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Doxygen-ify the comments on the public interface for BPI. Also, move the

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two more subtle routines to the bottom and expand on their cautionary
comments a bit. No functionality or actual interface change here.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@142789 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chandler Carruth 2011-10-24 05:55:58 +00:00
parent 5bef0eb1de
commit f46c674a16
1 changed files with 49 additions and 20 deletions
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69
include/llvm/Analysis/BranchProbabilityInfo.h
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@ -23,6 +23,15 @@ namespace llvm {
class LoopInfo;
class raw_ostream;
/// \brief Analysis pass providing branch probability information.
///
/// 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%).
class BranchProbabilityInfo : public FunctionPass {
public:
static char ID;
@ -35,32 +44,52 @@ public:
bool runOnFunction(Function &F);
void print(raw_ostream &OS, const Module *M = 0) const;
// Returned value is between 1 and UINT32_MAX. Look at
// BranchProbabilityInfo.cpp for details.
uint32_t getEdgeWeight(const BasicBlock *Src, const BasicBlock *Dst) const;
// Look at BranchProbabilityInfo.cpp for details. Use it with caution!
void setEdgeWeight(const BasicBlock *Src, const BasicBlock *Dst,
uint32_t Weight);
// A 'Hot' edge is an edge which probability is >= 80%.
bool isEdgeHot(const BasicBlock *Src, const BasicBlock *Dst) const;
// Return a hot successor for the block BB or null if there isn't one.
BasicBlock *getHotSucc(BasicBlock *BB) const;
// Return a probability as a fraction between 0 (0% probability) and
// 1 (100% probability), however the value is never equal to 0, and can be 1
// only iff SRC block has only one successor.
/// \brief Get an edge's probability, relative to other out-edges of the Src.
///
/// This routine provides access to the fractional probability between zero
/// (0%) and one (100%) of this edge executing, relative to other edges
/// 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,
const BasicBlock *Dst) const;
// Print value between 0 (0% probability) and 1 (100% probability),
// however the value is never equal to 0, and can be 1 only iff SRC block
// has only one successor.
/// \brief Test if an edge is hot relative to other out-edges of the Src.
///
/// Check whether this edge out of the source block is 'hot'. We define hot
/// as having a relative probability >= 80%.
bool isEdgeHot(const BasicBlock *Src, const BasicBlock *Dst) const;
/// \brief Retrieve the hot successor of a block if one exists.
///
/// Given a basic block, look through its successors and if one exists for
/// which \see isEdgeHot would return true, return that successor block.
BasicBlock *getHotSucc(BasicBlock *BB) const;
/// \brief Print an edge's probability.
///
/// Retrieves an edge's probability similarly to \see getEdgeProbability, but
/// then prints that probability to the provided stream. That stream is then
/// returned.
raw_ostream &printEdgeProbability(raw_ostream &OS, const BasicBlock *Src,
const BasicBlock *Dst) const;
/// \brief Get the raw edge weight calculated for the block pair.
///
/// 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, const BasicBlock *Dst) const;
/// \brief Set the raw edge weight for the block pair.
///
/// This allows a pass to explicitly set the edge weight for a block. 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,
uint32_t Weight);
private:
typedef std::pair<const BasicBlock *, const BasicBlock *> Edge;