[mlir][OpenMP] Implement the ConvertToLLVMPatternInterface

[fabianmcg]

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

[llvmbot]

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@llvm/pr-subscribers-flang-openmp

Author: Fabian Mora (fabianmcg)

Changes

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

---

Full diff: https://github.com/llvm/llvm-project/pull/101997.diff

4 Files Affected:

• (modified) mlir/include/mlir/Conversion/OpenMPToLLVM/ConvertOpenMPToLLVM.h (+5)
• (modified) mlir/include/mlir/InitAllExtensions.h (+2)
• (modified) mlir/lib/Conversion/OpenMPToLLVM/OpenMPToLLVM.cpp (+29)
• (modified) mlir/test/Conversion/OpenMPToLLVM/convert-to-llvmir.mlir (+1)

diff --git a/mlir/include/mlir/Conversion/OpenMPToLLVM/ConvertOpenMPToLLVM.h b/mlir/include/mlir/Conversion/OpenMPToLLVM/ConvertOpenMPToLLVM.h
index 2ed077f8f83e9..808586074c536 100644
--- a/mlir/include/mlir/Conversion/OpenMPToLLVM/ConvertOpenMPToLLVM.h
+++ b/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(ConversionTarget &target,
 /// 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
diff --git a/mlir/include/mlir/InitAllExtensions.h b/mlir/include/mlir/InitAllExtensions.h
index 20a4ab6f18a28..91b3cc160eb62 100644
--- a/mlir/include/mlir/InitAllExtensions.h
+++ b/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"
@@ -64,6 +65,7 @@ inline void registerAllExtensions(DialectRegistry &registry) {
   registerConvertMathToLLVMInterface(registry);
   registerConvertMemRefToLLVMInterface(registry);
   registerConvertNVVMToLLVMInterface(registry);
+  registerConvertOpenMPToLLVMInterface(registry);
   ub::registerConvertUBToLLVMInterface(registry);
 
   // Register all transform dialect extensions.
diff --git a/mlir/lib/Conversion/OpenMPToLLVM/OpenMPToLLVM.cpp b/mlir/lib/Conversion/OpenMPToLLVM/OpenMPToLLVM.cpp
index f6a6d1d7228a0..68d4e1b34d065 100644
--- a/mlir/lib/Conversion/OpenMPToLLVM/OpenMPToLLVM.cpp
+++ b/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"
@@ -307,3 +308,31 @@ 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>();
+  });
+}
diff --git a/mlir/test/Conversion/OpenMPToLLVM/convert-to-llvmir.mlir b/mlir/test/Conversion/OpenMPToLLVM/convert-to-llvmir.mlir
index d81487daf34f6..e7cb3d15f861e 100644
--- a/mlir/test/Conversion/OpenMPToLLVM/convert-to-llvmir.mlir
+++ b/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)

[kiranchandramohan]

@fabianmcg This would need an RFC. And you might want to tag Mehdi and Alex Zinenko.

[fabianmcg]

@kiranchandramohan I can do an RFC.
However, I didn't think there was a need because this is a pretty small change. Many upstream dialects already implement this interface, for example: arith, complex, cf, func, index, nvvm, math, memref, ub. Also, many dialects that don't have it, is simply because no one has implemented it.

This interface simply removes the necessity of invoking convert-openmp-to-llvm in production pipelines and allows using instead convert-to-llvm.

[kiranchandramohan]

Thanks for the details @fabianmcg. The only question is whether there will be a confusion here because other conversions (of arith, memref etc) fully convert to LLVM dialect whereas OpenMP only converts the types and retains the OpenMP operations.

[fabianmcg]

The only question is whether there will be a confusion here because other conversions (of arith, memref etc) fully convert to LLVM dialect whereas OpenMP only converts the types and retains the OpenMP operations.

Not likely, this interface only picks up upstream OpenMP to LLVM patterns (the exact same patterns as ConvertOpenMPToLLVM), hence users shouldn't expect different behavior.

I'll also say that this is a pretty overridable change. For example, if one day a downstream user creates explicit lowerings to LLVM, they can implement the ToLLVM interface and substitute the registration call with theirs and the convert-to-llvm pass would use the downstream implementation. What I'm trying to say, is that this change is pretty localized to upstream MLIR.

[kiranchandramohan]

LG. Please wait a couple of days before you submit.

[kiranchandramohan]

reverse ping.

[fabianmcg]

Apologies @kiranchandramohan I was busy with school and missed the approval. I rebased the PR just to check it again (locally everything seemed to pass). As soon as it passes I'll merge it.