On Tue, Feb 04, 2003 at 05:02:10AM +0200, Marko Kreen wrote:
> Package: gcc-3.2
> Version: 1:3.2.2-0pre8
> Severity: normal
>
>
> gcc-3.2 -O2 miscompiles following program:
>
> ---------------------------------------------
> extern int write(int fd, void *buf, int len);
> extern int toupper(int c);
>
> void strupr (char *s)
> {
> while (*s)
> *s++ = toupper(*s);
> }
>
> int main(int argc, char *argv[])
> {
> char s[] = "foo";
> strupr(s);
> write(1, s, 3);
> write(1, "\n", 1);
> return 0;
> }
>
> ---------------------------------------------
> $ gcc-3.2 -Wall -O2 -o test test.c
> test.c: In function `strupr':
> test.c:7: warning: operation on `s' may be undefined
> $ ./test
> OO
> $
> ---------------------------------------------
>
> gcc-2.95 compiles it correctly, also gcc-3.2 when optimizing
> less than -O2. When the "toupper(*s)" is replaced with "*s & 0x5f"
> gcc-3.2 -O2 also works and without warning.
I think the lack of warning in that case is actually the bug, but I'm
not sure. C doesn't guarantee order-of-operation across an equals
sign; it's not a sequence point. The function call is a sequence point
but it isn't specified which side of the sequence point the increment
will happen on.
--
Daniel Jacobowitz
MontaVista Software Debian GNU/Linux Developer
