File: //usr/include/llvm/Transforms/Utils/CodeExtractor.h
//===- 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 <limits>
namespace llvm {
template <typename PtrType> class SmallPtrSetImpl;
class AllocaInst;
class BasicBlock;
class BlockFrequency;
class BlockFrequencyInfo;
class BranchProbabilityInfo;
class AssumptionCache;
class CallInst;
class DominatorTree;
class Function;
class Instruction;
class Module;
class Type;
class Value;
class StructType;
/// 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;
// A block outside of the extraction set where any intermediate
// allocations will be placed inside. If this is null, allocations
// will be placed in the entry block of the function.
BasicBlock *AllocationBlock;
// If true, varargs functions can be extracted.
bool AllowVarArgs;
// Bits of intermediate state computed at various phases of extraction.
SetVector<BasicBlock *> Blocks;
/// Lists of blocks that are branched from the code region to be extracted,
/// also called the exit blocks. Each block is contained at most once. Its
/// order defines the return value of the extracted function.
///
/// When there is just one (or no) exit block, the return value is
/// irrelevant.
///
/// When there are exactly two exit blocks, the extracted function returns a
/// boolean. For ExtractedFuncRetVals[0], it returns 'true'. For
/// ExtractedFuncRetVals[1] it returns 'false'.
/// NOTE: Since a boolean is represented by i1, ExtractedFuncRetVals[0]
/// returns 1 and ExtractedFuncRetVals[1] returns 0, which opposite
/// of the regular pattern below.
///
/// When there are 3 or more exit blocks, leaving the extracted function via
/// the first block it returns 0. When leaving via the second entry it
/// returns 1, etc.
SmallVector<BasicBlock *> ExtractedFuncRetVals;
// 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;
// If true, the outlined function has aggregate argument in zero address
// space.
bool ArgsInZeroAddressSpace;
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.
/// Any new allocations will be placed in the AllocationBlock, unless
/// it is null, in which case it will be placed in the entry block of
/// the function from which the code is being extracted.
/// If ArgsInZeroAddressSpace param is set to true, then the aggregate
/// param pointer of the outlined function is declared in zero address
/// space.
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,
BasicBlock *AllocationBlock = nullptr,
std::string Suffix = "", bool ArgsInZeroAddressSpace = false);
/// Perform the extraction, returning the new function.
///
/// Returns zero when called on a CodeExtractor instance where isEligible
/// returns false.
Function *extractCodeRegion(const CodeExtractorAnalysisCache &CEAC);
/// Perform the extraction, returning the new function and providing an
/// interface to see what was categorized as inputs and outputs.
///
/// \param CEAC - Cache to speed up operations for the CodeExtractor when
/// hoisting, and extracting lifetime values and assumes.
/// \param Inputs [out] - filled with values marked as inputs to the
/// newly outlined function.
/// \param Outputs [out] - filled with values marked as outputs to the
/// newly outlined function.
/// \returns zero when called on a CodeExtractor instance where isEligible
/// returns false.
Function *extractCodeRegion(const CodeExtractorAnalysisCache &CEAC,
ValueSet &Inputs, ValueSet &Outputs);
/// Verify that assumption cache isn't stale after a region is extracted.
/// Returns true when verifier finds errors. AssumptionCache is passed as
/// parameter to make this function stateless.
static bool verifyAssumptionCache(const Function &OldFunc,
const Function &NewFunc,
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,
bool CollectGlobalInputs = false) 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);
/// Exclude a value from aggregate argument passing when extracting a code
/// region, passing it instead as a scalar.
void excludeArgFromAggregate(Value *Arg);
private:
struct LifetimeMarkerInfo {
bool SinkLifeStart = false;
bool HoistLifeEnd = false;
Instruction *LifeStart = nullptr;
Instruction *LifeEnd = nullptr;
};
ValueSet ExcludeArgsFromAggregate;
LifetimeMarkerInfo
getLifetimeMarkers(const CodeExtractorAnalysisCache &CEAC,
Instruction *Addr, BasicBlock *ExitBlock) const;
/// Updates the list of SwitchCases (corresponding to exit blocks) after
/// changes of the control flow or the Blocks list.
void computeExtractedFuncRetVals();
/// Return the type used for the return code of the extracted function to
/// indicate which exit block to jump to.
Type *getSwitchType();
void severSplitPHINodesOfEntry(BasicBlock *&Header);
void severSplitPHINodesOfExits();
void splitReturnBlocks();
void moveCodeToFunction(Function *newFunction);
void calculateNewCallTerminatorWeights(
BasicBlock *CodeReplacer,
const DenseMap<BasicBlock *, BlockFrequency> &ExitWeights,
BranchProbabilityInfo *BPI);
/// Normalizes the control flow of the extracted regions, such as ensuring
/// that the extracted region does not contain a return instruction.
void normalizeCFGForExtraction(BasicBlock *&header);
/// Generates the function declaration for the function containing the
/// extracted code.
Function *constructFunctionDeclaration(const ValueSet &inputs,
const ValueSet &outputs,
BlockFrequency EntryFreq,
const Twine &Name,
ValueSet &StructValues,
StructType *&StructTy);
/// Generates the code for the extracted function. That is: a prolog, the
/// moved or copied code from the original function, and epilogs for each
/// exit.
void emitFunctionBody(const ValueSet &inputs, const ValueSet &outputs,
const ValueSet &StructValues, Function *newFunction,
StructType *StructArgTy, BasicBlock *header,
const ValueSet &SinkingCands);
/// Generates a Basic Block that calls the extracted function.
CallInst *emitReplacerCall(const ValueSet &inputs, const ValueSet &outputs,
const ValueSet &StructValues,
Function *newFunction, StructType *StructArgTy,
Function *oldFunction, BasicBlock *ReplIP,
BlockFrequency EntryFreq,
ArrayRef<Value *> LifetimesStart,
std::vector<Value *> &Reloads);
/// Connects the basic block containing the call to the extracted function
/// into the original function's control flow.
void insertReplacerCall(
Function *oldFunction, BasicBlock *header, BasicBlock *codeReplacer,
const ValueSet &outputs, ArrayRef<Value *> Reloads,
const DenseMap<BasicBlock *, BlockFrequency> &ExitWeights);
};
} // end namespace llvm
#endif // LLVM_TRANSFORMS_UTILS_CODEEXTRACTOR_H