[Bug tree-optimization/50328] loop interchange confuses vectorizer

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50328

--- Comment #3 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-09-08 13:40:30 UTC ---
Triggered by report http://gcc.gnu.org/ml/gcc/2011-09/msg00052.html
OpenCC then unrolls the outer loop to get

.LBB16_double_array_mults_by_const:
 #<loop> Loop body line 62, nesting depth: 2, iterations: 16384
 #<loop> unrolled 4 times
        mulpd %xmm6,%xmm0               # [0]
        movaps %xmm0,%xmm1              # [4]
        mulpd %xmm6,%xmm1               # [6]
        mulpd %xmm6,%xmm1               # [10]
        addq $8,%rax                    # [14]
        mulpd %xmm6,%xmm1               # [14]
        cmpq $131071,%rax               # [15]
        setle %dil                      # [16]
        testb %dil,%dil                 # [17]
        movaps %xmm1,%xmm0              # [18]
        jne .LBB16_double_array_mults_by_const  # [18]

instead of what we get with the patch

.L2:
        subl    $1, %eax
        mulpd   %xmm1, %xmm0
        jne     .L2

we don't have outer loop unrolling either.