
63 return (uint64_t)Weight * 5 > (uint64_t)Sum * 4;
67 MachineBranchProbabilityInfo::getHotSucc(MachineBasicBlock *MBB) const {
69 uint32_t MaxWeight = 0;
70 MachineBasicBlock *MaxSucc = 0;
72 for (MachineBasicBlock::const_succ_iterator I = MBB->succ_begin(),
73 E = MBB->succ_end(); I != E; ++I) {
74 MachineBasicBlock *Succ = *I;
75 uint32_t Weight = getEdgeWeight(MBB, Succ);
76 uint32_t PrevSum = Sum;
79 assert(Sum > PrevSum); (void) PrevSum;
81 if (Weight > MaxWeight) {
87 // FIXME: Use BranchProbability::compare.
88 if ((uint64_t)MaxWeight * 5 >= (uint64_t)Sum * 4)
95 MachineBranchProbabilityInfo::getEdgeProbability(MachineBasicBlock *Src,
96 MachineBasicBlock *Dst) const {
97 uint32_t N = getEdgeWeight(Src, Dst);
98 uint32_t D = getSumForBlock(Src);
100 return BranchProbability(N, D);
103 raw_ostream &MachineBranchProbabilityInfo::
104 printEdgeProbability(raw_ostream &OS, MachineBasicBlock *Src,
105 MachineBasicBlock *Dst) const {
107 const BranchProbability Prob = getEdgeProbability(Src, Dst);
108 OS << "edge MBB#" << Src->getNumber() << " -> MBB#" << Dst->getNumber()
109 << " probability is " << Prob
110 << (isEdgeHot(Src, Dst) ? " [HOT edge]\n" : "\n");