236 lines
9.6 KiB
C
236 lines
9.6 KiB
C
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//===- Transform/Utils/CodeExtractor.h - Code extraction util ---*- C++ -*-===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// A utility to support extracting code from one function into its own
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// stand-alone function.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_TRANSFORMS_UTILS_CODEEXTRACTOR_H
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#define LLVM_TRANSFORMS_UTILS_CODEEXTRACTOR_H
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#include "llvm/ADT/ArrayRef.h"
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#include "llvm/ADT/DenseMap.h"
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#include "llvm/ADT/SetVector.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include <limits>
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namespace llvm {
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class AllocaInst;
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class BasicBlock;
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class BlockFrequency;
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class BlockFrequencyInfo;
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class BranchProbabilityInfo;
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class AssumptionCache;
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class CallInst;
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class DominatorTree;
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class Function;
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class Instruction;
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class Loop;
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class Module;
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class Type;
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class Value;
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/// A cache for the CodeExtractor analysis. The operation \ref
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/// CodeExtractor::extractCodeRegion is guaranteed not to invalidate this
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/// object. This object should conservatively be considered invalid if any
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/// other mutating operations on the IR occur.
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///
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/// Constructing this object is O(n) in the size of the function.
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class CodeExtractorAnalysisCache {
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/// The allocas in the function.
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SmallVector<AllocaInst *, 16> Allocas;
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/// Base memory addresses of load/store instructions, grouped by block.
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DenseMap<BasicBlock *, DenseSet<Value *>> BaseMemAddrs;
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/// Blocks which contain instructions which may have unknown side-effects
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/// on memory.
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DenseSet<BasicBlock *> SideEffectingBlocks;
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void findSideEffectInfoForBlock(BasicBlock &BB);
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public:
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CodeExtractorAnalysisCache(Function &F);
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/// Get the allocas in the function at the time the analysis was created.
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/// Note that some of these allocas may no longer be present in the function,
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/// due to \ref CodeExtractor::extractCodeRegion.
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ArrayRef<AllocaInst *> getAllocas() const { return Allocas; }
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/// Check whether \p BB contains an instruction thought to load from, store
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/// to, or otherwise clobber the alloca \p Addr.
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bool doesBlockContainClobberOfAddr(BasicBlock &BB, AllocaInst *Addr) const;
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};
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/// Utility class for extracting code into a new function.
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///
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/// This utility provides a simple interface for extracting some sequence of
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/// code into its own function, replacing it with a call to that function. It
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/// also provides various methods to query about the nature and result of
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/// such a transformation.
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///
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/// The rough algorithm used is:
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/// 1) Find both the inputs and outputs for the extracted region.
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/// 2) Pass the inputs as arguments, remapping them within the extracted
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/// function to arguments.
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/// 3) Add allocas for any scalar outputs, adding all of the outputs' allocas
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/// as arguments, and inserting stores to the arguments for any scalars.
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class CodeExtractor {
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using ValueSet = SetVector<Value *>;
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// Various bits of state computed on construction.
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DominatorTree *const DT;
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const bool AggregateArgs;
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BlockFrequencyInfo *BFI;
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BranchProbabilityInfo *BPI;
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AssumptionCache *AC;
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// If true, varargs functions can be extracted.
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bool AllowVarArgs;
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// Bits of intermediate state computed at various phases of extraction.
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SetVector<BasicBlock *> Blocks;
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unsigned NumExitBlocks = std::numeric_limits<unsigned>::max();
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Type *RetTy;
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// Suffix to use when creating extracted function (appended to the original
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// function name + "."). If empty, the default is to use the entry block
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// label, if non-empty, otherwise "extracted".
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std::string Suffix;
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public:
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/// Create a code extractor for a sequence of blocks.
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///
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/// Given a sequence of basic blocks where the first block in the sequence
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/// dominates the rest, prepare a code extractor object for pulling this
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/// sequence out into its new function. When a DominatorTree is also given,
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/// extra checking and transformations are enabled. If AllowVarArgs is true,
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/// vararg functions can be extracted. This is safe, if all vararg handling
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/// code is extracted, including vastart. If AllowAlloca is true, then
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/// extraction of blocks containing alloca instructions would be possible,
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/// however code extractor won't validate whether extraction is legal.
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CodeExtractor(ArrayRef<BasicBlock *> BBs, DominatorTree *DT = nullptr,
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bool AggregateArgs = false, BlockFrequencyInfo *BFI = nullptr,
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BranchProbabilityInfo *BPI = nullptr,
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AssumptionCache *AC = nullptr,
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bool AllowVarArgs = false, bool AllowAlloca = false,
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std::string Suffix = "");
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/// Create a code extractor for a loop body.
