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//===------ LoopGenerators.cpp - IR helper to create loops ---------------===//
// 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
// This file contains functions to create scalar loops and orchestrate the
// creation of parallel loops as LLVM-IR.
#include "polly/CodeGen/LoopGenerators.h"
#include "polly/Options.h"
#include "polly/ScopDetection.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Module.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
using namespace llvm;
using namespace polly;
int polly::PollyNumThreads;
OMPGeneralSchedulingType polly::PollyScheduling;
int polly::PollyChunkSize;
static cl::opt<int, true>
cl::desc("Number of threads to use (0 = auto)"),
cl::Hidden, cl::location(polly::PollyNumThreads),
cl::init(0), cl::cat(PollyCategory));
static cl::opt<OMPGeneralSchedulingType, true> XPollyScheduling(
cl::desc("Scheduling type of parallel OpenMP for loops"),
cl::values(clEnumValN(OMPGeneralSchedulingType::StaticChunked, "static",
"Static scheduling"),
clEnumValN(OMPGeneralSchedulingType::Dynamic, "dynamic",
"Dynamic scheduling"),
clEnumValN(OMPGeneralSchedulingType::Guided, "guided",
"Guided scheduling"),
clEnumValN(OMPGeneralSchedulingType::Runtime, "runtime",
"Runtime determined (OMP_SCHEDULE)")),
cl::Hidden, cl::location(polly::PollyScheduling),
cl::init(OMPGeneralSchedulingType::Runtime), cl::Optional,
static cl::opt<int, true>
cl::desc("Chunksize to use by the OpenMP runtime calls"),
cl::Hidden, cl::location(polly::PollyChunkSize),
cl::init(0), cl::Optional, cl::cat(PollyCategory));
// We generate a loop of either of the following structures:
// BeforeBB BeforeBB
// | |
// v v
// GuardBB PreHeaderBB
// / | | _____
// __ PreHeaderBB | v \/ |
// / \ / | HeaderBB latch
// latch HeaderBB | |\ |
// \ / \ / | \------/
// < \ / |
// \ / v
// ExitBB ExitBB
// depending on whether or not we know that it is executed at least once. If
// not, GuardBB checks if the loop is executed at least once. If this is the
// case we branch to PreHeaderBB and subsequently to the HeaderBB, which
// contains the loop iv 'polly.indvar', the incremented loop iv
// 'polly.indvar_next' as well as the condition to check if we execute another
// iteration of the loop. After the loop has finished, we branch to ExitBB.
// We expect the type of UB, LB, UB+Stride to be large enough for values that
// UB may take throughout the execution of the loop, including the computation
// of indvar + Stride before the final abort.
Value *polly::createLoop(Value *LB, Value *UB, Value *Stride,
PollyIRBuilder &Builder, LoopInfo &LI,
DominatorTree &DT, BasicBlock *&ExitBB,
ICmpInst::Predicate Predicate,
ScopAnnotator *Annotator, bool Parallel, bool UseGuard,
bool LoopVectDisabled) {
Function *F = Builder.GetInsertBlock()->getParent();
LLVMContext &Context = F->getContext();
assert(LB->getType() == UB->getType() && "Types of loop bounds do not match");
IntegerType *LoopIVType = dyn_cast<IntegerType>(UB->getType());
assert(LoopIVType && "UB is not integer?");
BasicBlock *BeforeBB = Builder.GetInsertBlock();
BasicBlock *GuardBB =
UseGuard ? BasicBlock::Create(Context, "polly.loop_if", F) : nullptr;
BasicBlock *HeaderBB = BasicBlock::Create(Context, "polly.loop_header", F);
BasicBlock *PreHeaderBB =
BasicBlock::Create(Context, "polly.loop_preheader", F);
// Update LoopInfo
Loop *OuterLoop = LI.getLoopFor(BeforeBB);
Loop *NewLoop = LI.AllocateLoop();
if (OuterLoop)
if (OuterLoop) {
if (GuardBB)
OuterLoop->addBasicBlockToLoop(GuardBB, LI);
OuterLoop->addBasicBlockToLoop(PreHeaderBB, LI);
NewLoop->addBasicBlockToLoop(HeaderBB, LI);
// Notify the annotator (if present) that we have a new loop, but only
// after the header block is set.
