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//===- IROutliner.cpp -- Outline Similar Regions ----------------*- C++ -*-===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
/// \file
// Implementation for the IROutliner which is used by the IROutliner Pass.
#include "llvm/Transforms/IPO/IROutliner.h"
#include "llvm/Analysis/IRSimilarityIdentifier.h"
#include "llvm/Analysis/OptimizationRemarkEmitter.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/IR/Attributes.h"
#include "llvm/IR/PassManager.h"
#include "llvm/InitializePasses.h"
#include "llvm/Pass.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Transforms/IPO.h"
#include <map>
#include <set>
#include <vector>
#define DEBUG_TYPE "iroutliner"
using namespace llvm;
using namespace IRSimilarity;
// Set to true if the user wants the ir outliner to run on linkonceodr linkage
// functions. This is false by default because the linker can dedupe linkonceodr
// functions. Since the outliner is confined to a single module (modulo LTO),
// this is off by default. It should, however, be the default behavior in
// LTO.
static cl::opt<bool> EnableLinkOnceODRIROutlining(
"enable-linkonceodr-ir-outlining", cl::Hidden,
cl::desc("Enable the IR outliner on linkonceodr functions"),
// This is a debug option to test small pieces of code to ensure that outlining
// works correctly.
static cl::opt<bool> NoCostModel(
"ir-outlining-no-cost", cl::init(false), cl::ReallyHidden,
cl::desc("Debug option to outline greedily, without restriction that "
"calculated benefit outweighs cost"));
/// The OutlinableGroup holds all the overarching information for outlining
/// a set of regions that are structurally similar to one another, such as the
/// types of the overall function, the output blocks, the sets of stores needed
/// and a list of the different regions. This information is used in the
/// deduplication of extracted regions with the same structure.
struct OutlinableGroup {
/// The sections that could be outlined
std::vector<OutlinableRegion *> Regions;
/// The argument types for the function created as the overall function to
/// replace the extracted function for each region.
std::vector<Type *> ArgumentTypes;
/// The FunctionType for the overall function.
FunctionType *OutlinedFunctionType = nullptr;
/// The Function for the collective overall function.
Function *OutlinedFunction = nullptr;
/// Flag for whether we should not consider this group of OutlinableRegions
/// for extraction.
bool IgnoreGroup = false;
/// The return block for the overall function.
BasicBlock *EndBB = nullptr;
/// A set containing the different GVN store sets needed. Each array contains
/// a sorted list of the different values that need to be stored into output
/// registers.
DenseSet<ArrayRef<unsigned>> OutputGVNCombinations;
/// Flag for whether the \ref ArgumentTypes have been defined after the
/// extraction of the first region.
bool InputTypesSet = false;
/// The number of input values in \ref ArgumentTypes. Anything after this
/// index in ArgumentTypes is an output argument.
unsigned NumAggregateInputs = 0;
/// The number of instructions that will be outlined by extracting \ref
/// Regions.
InstructionCost Benefit = 0;
/// The number of added instructions needed for the outlining of the \ref
/// Regions.
InstructionCost Cost = 0;
/// The argument that needs to be marked with the swifterr attribute. If not
/// needed, there is no value.
Optional<unsigned> SwiftErrorArgument;
/// For the \ref Regions, we look at every Value. If it is a constant,
/// we check whether it is the same in Region.
/// \param [in,out] NotSame contains the global value numbers where the
/// constant is not always the same, and must be passed in as an argument.
void findSameConstants(DenseSet<unsigned> &NotSame);
/// For the regions, look at each set of GVN stores needed and account for
/// each combination. Add an argument to the argument types if there is
/// more than one combination.
/// \param [in] M - The module we are outlining from.
void collectGVNStoreSets(Module &M);
/// Move the contents of \p SourceBB to before the last instruction of \p
/// TargetBB.
/// \param SourceBB - the BasicBlock to pull Instructions from.
/// \param TargetBB - the BasicBlock to put Instruction into.
static void moveBBContents(BasicBlock &SourceBB, BasicBlock &TargetBB) {
BasicBlock::iterator BBCurr, BBEnd, BBNext;
for (BBCurr = SourceBB.begin(), BBEnd = SourceBB.end(); BBCurr != BBEnd;
BBCurr = BBNext) {
BBNext = std::next(BBCurr);
BBCurr->moveBefore(TargetBB, TargetBB.end());
void OutlinableRegion::splitCandidate() {
assert(!CandidateSplit && "Candidate already split!");
Instruction *StartInst = (*Candidate->begin()).Inst;
Instruction *EndInst = (*Candidate->end()).Inst;
assert(StartInst && EndInst && "Expected a start and end instruction?");
StartBB = StartInst->getParent();
PrevBB = StartBB;
// The basic block gets split like so:
// block: block:
// inst1 inst1
// inst2 inst2
// region1 br block_to_outline
// region2 block_to_outline:
// region3 -> region1
// region4 region2
// inst3 region3
// inst4 region4
// br block_after_outline
// block_after_outline:
// inst3
// inst4
std::string OriginalName = PrevBB->getName().str();
StartBB = PrevBB->splitBasicBlock(StartInst, OriginalName + "_to_outline");
// This is the case for the inner block since we do not have to include
// multiple blocks.
EndBB = StartBB;
FollowBB = EndBB->splitBasicBlock(EndInst, OriginalName + "_after_outline");
CandidateSplit = true;
void OutlinableRegion::reattachCandidate() {
assert(CandidateSplit && "Candidate is not split!");
// The basic block gets reattached like so:
// block: block:
// inst1 inst1
// inst2 inst2
// br block_to_outline region1
// block_to_outline: -> region2
// region1 region3
// region2 region4
// region3 inst3
// region4 inst4
// br block_after_outline
// block_after_outline:
// inst3
// inst4
assert(StartBB != nullptr && "StartBB for Candidate is not defined!");
assert(FollowBB != nullptr && "StartBB for Candidate is not defined!");
// StartBB should only have one predecessor since we put an unconditional
// branch at the end of PrevBB when we split the BasicBlock.
PrevBB = StartBB->getSinglePredecessor();
assert(PrevBB != nullptr &&
"No Predecessor for the region start basic block!");
assert(PrevBB->getTerminator() && "Terminator removed from PrevBB!");
assert(EndBB->getTerminator() && "Terminator removed from EndBB!");
moveBBContents(*StartBB, *PrevBB);
BasicBlock *PlacementBB = PrevBB;
if (StartBB != EndBB)
PlacementBB = EndBB;
moveBBContents(*FollowBB, *PlacementBB);
PrevBB->replaceSuccessorsPhiUsesWith(StartBB, PrevBB);
PrevBB->replaceSuccessorsPhiUsesWith(FollowBB, PlacementBB);
// Make sure to save changes back to the StartBB.
StartBB = PrevBB;
EndBB = nullptr;
PrevBB = nullptr;
FollowBB = nullptr;
CandidateSplit = false;
/// Find whether \p V matches the Constants previously found for the \p GVN.
/// \param V - The value to check for consistency.
/// \param GVN - The global value number assigned to \p V.
/// \param GVNToConstant - The mapping of global value number to Constants.
/// \returns true if the Value matches the Constant mapped to by V and false if
/// it \p V is a Constant but does not match.
/// \returns None if \p V is not a Constant.
static Optional<bool>
constantMatches(Value *V, unsigned GVN,
DenseMap<unsigned, Constant *> &GVNToConstant) {
// See if we have a constants
Constant *CST = dyn_cast<Constant>(V);
if (!CST)
return None;
// Holds a mapping from a global value number to a Constant.
