SPIRVConversion.h

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//===- SPIRVConversion.h - SPIR-V Conversion Utilities ----------*- 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
//
//===----------------------------------------------------------------------===//
//
// Defines utilities to use while converting to the SPIR-V dialect.
//
//===----------------------------------------------------------------------===//
 
#ifndef MLIR_DIALECT_SPIRV_TRANSFORMS_SPIRVCONVERSION_H
#define MLIR_DIALECT_SPIRV_TRANSFORMS_SPIRVCONVERSION_H
 
#include "mlir/Dialect/SPIRV/IR/SPIRVAttributes.h"
#include "mlir/Dialect/SPIRV/IR/SPIRVOps.h"
#include "mlir/Dialect/SPIRV/IR/SPIRVTypes.h"
#include "mlir/Dialect/SPIRV/IR/TargetAndABI.h"
#include "mlir/Dialect/Vector/Transforms/VectorRewritePatterns.h"
#include "mlir/Transforms/DialectConversion.h"
#include "mlir/Transforms/GreedyPatternRewriteDriver.h"
#include "mlir/Transforms/OneToNTypeConversion.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/Support/LogicalResult.h"
 
namespace mlir {
 
//===----------------------------------------------------------------------===//
// Type Converter
//===----------------------------------------------------------------------===//
 
/// How sub-byte values are storaged in memory.
enum class SPIRVSubByteTypeStorage {
  /// Sub-byte values are tightly packed without any padding, e.g., 4xi2 -> i8.
  Packed,
};
 
struct SPIRVConversionOptions {
  /// The number of bits to store a boolean value.
  unsigned boolNumBits{8};
 
  /// How sub-byte values are storaged in memory.
  SPIRVSubByteTypeStorage subByteTypeStorage{SPIRVSubByteTypeStorage::Packed};
 
  /// Whether to emulate narrower scalar types with 32-bit scalar types if not
  /// supported by the target.
  ///
  /// Non-32-bit scalar types require special hardware support that may not
  /// exist on all GPUs. This is reflected in SPIR-V as that non-32-bit scalar
  /// types require special capabilities or extensions. This option controls
  /// whether to use 32-bit types to emulate < 32-bits-wide scalars, if a scalar
  /// type of a certain bitwidth is not supported in the target environment.
  /// This requires the runtime to also feed in data with a matched bitwidth and
  /// layout for interface types. The runtime can do that by inspecting the
  /// SPIR-V module.
  ///
  /// If the original scalar type has less than 32-bit, a multiple of its
  /// values will be packed into one 32-bit value to be memory efficient.
  bool emulateLT32BitScalarTypes{true};
 
  /// Use 64-bit integers when converting index types.
  bool use64bitIndex{false};
};
 
/// Type conversion from builtin types to SPIR-V types for shader interface.
///
/// For memref types, this converter additionally performs type wrapping to
/// satisfy shader interface requirements: shader interface types must be
/// pointers to structs.
class SPIRVTypeConverter : public TypeConverter {
public:
  explicit SPIRVTypeConverter(spirv::TargetEnvAttr targetAttr,
                              const SPIRVConversionOptions &options = {});
 
  /// Gets the SPIR-V correspondence for the standard index type.
  Type getIndexType() const;
 
  /// Gets the bitwidth of the index type when converted to SPIR-V.
  unsigned getIndexTypeBitwidth() const {
    return options.use64bitIndex ? 64 : 32;
  }
 
  const spirv::TargetEnv &getTargetEnv() const { return targetEnv; }
 
  /// Returns the options controlling the SPIR-V type converter.
  const SPIRVConversionOptions &getOptions() const { return options; }
 
  /// Checks if the SPIR-V capability inquired is supported.
  bool allows(spirv::Capability capability) const;
 
private:
  spirv::TargetEnv targetEnv;
  SPIRVConversionOptions options;
 
  MLIRContext *getContext() const;
};
 
//===----------------------------------------------------------------------===//
// Conversion Target
//===----------------------------------------------------------------------===//
 
// The default SPIR-V conversion target.
//
// It takes a SPIR-V target environment and controls operation legality based on
// the their availability in the target environment.
class SPIRVConversionTarget : public ConversionTarget {
public:
  /// Creates a SPIR-V conversion target for the given target environment.
  static std::unique_ptr<SPIRVConversionTarget>
  get(spirv::TargetEnvAttr targetAttr);
 
private:
  explicit SPIRVConversionTarget(spirv::TargetEnvAttr targetAttr);
 
