1 //=- MachineBranchProbabilityInfo.h - Branch Probability Analysis -*- C++ -*-=//
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 pass is used to evaluate branch probabilties on machine basic blocks.
12 //===----------------------------------------------------------------------===//
14 #ifndef LLVM_CODEGEN_MACHINEBRANCHPROBABILITYINFO_H
15 #define LLVM_CODEGEN_MACHINEBRANCHPROBABILITYINFO_H
17 #include "llvm/CodeGen/MachineBasicBlock.h"
18 #include "llvm/Pass.h"
19 #include "llvm/Support/BranchProbability.h"
25 class MachineBranchProbabilityInfo : public ImmutablePass {
26 virtual void anchor();
28 // Default weight value. Used when we don't have information about the edge.
29 // TODO: DEFAULT_WEIGHT makes sense during static predication, when none of
30 // the successors have a weight yet. But it doesn't make sense when providing
31 // weight to an edge that may have siblings with non-zero weights. This can
32 // be handled various ways, but it's probably fine for an edge with unknown
33 // weight to just "inherit" the non-zero weight of an adjacent successor.
34 static const uint32_t DEFAULT_WEIGHT = 16;
39 MachineBranchProbabilityInfo() : ImmutablePass(ID) {
40 PassRegistry &Registry = *PassRegistry::getPassRegistry();
41 initializeMachineBranchProbabilityInfoPass(Registry);
44 void getAnalysisUsage(AnalysisUsage &AU) const override {
48 // Return edge probability.
49 BranchProbability getEdgeProbability(const MachineBasicBlock *Src,
50 const MachineBasicBlock *Dst) const;
52 // Same as above, but using a const_succ_iterator from Src. This is faster
53 // when the iterator is already available.
55 getEdgeProbability(const MachineBasicBlock *Src,
56 MachineBasicBlock::const_succ_iterator Dst) const;
58 // A 'Hot' edge is an edge which probability is >= 80%.
59 bool isEdgeHot(const MachineBasicBlock *Src,
60 const MachineBasicBlock *Dst) const;
62 // Return a hot successor for the block BB or null if there isn't one.
63 // NB: This routine's complexity is linear on the number of successors.
64 MachineBasicBlock *getHotSucc(MachineBasicBlock *MBB) const;
66 // Print value between 0 (0% probability) and 1 (100% probability),
67 // however the value is never equal to 0, and can be 1 only iff SRC block
68 // has only one successor.
69 raw_ostream &printEdgeProbability(raw_ostream &OS,
70 const MachineBasicBlock *Src,
71 const MachineBasicBlock *Dst) const;