[Bug c/47409] volatile struct member bug

["rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47409

--- Comment #18 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Francesco Zappa Nardelli from comment #16)
> Dear all
> 
> a possibly related issue.  Consider
> 
> struct S1 {
>   long f;
> };
> volatile struct S1 g;
> 
> struct S1 func_1 () {
>   return g;
> }
> 
> void main () {
>   func_1 ();
> }
> 
> This program, if compiled with a recent gcc svn:
> 
> $ gcc -v
> Target: x86_64-unknown-linux-gnu
> gcc version 4.9.0 20130625 (experimental) (GCC) 
> 
> correctly loads the long at g.f at -O0.  However the assembly generated at
> -O2:
> 
> func_1:
>       movq    g(%rip), %rax
>       ret
> main:
>       rep; ret 
> 
> does not perform the volatile load access, which, as far as I understand, is
> incorrect.

It does starting with GCC 4.8.2 and was a bug in older GCC versions.

Richard.

> -francesco