LLVM  6.0.0svn
MachineBranchProbabilityInfo.h
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1 //=- MachineBranchProbabilityInfo.h - Branch Probability Analysis -*- C++ -*-=//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This pass is used to evaluate branch probabilties on machine basic blocks.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #ifndef LLVM_CODEGEN_MACHINEBRANCHPROBABILITYINFO_H
15 #define LLVM_CODEGEN_MACHINEBRANCHPROBABILITYINFO_H
16 
18 #include "llvm/Pass.h"
20 #include <climits>
21 #include <numeric>
22 
23 namespace llvm {
24 
26  virtual void anchor();
27 
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;
35 
36 public:
37  static char ID;
38 
42  }
43 
44  void getAnalysisUsage(AnalysisUsage &AU) const override {
45  AU.setPreservesAll();
46  }
47 
48  // Return edge probability.
50  const MachineBasicBlock *Dst) const;
51 
52  // Same as above, but using a const_succ_iterator from Src. This is faster
53  // when the iterator is already available.
57 
58  // A 'Hot' edge is an edge which probability is >= 80%.
59  bool isEdgeHot(const MachineBasicBlock *Src,
60  const MachineBasicBlock *Dst) const;
61 
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.
65 
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.
70  const MachineBasicBlock *Src,
71  const MachineBasicBlock *Dst) const;
72 };
73 
74 }
75 
76 
77 #endif
static PassRegistry * getPassRegistry()
getPassRegistry - Access the global registry object, which is automatically initialized at applicatio...
Compute iterated dominance frontiers using a linear time algorithm.
Definition: AllocatorList.h:24
A global registry used in conjunction with static constructors to make pluggable components (like tar...
Definition: Registry.h:45
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:266
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:44
PassRegistry - This class manages the registration and intitialization of the pass subsystem as appli...
Definition: PassRegistry.h:40