[mlir][Func] Delete DecomposeCallGraphTypes.cpp (llvm#117424)

`DecomposeCallGraphTypes.cpp` was a workaround around missing 1:N
support in the dialect conversion. Now that 1:N support was added, the
workaround can be deleted. The test remains in place, as an example for
how to write such a transformation with the dialect conversion
framework.

Note for LLVM integration: If you are using
`DecomposeCallGraphTypes.cpp`, switch to the patterns that are used in
`TestDecomposeCallGraphTypes.cpp`.

mlir/lib/Dialect/Func/Transforms/CMakeLists.txt

@@ -1,5 +1,4 @@
 add_mlir_dialect_library(MLIRFuncTransforms
-  DecomposeCallGraphTypes.cpp
   DuplicateFunctionElimination.cpp
   FuncConversions.cpp
   OneToNFuncConversions.cpp

mlir/lib/Dialect/Func/Transforms/FuncConversions.cpp

@@ -124,12 +124,10 @@ class ReturnOpTypeConversion : public OpConversionPattern<ReturnOp> {
   using OpConversionPattern<ReturnOp>::OpConversionPattern;
 
   LogicalResult
-  matchAndRewrite(ReturnOp op, OpAdaptor adaptor,
+  matchAndRewrite(ReturnOp op, OneToNOpAdaptor adaptor,
                   ConversionPatternRewriter &rewriter) const final {
-    // For a return, all operands go to the results of the parent, so
-    // rewrite them all.
-    rewriter.modifyOpInPlace(op,
-                             [&] { op->setOperands(adaptor.getOperands()); });
+    rewriter.replaceOpWithNewOp<ReturnOp>(op,
+                                          flattenValues(adaptor.getOperands()));
     return success();
   }
 };

mlir/test/lib/Dialect/Func/TestDecomposeCallGraphTypes.cpp

@@ -9,7 +9,7 @@
 #include "TestDialect.h"
 #include "TestOps.h"
 #include "mlir/Dialect/Func/IR/FuncOps.h"
-#include "mlir/Dialect/Func/Transforms/DecomposeCallGraphTypes.h"
+#include "mlir/Dialect/Func/Transforms/FuncConversions.h"
 #include "mlir/IR/Builders.h"
 #include "mlir/Pass/Pass.h"
 #include "mlir/Transforms/DialectConversion.h"
@@ -142,7 +142,10 @@ struct TestDecomposeCallGraphTypes
     typeConverter.addArgumentMaterialization(buildMakeTupleOp);
     typeConverter.addTargetMaterialization(buildDecomposeTuple);
 
-    populateDecomposeCallGraphTypesPatterns(context, typeConverter, patterns);
+    populateFunctionOpInterfaceTypeConversionPattern<func::FuncOp>(
+        patterns, typeConverter);
+    populateReturnOpTypeConversionPattern(patterns, typeConverter);
+    populateCallOpTypeConversionPattern(patterns, typeConverter);
 
     if (failed(applyPartialConversion(module, target, std::move(patterns))))
       return signalPassFailure();