Re: [PATCH] stdlib/longlong.h: Remove lvalue to rvalue conversion

["Fāng-ruì Sòng" <maskray@google.com>]

On Mon, Oct 11, 2021 at 11:37 PM Florian Weimer <fw@deneb.enyo.de> wrote:
>
> * Fangrui Song via Libc-alpha:
>
> > An output constraint takes a lvalue. While GCC happily strips the
> > incorrect lvalue to rvalue conversion, Clang Clang rejects the code by
> > default:
> >
> >     error: invalid use of a cast in a inline asm context requiring an lvalue: remove the cast or build with -fheinous-gnu-extensions
>
> As I wrote on the gcc-patches list, these casts may be needed in a few
> cases.  Just removing them may not be entirely correct.

You meant https://gcc.gnu.org/pipermail/gcc-patches/2021-October/581265.html

"This seems to alter the meanining of existing programs if sh and sl do
not have the expected type.
I think you need to add a compound expression and temporaries of type
USItype if you want to avoid the cast."


I tested this on x86-64 and aarch64 and saw no new failure.
If the concern is with exotic architectures like arc which we don't
have a good story, I can drop changes to these exotic architectures.

In addition, using a compound statement sorta defeats the purpose to
simplify the code.