Re: [RFC PATCH] Gather vectorization (PR tree-optimization/50789)

[Jakub Jelinek <jakub at redhat dot com>]

On Fri, Oct 28, 2011 at 12:59:48PM +0200, Richard Guenther wrote:
> It is also because of re-use of memory via memcpy (yes, some dubious
> TBAA case from C, but essentially we don't want to break that).  Thus
> we can't use TBAA on anonymous memory.

No, IMHO we always use a ref_all mem access in that case.
If you meant something like:

void
foo (int *intptr, float *floatptr)
{
  int i;
  for (i = 0; i < 256; ++i)
    {
      int tem;
      __builtin_memcpy (&tem, &intptr[i], sizeof (tem));
      floatptr[i] = (float) tem;
    }
}

which is valid C even if intptr == floatptr, we have:

<bb 2>:

<bb 3>:
  # i_21 = PHI <i_14(4), 0(2)>
  # ivtmp.12_27 = PHI <ivtmp.12_26(4), 256(2)>
  D.2709_3 = (long unsigned int) i_21;
  D.2710_4 = D.2709_3 * 4;
  D.2711_6 = intptr_5(D) + D.2710_4;
  D.2712_7 = MEM[(char * {ref-all})D.2711_6];
  D.2713_11 = floatptr_10(D) + D.2710_4;
  D.2715_13 = (float) D.2712_7;
  *D.2713_11 = D.2715_13;
  i_14 = i_21 + 1;
  ivtmp.12_26 = ivtmp.12_27 - 1;
  if (ivtmp.12_26 != 0)
    goto <bb 4>;
  else
    goto <bb 5>;

<bb 4>:
  goto <bb 3>;

which is just fine even with TBAA.
And similarly for
void
bar (int *intptr, float *floatptr)
{
  int i;
  for (i = 0; i < 256; ++i)
    {
      float tem;
      tem = (float) intptr[i];
      __builtin_memcpy (&floatptr[i], &tem, sizeof (tem));
    }
}

where the ref-all isn't used for load, but for store.

	Jakub