[flang] [llvm] [flang] Enhance show_descriptor intrinsic to avoid extra copies and extra descriptor creation (PR #173461)

[Razvan Lupusoru via llvm-commits]

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@@ -7893,9 +7893,24 @@ void IntrinsicLibrary::genShowDescriptor(
   assert(args.size() == 1 && "expected single argument for show_descriptor");
   const mlir::Value descriptor = fir::getBase(args[0]);
 
-  assert(fir::isa_box_type(descriptor.getType()) &&
-         "argument must have been lowered to box type");
-  fir::runtime::genShowDescriptor(builder, loc, descriptor);
+  // If it's already a reference to a box, pass it directly.
+  if (fir::isa_ref_type(descriptor.getType()) &&
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razvanlupusoru wrote:

Could you also add a test where the descriptor being passed in is the member of a derived type? I am hopeful it falls into the "isa_ref_type" case here not the "isa_box_type" case below. Thank you :)

https://github.com/llvm/llvm-project/pull/173461