[Bug middle-end/53338] [4.8 Regression] Unaligned store generated for aligned data

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53338

Richard Guenther <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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                 CC|                            |rguenth at gcc dot gnu.org

--- Comment #3 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-05-14 08:39:03 UTC ---
After IVOPTs we lose the ability to stick the aligned markers at the memory
references.  Before:

  # PT = anything
  # ALIGN = 16, MISALIGN = 0
  vect_pa.21_35 = vect_pa.21_33 + 16;
  MEM[(long int[10240] *)vect_pa.21_35] = vect_var_.20_31;

after:

  MEM[symbol: a, index: ivtmp.29_19, step: 2, offset: 16B] = vect_var_.20_31;

but as ivtmp.29_19 is not of pointer type we do not have 'alignment'
information
for it - thus we do not exploit that it is { 0, +, 16 } in
get_object_alignment_1.
Previously we conservatively assumed "alignment" of TYPE_ALIGN but now we
have "known" alignment due to

      if (TMR_INDEX (exp) && TMR_STEP (exp))
        {
          unsigned HOST_WIDE_INT step = TREE_INT_CST_LOW (TMR_STEP (exp));
          align = MIN (align, (step & -step) * BITS_PER_UNIT);
          known_alignment = true;
        }

(but that results in alignment of 2 bytes based on step) and disregard type
information.