[mlir][OpenMP] Implement the ConvertToLLVMPatternInterface (#101997)

This patch implements the `ConvertToLLVMPatternInterface` for the OpenMP
dialect, allowing `convert-to-llvm` to act on the OpenMP dialect.

Author: fabianmcg

mlir/include/mlir/Conversion/OpenMPToLLVM/ConvertOpenMPToLLVM.h

@@ -11,6 +11,7 @@
 #include <memory>
 
 namespace mlir {
+class DialectRegistry;
 class LLVMTypeConverter;
 class ConversionTarget;
 class MLIRContext;
@@ -28,6 +29,10 @@ void configureOpenMPToLLVMConversionLegality(
 /// Populate the given list with patterns that convert from OpenMP to LLVM.
 void populateOpenMPToLLVMConversionPatterns(LLVMTypeConverter &converter,
                                             RewritePatternSet &patterns);
+
+/// Registers the `ConvertToLLVMPatternInterface` interface in the `OpenMP`
+/// dialect.
+void registerConvertOpenMPToLLVMInterface(DialectRegistry &registry);
 } // namespace mlir
 
 #endif // MLIR_CONVERSION_OPENMPTOLLVM_CONVERTOPENMPTOLLVM_H

mlir/include/mlir/InitAllExtensions.h

@@ -22,6 +22,7 @@
 #include "mlir/Conversion/MathToLLVM/MathToLLVM.h"
 #include "mlir/Conversion/MemRefToLLVM/MemRefToLLVM.h"
 #include "mlir/Conversion/NVVMToLLVM/NVVMToLLVM.h"
+#include "mlir/Conversion/OpenMPToLLVM/ConvertOpenMPToLLVM.h"
 #include "mlir/Conversion/UBToLLVM/UBToLLVM.h"
 #include "mlir/Dialect/Affine/TransformOps/AffineTransformOps.h"
 #include "mlir/Dialect/Bufferization/TransformOps/BufferizationTransformOps.h"
@@ -67,6 +68,7 @@ inline void registerAllExtensions(DialectRegistry &registry) {
   registerConvertMathToLLVMInterface(registry);
   registerConvertMemRefToLLVMInterface(registry);
   registerConvertNVVMToLLVMInterface(registry);
+  registerConvertOpenMPToLLVMInterface(registry);
   ub::registerConvertUBToLLVMInterface(registry);
 
   // Register all transform dialect extensions.

mlir/lib/Conversion/OpenMPToLLVM/OpenMPToLLVM.cpp

@@ -10,6 +10,7 @@
 
 #include "mlir/Conversion/ArithToLLVM/ArithToLLVM.h"
 #include "mlir/Conversion/ControlFlowToLLVM/ControlFlowToLLVM.h"
+#include "mlir/Conversion/ConvertToLLVM/ToLLVMInterface.h"
 #include "mlir/Conversion/FuncToLLVM/ConvertFuncToLLVM.h"
 #include "mlir/Conversion/FuncToLLVM/ConvertFuncToLLVMPass.h"
 #include "mlir/Conversion/LLVMCommon/ConversionTarget.h"
@@ -314,3 +315,31 @@ void ConvertOpenMPToLLVMPass::runOnOperation() {
   if (failed(applyPartialConversion(module, target, std::move(patterns))))
     signalPassFailure();
 }
+
+//===----------------------------------------------------------------------===//
+// ConvertToLLVMPatternInterface implementation
+//===----------------------------------------------------------------------===//
+namespace {
+/// Implement the interface to convert OpenMP to LLVM.
+struct OpenMPToLLVMDialectInterface : public ConvertToLLVMPatternInterface {
+  using ConvertToLLVMPatternInterface::ConvertToLLVMPatternInterface;
+  void loadDependentDialects(MLIRContext *context) const final {
+    context->loadDialect<LLVM::LLVMDialect>();
+  }
+
+  /// Hook for derived dialect interface to provide conversion patterns
+  /// and mark dialect legal for the conversion target.
+  void populateConvertToLLVMConversionPatterns(
+      ConversionTarget &target, LLVMTypeConverter &typeConverter,
+      RewritePatternSet &patterns) const final {
+    configureOpenMPToLLVMConversionLegality(target, typeConverter);
+    populateOpenMPToLLVMConversionPatterns(typeConverter, patterns);
+  }
+};
+} // namespace
+
+void mlir::registerConvertOpenMPToLLVMInterface(DialectRegistry &registry) {
+  registry.addExtension(+[](MLIRContext *ctx, omp::OpenMPDialect *dialect) {
+    dialect->addInterfaces<OpenMPToLLVMDialectInterface>();
+  });
+}

mlir/lib/Dialect/OpenMP/IR/OpenMPDialect.cpp

@@ -11,6 +11,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "mlir/Dialect/OpenMP/OpenMPDialect.h"
+#include "mlir/Conversion/ConvertToLLVM/ToLLVMInterface.h"
 #include "mlir/Dialect/Func/IR/FuncOps.h"
 #include "mlir/Dialect/LLVMIR/LLVMTypes.h"
 #include "mlir/Dialect/OpenACCMPCommon/Interfaces/AtomicInterfaces.h"
@@ -83,6 +84,8 @@ void OpenMPDialect::initialize() {
 #include "mlir/Dialect/OpenMP/OpenMPOpsTypes.cpp.inc"
       >();
 
+  declarePromisedInterface<ConvertToLLVMPatternInterface, OpenMPDialect>();
+
   MemRefType::attachInterface<MemRefPointerLikeModel>(*getContext());
   LLVM::LLVMPointerType::attachInterface<LLVMPointerPointerLikeModel>(
       *getContext());

mlir/test/Conversion/OpenMPToLLVM/convert-to-llvmir.mlir

@@ -1,4 +1,5 @@
 // RUN: mlir-opt -convert-openmp-to-llvm -split-input-file %s | FileCheck %s
+// RUN: mlir-opt -convert-to-llvm -split-input-file %s | FileCheck %s
 
 // CHECK-LABEL: llvm.func @foo(i64, i64)
 func.func private @foo(index, index)