//===- LoopGenerators.h - IR helper to create loops -------------*- 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
//
//===----------------------------------------------------------------------===//
//
// This file contains functions to create scalar and OpenMP parallel loops
// as LLVM-IR.
//
//===----------------------------------------------------------------------===//
#ifndef POLLY_LOOP_GENERATORS_H
#define POLLY_LOOP_GENERATORS_H
#include "polly/CodeGen/IRBuilder.h"
#include "polly/Support/ScopHelper.h"
#include "llvm/ADT/SetVector.h"
namespace polly {
using llvm::AllocaInst;
using llvm::BasicBlock;
using llvm::DataLayout;
using llvm::DominatorTree;
using llvm::Function;
using llvm::ICmpInst;
using llvm::LoopInfo;
using llvm::Module;
using llvm::SetVector;
using llvm::Type;
using llvm::Value;
/// General scheduling types of parallel OpenMP for loops.
/// Initialization values taken from OpenMP's enum in kmp.h: sched_type.
/// Currently, only 'static' scheduling may change from chunked to non-chunked.
enum class OMPGeneralSchedulingType {
StaticChunked = 33,
StaticNonChunked = 34,
Dynamic = 35,
Guided = 36,
Runtime = 37
};
extern int PollyNumThreads;
extern OMPGeneralSchedulingType PollyScheduling;
extern int PollyChunkSize;
/// Create a scalar do/for-style loop.
///
/// @param LowerBound The starting value of the induction variable.
/// @param UpperBound The upper bound of the induction variable.
/// @param Stride The value by which the induction variable
/// is incremented.
///
/// @param Builder The builder used to create the loop.
/// @param P A pointer to the pass that uses this function.
/// It is used to update analysis information.
/// @param LI The loop info for the current function
/// @param DT The dominator tree we need to update
/// @param ExitBlock The block the loop will exit to.
/// @param Predicate The predicate used to generate the upper loop
/// bound.
/// @param Annotator This function can (optionally) take
/// a ScopAnnotator which
/// annotates loops and alias information in the SCoP.
/// @param Parallel If this loop should be marked parallel in
/// the Annotator.
/// @param UseGuard Create a guard in front of the header to check if
/// the loop is executed at least once, otherwise just
/// assume it.
/// @param LoopVectDisabled If the Loop vectorizer should be disabled for this
/// loop.
///
/// @return Value* The newly created induction variable for this loop.
Value *createLoop(Value *LowerBound, Value *UpperBound, Value *Stride,
PollyIRBuilder &Builder, LoopInfo &LI, DominatorTree &DT,
BasicBlock *&ExitBlock, ICmpInst::Predicate Predicate,
ScopAnnotator *Annotator = nullptr, bool Parallel = false,
bool UseGuard = true, bool LoopVectDisabled = false);
/// Create a DebugLoc representing generated instructions.
///
/// The IR verifier requires !dbg metadata to be set in some situations. For
/// instance, if an (inlinable) function has debug info, all its call site must
/// have debug info as well.
llvm::DebugLoc createDebugLocForGeneratedCode(Function *F);
/// The ParallelLoopGenerator allows to create parallelized loops
///
/// To parallelize a loop, we perform the following steps:
/// o Generate a subfunction which will hold the loop body.
/// o Create a struct to hold all outer values needed in the loop body.
/// o Create calls to a runtime library to achieve the actual parallelism.
/// These calls will spawn and join threads, define how the work (here the
/// iterations) are distributed between them and make sure each has access
/// to the struct holding all needed values.
///
/// At the moment we support only one parallel runtime, OpenMP.
///
/// If we parallelize the outer loop of the following loop nest,
///
/// S0;
/// for (int i = 0; i < N; i++)
/// for (int j = 0; j < M; j++)
/// S1(i, j);
/// S2;
///
/// we will generate the following code (with different runtime function names):
///
/// S0;
/// auto *values = storeValuesIntoStruct();
/// // Execute subfunction with multiple threads
/// spawn_threads(subfunction, values);
/// join_threads();
/// S2;
///
/// // This function is executed in parallel by different threads
/// void subfunction(values) {
/// while (auto *WorkItem = getWorkItem()) {
/// int LB = WorkItem.begin();
/// int UB = WorkItem.end();
/// for (int i = LB; i < UB; i++)
/// for (int j = 0; j < M; j++)
/// S1(i, j);
/// }
/// cleanup_thread();
/// }
class ParallelLoopGenerator {
public:
/// Create a parallel loop generator for the current function.