  // Be explicit that instance of this class cannot be copied or moved: there
  // are lambdas capturing fields of the instance.
  SPIRVConversionTarget(const SPIRVConversionTarget &) = delete;
  SPIRVConversionTarget(SPIRVConversionTarget &&) = delete;
  SPIRVConversionTarget &operator=(const SPIRVConversionTarget &) = delete;
  SPIRVConversionTarget &operator=(SPIRVConversionTarget &&) = delete;
 
  /// Returns true if the given `op` is legal to use under the current target
  /// environment.
  bool isLegalOp(Operation *op);
 
  spirv::TargetEnv targetEnv;
};
 
//===----------------------------------------------------------------------===//
// Patterns and Utility Functions
//===----------------------------------------------------------------------===//
 
/// Appends to a pattern list additional patterns for translating the builtin
/// `func` op to the SPIR-V dialect. These patterns do not handle shader
/// interface/ABI; they convert function parameters to be of SPIR-V allowed
/// types.
void populateBuiltinFuncToSPIRVPatterns(const SPIRVTypeConverter &typeConverter,
                                        RewritePatternSet &patterns);
 
void populateFuncOpVectorRewritePatterns(RewritePatternSet &patterns);
 
void populateReturnOpVectorRewritePatterns(RewritePatternSet &patterns);
 
namespace spirv {
class AccessChainOp;
 
/// Returns the value for the given `builtin` variable. This function gets or
/// inserts the global variable associated for the builtin within the nearest
/// symbol table enclosing `op`. Returns null Value on error.
///
/// The global name being generated will be mangled using `preffix` and
/// `suffix`.
Value getBuiltinVariableValue(Operation *op, BuiltIn builtin, Type integerType,
                              OpBuilder &builder,
                              StringRef prefix = "__builtin__",
                              StringRef suffix = "__");
 
/// Gets the value at the given `offset` of the push constant storage with a
/// total of `elementCount` `integerType` integers. A global variable will be
/// created in the nearest symbol table enclosing `op` for the push constant
/// storage if not existing. Load ops will be created via the given `builder` to
/// load values from the push constant. Returns null Value on error.
Value getPushConstantValue(Operation *op, unsigned elementCount,
                           unsigned offset, Type integerType,
                           OpBuilder &builder);
 
/// Generates IR to perform index linearization with the given `indices` and
/// their corresponding `strides`, adding an initial `offset`.
Value linearizeIndex(ValueRange indices, ArrayRef<int64_t> strides,
                     int64_t offset, Type integerType, Location loc,
                     OpBuilder &builder);
 
/// Performs the index computation to get to the element at `indices` of the
/// memory pointed to by `basePtr`, using the layout map of `baseType`.
/// Returns null if index computation cannot be performed.
 
// TODO: This method assumes that the `baseType` is a MemRefType with AffineMap
// that has static strides. Extend to handle dynamic strides.
Value getElementPtr(const SPIRVTypeConverter &typeConverter,
                    MemRefType baseType, Value basePtr, ValueRange indices,
                    Location loc, OpBuilder &builder);
 
// GetElementPtr implementation for Kernel/OpenCL flavored SPIR-V.
Value getOpenCLElementPtr(const SPIRVTypeConverter &typeConverter,
                          MemRefType baseType, Value basePtr,
                          ValueRange indices, Location loc, OpBuilder &builder);
 
// GetElementPtr implementation for Vulkan/Shader flavored SPIR-V.
Value getVulkanElementPtr(const SPIRVTypeConverter &typeConverter,
                          MemRefType baseType, Value basePtr,
                          ValueRange indices, Location loc, OpBuilder &builder);
 
// Find the largest factor of size among {2,3,4} for the lowest dimension of
// the target shape.
int getComputeVectorSize(int64_t size);
 
// GetNativeVectorShape implementation for reduction ops.
SmallVector<int64_t> getNativeVectorShapeImpl(vector::ReductionOp op);
 
// GetNativeVectorShape implementation for transpose ops.
SmallVector<int64_t> getNativeVectorShapeImpl(vector::TransposeOp op);
 
// For general ops.
std::optional<SmallVector<int64_t>> getNativeVectorShape(Operation *op);
 
// Unroll vectors in function signatures to native size.
LogicalResult unrollVectorsInSignatures(Operation *op);
 
// Unroll vectors in function bodies to native size.
LogicalResult unrollVectorsInFuncBodies(Operation *op);
 
} // namespace spirv
} // namespace mlir
 
#endif // MLIR_DIALECT_SPIRV_TRANSFORMS_SPIRVCONVERSION_H