[Bug middle-end/47397] Alignment of array element is not optimal in AVX mode due to use of TARGET_MEM_REFs

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47397

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2011.01.21 14:21:20
            Summary|Alignment of array element  |Alignment of array element
                   |is incorrect in AVX mode    |is not optimal in AVX mode
                   |                            |due to use of
                   |                            |TARGET_MEM_REFs
     Ever Confirmed|0                           |1

--- Comment #4 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-01-21 
14:21:20 UTC ---
This is because index is unknown in both

  vect_var_.13_20 = MEM[symbol: a, index: ivtmp.24_12, offset: 16B];

and

  MEM[symbol: b, index: ivtmp.24_12, offset: 0B] = vect_var_.14_22;

we don't have a way to record that ivtmp.24_12 is {0, +, 32} for
RTL expansion.  Which means that IVOPTs is responsible for the
loss of information.  Before IVOPTs we have

  # ALIGN = 32, MISALIGN = 16
  # vect_pa.9_18 = PHI <vect_pa.9_19(4), vect_pa.12_17(2)>
  # ALIGN = 32, MISALIGN = 0
  # vect_pb.16_24 = PHI <vect_pb.16_25(4), vect_pb.19_23(2)>
  vect_var_.13_20 = MEM[(double[1024] *)vect_pa.9_18];
  MEM[(double[1024] *)vect_pb.16_24] = vect_var_.14_22;

so we know that the pointers we dereference are properly aligned.