[mlir][index][spirv] Add conversion for index to spirv (#68085)

Due to an issue when lowering from scf to spirv as there was no
conversion pass for index to spirv, we are motivated to add a conversion
pass from the Index dialect to the SPIR-V dialect. Furthermore, we add
the new conversion patterns to the scf-to-spirv conversion.

Fixes #63713

Author: inbelic

mlir/include/mlir/Conversion/IndexToSPIRV/IndexToSPIRV.h

@@ -0,0 +1,30 @@
+//===- IndexToSPIRV.h - Index to SPIRV dialect conversion -------*- 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef MLIR_CONVERSION_INDEXTOSPIRV_INDEXTOSPIRV_H
+#define MLIR_CONVERSION_INDEXTOSPIRV_INDEXTOSPIRV_H
+
+#include "mlir/Pass/Pass.h"
+#include <memory>
+
+namespace mlir {
+class RewritePatternSet;
+class SPIRVTypeConverter;
+class Pass;
+
+#define GEN_PASS_DECL_CONVERTINDEXTOSPIRVPASS
+#include "mlir/Conversion/Passes.h.inc"
+
+namespace index {
+void populateIndexToSPIRVPatterns(SPIRVTypeConverter &converter,
+                                  RewritePatternSet &patterns);
+std::unique_ptr<OperationPass<>> createConvertIndexToSPIRVPass();
+} // namespace index
+} // namespace mlir
+
+#endif // MLIR_CONVERSION_INDEXTOSPIRV_INDEXTOSPIRV_H

mlir/include/mlir/Conversion/Passes.h

@@ -35,6 +35,7 @@
 #include "mlir/Conversion/GPUToSPIRV/GPUToSPIRVPass.h"
 #include "mlir/Conversion/GPUToVulkan/ConvertGPUToVulkanPass.h"
 #include "mlir/Conversion/IndexToLLVM/IndexToLLVM.h"
+#include "mlir/Conversion/IndexToSPIRV/IndexToSPIRV.h"
 #include "mlir/Conversion/LinalgToStandard/LinalgToStandard.h"
 #include "mlir/Conversion/MathToFuncs/MathToFuncs.h"
 #include "mlir/Conversion/MathToLLVM/MathToLLVM.h"

mlir/include/mlir/Conversion/Passes.td

@@ -644,6 +644,28 @@ def ConvertIndexToLLVMPass : Pass<"convert-index-to-llvm"> {
   ];
 }
 
+//===----------------------------------------------------------------------===//
+// ConvertIndexToSPIRVPass
+//===----------------------------------------------------------------------===//
+
+def ConvertIndexToSPIRVPass : Pass<"convert-index-to-spirv"> {
+  let summary = "Lower the `index` dialect to the `spirv` dialect.";
+  let description = [{
+    This pass lowers Index dialect operations to SPIR-V dialect operations.
+    Operation conversions are 1-to-1 except for the exotic divides: `ceildivs`,
+    `ceildivu`, and `floordivs`. The index bitwidth will be 32 or 64 as
+    specified by use-64bit-index.
+  }];
+
+  let dependentDialects = ["::mlir::spirv::SPIRVDialect"];
+
+  let options = [
+    Option<"use64bitIndex", "use-64bit-index",
+           "bool", /*default=*/"false",
+           "Use 64-bit integers to convert index types">
+  ];
+}
+
 //===----------------------------------------------------------------------===//
 // LinalgToStandard
 //===----------------------------------------------------------------------===//

mlir/include/mlir/Dialect/SPIRV/Transforms/SPIRVConversion.h

@@ -55,13 +55,13 @@ struct SPIRVConversionOptions {
   /// values will be packed into one 32-bit value to be memory efficient.
   bool emulateLT32BitScalarTypes{true};
 
-  /// Use 64-bit integers to convert index types.
-  bool use64bitIndex{false};
-
   /// Whether to enable fast math mode during conversion. If true, various
   /// patterns would assume no NaN/infinity numbers as inputs, and thus there
   /// will be no special guards emitted to check and handle such cases.
   bool enableFastMathMode{false};
+
+  /// Use 64-bit integers when converting index types.
+  bool use64bitIndex{false};
 };
 
 /// Type conversion from builtin types to SPIR-V types for shader interface.
@@ -77,6 +77,11 @@ class SPIRVTypeConverter : public TypeConverter {
   /// 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.

mlir/lib/Conversion/CMakeLists.txt

@@ -24,6 +24,7 @@ add_subdirectory(GPUToROCDL)
 add_subdirectory(GPUToSPIRV)
 add_subdirectory(GPUToVulkan)
 add_subdirectory(IndexToLLVM)
+add_subdirectory(IndexToSPIRV)
 add_subdirectory(LinalgToStandard)
 add_subdirectory(LLVMCommon)
 add_subdirectory(MathToFuncs)

mlir/lib/Conversion/IndexToSPIRV/CMakeLists.txt

@@ -0,0 +1,15 @@
+add_mlir_conversion_library(MLIRIndexToSPIRV
+  IndexToSPIRV.cpp
+
+  ADDITIONAL_HEADER_DIRS
+  ${MLIR_MAIN_INCLUDE_DIR}/mlir/Conversion/IndexToSPIRV
+
+  DEPENDS
+  MLIRConversionPassIncGen
+
+  LINK_COMPONENTS
+  Core
+
+  LINK_LIBS PUBLIC
+  MLIRIndexDialect
+  )