LLVM  10.0.0svn
MachineBranchProbabilityInfo.h
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1 //=- MachineBranchProbabilityInfo.h - Branch Probability Analysis -*- C++ -*-=//
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 pass is used to evaluate branch probabilties on machine basic blocks.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #ifndef LLVM_CODEGEN_MACHINEBRANCHPROBABILITYINFO_H
14 #define LLVM_CODEGEN_MACHINEBRANCHPROBABILITYINFO_H
15 
17 #include "llvm/Pass.h"
19 #include <climits>
20 #include <numeric>
21 
22 namespace llvm {
23 
25  virtual void anchor();
26 
27  // Default weight value. Used when we don't have information about the edge.
28  // TODO: DEFAULT_WEIGHT makes sense during static predication, when none of
29  // the successors have a weight yet. But it doesn't make sense when providing
30  // weight to an edge that may have siblings with non-zero weights. This can
31  // be handled various ways, but it's probably fine for an edge with unknown
32  // weight to just "inherit" the non-zero weight of an adjacent successor.
33  static const uint32_t DEFAULT_WEIGHT = 16;
34 
35 public:
36  static char ID;
37 
41  }
42 
43  void getAnalysisUsage(AnalysisUsage &AU) const override {
44  AU.setPreservesAll();
45  }
46 
47  // Return edge probability.
49  const MachineBasicBlock *Dst) const;
50 
51  // Same as above, but using a const_succ_iterator from Src. This is faster
52  // when the iterator is already available.
56 
57  // A 'Hot' edge is an edge which probability is >= 80%.
58  bool isEdgeHot(const MachineBasicBlock *Src,
59  const MachineBasicBlock *Dst) const;
60 
61  // Return a hot successor for the block BB or null if there isn't one.
62  // NB: This routine's complexity is linear on the number of successors.
64 
65  // Print value between 0 (0% probability) and 1 (100% probability),
66  // however the value is never equal to 0, and can be 1 only iff SRC block
67  // has only one successor.
69  const MachineBasicBlock *Src,
70  const MachineBasicBlock *Dst) const;
71 };
72 
73 }
74 
75 
76 #endif
static PassRegistry * getPassRegistry()
getPassRegistry - Access the global registry object, which is automatically initialized at applicatio...
This class represents lattice values for constants.
Definition: AllocatorList.h:23
A global registry used in conjunction with static constructors to make pluggable components (like tar...
Definition: Registry.h:44
raw_ostream & printEdgeProbability(raw_ostream &OS, const MachineBasicBlock *Src, const MachineBasicBlock *Dst) const
MachineBasicBlock * getHotSucc(MachineBasicBlock *MBB) const
Represent the analysis usage information of a pass.
void getAnalysisUsage(AnalysisUsage &AU) const override
getAnalysisUsage - This function should be overriden by passes that need analysis information to do t...
std::vector< MachineBasicBlock * >::const_iterator const_succ_iterator
ImmutablePass class - This class is used to provide information that does not need to be run...
Definition: Pass.h:255
void setPreservesAll()
Set by analyses that do not transform their input at all.
BranchProbability getEdgeProbability(const MachineBasicBlock *Src, const MachineBasicBlock *Dst) const
void initializeMachineBranchProbabilityInfoPass(PassRegistry &)
bool isEdgeHot(const MachineBasicBlock *Src, const MachineBasicBlock *Dst) const
This class implements an extremely fast bulk output stream that can only output to a stream...
Definition: raw_ostream.h:45
PassRegistry - This class manages the registration and intitialization of the pass subsystem as appli...
Definition: PassRegistry.h:38