llvm/mlir/lib/Conversion/SCFToOpenMP/SCFToOpenMP.cpp

//===- SCFToOpenMP.cpp - Structured Control Flow to OpenMP conversion -----===//
//
// 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 implements a pass to convert scf.parallel operations into OpenMP
// parallel loops.
//
//===----------------------------------------------------------------------===//

#include "mlir/Conversion/SCFToOpenMP/SCFToOpenMP.h"

#include "mlir/Analysis/SliceAnalysis.h"
#include "mlir/Dialect/Affine/Analysis/LoopAnalysis.h"
#include "mlir/Dialect/Arith/IR/Arith.h"
#include "mlir/Dialect/LLVMIR/LLVMDialect.h"
#include "mlir/Dialect/MemRef/IR/MemRef.h"
#include "mlir/Dialect/OpenMP/OpenMPDialect.h"
#include "mlir/Dialect/SCF/IR/SCF.h"
#include "mlir/IR/ImplicitLocOpBuilder.h"
#include "mlir/IR/SymbolTable.h"
#include "mlir/Pass/Pass.h"
#include "mlir/Transforms/DialectConversion.h"

namespace mlir {
#define GEN_PASS_DEF_CONVERTSCFTOOPENMPPASS
#include "mlir/Conversion/Passes.h.inc"
} // namespace mlir

usingnamespacemlir;

/// Matches a block containing a "simple" reduction. The expected shape of the
/// block is as follows.
///
///   ^bb(%arg0, %arg1):
///     %0 = OpTy(%arg0, %arg1)
///     scf.reduce.return %0
template <typename... OpTy>
static bool matchSimpleReduction(Block &block) { … }

/// Matches a block containing a select-based min/max reduction. The types of
/// select and compare operations are provided as template arguments. The
/// comparison predicates suitable for min and max are provided as function
/// arguments. If a reduction is matched, `ifMin` will be set if the reduction
/// compute the minimum and unset if it computes the maximum, otherwise it
/// remains unmodified. The expected shape of the block is as follows.
///
///   ^bb(%arg0, %arg1):
///     %0 = CompareOpTy(<one-of-predicates>, %arg0, %arg1)
///     %1 = SelectOpTy(%0, %arg0, %arg1)  // %arg0, %arg1 may be swapped here.
///     scf.reduce.return %1
template <
    typename CompareOpTy, typename SelectOpTy,
    typename Predicate = decltype(std::declval<CompareOpTy>().getPredicate())>
static bool
matchSelectReduction(Block &block, ArrayRef<Predicate> lessThanPredicates,
                     ArrayRef<Predicate> greaterThanPredicates, bool &isMin) { … }

/// Returns the float semantics for the given float type.
static const llvm::fltSemantics &fltSemanticsForType(FloatType type) { … }

/// Returns an attribute with the minimum (if `min` is set) or the maximum value
/// (otherwise) for the given float type.
static Attribute minMaxValueForFloat(Type type, bool min) { … }

/// Returns an attribute with the signed integer minimum (if `min` is set) or
/// the maximum value (otherwise) for the given integer type, regardless of its
/// signedness semantics (only the width is considered).
static Attribute minMaxValueForSignedInt(Type type, bool min) { … }

/// Returns an attribute with the unsigned integer minimum (if `min` is set) or
/// the maximum value (otherwise) for the given integer type, regardless of its
/// signedness semantics (only the width is considered).
static Attribute minMaxValueForUnsignedInt(Type type, bool min) { … }

/// Creates an OpenMP reduction declaration and inserts it into the provided
/// symbol table. The declaration has a constant initializer with the neutral
/// value `initValue`, and the `reductionIndex`-th reduction combiner carried
/// over from `reduce`.
static omp::DeclareReductionOp
createDecl(PatternRewriter &builder, SymbolTable &symbolTable,
           scf::ReduceOp reduce, int64_t reductionIndex, Attribute initValue) { … }

/// Adds an atomic reduction combiner to the given OpenMP reduction declaration
/// using llvm.atomicrmw of the given kind.
static omp::DeclareReductionOp addAtomicRMW(OpBuilder &builder,
                                            LLVM::AtomicBinOp atomicKind,
                                            omp::DeclareReductionOp decl,
                                            scf::ReduceOp reduce,
                                            int64_t reductionIndex) { … }

/// Creates an OpenMP reduction declaration that corresponds to the given SCF
/// reduction and returns it. Recognizes common reductions in order to identify
/// the neutral value, necessary for the OpenMP declaration. If the reduction
/// cannot be recognized, returns null.
static omp::DeclareReductionOp declareReduction(PatternRewriter &builder,
                                                scf::ReduceOp reduce,
                                                int64_t reductionIndex) { … }

namespace {

struct ParallelOpLowering : public OpRewritePattern<scf::ParallelOp> { … };

/// Applies the conversion patterns in the given function.
static LogicalResult applyPatterns(ModuleOp module, unsigned numThreads) { … }

/// A pass converting SCF operations to OpenMP operations.
struct SCFToOpenMPPass
    : public impl::ConvertSCFToOpenMPPassBase<SCFToOpenMPPass> { … };

} // namespace