DenseMap<unsigned, Constant *>::iterator GVNToConstantIt;
bool Inserted;
// If we have a constant, try to make a new entry in the GVNToConstant.
std::tie(GVNToConstantIt, Inserted) =
GVNToConstant.insert(std::make_pair(GVN, CST));
// If it was found and is not equal, it is not the same. We do not
// handle this case yet, and exit early.
if (Inserted || (GVNToConstantIt->second == CST))
return true;
return false;
InstructionCost OutlinableRegion::getBenefit(TargetTransformInfo &TTI) {
InstructionCost Benefit = 0;
// Estimate the benefit of outlining a specific sections of the program. We
// delegate mostly this task to the TargetTransformInfo so that if the target
// has specific changes, we can have a more accurate estimate.
// However, getInstructionCost delegates the code size calculation for
// arithmetic instructions to getArithmeticInstrCost in
// include/Analysis/TargetTransformImpl.h, where it always estimates that the
// code size for a division and remainder instruction to be equal to 4, and
// everything else to 1. This is not an accurate representation of the
// division instruction for targets that have a native division instruction.
// To be overly conservative, we only add 1 to the number of instructions for
// each division instruction.
for (Instruction &I : *StartBB) {
switch (I.getOpcode()) {
case Instruction::FDiv:
case Instruction::FRem:
case Instruction::SDiv:
case Instruction::SRem:
case Instruction::UDiv:
case Instruction::URem:
Benefit += 1;
Benefit += TTI.getInstructionCost(&I, TargetTransformInfo::TCK_CodeSize);
return Benefit;
/// Find whether \p Region matches the global value numbering to Constant
/// mapping found so far.
/// \param Region - The OutlinableRegion we are checking for constants
/// \param GVNToConstant - The mapping of global value number to Constants.
/// \param NotSame - The set of global value numbers that do not have the same
/// constant in each region.
/// \returns true if all Constants are the same in every use of a Constant in \p
/// Region and false if not
static bool
collectRegionsConstants(OutlinableRegion &Region,
DenseMap<unsigned, Constant *> &GVNToConstant,
DenseSet<unsigned> &NotSame) {
bool ConstantsTheSame = true;
IRSimilarityCandidate &C = *Region.Candidate;
for (IRInstructionData &ID : C) {
// Iterate over the operands in an instruction. If the global value number,
// assigned by the IRSimilarityCandidate, has been seen before, we check if
// the the number has been found to be not the same value in each instance.
for (Value *V : ID.OperVals) {
Optional<unsigned> GVNOpt = C.getGVN(V);
assert(GVNOpt.hasValue() && "Expected a GVN for operand?");
unsigned GVN = GVNOpt.getValue();
// Check if this global value has been found to not be the same already.
if (NotSame.contains(GVN)) {
if (isa<Constant>(V))
ConstantsTheSame = false;
// If it has been the same so far, we check the value for if the
// associated Constant value match the previous instances of the same
// global value number. If the global value does not map to a Constant,
// it is considered to not be the same value.
Optional<bool> ConstantMatches = constantMatches(V, GVN, GVNToConstant);
if (ConstantMatches.hasValue()) {
if (ConstantMatches.getValue())
ConstantsTheSame = false;
// While this value is a register, it might not have been previously,
// make sure we don't already have a constant mapped to this global value
// number.
if (GVNToConstant.find(GVN) != GVNToConstant.end())
ConstantsTheSame = false;
return ConstantsTheSame;
void OutlinableGroup::findSameConstants(DenseSet<unsigned> &NotSame) {
DenseMap<unsigned, Constant *> GVNToConstant;
for (OutlinableRegion *Region : Regions)
collectRegionsConstants(*Region, GVNToConstant, NotSame);
void OutlinableGroup::collectGVNStoreSets(Module &M) {
for (OutlinableRegion *OS : Regions)
// We are adding an extracted argument to decide between which output path
// to use in the basic block. It is used in a switch statement and only
// needs to be an integer.
if (OutputGVNCombinations.size() > 1)
Function *IROutliner::createFunction(Module &M, OutlinableGroup &Group,
unsigned FunctionNameSuffix) {
assert(!Group.OutlinedFunction && "Function is already defined!");
Group.OutlinedFunctionType = FunctionType::get(
Type::getVoidTy(M.getContext()), Group.ArgumentTypes, false);
// These functions will only be called from within the same module, so
// we can set an internal linkage.
Group.OutlinedFunction = Function::Create(
Group.OutlinedFunctionType, GlobalValue::InternalLinkage,
"outlined_ir_func_" + std::to_string(FunctionNameSuffix), M);
// Transfer the swifterr attribute to the correct function parameter.
if (Group.SwiftErrorArgument.hasValue())
return Group.OutlinedFunction;
/// Move each BasicBlock in \p Old to \p New.
/// \param [in] Old - the function to move the basic blocks from.
/// \param [in] New - The function to move the basic blocks to.
/// \returns the first return block for the function in New.
static BasicBlock *moveFunctionData(Function &Old, Function &New) {
Function::iterator CurrBB, NextBB, FinalBB;
BasicBlock *NewEnd = nullptr;
std::vector<Instruction *> DebugInsts;
for (CurrBB = Old.begin(), FinalBB = Old.end(); CurrBB != FinalBB;
CurrBB = NextBB) {
NextBB = std::next(CurrBB);
Instruction *I = CurrBB->getTerminator();
if (isa<ReturnInst>(I))
NewEnd = &(*CurrBB);
assert(NewEnd && "No return instruction for new function?");
return NewEnd;
/// Find the the constants that will need to be lifted into arguments
/// as they are not the same in each instance of the region.
/// \param [in] C - The IRSimilarityCandidate containing the region we are
/// analyzing.
/// \param [in] NotSame - The set of global value numbers that do not have a
/// single Constant across all OutlinableRegions similar to \p C.
/// \param [out] Inputs - The list containing the global value numbers of the
/// arguments needed for the region of code.
static void findConstants(IRSimilarityCandidate &C, DenseSet<unsigned> &NotSame,
std::vector<unsigned> &Inputs) {
DenseSet<unsigned> Seen;
// Iterate over the instructions, and find what constants will need to be
// extracted into arguments.
for (IRInstructionDataList::iterator IDIt = C.begin(), EndIDIt = C.end();
IDIt != EndIDIt; IDIt++) {
for (Value *V : (*IDIt).OperVals) {
// Since these are stored before any outlining, they will be in the
// global value numbering.
unsigned GVN = C.getGVN(V).getValue();
if (isa<Constant>(V))
if (NotSame.contains(GVN) && !Seen.contains(GVN)) {
/// Find the GVN for the inputs that have been found by the CodeExtractor.
/// \param [in] C - The IRSimilarityCandidate containing the region we are
/// analyzing.
/// \param [in] CurrentInputs - The set of inputs found by the
/// CodeExtractor.
/// \param [in] OutputMappings - The mapping of values that have been replaced
/// by a new output value.
/// \param [out] EndInputNumbers - The global value numbers for the extracted
/// arguments.
static void mapInputsToGVNs(IRSimilarityCandidate &C,
SetVector<Value *> &CurrentInputs,
const DenseMap<Value *, Value *> &OutputMappings,
std::vector<unsigned> &EndInputNumbers) {
// Get the Global Value Number for each input. We check if the Value has been
// replaced by a different value at output, and use the original value before
// replacement.
for (Value *Input : CurrentInputs) {
assert(Input && "Have a nullptr as an input");
if (OutputMappings.find(Input) != OutputMappings.end())
Input = OutputMappings.find(Input)->second;
assert(C.getGVN(Input).hasValue() &&
"Could not find a numbering for the given input");
/// Find the original value for the \p ArgInput values if any one of them was
/// replaced during a previous extraction.
/// \param [in] ArgInputs - The inputs to be extracted by the code extractor.
/// \param [in] OutputMappings - The mapping of values that have been replaced
/// by a new output value.
