On Tue, Mar 11, 2014 at 04:16:13PM -0700, Cong Hou wrote:
> This patch is fixing PR60505 in which the vectorizer may produce
> unnecessary epilogues.
>
> Bootstrapped and tested on a x86_64 machine.
>
> OK for trunk?
That looks wrong. Consider the case where the loop isn't versioned,
if you disable generation of the epilogue loop, you end up only with
a vector loop.
Say:
unsigned char ovec[16] __attribute__((aligned (16))) = { 0 };
void
foo (char *__restrict in, char *__restrict out, int num)
{
int i;
in = __builtin_assume_aligned (in, 16);
out = __builtin_assume_aligned (out, 16);
for (i = 0; i < num; ++i)
out[i] = (ovec[i] = in[i]);
out[num] = ovec[num / 2];
}
-O2 -ftree-vectorize. Now, consider if this function is called
with num != 16 (num > 16 is of course invalid, but num 0 to 15 is
valid and your patch will cause a wrong-code in this case).
Jakub
