2 //==- MachineBranchProbabilityInfo.h - Machine Branch Probability Analysis -==//
4 // The LLVM Compiler Infrastructure
6 // This file is distributed under the University of Illinois Open Source
7 // License. See LICENSE.TXT for details.
9 //===----------------------------------------------------------------------===//
11 // This pass is used to evaluate branch probabilties on machine basic blocks.
13 //===----------------------------------------------------------------------===//
15 #ifndef LLVM_CODEGEN_MACHINEBRANCHPROBABILITYINFO_H
16 #define LLVM_CODEGEN_MACHINEBRANCHPROBABILITYINFO_H
18 #include "llvm/Pass.h"
19 #include "llvm/Support/BranchProbability.h"
26 class MachineBranchProbabilityInfo : public ImmutablePass {
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;
36 // Get sum of the block successors' weights.
37 uint32_t getSumForBlock(MachineBasicBlock *MBB) const;
42 MachineBranchProbabilityInfo() : ImmutablePass(ID) {
43 PassRegistry &Registry = *PassRegistry::getPassRegistry();
44 initializeMachineBranchProbabilityInfoPass(Registry);
47 void getAnalysisUsage(AnalysisUsage &AU) const {
51 // Return edge weight. If we don't have any informations about it - return
53 uint32_t getEdgeWeight(MachineBasicBlock *Src, MachineBasicBlock *Dst) const;
55 // A 'Hot' edge is an edge which probability is >= 80%.
56 bool isEdgeHot(MachineBasicBlock *Src, MachineBasicBlock *Dst) const;
58 // Return a hot successor for the block BB or null if there isn't one.
59 MachineBasicBlock *getHotSucc(MachineBasicBlock *MBB) const;
61 // Return a probability as a fraction between 0 (0% probability) and
62 // 1 (100% probability), however the value is never equal to 0, and can be 1
63 // only iff SRC block has only one successor.
64 BranchProbability getEdgeProbability(MachineBasicBlock *Src,
65 MachineBasicBlock *Dst) const;
67 // Print value between 0 (0% probability) and 1 (100% probability),
68 // however the value is never equal to 0, and can be 1 only iff SRC block
69 // has only one successor.
70 raw_ostream &printEdgeProbability(raw_ostream &OS, MachineBasicBlock *Src,
71 MachineBasicBlock *Dst) const;