/// \param [out] RemappedArgInputs - The remapped values according to
/// \p OutputMappings that will be extracted.
static void
remapExtractedInputs(const ArrayRef<Value *> ArgInputs,
const DenseMap<Value *, Value *> &OutputMappings,
SetVector<Value *> &RemappedArgInputs) {
// Get the global value number for each input that will be extracted as an
// argument by the code extractor, remapping if needed for reloaded values.
for (Value *Input : ArgInputs) {
if (OutputMappings.find(Input) != OutputMappings.end())
Input = OutputMappings.find(Input)->second;
/// Find the input GVNs and the output values for a region of Instructions.
/// Using the code extractor, we collect the inputs to the extracted function.
/// The \p Region can be identified as needing to be ignored in this function.
/// It should be checked whether it should be ignored after a call to this
/// function.
/// \param [in,out] Region - The region of code to be analyzed.
/// \param [out] InputGVNs - The global value numbers for the extracted
/// arguments.
/// \param [in] NotSame - The global value numbers in the region that do not
/// have the same constant value in the regions structurally similar to
/// \p Region.
/// \param [in] OutputMappings - The mapping of values that have been replaced
/// by a new output value after extraction.
/// \param [out] ArgInputs - The values of the inputs to the extracted function.
/// \param [out] Outputs - The set of values extracted by the CodeExtractor
/// as outputs.
static void getCodeExtractorArguments(
OutlinableRegion &Region, std::vector<unsigned> &InputGVNs,
DenseSet<unsigned> &NotSame, DenseMap<Value *, Value *> &OutputMappings,
SetVector<Value *> &ArgInputs, SetVector<Value *> &Outputs) {
IRSimilarityCandidate &C = *Region.Candidate;
// OverallInputs are the inputs to the region found by the CodeExtractor,
// SinkCands and HoistCands are used by the CodeExtractor to find sunken
// allocas of values whose lifetimes are contained completely within the
// outlined region. PremappedInputs are the arguments found by the
// CodeExtractor, removing conditions such as sunken allocas, but that
// may need to be remapped due to the extracted output values replacing
// the original values. We use DummyOutputs for this first run of finding
// inputs and outputs since the outputs could change during findAllocas,
// the correct set of extracted outputs will be in the final Outputs ValueSet.
SetVector<Value *> OverallInputs, PremappedInputs, SinkCands, HoistCands,
// Use the code extractor to get the inputs and outputs, without sunken
// allocas or removing llvm.assumes.
CodeExtractor *CE = Region.CE;
CE->findInputsOutputs(OverallInputs, DummyOutputs, SinkCands);
assert(Region.StartBB && "Region must have a start BasicBlock!");
Function *OrigF = Region.StartBB->getParent();
CodeExtractorAnalysisCache CEAC(*OrigF);
BasicBlock *Dummy = nullptr;
// The region may be ineligible due to VarArgs in the parent function. In this
// case we ignore the region.
if (!CE->isEligible()) {
Region.IgnoreRegion = true;
// Find if any values are going to be sunk into the function when extracted
CE->findAllocas(CEAC, SinkCands, HoistCands, Dummy);
CE->findInputsOutputs(PremappedInputs, Outputs, SinkCands);
// TODO: Support regions with sunken allocas: values whose lifetimes are
// contained completely within the outlined region. These are not guaranteed
// to be the same in every region, so we must elevate them all to arguments
// when they appear. If these values are not equal, it means there is some
// Input in OverallInputs that was removed for ArgInputs.
if (OverallInputs.size() != PremappedInputs.size()) {
Region.IgnoreRegion = true;
findConstants(C, NotSame, InputGVNs);
mapInputsToGVNs(C, OverallInputs, OutputMappings, InputGVNs);
remapExtractedInputs(PremappedInputs.getArrayRef(), OutputMappings,
// Sort the GVNs, since we now have constants included in the \ref InputGVNs
// we need to make sure they are in a deterministic order.
/// Look over the inputs and map each input argument to an argument in the
/// overall function for the OutlinableRegions. This creates a way to replace
/// the arguments of the extracted function with the arguments of the new
/// overall function.
/// \param [in,out] Region - The region of code to be analyzed.
/// \param [in] InputGVNs - The global value numbering of the input values
/// collected.
/// \param [in] ArgInputs - The values of the arguments to the extracted
/// function.
static void
findExtractedInputToOverallInputMapping(OutlinableRegion &Region,
std::vector<unsigned> &InputGVNs,
SetVector<Value *> &ArgInputs) {
IRSimilarityCandidate &C = *Region.Candidate;
OutlinableGroup &Group = *Region.Parent;
// This counts the argument number in the overall function.
unsigned TypeIndex = 0;
// This counts the argument number in the extracted function.
unsigned OriginalIndex = 0;
// Find the mapping of the extracted arguments to the arguments for the
// overall function. Since there may be extra arguments in the overall
// function to account for the extracted constants, we have two different
// counters as we find extracted arguments, and as we come across overall
// arguments.
for (unsigned InputVal : InputGVNs) {
Optional<Value *> InputOpt = C.fromGVN(InputVal);
assert(InputOpt.hasValue() && "Global value number not found?");
Value *Input = InputOpt.getValue();
if (!Group.InputTypesSet) {
// If the input value has a swifterr attribute, make sure to mark the
// argument in the overall function.
if (Input->isSwiftError()) {
!Group.SwiftErrorArgument.hasValue() &&
"Argument already marked with swifterr for this OutlinableGroup!");
Group.SwiftErrorArgument = TypeIndex;
// Check if we have a constant. If we do add it to the overall argument
// number to Constant map for the region, and continue to the next input.
if (Constant *CST = dyn_cast<Constant>(Input)) {
Region.AggArgToConstant.insert(std::make_pair(TypeIndex, CST));
// It is not a constant, we create the mapping from extracted argument list
// to the overall argument list.
assert(ArgInputs.count(Input) && "Input cannot be found!");
Region.ExtractedArgToAgg.insert(std::make_pair(OriginalIndex, TypeIndex));
Region.AggArgToExtracted.insert(std::make_pair(TypeIndex, OriginalIndex));
// If the function type definitions for the OutlinableGroup holding the region
// have not been set, set the length of the inputs here. We should have the
// same inputs for all of the different regions contained in the
// OutlinableGroup since they are all structurally similar to one another.
if (!Group.InputTypesSet) {
Group.NumAggregateInputs = TypeIndex;
Group.InputTypesSet = true;
Region.NumExtractedInputs = OriginalIndex;
/// Create a mapping of the output arguments for the \p Region to the output
/// arguments of the overall outlined function.
/// \param [in,out] Region - The region of code to be analyzed.
/// \param [in] Outputs - The values found by the code extractor.
static void
findExtractedOutputToOverallOutputMapping(OutlinableRegion &Region,
ArrayRef<Value *> Outputs) {
OutlinableGroup &Group = *Region.Parent;
IRSimilarityCandidate &C = *Region.Candidate;
// This counts the argument number in the extracted function.
unsigned OriginalIndex = Region.NumExtractedInputs;
// This counts the argument number in the overall function.
unsigned TypeIndex = Group.NumAggregateInputs;
bool TypeFound;
DenseSet<unsigned> AggArgsUsed;
// Iterate over the output types and identify if there is an aggregate pointer
// type whose base type matches the current output type. If there is, we mark
// that we will use this output register for this value. If not we add another
// type to the overall argument type list. We also store the GVNs used for
// stores to identify which values will need to be moved into an special
// block that holds the stores to the output registers.
for (Value *Output : Outputs) {
TypeFound = false;
// We can do this since it is a result value, and will have a number
// that is necessarily the same. BUT if in the future, the instructions
// do not have to be in same order, but are functionally the same, we will
// have to use a different scheme, as one-to-one correspondence is not
// guaranteed.
unsigned GlobalValue = C.getGVN(Output).getValue();
unsigned ArgumentSize = Group.ArgumentTypes.size();
for (unsigned Jdx = TypeIndex; Jdx < ArgumentSize; Jdx++) {
if (Group.ArgumentTypes[Jdx] != PointerType::getUnqual(Output->getType()))
if (AggArgsUsed.contains(Jdx))
TypeFound = true;
Region.ExtractedArgToAgg.insert(std::make_pair(OriginalIndex, Jdx));
Region.AggArgToExtracted.insert(std::make_pair(Jdx, OriginalIndex));
// We were unable to find an unused type in the output type set that matches
// the output, so we add a pointer type to the argument types of the overall
// function to handle this output and create a mapping to it.
