[mlir][Transforms] Fix replaceUsesOfBlockArgument API (#144706)

Before this PR, users had to pass the "old" block argument when
replacing the uses of a block argument in a newly converted block. Users
can now pass the actual block argument that should be replaced.

Note for LLVM integration: Make sure to pass the current block argument
instead of the old one.

Author: matthias-springer

mlir/lib/Conversion/FuncToLLVM/FuncToLLVM.cpp

@@ -295,7 +295,7 @@ static void restoreByValRefArgumentType(
         cast<TypeAttr>(byValRefAttr->getValue()).getValue());
 
     auto valueArg = rewriter.create<LLVM::LoadOp>(arg.getLoc(), resTy, arg);
-    rewriter.replaceUsesOfBlockArgument(oldArg, valueArg);
+    rewriter.replaceUsesOfBlockArgument(arg, valueArg);
   }
 }
 

mlir/lib/Transforms/Utils/DialectConversion.cpp

@@ -1743,7 +1743,7 @@ void ConversionPatternRewriter::replaceUsesOfBlockArgument(BlockArgument from,
   });
   impl->appendRewrite<ReplaceBlockArgRewrite>(from.getOwner(), from,
                                               impl->currentTypeConverter);
-  impl->mapping.map(impl->mapping.lookupOrDefault(from), to);
+  impl->mapping.map(from, to);
 }
 
 Value ConversionPatternRewriter::getRemappedValue(Value key) {