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+//===- BranchProbabilityInfo.h - Branch Probability Analysis ----*- C++ -*-===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass is used to evaluate branch probabilties.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ANALYSIS_BRANCHPROBABILITYINFO_H
+#define LLVM_ANALYSIS_BRANCHPROBABILITYINFO_H
+
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/DenseMapInfo.h"
+#include "llvm/ADT/DenseSet.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/IR/BasicBlock.h"
+#include "llvm/IR/CFG.h"
+#include "llvm/IR/PassManager.h"
+#include "llvm/IR/ValueHandle.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/BranchProbability.h"
+#include "llvm/Support/Casting.h"
+#include <algorithm>
+#include <cassert>
+#include <cstdint>
+#include <utility>
+
+namespace llvm {
+
+class Function;
+class LoopInfo;
+class raw_ostream;
+class TargetLibraryInfo;
+class Value;
+
+/// \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:
+ BranchProbabilityInfo() = default;
+
+ BranchProbabilityInfo(const Function &F, const LoopInfo &LI,
+ const TargetLibraryInfo *TLI = nullptr) {
+ calculate(F, LI, TLI);
+ }
+
+ BranchProbabilityInfo(BranchProbabilityInfo &&Arg)
+ : Probs(std::move(Arg.Probs)), LastF(Arg.LastF),
+ PostDominatedByUnreachable(std::move(Arg.PostDominatedByUnreachable)),
+ PostDominatedByColdCall(std::move(Arg.PostDominatedByColdCall)) {}
+
+ BranchProbabilityInfo(const BranchProbabilityInfo &) = delete;
+ BranchProbabilityInfo &operator=(const BranchProbabilityInfo &) = delete;
+
+ BranchProbabilityInfo &operator=(BranchProbabilityInfo &&RHS) {
+ releaseMemory();
+ Probs = std::move(RHS.Probs);
+ PostDominatedByColdCall = std::move(RHS.PostDominatedByColdCall);
+ PostDominatedByUnreachable = std::move(RHS.PostDominatedByUnreachable);
+ return *this;
+ }
+
+ 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;
+
+ BranchProbability getEdgeProbability(const BasicBlock *Src,
+ succ_const_iterator 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.
+ const BasicBlock *getHotSucc(const 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 Set the raw edge probability for the given edge.
+ ///
+ /// This allows a pass to explicitly set the edge probability 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
+ /// probabilities are calculated carefully before using!
+ void setEdgeProbability(const BasicBlock *Src, unsigned IndexInSuccessors,
+ BranchProbability Prob);
+
+ static BranchProbability getBranchProbStackProtector(bool IsLikely) {
+ static const BranchProbability LikelyProb((1u << 20) - 1, 1u << 20);
+ return IsLikely ? LikelyProb : LikelyProb.getCompl();
+ }
+
+ void calculate(const Function &F, const LoopInfo &LI,
+ const TargetLibraryInfo *TLI = nullptr);
+
+ /// Forget analysis results for the given basic block.
+ void eraseBlock(const BasicBlock *BB);
+
+ // Use to track SCCs for handling irreducible loops.
+ using SccMap = DenseMap<const BasicBlock *, int>;
+ using SccHeaderMap = DenseMap<const BasicBlock *, bool>;
+ using SccHeaderMaps = std::vector<SccHeaderMap>;
+ struct SccInfo {
+ SccMap SccNums;
+ SccHeaderMaps SccHeaders;
+ };
+
+private:
+ // We need to store CallbackVH's in order to correctly handle basic block
+ // removal.
+ class BasicBlockCallbackVH final : public CallbackVH {
+ BranchProbabilityInfo *BPI;
+
+ void deleted() override {
+ assert(BPI != nullptr);
+ BPI->eraseBlock(cast<BasicBlock>(getValPtr()));
+ BPI->Handles.erase(*this);
+ }
+
+ public:
+ BasicBlockCallbackVH(const Value *V, BranchProbabilityInfo *BPI = nullptr)
+ : CallbackVH(const_cast<Value *>(V)), BPI(BPI) {}
+ };
+
+ DenseSet<BasicBlockCallbackVH, DenseMapInfo<Value*>> Handles;
+
+ // 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.
+ using Edge = std::pair<const BasicBlock *, unsigned>;
+
+ // 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, BranchProbability> Probs;
+
+ /// \brief Track the last function we run over for printing.
+ const Function *LastF;
+
+ /// \brief Track the set of blocks directly succeeded by a returning block.
+ SmallPtrSet<const BasicBlock *, 16> PostDominatedByUnreachable;
+
+ /// \brief Track the set of blocks that always lead to a cold call.
+ SmallPtrSet<const BasicBlock *, 16> PostDominatedByColdCall;
+
+ void updatePostDominatedByUnreachable(const BasicBlock *BB);
+ void updatePostDominatedByColdCall(const BasicBlock *BB);
+ bool calcUnreachableHeuristics(const BasicBlock *BB);
+ bool calcMetadataWeights(const BasicBlock *BB);
+ bool calcColdCallHeuristics(const BasicBlock *BB);
+ bool calcPointerHeuristics(const BasicBlock *BB);
+ bool calcLoopBranchHeuristics(const BasicBlock *BB, const LoopInfo &LI,
+ SccInfo &SccI);
+ bool calcZeroHeuristics(const BasicBlock *BB, const TargetLibraryInfo *TLI);
+ bool calcFloatingPointHeuristics(const BasicBlock *BB);
+ bool calcInvokeHeuristics(const BasicBlock *BB);
+};
+
+/// \brief Analysis pass which computes \c BranchProbabilityInfo.
+class BranchProbabilityAnalysis
+ : public AnalysisInfoMixin<BranchProbabilityAnalysis> {
+ friend AnalysisInfoMixin<BranchProbabilityAnalysis>;
+
+ static AnalysisKey Key;
+
+public:
+ /// \brief Provide the result type for this analysis pass.
+ using Result = BranchProbabilityInfo;
+
+ /// \brief Run the analysis pass over a function and produce BPI.
+ BranchProbabilityInfo run(Function &F, FunctionAnalysisManager &AM);
+};
+
+/// \brief Printer pass for the \c BranchProbabilityAnalysis results.
+class BranchProbabilityPrinterPass
+ : public PassInfoMixin<BranchProbabilityPrinterPass> {
+ raw_ostream &OS;
+
+public:
+ explicit BranchProbabilityPrinterPass(raw_ostream &OS) : OS(OS) {}
+
+ PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM);
+};
+
+/// \brief Legacy analysis pass which computes \c BranchProbabilityInfo.
+class BranchProbabilityInfoWrapperPass : public FunctionPass {
+ BranchProbabilityInfo BPI;
+
+public:
+ static char ID;
+
+ BranchProbabilityInfoWrapperPass() : FunctionPass(ID) {
+ initializeBranchProbabilityInfoWrapperPassPass(
+ *PassRegistry::getPassRegistry());
+ }
+
+ BranchProbabilityInfo &getBPI() { return BPI; }
+ const BranchProbabilityInfo &getBPI() const { return BPI; }
+
+ 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;
+};
+
+} // end namespace llvm
+
+#endif // LLVM_ANALYSIS_BRANCHPROBABILITYINFO_H