if (!TypeFound) {
AggArgsUsed.insert(Group.ArgumentTypes.size() - 1);
std::make_pair(OriginalIndex, Group.ArgumentTypes.size() - 1));
std::make_pair(Group.ArgumentTypes.size() - 1, OriginalIndex));
void IROutliner::findAddInputsOutputs(Module &M, OutlinableRegion &Region,
DenseSet<unsigned> &NotSame) {
std::vector<unsigned> Inputs;
SetVector<Value *> ArgInputs, Outputs;
getCodeExtractorArguments(Region, Inputs, NotSame, OutputMappings, ArgInputs,
if (Region.IgnoreRegion)
// Map the inputs found by the CodeExtractor to the arguments found for
// the overall function.
findExtractedInputToOverallInputMapping(Region, Inputs, ArgInputs);
// Map the outputs found by the CodeExtractor to the arguments found for
// the overall function.
findExtractedOutputToOverallOutputMapping(Region, Outputs.getArrayRef());
/// Replace the extracted function in the Region with a call to the overall
/// function constructed from the deduplicated similar regions, replacing and
/// remapping the values passed to the extracted function as arguments to the
/// new arguments of the overall function.
/// \param [in] M - The module to outline from.
/// \param [in] Region - The regions of extracted code to be replaced with a new
/// function.
/// \returns a call instruction with the replaced function.
CallInst *replaceCalledFunction(Module &M, OutlinableRegion &Region) {
std::vector<Value *> NewCallArgs;
DenseMap<unsigned, unsigned>::iterator ArgPair;
OutlinableGroup &Group = *Region.Parent;
CallInst *Call = Region.Call;
assert(Call && "Call to replace is nullptr?");
Function *AggFunc = Group.OutlinedFunction;
assert(AggFunc && "Function to replace with is nullptr?");
// If the arguments are the same size, there are not values that need to be
// made argument, or different output registers to handle. We can simply
// replace the called function in this case.
if (AggFunc->arg_size() == Call->arg_size()) {
LLVM_DEBUG(dbgs() << "Replace call to " << *Call << " with call to "
<< *AggFunc << " with same number of arguments\n");
return Call;
// We have a different number of arguments than the new function, so
// we need to use our previously mappings off extracted argument to overall
// function argument, and constants to overall function argument to create the
// new argument list.
for (unsigned AggArgIdx = 0; AggArgIdx < AggFunc->arg_size(); AggArgIdx++) {
if (AggArgIdx == AggFunc->arg_size() - 1 &&
Group.OutputGVNCombinations.size() > 1) {
// If we are on the last argument, and we need to differentiate between
// output blocks, add an integer to the argument list to determine
// what block to take
LLVM_DEBUG(dbgs() << "Set switch block argument to "
<< Region.OutputBlockNum << "\n");
ArgPair = Region.AggArgToExtracted.find(AggArgIdx);
if (ArgPair != Region.AggArgToExtracted.end()) {
Value *ArgumentValue = Call->getArgOperand(ArgPair->second);
// If we found the mapping from the extracted function to the overall
// function, we simply add it to the argument list. We use the same
// value, it just needs to honor the new order of arguments.
LLVM_DEBUG(dbgs() << "Setting argument " << AggArgIdx << " to value "
<< *ArgumentValue << "\n");
// If it is a constant, we simply add it to the argument list as a value.
if (Region.AggArgToConstant.find(AggArgIdx) !=
Region.AggArgToConstant.end()) {
Constant *CST = Region.AggArgToConstant.find(AggArgIdx)->second;
LLVM_DEBUG(dbgs() << "Setting argument " << AggArgIdx << " to value "
<< *CST << "\n");
// Add a nullptr value if the argument is not found in the extracted
// function. If we cannot find a value, it means it is not in use
// for the region, so we should not pass anything to it.
LLVM_DEBUG(dbgs() << "Setting argument " << AggArgIdx << " to nullptr\n");
static_cast<PointerType *>(AggFunc->getArg(AggArgIdx)->getType())));
LLVM_DEBUG(dbgs() << "Replace call to " << *Call << " with call to "
<< *AggFunc << " with new set of arguments\n");
// Create the new call instruction and erase the old one.
Call = CallInst::Create(AggFunc->getFunctionType(), AggFunc, NewCallArgs, "",
// It is possible that the call to the outlined function is either the first
// instruction is in the new block, the last instruction, or both. If either
// of these is the case, we need to make sure that we replace the instruction
// in the IRInstructionData struct with the new call.
CallInst *OldCall = Region.Call;
if (Region.NewFront->Inst == OldCall)
Region.NewFront->Inst = Call;
if (Region.NewBack->Inst == OldCall)
Region.NewBack->Inst = Call;
// Transfer any debug information.
// Remove the old instruction.
Region.Call = Call;
// Make sure that the argument in the new function has the SwiftError
// argument.
if (Group.SwiftErrorArgument.hasValue())
return Call;
// Within an extracted function, replace the argument uses of the extracted
// region with the arguments of the function for an OutlinableGroup.
/// \param [in] Region - The region of extracted code to be changed.
/// \param [in,out] OutputBB - The BasicBlock for the output stores for this
/// region.
static void replaceArgumentUses(OutlinableRegion &Region,
BasicBlock *OutputBB) {
OutlinableGroup &Group = *Region.Parent;
assert(Region.ExtractedFunction && "Region has no extracted function?");
for (unsigned ArgIdx = 0; ArgIdx < Region.ExtractedFunction->arg_size();
ArgIdx++) {
assert(Region.ExtractedArgToAgg.find(ArgIdx) !=
Region.ExtractedArgToAgg.end() &&
"No mapping from extracted to outlined?");
unsigned AggArgIdx = Region.ExtractedArgToAgg.find(ArgIdx)->second;
Argument *AggArg = Group.OutlinedFunction->getArg(AggArgIdx);
Argument *Arg = Region.ExtractedFunction->getArg(ArgIdx);
// The argument is an input, so we can simply replace it with the overall
// argument value
if (ArgIdx < Region.NumExtractedInputs) {
LLVM_DEBUG(dbgs() << "Replacing uses of input " << *Arg << " in function "
<< *Region.ExtractedFunction << " with " << *AggArg
<< " in function " << *Group.OutlinedFunction << "\n");
// If we are replacing an output, we place the store value in its own
// block inside the overall function before replacing the use of the output
// in the function.
assert(Arg->hasOneUse() && "Output argument can only have one use");
User *InstAsUser = Arg->user_back();
assert(InstAsUser && "User is nullptr!");
Instruction *I = cast<Instruction>(InstAsUser);
LLVM_DEBUG(dbgs() << "Move store for instruction " << *I << " to "
<< *OutputBB << "\n");
I->moveBefore(*OutputBB, OutputBB->end());
LLVM_DEBUG(dbgs() << "Replacing uses of output " << *Arg << " in function "
<< *Region.ExtractedFunction << " with " << *AggArg
<< " in function " << *Group.OutlinedFunction << "\n");
/// Within an extracted function, replace the constants that need to be lifted
/// into arguments with the actual argument.
/// \param Region [in] - The region of extracted code to be changed.
void replaceConstants(OutlinableRegion &Region) {
OutlinableGroup &Group = *Region.Parent;
// Iterate over the constants that need to be elevated into arguments
for (std::pair<unsigned, Constant *> &Const : Region.AggArgToConstant) {
unsigned AggArgIdx = Const.first;
Function *OutlinedFunction = Group.OutlinedFunction;
assert(OutlinedFunction && "Overall Function is not defined?");
Constant *CST = Const.second;
Argument *Arg = Group.OutlinedFunction->getArg(AggArgIdx);
// Identify the argument it will be elevated to, and replace instances of
// that constant in the function.
