diff options
Diffstat (limited to 'include/llvm/Analysis/BranchProbabilityInfo.h')
| -rw-r--r-- | include/llvm/Analysis/BranchProbabilityInfo.h | 38 |
1 files changed, 28 insertions, 10 deletions
diff --git a/include/llvm/Analysis/BranchProbabilityInfo.h b/include/llvm/Analysis/BranchProbabilityInfo.h index 006daa0..c0567da 100644 --- a/include/llvm/Analysis/BranchProbabilityInfo.h +++ b/include/llvm/Analysis/BranchProbabilityInfo.h @@ -28,11 +28,14 @@ class raw_ostream; /// /// This is a function analysis pass which provides information on the relative /// probabilities of each "edge" in the function's CFG where such an edge is -/// defined by a pair of basic blocks. The probability for a given block and -/// a successor block are always relative to the probabilities of the other -/// successor blocks. Another way of looking at it is that the probabilities -/// for a given block B and each of its successors should sum to exactly -/// one (100%). +/// defined by a pair (PredBlock and an index in the successors). The +/// probability of an edge from one block is always relative to the +/// probabilities of other edges from the block. The probabilites of all edges +/// from a block sum to exactly one (100%). +/// We use a pair (PredBlock and an index in the successors) to uniquely +/// identify an edge, since we can have multiple edges from Src to Dst. +/// As an example, we can have a switch which jumps to Dst with value 0 and +/// value 10. class BranchProbabilityInfo : public FunctionPass { public: static char ID; @@ -52,6 +55,12 @@ public: /// leaving the 'Src' block. The returned probability is never zero, and can /// only be one if the source block has only one successor. BranchProbability getEdgeProbability(const BasicBlock *Src, + unsigned IndexInSuccessors) const; + + /// \brief Get the probability of going from Src to Dst. + /// + /// It returns the sum of all probabilities for edges from Src to Dst. + BranchProbability getEdgeProbability(const BasicBlock *Src, const BasicBlock *Dst) const; /// \brief Test if an edge is hot relative to other out-edges of the Src. @@ -74,25 +83,34 @@ public: raw_ostream &printEdgeProbability(raw_ostream &OS, const BasicBlock *Src, const BasicBlock *Dst) const; - /// \brief Get the raw edge weight calculated for the block pair. + /// \brief Get the raw edge weight calculated for the edge. /// /// This returns the raw edge weight. It is guaranteed to fall between 1 and /// UINT32_MAX. Note that the raw edge weight is not meaningful in isolation. /// This interface should be very carefully, and primarily by routines that /// are updating the analysis by later calling setEdgeWeight. + uint32_t getEdgeWeight(const BasicBlock *Src, + unsigned IndexInSuccessors) const; + + /// \brief Get the raw edge weight calculated for the block pair. + /// + /// This returns the sum of all raw edge weights from Src to Dst. + /// It is guaranteed to fall between 1 and UINT32_MAX. uint32_t getEdgeWeight(const BasicBlock *Src, const BasicBlock *Dst) const; - /// \brief Set the raw edge weight for the block pair. + /// \brief Set the raw edge weight for a given edge. /// - /// This allows a pass to explicitly set the edge weight for a block. It can + /// This allows a pass to explicitly set the edge weight for an edge. It can /// be used when updating the CFG to update and preserve the branch /// probability information. Read the implementation of how these edge /// weights are calculated carefully before using! - void setEdgeWeight(const BasicBlock *Src, const BasicBlock *Dst, + void setEdgeWeight(const BasicBlock *Src, unsigned IndexInSuccessors, uint32_t Weight); private: - typedef std::pair<const BasicBlock *, const BasicBlock *> Edge; + // Since we allow duplicate edges from one basic block to another, we use + // a pair (PredBlock and an index in the successors) to specify an edge. + typedef std::pair<const BasicBlock *, unsigned> Edge; // Default weight value. Used when we don't have information about the edge. // TODO: DEFAULT_WEIGHT makes sense during static predication, when none of |
