#ifndef LLVM_ANALYSIS_BRANCHPROBABILITYINFO_H
#define LLVM_ANALYSIS_BRANCHPROBABILITYINFO_H
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/IR/CFG.h"
#include "llvm/InitializePasses.h"
+#include "llvm/Pass.h"
#include "llvm/Support/BranchProbability.h"
-#include "llvm/Analysis/LoopInfo.h"
namespace llvm {
-
+class LoopInfo;
class raw_ostream;
-class BranchProbabilityInfo : public FunctionPass {
+/// \brief Analysis providing branch probability information.
+///
+/// This is a function analysis which provides information on the relative
+/// probabilities of each "edge" in the function's CFG where such an edge is
+/// 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:
+ void releaseMemory();
+
+ void print(raw_ostream &OS) 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,
+ 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.
+ ///
+ /// 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 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;
+
+ uint32_t getEdgeWeight(const BasicBlock *Src,
+ succ_const_iterator Dst) const;
+
+ /// \brief Set the raw edge weight for a given edge.
+ ///
+ /// 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, unsigned IndexInSuccessors,
+ uint32_t Weight);
+
+ static uint32_t getBranchWeightStackProtector(bool IsLikely) {
+ return IsLikely ? (1u << 20) - 1 : 1;
+ }
+
+ void calculate(Function &F, const LoopInfo& LI);
+
+private:
+ // 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
// 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;
+ /// \brief Handle to the LoopInfo analysis.
+ LoopInfo *LI;
-public:
- static char ID;
+ /// \brief Track the last function we run over for printing.
+ Function *LastF;
- BranchProbabilityInfo() : FunctionPass(ID) {
- initializeBranchProbabilityInfoPass(*PassRegistry::getPassRegistry());
- }
+ /// \brief Track the set of blocks directly succeeded by a returning block.
+ SmallPtrSet<BasicBlock *, 16> PostDominatedByUnreachable;
- void getAnalysisUsage(AnalysisUsage &AU) const {
- AU.addRequired<LoopInfo>();
- AU.setPreservesAll();
- }
+ /// \brief Track the set of blocks that always lead to a cold call.
+ SmallPtrSet<BasicBlock *, 16> PostDominatedByColdCall;
- bool runOnFunction(Function &F);
+ /// \brief Get sum of the block successors' weights.
+ uint32_t getSumForBlock(const 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;
+ bool calcUnreachableHeuristics(BasicBlock *BB);
+ bool calcMetadataWeights(BasicBlock *BB);
+ bool calcColdCallHeuristics(BasicBlock *BB);
+ bool calcPointerHeuristics(BasicBlock *BB);
+ bool calcLoopBranchHeuristics(BasicBlock *BB, const LoopInfo &LI);
+ bool calcZeroHeuristics(BasicBlock *BB);
+ bool calcFloatingPointHeuristics(BasicBlock *BB);
+ bool calcInvokeHeuristics(BasicBlock *BB);
+};
- // Look at BranchProbabilityInfo.cpp for details. Use it with caution!
- void setEdgeWeight(BasicBlock *Src, BasicBlock *Dst, uint32_t Weight);
+/// \brief Legacy analysis pass which computes \c BranchProbabilityInfo.
+class BranchProbabilityInfoWrapperPass : public FunctionPass {
+ BranchProbabilityInfo BPI;
- // A 'Hot' edge is an edge which probability is >= 80%.
- bool isEdgeHot(BasicBlock *Src, BasicBlock *Dst) const;
+public:
+ static char ID;
- // Return a hot successor for the block BB or null if there isn't one.
- BasicBlock *getHotSucc(BasicBlock *BB) const;
+ BranchProbabilityInfoWrapperPass() : FunctionPass(ID) {
+ initializeBranchProbabilityInfoWrapperPassPass(
+ *PassRegistry::getPassRegistry());
+ }
- // 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;
+ BranchProbabilityInfo &getBPI() { return BPI; }
+ const BranchProbabilityInfo &getBPI() const { return BPI; }
- // 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;
+ void getAnalysisUsage(AnalysisUsage &AU) const override;
+ bool runOnFunction(Function &F) override;
+ void releaseMemory() override;
+ void print(raw_ostream &OS, const Module *M = nullptr) const override;
};
}
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