// TODO: If in the future constants do not have one global value number,
// i.e. a constant 1 could be mapped to several values, this check will
// have to be more strict. It cannot be using only replaceUsesWithIf.
LLVM_DEBUG(dbgs() << "Replacing uses of constant " << *CST
<< " in function " << *OutlinedFunction << " with "
<< *Arg << "\n");
CST->replaceUsesWithIf(Arg, [OutlinedFunction](Use &U) {
if (Instruction *I = dyn_cast<Instruction>(U.getUser()))
return I->getFunction() == OutlinedFunction;
return false;
/// For the given function, find all the nondebug or lifetime instructions,
/// and return them as a vector. Exclude any blocks in \p ExludeBlocks.
/// \param [in] F - The function we collect the instructions from.
/// \param [in] ExcludeBlocks - BasicBlocks to ignore.
/// \returns the list of instructions extracted.
static std::vector<Instruction *>
collectRelevantInstructions(Function &F,
DenseSet<BasicBlock *> &ExcludeBlocks) {
std::vector<Instruction *> RelevantInstructions;
for (BasicBlock &BB : F) {
if (ExcludeBlocks.contains(&BB))
for (Instruction &Inst : BB) {
if (Inst.isLifetimeStartOrEnd())
if (isa<DbgInfoIntrinsic>(Inst))
return RelevantInstructions;
/// It is possible that there is a basic block that already performs the same
/// stores. This returns a duplicate block, if it exists
/// \param OutputBB [in] the block we are looking for a duplicate of.
/// \param OutputStoreBBs [in] The existing output blocks.
/// \returns an optional value with the number output block if there is a match.
findDuplicateOutputBlock(BasicBlock *OutputBB,
ArrayRef<BasicBlock *> OutputStoreBBs) {
bool WrongInst = false;
bool WrongSize = false;
unsigned MatchingNum = 0;
for (BasicBlock *CompBB : OutputStoreBBs) {
WrongInst = false;
if (CompBB->size() - 1 != OutputBB->size()) {
WrongSize = true;
WrongSize = false;
BasicBlock::iterator NIt = OutputBB->begin();
for (Instruction &I : *CompBB) {
if (isa<BranchInst>(&I))
if (!I.isIdenticalTo(&(*NIt))) {
WrongInst = true;
if (!WrongInst && !WrongSize)
return MatchingNum;
return None;
/// For the outlined section, move needed the StoreInsts for the output
/// registers into their own block. Then, determine if there is a duplicate
/// output block already created.
/// \param [in] OG - The OutlinableGroup of regions to be outlined.
/// \param [in] Region - The OutlinableRegion that is being analyzed.
/// \param [in,out] OutputBB - the block that stores for this region will be
/// placed in.
/// \param [in] EndBB - the final block of the extracted function.
/// \param [in] OutputMappings - OutputMappings the mapping of values that have
/// been replaced by a new output value.
/// \param [in,out] OutputStoreBBs - The existing output blocks.
static void
alignOutputBlockWithAggFunc(OutlinableGroup &OG, OutlinableRegion &Region,
BasicBlock *OutputBB, BasicBlock *EndBB,
const DenseMap<Value *, Value *> &OutputMappings,
std::vector<BasicBlock *> &OutputStoreBBs) {
DenseSet<unsigned> ValuesToFind(Region.GVNStores.begin(),
// We iterate over the instructions in the extracted function, and find the
// global value number of the instructions. If we find a value that should
// be contained in a store, we replace the uses of the value with the value
// from the overall function, so that the store is storing the correct
// value from the overall function.
DenseSet<BasicBlock *> ExcludeBBs(OutputStoreBBs.begin(),
std::vector<Instruction *> ExtractedFunctionInsts =
collectRelevantInstructions(*(Region.ExtractedFunction), ExcludeBBs);
std::vector<Instruction *> OverallFunctionInsts =
collectRelevantInstructions(*OG.OutlinedFunction, ExcludeBBs);
assert(ExtractedFunctionInsts.size() == OverallFunctionInsts.size() &&
"Number of relevant instructions not equal!");
unsigned NumInstructions = ExtractedFunctionInsts.size();
for (unsigned Idx = 0; Idx < NumInstructions; Idx++) {
Value *V = ExtractedFunctionInsts[Idx];
if (OutputMappings.find(V) != OutputMappings.end())
V = OutputMappings.find(V)->second;
Optional<unsigned> GVN = Region.Candidate->getGVN(V);
// If we have found one of the stored values for output, replace the value
// with the corresponding one from the overall function.
if (GVN.hasValue() && ValuesToFind.erase(GVN.getValue())) {
if (ValuesToFind.size() == 0)
if (ValuesToFind.size() == 0)
assert(ValuesToFind.size() == 0 && "Not all store values were handled!");
// If the size of the block is 0, then there are no stores, and we do not
// need to save this block.
if (OutputBB->size() == 0) {
Region.OutputBlockNum = -1;
// Determine is there is a duplicate block.
Optional<unsigned> MatchingBB =
findDuplicateOutputBlock(OutputBB, OutputStoreBBs);
// If there is, we remove the new output block. If it does not,
// we add it to our list of output blocks.
if (MatchingBB.hasValue()) {
LLVM_DEBUG(dbgs() << "Set output block for region in function"
<< Region.ExtractedFunction << " to "
<< MatchingBB.getValue());
Region.OutputBlockNum = MatchingBB.getValue();
Region.OutputBlockNum = OutputStoreBBs.size();
LLVM_DEBUG(dbgs() << "Create output block for region in"
<< Region.ExtractedFunction << " to "
<< *OutputBB);
BranchInst::Create(EndBB, OutputBB);
/// Create the switch statement for outlined function to differentiate between
/// all the output blocks.
/// For the outlined section, determine if an outlined block already exists that
/// matches the needed stores for the extracted section.
/// \param [in] M - The module we are outlining from.
/// \param [in] OG - The group of regions to be outlined.
/// \param [in] EndBB - The final block of the extracted function.
/// \param [in,out] OutputStoreBBs - The existing output blocks.
void createSwitchStatement(Module &M, OutlinableGroup &OG, BasicBlock *EndBB,
ArrayRef<BasicBlock *> OutputStoreBBs) {
// We only need the switch statement if there is more than one store
// combination.
if (OG.OutputGVNCombinations.size() > 1) {
Function *AggFunc = OG.OutlinedFunction;
// Create a final block
BasicBlock *ReturnBlock =
BasicBlock::Create(M.getContext(), "final_block", AggFunc);
Instruction *Term = EndBB->getTerminator();
Term->moveBefore(*ReturnBlock, ReturnBlock->end());
// Put the switch statement in the old end basic block for the function with
// a fall through to the new return block
LLVM_DEBUG(dbgs() << "Create switch statement in " << *AggFunc << " for "
<< OutputStoreBBs.size() << "\n");
SwitchInst *SwitchI =
SwitchInst::Create(AggFunc->getArg(AggFunc->arg_size() - 1),
ReturnBlock, OutputStoreBBs.size(), EndBB);
unsigned Idx = 0;
for (BasicBlock *BB : OutputStoreBBs) {
SwitchI->addCase(ConstantInt::get(Type::getInt32Ty(M.getContext()), Idx),
Term = BB->getTerminator();
Term->setSuccessor(0, ReturnBlock);
// If there needs to be stores, move them from the output block to the end
// block to save on branching instructions.
if (OutputStoreBBs.size() == 1) {
LLVM_DEBUG(dbgs() << "Move store instructions to the end block in "
<< *OG.OutlinedFunction << "\n");
BasicBlock *OutputBlock = OutputStoreBBs[0];
Instruction *Term = OutputBlock->getTerminator();
Term = EndBB->getTerminator();
moveBBContents(*OutputBlock, *EndBB);
Term->moveBefore(*EndBB, EndBB->end());
/// Fill the new function that will serve as the replacement function for all of
/// the extracted regions of a certain structure from the first region in the
/// list of regions. Replace this first region's extracted function with the
/// new overall function.
