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This commit fixes a bug in stack protector pass where edge weights were not set when new basic blocks were added to lists of successor basic blocks. Differential Revision: http://reviews.llvm.org/D5766 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222987 91177308-0d34-0410-b5e6-96231b3b80d8
161 lines
6.6 KiB
C++
161 lines
6.6 KiB
C++
//===--- BranchProbabilityInfo.h - Branch Probability Analysis --*- C++ -*-===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This pass is used to evaluate branch probabilties.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_ANALYSIS_BRANCHPROBABILITYINFO_H
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#define LLVM_ANALYSIS_BRANCHPROBABILITYINFO_H
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#include "llvm/ADT/DenseMap.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/IR/CFG.h"
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#include "llvm/InitializePasses.h"
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#include "llvm/Pass.h"
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#include "llvm/Support/BranchProbability.h"
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namespace llvm {
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class LoopInfo;
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class raw_ostream;
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/// \brief Analysis pass providing branch probability information.
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///
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/// This is a function analysis pass which provides information on the relative
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/// probabilities of each "edge" in the function's CFG where such an edge is
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/// defined by a pair (PredBlock and an index in the successors). The
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/// probability of an edge from one block is always relative to the
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/// probabilities of other edges from the block. The probabilites of all edges
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/// from a block sum to exactly one (100%).
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/// We use a pair (PredBlock and an index in the successors) to uniquely
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/// identify an edge, since we can have multiple edges from Src to Dst.
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/// As an example, we can have a switch which jumps to Dst with value 0 and
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/// value 10.
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class BranchProbabilityInfo : public FunctionPass {
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public:
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static char ID;
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BranchProbabilityInfo() : FunctionPass(ID) {
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initializeBranchProbabilityInfoPass(*PassRegistry::getPassRegistry());
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}
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void getAnalysisUsage(AnalysisUsage &AU) const override;
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bool runOnFunction(Function &F) override;
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void print(raw_ostream &OS, const Module *M = nullptr) const override;
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/// \brief Get an edge's probability, relative to other out-edges of the Src.
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///
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/// This routine provides access to the fractional probability between zero
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/// (0%) and one (100%) of this edge executing, relative to other edges
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/// leaving the 'Src' block. The returned probability is never zero, and can
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/// only be one if the source block has only one successor.
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BranchProbability getEdgeProbability(const BasicBlock *Src,
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unsigned IndexInSuccessors) const;
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/// \brief Get the probability of going from Src to Dst.
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///
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/// It returns the sum of all probabilities for edges from Src to Dst.
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BranchProbability getEdgeProbability(const BasicBlock *Src,
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const BasicBlock *Dst) const;
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/// \brief Test if an edge is hot relative to other out-edges of the Src.
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///
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/// Check whether this edge out of the source block is 'hot'. We define hot
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/// as having a relative probability >= 80%.
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bool isEdgeHot(const BasicBlock *Src, const BasicBlock *Dst) const;
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/// \brief Retrieve the hot successor of a block if one exists.
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///
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/// Given a basic block, look through its successors and if one exists for
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/// which \see isEdgeHot would return true, return that successor block.
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BasicBlock *getHotSucc(BasicBlock *BB) const;
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/// \brief Print an edge's probability.
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///
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/// Retrieves an edge's probability similarly to \see getEdgeProbability, but
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/// then prints that probability to the provided stream. That stream is then
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/// returned.
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raw_ostream &printEdgeProbability(raw_ostream &OS, const BasicBlock *Src,
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const BasicBlock *Dst) const;
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/// \brief Get the raw edge weight calculated for the edge.
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///
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/// This returns the raw edge weight. It is guaranteed to fall between 1 and
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/// UINT32_MAX. Note that the raw edge weight is not meaningful in isolation.
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/// This interface should be very carefully, and primarily by routines that
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/// are updating the analysis by later calling setEdgeWeight.
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uint32_t getEdgeWeight(const BasicBlock *Src,
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unsigned IndexInSuccessors) const;
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/// \brief Get the raw edge weight calculated for the block pair.
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///
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/// This returns the sum of all raw edge weights from Src to Dst.
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/// It is guaranteed to fall between 1 and UINT32_MAX.
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uint32_t getEdgeWeight(const BasicBlock *Src, const BasicBlock *Dst) const;
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uint32_t getEdgeWeight(const BasicBlock *Src,
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succ_const_iterator Dst) const;
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/// \brief Set the raw edge weight for a given edge.
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///
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/// This allows a pass to explicitly set the edge weight for an edge. It can
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/// be used when updating the CFG to update and preserve the branch
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/// probability information. Read the implementation of how these edge
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/// weights are calculated carefully before using!
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void setEdgeWeight(const BasicBlock *Src, unsigned IndexInSuccessors,
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uint32_t Weight);
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static uint32_t getBranchWeightStackProtector(bool IsLikely) {
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return IsLikely ? (1u << 20) - 1 : 1;
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}
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private:
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// Since we allow duplicate edges from one basic block to another, we use
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// a pair (PredBlock and an index in the successors) to specify an edge.
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typedef std::pair<const BasicBlock *, unsigned> Edge;
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// Default weight value. Used when we don't have information about the edge.
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// TODO: DEFAULT_WEIGHT makes sense during static predication, when none of
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// the successors have a weight yet. But it doesn't make sense when providing
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// weight to an edge that may have siblings with non-zero weights. This can
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// be handled various ways, but it's probably fine for an edge with unknown
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// weight to just "inherit" the non-zero weight of an adjacent successor.
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static const uint32_t DEFAULT_WEIGHT = 16;
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DenseMap<Edge, uint32_t> Weights;
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/// \brief Handle to the LoopInfo analysis.
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LoopInfo *LI;
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/// \brief Track the last function we run over for printing.
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Function *LastF;
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/// \brief Track the set of blocks directly succeeded by a returning block.
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SmallPtrSet<BasicBlock *, 16> PostDominatedByUnreachable;
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/// \brief Track the set of blocks that always lead to a cold call.
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SmallPtrSet<BasicBlock *, 16> PostDominatedByColdCall;
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/// \brief Get sum of the block successors' weights.
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uint32_t getSumForBlock(const BasicBlock *BB) const;
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bool calcUnreachableHeuristics(BasicBlock *BB);
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bool calcMetadataWeights(BasicBlock *BB);
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bool calcColdCallHeuristics(BasicBlock *BB);
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bool calcPointerHeuristics(BasicBlock *BB);
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bool calcLoopBranchHeuristics(BasicBlock *BB);
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bool calcZeroHeuristics(BasicBlock *BB);
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bool calcFloatingPointHeuristics(BasicBlock *BB);
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bool calcInvokeHeuristics(BasicBlock *BB);
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};
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}
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#endif
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