if (Annotator)
Annotator->pushLoop(NewLoop, Parallel);
// ExitBB
ExitBB = SplitBlock(BeforeBB, &*Builder.GetInsertPoint(), &DT, &LI);
// BeforeBB
if (GuardBB) {
BeforeBB->getTerminator()->setSuccessor(0, GuardBB);
DT.addNewBlock(GuardBB, BeforeBB);
// GuardBB
Value *LoopGuard;
LoopGuard = Builder.CreateICmp(Predicate, LB, UB);
Builder.CreateCondBr(LoopGuard, PreHeaderBB, ExitBB);
DT.addNewBlock(PreHeaderBB, GuardBB);
} else {
BeforeBB->getTerminator()->setSuccessor(0, PreHeaderBB);
DT.addNewBlock(PreHeaderBB, BeforeBB);
// PreHeaderBB
// HeaderBB
DT.addNewBlock(HeaderBB, PreHeaderBB);
PHINode *IV = Builder.CreatePHI(LoopIVType, 2, "polly.indvar");
IV->addIncoming(LB, PreHeaderBB);
Stride = Builder.CreateZExtOrBitCast(Stride, LoopIVType);
Value *IncrementedIV = Builder.CreateNSWAdd(IV, Stride, "polly.indvar_next");
Value *LoopCondition =
Builder.CreateICmp(Predicate, IncrementedIV, UB, "polly.loop_cond");
// Create the loop latch and annotate it as such.
BranchInst *B = Builder.CreateCondBr(LoopCondition, HeaderBB, ExitBB);
if (Annotator)
Annotator->annotateLoopLatch(B, NewLoop, Parallel, LoopVectDisabled);
IV->addIncoming(IncrementedIV, HeaderBB);
if (GuardBB)
DT.changeImmediateDominator(ExitBB, GuardBB);
DT.changeImmediateDominator(ExitBB, HeaderBB);
// The loop body should be added here.
return IV;
Value *ParallelLoopGenerator::createParallelLoop(
Value *LB, Value *UB, Value *Stride, SetVector<Value *> &UsedValues,
ValueMapT &Map, BasicBlock::iterator *LoopBody) {
AllocaInst *Struct = storeValuesIntoStruct(UsedValues);
BasicBlock::iterator BeforeLoop = Builder.GetInsertPoint();
Value *IV;
Function *SubFn;
std::tie(IV, SubFn) = createSubFn(Stride, Struct, UsedValues, Map);
*LoopBody = Builder.GetInsertPoint();
Value *SubFnParam = Builder.CreateBitCast(Struct, Builder.getInt8PtrTy(),
// Add one as the upper bound provided by OpenMP is a < comparison
// whereas the codegenForSequential function creates a <= comparison.
UB = Builder.CreateAdd(UB, ConstantInt::get(LongType, 1));
// Execute the prepared subfunction in parallel.
deployParallelExecution(SubFn, SubFnParam, LB, UB, Stride);
return IV;
Function *ParallelLoopGenerator::createSubFnDefinition() {
Function *F = Builder.GetInsertBlock()->getParent();
Function *SubFn = prepareSubFnDefinition(F);
// Certain backends (e.g., NVPTX) do not support '.'s in function names.
// Hence, we ensure that all '.'s are replaced by '_'s.
std::string FunctionName = SubFn->getName();
std::replace(FunctionName.begin(), FunctionName.end(), '.', '_');
// Do not run any polly pass on the new function.
return SubFn;
AllocaInst *
ParallelLoopGenerator::storeValuesIntoStruct(SetVector<Value *> &Values) {
SmallVector<Type *, 8> Members;
for (Value *V : Values)
const DataLayout &DL = Builder.GetInsertBlock()->getModule()->getDataLayout();
// We do not want to allocate the alloca inside any loop, thus we allocate it
// in the entry block of the function and use annotations to denote the actual
// live span (similar to clang).
BasicBlock &EntryBB = Builder.GetInsertBlock()->getParent()->getEntryBlock();
Instruction *IP = &*EntryBB.getFirstInsertionPt();
StructType *Ty = StructType::get(Builder.getContext(), Members);
AllocaInst *Struct = new AllocaInst(Ty, DL.getAllocaAddrSpace(), nullptr,
"polly.par.userContext", IP);
for (unsigned i = 0; i < Values.size(); i++) {
Value *Address = Builder.CreateStructGEP(Ty, Struct, i);
Address->setName("polly.subfn.storeaddr." + Values[i]->getName());
Builder.CreateStore(Values[i], Address);
return Struct;
void ParallelLoopGenerator::extractValuesFromStruct(
SetVector<Value *> OldValues, Type *Ty, Value *Struct, ValueMapT &Map) {
for (unsigned i = 0; i < OldValues.size(); i++) {
Value *Address = Builder.CreateStructGEP(Ty, Struct, i);
Value *NewValue = Builder.CreateLoad(Address);
NewValue->setName("polly.subfunc.arg." + OldValues[i]->getName());
Map[OldValues[i]] = NewValue;