/// \param [in] M - The module we are outlining from.
/// \param [in] CurrentGroup - The group of regions to be outlined.
/// \param [in,out] OutputStoreBBs - The output blocks for each different
/// set of stores needed for the different functions.
/// \param [in,out] FuncsToRemove - Extracted functions to erase from module
/// once outlining is complete.
static void fillOverallFunction(Module &M, OutlinableGroup &CurrentGroup,
std::vector<BasicBlock *> &OutputStoreBBs,
std::vector<Function *> &FuncsToRemove) {
OutlinableRegion *CurrentOS = CurrentGroup.Regions[0];
// Move first extracted function's instructions into new function.
LLVM_DEBUG(dbgs() << "Move instructions from "
<< *CurrentOS->ExtractedFunction << " to instruction "
<< *CurrentGroup.OutlinedFunction << "\n");
CurrentGroup.EndBB = moveFunctionData(*CurrentOS->ExtractedFunction,
// Transfer the attributes from the function to the new function.
for (Attribute A :
// Create an output block for the first extracted function.
BasicBlock *NewBB = BasicBlock::Create(
M.getContext(), Twine("output_block_") + Twine(static_cast<unsigned>(0)),
CurrentOS->OutputBlockNum = 0;
replaceArgumentUses(*CurrentOS, NewBB);
// If the new basic block has no new stores, we can erase it from the module.
// It it does, we create a branch instruction to the last basic block from the
// new one.
if (NewBB->size() == 0) {
CurrentOS->OutputBlockNum = -1;
} else {
BranchInst::Create(CurrentGroup.EndBB, NewBB);
// Replace the call to the extracted function with the outlined function.
CurrentOS->Call = replaceCalledFunction(M, *CurrentOS);
// We only delete the extracted functions at the end since we may need to
// reference instructions contained in them for mapping purposes.
void IROutliner::deduplicateExtractedSections(
Module &M, OutlinableGroup &CurrentGroup,
std::vector<Function *> &FuncsToRemove, unsigned &OutlinedFunctionNum) {
createFunction(M, CurrentGroup, OutlinedFunctionNum);
std::vector<BasicBlock *> OutputStoreBBs;
OutlinableRegion *CurrentOS;
fillOverallFunction(M, CurrentGroup, OutputStoreBBs, FuncsToRemove);
for (unsigned Idx = 1; Idx < CurrentGroup.Regions.size(); Idx++) {
CurrentOS = CurrentGroup.Regions[Idx];
// Create a new BasicBlock to hold the needed store instructions.
BasicBlock *NewBB = BasicBlock::Create(
M.getContext(), "output_block_" + std::to_string(Idx),
replaceArgumentUses(*CurrentOS, NewBB);
alignOutputBlockWithAggFunc(CurrentGroup, *CurrentOS, NewBB,
CurrentGroup.EndBB, OutputMappings,
CurrentOS->Call = replaceCalledFunction(M, *CurrentOS);
// Create a switch statement to handle the different output schemes.
createSwitchStatement(M, CurrentGroup, CurrentGroup.EndBB, OutputStoreBBs);
void IROutliner::pruneIncompatibleRegions(
std::vector<IRSimilarityCandidate> &CandidateVec,
OutlinableGroup &CurrentGroup) {
bool PreviouslyOutlined;
// Sort from beginning to end, so the IRSimilarityCandidates are in order.
stable_sort(CandidateVec, [](const IRSimilarityCandidate &LHS,
const IRSimilarityCandidate &RHS) {
return LHS.getStartIdx() < RHS.getStartIdx();
unsigned CurrentEndIdx = 0;
for (IRSimilarityCandidate &IRSC : CandidateVec) {
PreviouslyOutlined = false;
unsigned StartIdx = IRSC.getStartIdx();
unsigned EndIdx = IRSC.getEndIdx();
for (unsigned Idx = StartIdx; Idx <= EndIdx; Idx++)
if (Outlined.contains(Idx)) {
PreviouslyOutlined = true;
if (PreviouslyOutlined)
// TODO: If in the future we can outline across BasicBlocks, we will need to
// check all BasicBlocks contained in the region.
if (IRSC.getStartBB()->hasAddressTaken())
if (IRSC.front()->Inst->getFunction()->hasLinkOnceODRLinkage() &&
// Greedily prune out any regions that will overlap with already chosen
// regions.
if (CurrentEndIdx != 0 && StartIdx <= CurrentEndIdx)
bool BadInst = any_of(IRSC, [this](IRInstructionData &ID) {
// We check if there is a discrepancy between the InstructionDataList
// and the actual next instruction in the module. If there is, it means
// that an extra instruction was added, likely by the CodeExtractor.
// Since we do not have any similarity data about this particular
// instruction, we cannot confidently outline it, and must discard this
// candidate.
if (std::next(ID.getIterator())->Inst !=
return true;
return !this->InstructionClassifier.visit(ID.Inst);
if (BadInst)
OutlinableRegion *OS = new (RegionAllocator.Allocate())
OutlinableRegion(IRSC, CurrentGroup);
CurrentEndIdx = EndIdx;
IROutliner::findBenefitFromAllRegions(OutlinableGroup &CurrentGroup) {
InstructionCost RegionBenefit = 0;
for (OutlinableRegion *Region : CurrentGroup.Regions) {
TargetTransformInfo &TTI = getTTI(*Region->StartBB->getParent());
// We add the number of instructions in the region to the benefit as an
// estimate as to how much will be removed.
RegionBenefit += Region->getBenefit(TTI);
LLVM_DEBUG(dbgs() << "Adding: " << RegionBenefit
<< " saved instructions to overfall benefit.\n");
return RegionBenefit;
IROutliner::findCostOutputReloads(OutlinableGroup &CurrentGroup) {
InstructionCost OverallCost = 0;
for (OutlinableRegion *Region : CurrentGroup.Regions) {
TargetTransformInfo &TTI = getTTI(*Region->StartBB->getParent());
// Each output incurs a load after the call, so we add that to the cost.
for (unsigned OutputGVN : Region->GVNStores) {
Optional<Value *> OV = Region->Candidate->fromGVN(OutputGVN);
assert(OV.hasValue() && "Could not find value for GVN?");
Value *V = OV.getValue();
InstructionCost LoadCost =
TTI.getMemoryOpCost(Instruction::Load, V->getType(), Align(1), 0,
LLVM_DEBUG(dbgs() << "Adding: " << LoadCost
<< " instructions to cost for output of type "
<< *V->getType() << "\n");
OverallCost += LoadCost;
return OverallCost;
/// Find the extra instructions needed to handle any output values for the
/// region.
/// \param [in] M - The Module to outline from.
/// \param [in] CurrentGroup - The collection of OutlinableRegions to analyze.
/// \param [in] TTI - The TargetTransformInfo used to collect information for
/// new instruction costs.
/// \returns the additional cost to handle the outputs.
static InstructionCost findCostForOutputBlocks(Module &M,
OutlinableGroup &CurrentGroup,
TargetTransformInfo &TTI) {
InstructionCost OutputCost = 0;
for (const ArrayRef<unsigned> &OutputUse :
CurrentGroup.OutputGVNCombinations) {
IRSimilarityCandidate &Candidate = *CurrentGroup.Regions[0]->Candidate;
for (unsigned GVN : OutputUse) {
Optional<Value *> OV = Candidate.fromGVN(GVN);
assert(OV.hasValue() && "Could not find value for GVN?");
Value *V = OV.getValue();
InstructionCost StoreCost =
TTI.getMemoryOpCost(Instruction::Load, V->getType(), Align(1), 0,
// An instruction cost is added for each store set that needs to occur for
// various output combinations inside the function, plus a branch to
// return to the exit block.
