[hjl@gnu-cfl-2 tmp]$ cat x.c
#include <stdlib.h>
[hjl@gnu-cfl-2 tmp]$ gcc -S -mno-sse x.c
[hjl@gnu-cfl-2 tmp]$ gcc -S -mno-sse x.c -O
In file included from /usr/include/stdlib.h:1014,
                 from x.c:1:
/usr/include/bits/stdlib-float.h: In function ‘atof’:
/usr/include/bits/stdlib-float.h:26:1: error: SSE register return with SSE disabled
   26 | {
      | ^
[hjl@gnu-cfl-2 tmp]$