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8980e4aeb2
The getSumForBlock function was quadratic in the number of successors because getSuccWeight would perform a linear search for an already known iterator. This patch was originally committed as r161460, but reverted again because of assertion failures. Now that duplicate Machine CFG edges have been eliminated, this works properly. llvm-svn: 162233
90 lines
3.5 KiB
C++
90 lines
3.5 KiB
C++
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//==- MachineBranchProbabilityInfo.h - Machine Branch Probability Analysis -==//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This pass is used to evaluate branch probabilties on machine basic blocks.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_CODEGEN_MACHINEBRANCHPROBABILITYINFO_H
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#define LLVM_CODEGEN_MACHINEBRANCHPROBABILITYINFO_H
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#include "llvm/Pass.h"
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#include "llvm/CodeGen/MachineBasicBlock.h"
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#include "llvm/Support/BranchProbability.h"
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#include <climits>
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namespace llvm {
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class MachineBranchProbabilityInfo : public ImmutablePass {
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virtual void anchor();
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// Default weight value. Used when we don't have information about the edge.
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// TODO: DEFAULT_WEIGHT makes sense during static predication, when none of
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// the successors have a weight yet. But it doesn't make sense when providing
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// weight to an edge that may have siblings with non-zero weights. This can
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// be handled various ways, but it's probably fine for an edge with unknown
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// weight to just "inherit" the non-zero weight of an adjacent successor.
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static const uint32_t DEFAULT_WEIGHT = 16;
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public:
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static char ID;
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MachineBranchProbabilityInfo() : ImmutablePass(ID) {
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PassRegistry &Registry = *PassRegistry::getPassRegistry();
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initializeMachineBranchProbabilityInfoPass(Registry);
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}
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void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.setPreservesAll();
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}
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// Return edge weight. If we don't have any informations about it - return
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// DEFAULT_WEIGHT.
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uint32_t getEdgeWeight(const MachineBasicBlock *Src,
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const MachineBasicBlock *Dst) const;
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// Same thing, but using a const_succ_iterator from Src. This is faster when
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// the iterator is already available.
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uint32_t getEdgeWeight(const MachineBasicBlock *Src,
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MachineBasicBlock::const_succ_iterator Dst) const;
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// Get sum of the block successors' weights, potentially scaling them to fit
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// within 32-bits. If scaling is required, sets Scale based on the necessary
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// adjustment. Any edge weights used with the sum should be divided by Scale.
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uint32_t getSumForBlock(const MachineBasicBlock *MBB, uint32_t &Scale) const;
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// A 'Hot' edge is an edge which probability is >= 80%.
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bool isEdgeHot(MachineBasicBlock *Src, MachineBasicBlock *Dst) const;
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// Return a hot successor for the block BB or null if there isn't one.
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// NB: This routine's complexity is linear on the number of successors.
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MachineBasicBlock *getHotSucc(MachineBasicBlock *MBB) const;
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// Return a probability as a fraction between 0 (0% probability) and
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// 1 (100% probability), however the value is never equal to 0, and can be 1
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// only iff SRC block has only one successor.
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// NB: This routine's complexity is linear on the number of successors of
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// Src. Querying sequentially for each successor's probability is a quadratic
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// query pattern.
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BranchProbability getEdgeProbability(MachineBasicBlock *Src,
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MachineBasicBlock *Dst) const;
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// Print value between 0 (0% probability) and 1 (100% probability),
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// however the value is never equal to 0, and can be 1 only iff SRC block
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// has only one successor.
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raw_ostream &printEdgeProbability(raw_ostream &OS, MachineBasicBlock *Src,
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MachineBasicBlock *Dst) const;
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};
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}
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#endif
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