LLVM_DEBUG(dbgs() << "Adding: " << StoreCost
<< " instructions to cost for output of type "
<< *V->getType() << "\n");
OutputCost += StoreCost;
InstructionCost BranchCost =
TTI.getCFInstrCost(Instruction::Br, TargetTransformInfo::TCK_CodeSize);
LLVM_DEBUG(dbgs() << "Adding " << BranchCost << " to the current cost for"
<< " a branch instruction\n");
OutputCost += BranchCost;
// If there is more than one output scheme, we must have a comparison and
// branch for each different item in the switch statement.
if (CurrentGroup.OutputGVNCombinations.size() > 1) {
InstructionCost ComparisonCost = TTI.getCmpSelInstrCost(
Instruction::ICmp, Type::getInt32Ty(M.getContext()),
Type::getInt32Ty(M.getContext()), CmpInst::BAD_ICMP_PREDICATE,
InstructionCost BranchCost =
TTI.getCFInstrCost(Instruction::Br, TargetTransformInfo::TCK_CodeSize);
unsigned DifferentBlocks = CurrentGroup.OutputGVNCombinations.size();
InstructionCost TotalCost = ComparisonCost * BranchCost * DifferentBlocks;
LLVM_DEBUG(dbgs() << "Adding: " << TotalCost
<< " instructions for each switch case for each different"
<< " output path in a function\n");
OutputCost += TotalCost;
return OutputCost;
void IROutliner::findCostBenefit(Module &M, OutlinableGroup &CurrentGroup) {
InstructionCost RegionBenefit = findBenefitFromAllRegions(CurrentGroup);
CurrentGroup.Benefit += RegionBenefit;
LLVM_DEBUG(dbgs() << "Current Benefit: " << CurrentGroup.Benefit << "\n");
InstructionCost OutputReloadCost = findCostOutputReloads(CurrentGroup);
CurrentGroup.Cost += OutputReloadCost;
LLVM_DEBUG(dbgs() << "Current Cost: " << CurrentGroup.Cost << "\n");
InstructionCost AverageRegionBenefit =
RegionBenefit / CurrentGroup.Regions.size();
unsigned OverallArgumentNum = CurrentGroup.ArgumentTypes.size();
unsigned NumRegions = CurrentGroup.Regions.size();
TargetTransformInfo &TTI =
// We add one region to the cost once, to account for the instructions added
// inside of the newly created function.
LLVM_DEBUG(dbgs() << "Adding: " << AverageRegionBenefit
<< " instructions to cost for body of new function.\n");
CurrentGroup.Cost += AverageRegionBenefit;
LLVM_DEBUG(dbgs() << "Current Cost: " << CurrentGroup.Cost << "\n");
// For each argument, we must add an instruction for loading the argument
// out of the register and into a value inside of the newly outlined function.
LLVM_DEBUG(dbgs() << "Adding: " << OverallArgumentNum
<< " instructions to cost for each argument in the new"
<< " function.\n");
CurrentGroup.Cost +=
OverallArgumentNum * TargetTransformInfo::TCC_Basic;
LLVM_DEBUG(dbgs() << "Current Cost: " << CurrentGroup.Cost << "\n");
// Each argument needs to either be loaded into a register or onto the stack.
// Some arguments will only be loaded into the stack once the argument
// registers are filled.
LLVM_DEBUG(dbgs() << "Adding: " << OverallArgumentNum
<< " instructions to cost for each argument in the new"
<< " function " << NumRegions << " times for the "
<< "needed argument handling at the call site.\n");
CurrentGroup.Cost +=
2 * OverallArgumentNum * TargetTransformInfo::TCC_Basic * NumRegions;
LLVM_DEBUG(dbgs() << "Current Cost: " << CurrentGroup.Cost << "\n");
CurrentGroup.Cost += findCostForOutputBlocks(M, CurrentGroup, TTI);
LLVM_DEBUG(dbgs() << "Current Cost: " << CurrentGroup.Cost << "\n");
void IROutliner::updateOutputMapping(OutlinableRegion &Region,
ArrayRef<Value *> Outputs,
LoadInst *LI) {
// For and load instructions following the call
Value *Operand = LI->getPointerOperand();
Optional<unsigned> OutputIdx = None;
// Find if the operand it is an output register.
for (unsigned ArgIdx = Region.NumExtractedInputs;
ArgIdx < Region.Call->arg_size(); ArgIdx++) {
if (Operand == Region.Call->getArgOperand(ArgIdx)) {
OutputIdx = ArgIdx - Region.NumExtractedInputs;
// If we found an output register, place a mapping of the new value
// to the original in the mapping.
if (!OutputIdx.hasValue())
if (OutputMappings.find(Outputs[OutputIdx.getValue()]) ==
OutputMappings.end()) {
LLVM_DEBUG(dbgs() << "Mapping extracted output " << *LI << " to "
<< *Outputs[OutputIdx.getValue()] << "\n");
OutputMappings.insert(std::make_pair(LI, Outputs[OutputIdx.getValue()]));
} else {
Value *Orig = OutputMappings.find(Outputs[OutputIdx.getValue()])->second;
LLVM_DEBUG(dbgs() << "Mapping extracted output " << *Orig << " to "
<< *Outputs[OutputIdx.getValue()] << "\n");
OutputMappings.insert(std::make_pair(LI, Orig));
bool IROutliner::extractSection(OutlinableRegion &Region) {
SetVector<Value *> ArgInputs, Outputs, SinkCands;
Region.CE->findInputsOutputs(ArgInputs, Outputs, SinkCands);
assert(Region.StartBB && "StartBB for the OutlinableRegion is nullptr!");
assert(Region.FollowBB && "FollowBB for the OutlinableRegion is nullptr!");
Function *OrigF = Region.StartBB->getParent();
CodeExtractorAnalysisCache CEAC(*OrigF);
Region.ExtractedFunction = Region.CE->extractCodeRegion(CEAC);
// If the extraction was successful, find the BasicBlock, and reassign the
// OutlinableRegion blocks
if (!Region.ExtractedFunction) {
LLVM_DEBUG(dbgs() << "CodeExtractor failed to outline " << Region.StartBB
<< "\n");
return false;
BasicBlock *RewrittenBB = Region.FollowBB->getSinglePredecessor();
Region.StartBB = RewrittenBB;
Region.EndBB = RewrittenBB;
// The sequences of outlinable regions has now changed. We must fix the
// IRInstructionDataList for consistency. Although they may not be illegal
// instructions, they should not be compared with anything else as they
// should not be outlined in this round. So marking these as illegal is
// allowed.
IRInstructionDataList *IDL = Region.Candidate->front()->IDL;
Instruction *BeginRewritten = &*RewrittenBB->begin();
Instruction *EndRewritten = &*RewrittenBB->begin();
Region.NewFront = new (InstDataAllocator.Allocate()) IRInstructionData(
*BeginRewritten, InstructionClassifier.visit(*BeginRewritten), *IDL);
Region.NewBack = new (InstDataAllocator.Allocate()) IRInstructionData(
*EndRewritten, InstructionClassifier.visit(*EndRewritten), *IDL);
// Insert the first IRInstructionData of the new region in front of the
// first IRInstructionData of the IRSimilarityCandidate.
IDL->insert(Region.Candidate->begin(), *Region.NewFront);
// Insert the first IRInstructionData of the new region after the
// last IRInstructionData of the IRSimilarityCandidate.
IDL->insert(Region.Candidate->end(), *Region.NewBack);
// Remove the IRInstructionData from the IRSimilarityCandidate.
