#include "llvm/InitializePasses.h"
#include "llvm/Pass.h"
#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/Support/BranchProbability.h"
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 {
-
- // Default weight value. Used when we don't have information about the edge.
- // TODO: DEFAULT_WEIGHT makes sense during static predication, when none of
- // the successors have a weight yet. But it doesn't make sense when providing
- // weight to an edge that may have siblings with non-zero weights. This can
- // be handled various ways, but it's probably fine for an edge with unknown
- // weight to just "inherit" the non-zero weight of an adjacent successor.
- static const uint32_t DEFAULT_WEIGHT = 16;
-
- typedef std::pair<BasicBlock *, BasicBlock *> Edge;
-
- DenseMap<Edge, uint32_t> Weights;
-
- // Get sum of the block successors' weights.
- uint32_t getSumForBlock(BasicBlock *BB) const;
-
public:
static char ID;
}
void getAnalysisUsage(AnalysisUsage &AU) const;
-
bool runOnFunction(Function &F);
+ void print(raw_ostream &OS, const Module *M = 0) const;
+
+ /// \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;
+
+ /// \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;
- // Returned value is between 1 and UINT32_MAX. Look at
- // BranchProbabilityInfo.cpp for details.
- uint32_t getEdgeWeight(BasicBlock *Src, BasicBlock *Dst) 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;
- // Look at BranchProbabilityInfo.cpp for details. Use it with caution!
- void setEdgeWeight(BasicBlock *Src, BasicBlock *Dst, uint32_t Weight);
+ // Default weight value. Used when we don't have information about the edge.
+ // TODO: DEFAULT_WEIGHT makes sense during static predication, when none of
+ // the successors have a weight yet. But it doesn't make sense when providing
+ // weight to an edge that may have siblings with non-zero weights. This can
+ // be handled various ways, but it's probably fine for an edge with unknown
+ // weight to just "inherit" the non-zero weight of an adjacent successor.
+ static const uint32_t DEFAULT_WEIGHT = 16;
+
+ DenseMap<Edge, uint32_t> Weights;
- // A 'Hot' edge is an edge which probability is >= 80%.
- bool isEdgeHot(BasicBlock *Src, BasicBlock *Dst) const;
+ /// \brief Handle to the LoopInfo analysis.
+ LoopInfo *LI;
- // Return a hot successor for the block BB or null if there isn't one.
- BasicBlock *getHotSucc(BasicBlock *BB) const;
+ /// \brief Track the last function we run over for printing.
+ Function *LastF;
+
+ /// \brief Track the set of blocks directly succeeded by a returning block.
+ SmallPtrSet<BasicBlock *, 16> PostDominatedByUnreachable;
- // 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.
- BranchProbability getEdgeProbability(BasicBlock *Src, BasicBlock *Dst) const;
+ /// \brief Get sum of the block successors' weights.
+ uint32_t getSumForBlock(const BasicBlock *BB) 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.
- raw_ostream &printEdgeProbability(raw_ostream &OS, BasicBlock *Src,
- BasicBlock *Dst) const;
+ bool calcUnreachableHeuristics(BasicBlock *BB);
+ bool calcMetadataWeights(BasicBlock *BB);
+ bool calcPointerHeuristics(BasicBlock *BB);
+ bool calcLoopBranchHeuristics(BasicBlock *BB);
+ bool calcZeroHeuristics(BasicBlock *BB);
+ bool calcFloatingPointHeuristics(BasicBlock *BB);
};
}
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