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