IDL->erase(Region.Candidate->begin(), std::prev(Region.Candidate->end()));
assert(RewrittenBB != nullptr &&
"Could not find a predecessor after extraction!");
// Iterate over the new set of instructions to find the new call
// instruction.
for (Instruction &I : *RewrittenBB)
if (CallInst *CI = dyn_cast<CallInst>(&I)) {
if (Region.ExtractedFunction == CI->getCalledFunction())
Region.Call = CI;
} else if (LoadInst *LI = dyn_cast<LoadInst>(&I))
updateOutputMapping(Region, Outputs.getArrayRef(), LI);
return true;
unsigned IROutliner::doOutline(Module &M) {
// Find the possible similarity sections.
IRSimilarityIdentifier &Identifier = getIRSI(M);
SimilarityGroupList &SimilarityCandidates = *Identifier.getSimilarity();
// Sort them by size of extracted sections
unsigned OutlinedFunctionNum = 0;
// If we only have one SimilarityGroup in SimilarityCandidates, we do not have
// to sort them by the potential number of instructions to be outlined
if (SimilarityCandidates.size() > 1)
[](const std::vector<IRSimilarityCandidate> &LHS,
const std::vector<IRSimilarityCandidate> &RHS) {
return LHS[0].getLength() * LHS.size() >
RHS[0].getLength() * RHS.size();
DenseSet<unsigned> NotSame;
std::vector<Function *> FuncsToRemove;
// Iterate over the possible sets of similarity.
for (SimilarityGroup &CandidateVec : SimilarityCandidates) {
OutlinableGroup CurrentGroup;
// Remove entries that were previously outlined
pruneIncompatibleRegions(CandidateVec, CurrentGroup);
// We pruned the number of regions to 0 to 1, meaning that it's not worth
// trying to outlined since there is no compatible similar instance of this
// code.
if (CurrentGroup.Regions.size() < 2)
// Determine if there are any values that are the same constant throughout
// each section in the set.
if (CurrentGroup.IgnoreGroup)
// Create a CodeExtractor for each outlinable region. Identify inputs and
// outputs for each section using the code extractor and create the argument
// types for the Aggregate Outlining Function.
std::vector<OutlinableRegion *> OutlinedRegions;
for (OutlinableRegion *OS : CurrentGroup.Regions) {
// Break the outlinable region out of its parent BasicBlock into its own
// BasicBlocks (see function implementation).
std::vector<BasicBlock *> BE = {OS->StartBB};
OS->CE = new (ExtractorAllocator.Allocate())
CodeExtractor(BE, nullptr, false, nullptr, nullptr, nullptr, false,
false, "outlined");
findAddInputsOutputs(M, *OS, NotSame);
if (!OS->IgnoreRegion)
CurrentGroup.Regions = std::move(OutlinedRegions);
if (CurrentGroup.Regions.empty())
if (CostModel)
findCostBenefit(M, CurrentGroup);
// If we are adhering to the cost model, reattach all the candidates
if (CurrentGroup.Cost >= CurrentGroup.Benefit && CostModel) {
for (OutlinableRegion *OS : CurrentGroup.Regions)
OptimizationRemarkEmitter &ORE = getORE(
ORE.emit([&]() {
IRSimilarityCandidate *C = CurrentGroup.Regions[0]->Candidate;
OptimizationRemarkMissed R(DEBUG_TYPE, "WouldNotDecreaseSize",
R << "did not outline "
<< ore::NV(std::to_string(CurrentGroup.Regions.size()))
<< " regions due to estimated increase of "
<< ore::NV("InstructionIncrease",
CurrentGroup.Cost - CurrentGroup.Benefit)
<< " instructions at locations ";
CurrentGroup.Regions.begin(), CurrentGroup.Regions.end(),
[&R](OutlinableRegion *Region) {
R << ore::NV(
[&R]() { R << " "; });
return R;
LLVM_DEBUG(dbgs() << "Outlining regions with cost " << CurrentGroup.Cost
<< " and benefit " << CurrentGroup.Benefit << "\n");
// Create functions out of all the sections, and mark them as outlined.
for (OutlinableRegion *OS : CurrentGroup.Regions) {
bool FunctionOutlined = extractSection(*OS);
if (FunctionOutlined) {
unsigned StartIdx = OS->Candidate->getStartIdx();
unsigned EndIdx = OS->Candidate->getEndIdx();
for (unsigned Idx = StartIdx; Idx <= EndIdx; Idx++)
LLVM_DEBUG(dbgs() << "Outlined " << OutlinedRegions.size()
<< " with benefit " << CurrentGroup.Benefit
<< " and cost " << CurrentGroup.Cost << "\n");
CurrentGroup.Regions = std::move(OutlinedRegions);
if (CurrentGroup.Regions.empty())
OptimizationRemarkEmitter &ORE =
ORE.emit([&]() {
IRSimilarityCandidate *C = CurrentGroup.Regions[0]->Candidate;
OptimizationRemark R(DEBUG_TYPE, "Outlined", C->front()->Inst);
R << "outlined " << ore::NV(std::to_string(CurrentGroup.Regions.size()))
<< " regions with decrease of "
<< ore::NV("Benefit", CurrentGroup.Benefit - CurrentGroup.Cost)
<< " instructions at locations ";
CurrentGroup.Regions.begin(), CurrentGroup.Regions.end(),
[&R](OutlinableRegion *Region) {
R << ore::NV("DebugLoc",
[&R]() { R << " "; });
return R;
deduplicateExtractedSections(M, CurrentGroup, FuncsToRemove,
for (Function *F : FuncsToRemove)
return OutlinedFunctionNum;
bool IROutliner::run(Module &M) {
CostModel = !NoCostModel;
OutlineFromLinkODRs = EnableLinkOnceODRIROutlining;
return doOutline(M) > 0;
// Pass Manager Boilerplate
class IROutlinerLegacyPass : public ModulePass {
static char ID;
IROutlinerLegacyPass() : ModulePass(ID) {
void getAnalysisUsage(AnalysisUsage &AU) const override {
bool runOnModule(Module &M) override;
bool IROutlinerLegacyPass::runOnModule(Module &M) {
if (skipModule(M))
return false;
std::unique_ptr<OptimizationRemarkEmitter> ORE;
auto GORE = [&ORE](Function &F) -> OptimizationRemarkEmitter & {
ORE.reset(new OptimizationRemarkEmitter(&F));
return *ORE.get();
auto GTTI = [this](Function &F) -> TargetTransformInfo & {
return this->getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
auto GIRSI = [this](Module &) -> IRSimilarityIdentifier & {
return this->getAnalysis<IRSimilarityIdentifierWrapperPass>().getIRSI();
return IROutliner(GTTI, GIRSI, GORE).run(M);
PreservedAnalyses IROutlinerPass::run(Module &M, ModuleAnalysisManager &AM) {
auto &FAM = AM.getResult<FunctionAnalysisManagerModuleProxy>(M).getManager();
std::function<TargetTransformInfo &(Function &)> GTTI =
[&FAM](Function &F) -> TargetTransformInfo & {
return FAM.getResult<TargetIRAnalysis>(F);
std::function<IRSimilarityIdentifier &(Module &)> GIRSI =
[&AM](Module &M) -> IRSimilarityIdentifier & {
return AM.getResult<IRSimilarityAnalysis>(M);
std::unique_ptr<OptimizationRemarkEmitter> ORE;
std::function<OptimizationRemarkEmitter &(Function &)> GORE =
[&ORE](Function &F) -> OptimizationRemarkEmitter & {
ORE.reset(new OptimizationRemarkEmitter(&F));
return *ORE.get();
if (IROutliner(GTTI, GIRSI, GORE).run(M))
return PreservedAnalyses::none();
return PreservedAnalyses::all();
char IROutlinerLegacyPass::ID = 0;
INITIALIZE_PASS_BEGIN(IROutlinerLegacyPass, "iroutliner", "IR Outliner", false,
INITIALIZE_PASS_END(IROutlinerLegacyPass, "iroutliner", "IR Outliner", false,
ModulePass *llvm::createIROutlinerPass() { return new IROutlinerLegacyPass(); }