Re: more macOS Clang assume warnings

[Paul Eggert <eggert@cs.ucla.edu>]

On 8/24/20 11:54 AM, Mattias Engdegård wrote:
> The latest assume reformulation caused several warnings like the following when building with Clang:
> 
> ../../emacs/src/xwidget.h:171:72: warning: control reaches end of non-void
>        function [-Wreturn-type]
> INLINE struct xwidget *lookup_xwidget (Lisp_Object obj) { eassume (0); }
>                                                                         ^
> ../../emacs/src/eval.c:1571:1: warning: function declared 'noreturn' should not
>        return [-Winvalid-noreturn]
> }
> ^
> 
> This is with Apple clang version 11.0.0 (clang-1100.0.33.17) but it looks like the same applies to clang trunk.

Thanks for reporting that. I can reproduce the problem with Clang 9.0.1 on 
Fedora 31. For the program at the end of this message, 'clang -O2 -Wall' 
incorrectly complains "warning: function declared 'noreturn' should not return 
[-Winvalid-noreturn]".

Bruno, how about if we go back to how verify.h did 'assume' before the recent 
clang-related changes? That would avoid the complaints. It might cost us a few 
nanoseconds of performance with clang-generated code but that's no big deal. And 
anyway, clang ought to get fixed to generate the slightly-better code with 
'verify.h' just as it was.

#include <config.h>
#include <verify.h>
extern void error (int, int, char const *, ...);

_Noreturn void
f (void)
{
   error (1, 1, "error");
   assume (0);
}