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| 14 | pmbaty | 1 | //=- MachineBranchProbabilityInfo.h - Branch Probability Analysis -*- C++ -*-=// |
| 2 | // |
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| 3 | // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
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| 4 | // See https://llvm.org/LICENSE.txt for license information. |
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| 5 | // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
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| 6 | // |
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| 7 | //===----------------------------------------------------------------------===// |
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| 8 | // |
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| 9 | // This pass is used to evaluate branch probabilties on machine basic blocks. |
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| 10 | // |
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| 11 | //===----------------------------------------------------------------------===// |
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| 12 | |||
| 13 | #ifndef LLVM_CODEGEN_MACHINEBRANCHPROBABILITYINFO_H |
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| 14 | #define LLVM_CODEGEN_MACHINEBRANCHPROBABILITYINFO_H |
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| 15 | |||
| 16 | #include "llvm/CodeGen/MachineBasicBlock.h" |
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| 17 | #include "llvm/Pass.h" |
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| 18 | #include "llvm/Support/BranchProbability.h" |
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| 19 | |||
| 20 | namespace llvm { |
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| 21 | |||
| 22 | class MachineBranchProbabilityInfo : public ImmutablePass { |
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| 23 | virtual void anchor(); |
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| 24 | |||
| 25 | // Default weight value. Used when we don't have information about the edge. |
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| 26 | // TODO: DEFAULT_WEIGHT makes sense during static predication, when none of |
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| 27 | // the successors have a weight yet. But it doesn't make sense when providing |
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| 28 | // weight to an edge that may have siblings with non-zero weights. This can |
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| 29 | // be handled various ways, but it's probably fine for an edge with unknown |
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| 30 | // weight to just "inherit" the non-zero weight of an adjacent successor. |
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| 31 | static const uint32_t DEFAULT_WEIGHT = 16; |
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| 32 | |||
| 33 | public: |
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| 34 | static char ID; |
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| 35 | |||
| 36 | MachineBranchProbabilityInfo(); |
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| 37 | |||
| 38 | void getAnalysisUsage(AnalysisUsage &AU) const override { |
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| 39 | AU.setPreservesAll(); |
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| 40 | } |
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| 41 | |||
| 42 | // Return edge probability. |
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| 43 | BranchProbability getEdgeProbability(const MachineBasicBlock *Src, |
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| 44 | const MachineBasicBlock *Dst) const; |
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| 45 | |||
| 46 | // Same as above, but using a const_succ_iterator from Src. This is faster |
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| 47 | // when the iterator is already available. |
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| 48 | BranchProbability |
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| 49 | getEdgeProbability(const MachineBasicBlock *Src, |
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| 50 | MachineBasicBlock::const_succ_iterator Dst) const; |
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| 51 | |||
| 52 | // A 'Hot' edge is an edge which probability is >= 80%. |
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| 53 | bool isEdgeHot(const MachineBasicBlock *Src, |
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| 54 | const MachineBasicBlock *Dst) const; |
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| 55 | |||
| 56 | // Print value between 0 (0% probability) and 1 (100% probability), |
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| 57 | // however the value is never equal to 0, and can be 1 only iff SRC block |
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| 58 | // has only one successor. |
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| 59 | raw_ostream &printEdgeProbability(raw_ostream &OS, |
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| 60 | const MachineBasicBlock *Src, |
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| 61 | const MachineBasicBlock *Dst) const; |
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| 62 | }; |
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| 63 | |||
| 64 | } |
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| 65 | |||
| 66 | |||
| 67 | #endif |