Re: optimization/8220: return value of a function is forgotten/inlining assembler code

Re: optimization/8220: return value of a function is forgotten/inlining assembler code

[ebotcazou]

Synopsis: return value of a function is forgotten/inlining assembler code

State-Changed-From-To: open->closed
State-Changed-By: ebotcazou
State-Changed-When: Tue Feb 18 15:28:20 2003
State-Changed-Why:
    Not a bug. Output operands in extended asm must be placed
    after the _first_ colon and must use the "=" symbol.
    Moreover the extended asm has no side-effect so you must
    explicit declare it as "volatile".
    
    inline int getcputime(void) {
      int i;
      __asm__ __volatile__(
        "rdtsc ;"
        "movl %%eax, %0"
        : "=g" (i) : :"eax", "edx");
      return i;
    }
    
    int main(void) {
      int x = getcputime();
      int y = getcputime();
      printf ("Time measure resolution: %i\n", y - x);
      return 0;
    }

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=8220