[mlir][index] Add convert-index-to-llvm pass

This patch adds a lowering pass to convert `index` dialect ops to LLVM.

Depends on D135694

Reviewed By: rriddle

Differential Revision: https://reviews.llvm.org/D135697

Author: Jeff Niu

mlir/include/mlir/Conversion/IndexToLLVM/IndexToLLVM.h

@@ -0,0 +1,28 @@
+//===- IndexToLLVM.h - Index to LLVM 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_INDEXTOLLVM_INDEXTOLLVM_H
+#define MLIR_CONVERSION_INDEXTOLLVM_INDEXTOLLVM_H
+
+#include <memory>
+
+namespace mlir {
+class LLVMTypeConverter;
+class RewritePatternSet;
+class Pass;
+
+#define GEN_PASS_DECL_CONVERTINDEXTOLLVMPASS
+#include "mlir/Conversion/Passes.h.inc"
+
+namespace index {
+void populateIndexToLLVMConversionPatterns(LLVMTypeConverter &converter,
+                                           RewritePatternSet &patterns);
+} // namespace index
+} // namespace mlir
+
+#endif // MLIR_CONVERSION_INDEXTOLLVM_INDEXTOLLVM_H

mlir/include/mlir/Conversion/Passes.h

@@ -29,6 +29,7 @@
 #include "mlir/Conversion/GPUToROCDL/GPUToROCDLPass.h"
 #include "mlir/Conversion/GPUToSPIRV/GPUToSPIRVPass.h"
 #include "mlir/Conversion/GPUToVulkan/ConvertGPUToVulkanPass.h"
+#include "mlir/Conversion/IndexToLLVM/IndexToLLVM.h"
 #include "mlir/Conversion/LinalgToLLVM/LinalgToLLVM.h"
 #include "mlir/Conversion/LinalgToSPIRV/LinalgToSPIRVPass.h"
 #include "mlir/Conversion/LinalgToStandard/LinalgToStandard.h"

mlir/include/mlir/Conversion/Passes.td

@@ -439,6 +439,29 @@ def ConvertVulkanLaunchFuncToVulkanCalls
   let dependentDialects = ["LLVM::LLVMDialect"];
 }
 
+//===----------------------------------------------------------------------===//
+// ConvertIndexToLLVMPass
+//===----------------------------------------------------------------------===//
+
+def ConvertIndexToLLVMPass : Pass<"convert-index-to-llvm"> {
+  let summary = "Lower the `index` dialect to the `llvm` dialect.";
+  let description = [{
+    This pass lowers Index dialect operations to LLVM dialect operations.
+    Operation conversions are 1-to-1 except for the exotic divides: `ceildivs`,
+    `ceildivu`, and `floordivs`, which expand to series of LLVM operations.
+    Importantly, the index bitwidth should be correctly set to the target
+    pointer width via `index-bitwidth`.
+  }];
+
+  let dependentDialects = ["::mlir::LLVM::LLVMDialect"];
+
+  let options = [
+    Option<"indexBitwidth", "index-bitwidth", "unsigned",
+           /*default=kDeriveIndexBitwidthFromDataLayout*/"0",
+           "Bitwidth of the index type, 0 to use size of machine word">,
+  ];
+}
+
 //===----------------------------------------------------------------------===//
 // LinalgToLLVM
 //===----------------------------------------------------------------------===//

mlir/lib/Conversion/CMakeLists.txt

@@ -17,6 +17,7 @@ add_subdirectory(GPUToNVVM)
 add_subdirectory(GPUToROCDL)
 add_subdirectory(GPUToSPIRV)
 add_subdirectory(GPUToVulkan)
+add_subdirectory(IndexToLLVM)
 add_subdirectory(LinalgToLLVM)
 add_subdirectory(LinalgToSPIRV)
 add_subdirectory(LinalgToStandard)

mlir/lib/Conversion/IndexToLLVM/CMakeLists.txt

@@ -0,0 +1,17 @@
+add_mlir_conversion_library(MLIRIndexToLLVM
+  IndexToLLVM.cpp
+
+  ADDITIONAL_HEADER_DIRS
+  ${MLIR_MAIN_INCLUDE_DIR}/mlir/Conversion/IndexToLLVM
+
+  DEPENDS
+  MLIRConversionPassIncGen
+
+  LINK_COMPONENTS
+  Core
+
+  LINK_LIBS PUBLIC
+  MLIRIndexDialect
+  MLIRLLVMCommonConversion
+  MLIRLLVMDialect
+  )