ParallelLoopGenerator(PollyIRBuilder &Builder, LoopInfo &LI,
DominatorTree &DT, const DataLayout &DL)
: Builder(Builder), LI(LI), DT(DT),
LongType(
Type::getIntNTy(Builder.getContext(), DL.getPointerSizeInBits())),
M(Builder.GetInsertBlock()->getParent()->getParent()),
DLGenerated(createDebugLocForGeneratedCode(
Builder.GetInsertBlock()->getParent())) {}
virtual ~ParallelLoopGenerator() {}
/// Create a parallel loop.
///
/// This function is the main function to automatically generate a parallel
/// loop with all its components.
///
/// @param LB The lower bound for the loop we parallelize.
/// @param UB The upper bound for the loop we parallelize.
/// @param Stride The stride of the loop we parallelize.
/// @param Values A set of LLVM-IR Values that should be available in
/// the new loop body.
/// @param VMap A map to allow outside access to the new versions of
/// the values in @p Values.
/// @param LoopBody A pointer to an iterator that is set to point to the
/// body of the created loop. It should be used to insert
/// instructions that form the actual loop body.
///
/// @return The newly created induction variable for this loop.
Value *createParallelLoop(Value *LB, Value *UB, Value *Stride,
SetVector<Value *> &Values, ValueMapT &VMap,
BasicBlock::iterator *LoopBody);
protected:
/// The IR builder we use to create instructions.
PollyIRBuilder &Builder;
/// The loop info of the current function we need to update.
LoopInfo &LI;
/// The dominance tree of the current function we need to update.
DominatorTree &DT;
/// The type of a "long" on this hardware used for backend calls.
Type *LongType;
/// The current module
Module *M;
/// Debug location for generated code without direct link to any specific
/// line.
///
/// We only set the DebugLoc where the IR Verifier requires us to. Otherwise,
/// absent debug location for optimized code should be fine.
llvm::DebugLoc DLGenerated;
public:
/// Create a struct for all @p Values and store them in there.
///
/// @param Values The values which should be stored in the struct.
///
/// @return The created struct.
AllocaInst *storeValuesIntoStruct(SetVector<Value *> &Values);
/// Extract all values from the @p Struct and construct the mapping.
///
/// @param Values The values which were stored in the struct.
/// @param Struct The struct holding all the values in @p Values.
/// @param VMap A map to associate every element of @p Values with the
/// new llvm value loaded from the @p Struct.
void extractValuesFromStruct(SetVector<Value *> Values, Type *Ty,
Value *Struct, ValueMapT &VMap);
/// Create the definition of the parallel subfunction.
///
/// @return A pointer to the subfunction.
Function *createSubFnDefinition();
/// Create the runtime library calls for spawn and join of the worker threads.
/// Additionally, places a call to the specified subfunction.
///
/// @param SubFn The subfunction which holds the loop body.
/// @param SubFnParam The parameter for the subfunction (basically the struct
/// filled with the outside values).
/// @param LB The lower bound for the loop we parallelize.
/// @param UB The upper bound for the loop we parallelize.
/// @param Stride The stride of the loop we parallelize.
virtual void deployParallelExecution(Function *SubFn, Value *SubFnParam,
Value *LB, Value *UB, Value *Stride) = 0;
/// Prepare the definition of the parallel subfunction.
/// Creates the argument list and names them (as well as the subfunction).
///
/// @param F A pointer to the (parallel) subfunction's parent function.
///
/// @return The pointer to the (parallel) subfunction.
virtual Function *prepareSubFnDefinition(Function *F) const = 0;
/// Create the parallel subfunction.
///
/// @param Stride The induction variable increment.
/// @param Struct A struct holding all values in @p Values.
/// @param Values A set of LLVM-IR Values that should be available in
/// the new loop body.
/// @param VMap A map to allow outside access to the new versions of
/// the values in @p Values.
/// @param SubFn The newly created subfunction is returned here.
///
/// @return The newly created induction variable.
virtual std::tuple<Value *, Function *>
createSubFn(Value *Stride, AllocaInst *Struct, SetVector<Value *> UsedValues,
ValueMapT &VMap) = 0;
};
} // end namespace polly
#endif