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

[ubizjak at gmail dot com]

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

             Bug #: 53338
           Summary: [4.8 Regression] Unaligned store generated for aligned
                    data
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: ubizjak@gmail.com


Following testcase:

--cut here--
#define SIZE 10240

int b[SIZE], c[SIZE];
long long __attribute__((__aligned__ (128))) a[SIZE];

void
imul32_to_64 (void)
{
  int i;

  for (i = 0; i < SIZE; i++)
    a[i] = (long)b[i] * (long)c[i];
}
--cut here--

regressed from 4.7 when compiled with "-O3 -msse4". An unaligned store is
generated in 4.8, where in 4.7 aligned store is used.

4.8:

.L3:
        movdqa  b(%rax), %xmm1
        movdqa  c(%rax), %xmm0
        movdqa  %xmm1, %xmm3
        movdqa  %xmm0, %xmm2
        punpckldq       %xmm1, %xmm3
        punpckldq       %xmm0, %xmm2
        punpckhdq       %xmm1, %xmm1
        punpckhdq       %xmm0, %xmm0
        pmuldq  %xmm3, %xmm2
>>      movdqu  %xmm2, a(%rax,%rax)
        pmuldq  %xmm1, %xmm0
>>      movdqu  %xmm0, a+16(%rax,%rax)
        addq    $16, %rax
        cmpq    $40960, %rax
        jne     .L3

4.7.1:

.L2:
        movdqa  b(%rax), %xmm1
        movdqa  c(%rax), %xmm0
        movdqa  %xmm1, %xmm3
        movdqa  %xmm0, %xmm2
        punpckldq       %xmm1, %xmm3
        punpckldq       %xmm0, %xmm2
        punpckhdq       %xmm1, %xmm1
        punpckhdq       %xmm0, %xmm0
        pmuldq  %xmm3, %xmm2
>>      movdqa  %xmm2, a(%rax,%rax)
        pmuldq  %xmm1, %xmm0
>>      movdqa  %xmm0, a+16(%rax,%rax)
        addq    $16, %rax
        cmpq    $40960, %rax
        jne     .L2

The unaligned store is generated from expr.c, expand_assignment.