On Thu, May 16, 2013 at 04:07:44PM +0200, Marek Polacek wrote:
> --- gcc/tree-ssa-strlen.c.mp 2013-05-15 14:11:20.079707492 +0200
> +++ gcc/tree-ssa-strlen.c 2013-05-16 16:03:50.373504796 +0200
> @@ -1717,6 +1717,27 @@ handle_char_store (gimple_stmt_iterator
> si->endptr = ssaname;
> si->dont_invalidate = true;
> }
> + /* If si->length is non-zero constant, we aren't overwriting '\0',
> + and if we aren't storing '\0', we know that the length of the
The above line has 8 spaces instead of tab. Also, please write
"that the length of the string and any other zero terminated string in
memory remains the same."
> + string remains the same. In that case we move to the next
> + gimple statement and return to signal the caller that it shouldn't
> + invalidate anything.
> +
> + This is benefical for cases like:
> +
> + char p[] = "foobar";
> + size_t len = strlen (p);
> + p[0] = 'X'
Missing ; at the end of the above line.
> + size_t len2 = strlen (p);
Also, you could make it clear that it affects any other strings. Perhaps
char p[20];
void foo (char *q)
{
strcpy (p, "foobar");
size_t len = strlen (p); // This can be optimized into 6
size_t len2 = strlen (q); // This has to be computed
p[0] = 'X';
size_t len3 = strlen (p); // This can be optimized into 6
size_t len4 = strlen (q); // This can be optimized into len2
bar (len, len2, len3, len4);
}
As q could point to p, if we didn't do what your patch does on the p[0] = 'X';
store, then we'd need to invalidate the recorded length of the q string.
Similarly if there is p[0] = '\0' or p[0] = var.
Jakub
