[mlir][IR] Add SingleBlock trait to ModuleOp/GPUModuleOp

The region is already declared as `SizedRegion<1>`, but this will add an additional `getBlock()` convenience function to `ModuleOp`.

Author: matthias-springer

flang/lib/Lower/OpenMP/DataSharingProcessor.cpp

@@ -478,8 +478,7 @@ void DataSharingProcessor::doPrivatize(const semantics::Symbol *sym,
       return existingPrivatizer;
 
     mlir::OpBuilder::InsertionGuard guard(firOpBuilder);
-    firOpBuilder.setInsertionPoint(&moduleOp.getBodyRegion().front(),
-                                   moduleOp.getBodyRegion().front().begin());
+    firOpBuilder.setInsertionPointToStart(moduleOp.getBody());
     auto result = firOpBuilder.create<mlir::omp::PrivateClauseOp>(
         symLoc, uniquePrivatizerName, symType,
         isFirstPrivate ? mlir::omp::DataSharingClauseType::FirstPrivate

mlir/lib/Conversion/BufferizationToMemRef/BufferizationToMemRef.cpp

@@ -134,8 +134,7 @@ struct BufferizationToMemRefPass
 
     bufferization::DeallocHelperMap deallocHelperFuncMap;
     if (auto module = dyn_cast<ModuleOp>(getOperation())) {
-      OpBuilder builder =
-          OpBuilder::atBlockBegin(&module.getBodyRegion().front());
+      OpBuilder builder = OpBuilder::atBlockBegin(module.getBody());
 
       // Build dealloc helper function if there are deallocs.
       getOperation()->walk([&](bufferization::DeallocOp deallocOp) {

mlir/lib/Dialect/Bufferization/Transforms/LowerDeallocations.cpp

@@ -391,8 +391,7 @@ struct LowerDeallocationsPass
 
     bufferization::DeallocHelperMap deallocHelperFuncMap;
     if (auto module = dyn_cast<ModuleOp>(getOperation())) {
-      OpBuilder builder =
-          OpBuilder::atBlockBegin(&module.getBodyRegion().front());
+      OpBuilder builder = OpBuilder::atBlockBegin(module.getBody());
 
       // Build dealloc helper function if there are deallocs.
       getOperation()->walk([&](bufferization::DeallocOp deallocOp) {

mlir/lib/Dialect/SparseTensor/Transforms/SparseGPUCodegen.cpp

@@ -58,7 +58,7 @@ static gpu::GPUModuleOp genGPUModule(OpBuilder &builder, ModuleOp topModule) {
   for (auto op : topModule.getBodyRegion().getOps<gpu::GPUModuleOp>())
     return op; // existing
   markAsGPUContainer(topModule);
-  builder.setInsertionPointToStart(&topModule.getBodyRegion().front());
+  builder.setInsertionPointToStart(topModule.getBody());
   return builder.create<gpu::GPUModuleOp>(topModule->getLoc(),
                                           "sparse_kernels");
 }
@@ -75,7 +75,7 @@ static gpu::GPUFuncOp genGPUFunc(OpBuilder &builder, gpu::GPUModuleOp gpuModule,
     ("kernel" + Twine(kernelNumber++)).toStringRef(kernelName);
   } while (gpuModule.lookupSymbol(kernelName));
   // Then we insert a new kernel with given arguments into the module.
-  builder.setInsertionPointToStart(&gpuModule.getBodyRegion().front());
+  builder.setInsertionPointToStart(gpuModule.getBody());
   SmallVector<Type> argsTp;
   for (auto arg : args)
     argsTp.push_back(arg.getType());