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///
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/// Behaves just like the generic code sequence constructor, but uses the
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/// block sequence of the loop.
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CodeExtractor(DominatorTree &DT, Loop &L, bool AggregateArgs = false,
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BlockFrequencyInfo *BFI = nullptr,
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BranchProbabilityInfo *BPI = nullptr,
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AssumptionCache *AC = nullptr,
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std::string Suffix = "");
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/// Perform the extraction, returning the new function.
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///
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/// Returns zero when called on a CodeExtractor instance where isEligible
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/// returns false.
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Function *extractCodeRegion(const CodeExtractorAnalysisCache &CEAC);
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/// Verify that assumption cache isn't stale after a region is extracted.
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/// Returns true when verifier finds errors. AssumptionCache is passed as
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/// parameter to make this function stateless.
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static bool verifyAssumptionCache(const Function &OldFunc,
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const Function &NewFunc,
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AssumptionCache *AC);
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/// Test whether this code extractor is eligible.
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///
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/// Based on the blocks used when constructing the code extractor,
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/// determine whether it is eligible for extraction.
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///
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/// Checks that varargs handling (with vastart and vaend) is only done in
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/// the outlined blocks.
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bool isEligible() const;
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/// Compute the set of input values and output values for the code.
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///
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/// These can be used either when performing the extraction or to evaluate
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/// the expected size of a call to the extracted function. Note that this
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/// work cannot be cached between the two as once we decide to extract
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/// a code sequence, that sequence is modified, including changing these
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/// sets, before extraction occurs. These modifications won't have any
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/// significant impact on the cost however.
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void findInputsOutputs(ValueSet &Inputs, ValueSet &Outputs,
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const ValueSet &Allocas) const;
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/// Check if life time marker nodes can be hoisted/sunk into the outline
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/// region.
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///
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/// Returns true if it is safe to do the code motion.
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bool
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isLegalToShrinkwrapLifetimeMarkers(const CodeExtractorAnalysisCache &CEAC,
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Instruction *AllocaAddr) const;
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/// Find the set of allocas whose life ranges are contained within the
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/// outlined region.
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///
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/// Allocas which have life_time markers contained in the outlined region
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/// should be pushed to the outlined function. The address bitcasts that
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/// are used by the lifetime markers are also candidates for shrink-
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/// wrapping. The instructions that need to be sunk are collected in
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/// 'Allocas'.
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void findAllocas(const CodeExtractorAnalysisCache &CEAC,
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ValueSet &SinkCands, ValueSet &HoistCands,
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BasicBlock *&ExitBlock) const;
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/// Find or create a block within the outline region for placing hoisted
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/// code.
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///
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/// CommonExitBlock is block outside the outline region. It is the common
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/// successor of blocks inside the region. If there exists a single block
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/// inside the region that is the predecessor of CommonExitBlock, that block
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/// will be returned. Otherwise CommonExitBlock will be split and the
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/// original block will be added to the outline region.
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BasicBlock *findOrCreateBlockForHoisting(BasicBlock *CommonExitBlock);
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private:
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struct LifetimeMarkerInfo {
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bool SinkLifeStart = false;
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bool HoistLifeEnd = false;
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Instruction *LifeStart = nullptr;
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Instruction *LifeEnd = nullptr;
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};
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LifetimeMarkerInfo
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getLifetimeMarkers(const CodeExtractorAnalysisCache &CEAC,
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Instruction *Addr, BasicBlock *ExitBlock) const;
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void severSplitPHINodesOfEntry(BasicBlock *&Header);
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void severSplitPHINodesOfExits(const SmallPtrSetImpl<BasicBlock *> &Exits);
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void splitReturnBlocks();
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Function *constructFunction(const ValueSet &inputs,
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const ValueSet &outputs,
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BasicBlock *header,
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BasicBlock *newRootNode, BasicBlock *newHeader,
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Function *oldFunction, Module *M);
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void moveCodeToFunction(Function *newFunction);
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void calculateNewCallTerminatorWeights(
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BasicBlock *CodeReplacer,
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DenseMap<BasicBlock *, BlockFrequency> &ExitWeights,
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BranchProbabilityInfo *BPI);
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CallInst *emitCallAndSwitchStatement(Function *newFunction,
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BasicBlock *newHeader,
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ValueSet &inputs, ValueSet &outputs);
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};
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} // end namespace llvm
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#endif // LLVM_TRANSFORMS_UTILS_CODEEXTRACTOR_H
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