[MLIR][OpenMP] Add canonical loop LLVM-IR lowering (#147069)

Support for translating the operations introduced in #144785 to LLVM-IR.

In order to keep the lowering simple,
`OpenMPIRBuider::unrollLoopHeuristic` is applied when encountering the
`omp.unroll_heuristic` op. As a result, the operation that unrolling is
applied to (`omp.canonical_loop`) must have been emitted before even
though logically there is no such requirement.

Eventually, all transformations on a loop must be applied directly after
emitting `omp.canonical_loop`, i.e. future transformations must be
looked-up when encountering `omp.canonical_loop` itself. This is because
many OpenMPIRBuilder methods (e.g. `createParallel`) expect all the
region code to be emitted withing a callback. In the case of
`createParallel`, the region code is getting outlined into a new
function. Therefore, making the operation order a formal requirement
would not make the implementation any easier.

1 files changed, 10 insertions, 0 deletions

diff --git a/mlir/lib/Conversion/OpenMPToLLVM/OpenMPToLLVM.cpp b/mlir/lib/Conversion/OpenMPToLLVM/OpenMPToLLVM.cpp
index 77a2708..7ac9687 100644
--- a/mlir/lib/Conversion/OpenMPToLLVM/OpenMPToLLVM.cpp
+++ b/mlir/lib/Conversion/OpenMPToLLVM/OpenMPToLLVM.cpp
@@ -41,6 +41,16 @@ template <typename T>
 struct OpenMPOpConversion : public ConvertOpToLLVMPattern<T> {
   using ConvertOpToLLVMPattern<T>::ConvertOpToLLVMPattern;
 
+  OpenMPOpConversion(LLVMTypeConverter &typeConverter,
+                     PatternBenefit benefit = 1)
+      : ConvertOpToLLVMPattern<T>(typeConverter, benefit) {
+    // Operations using CanonicalLoopInfoType are lowered only by
+    // mlir::translateModuleToLLVMIR() using the OpenMPIRBuilder. Until then,
+    // the type and operations using it must be preserved.
+    typeConverter.addConversion(
+        [&](::mlir::omp::CanonicalLoopInfoType type) { return type; });
+  }
+
   LogicalResult
   matchAndRewrite(T op, typename T::Adaptor adaptor,
                   ConversionPatternRewriter &rewriter) const override {