[Bug tree-optimization/46928] data dependence analysis fails on constant array accesses

["sebpop at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46928

--- Comment #4 from sebpop at gmail dot com <sebpop at gmail dot com> 2010-12-13 19:05:58 UTC ---
The code that is produced looks like this just after loop
distribution, i.e., we generate memset zero only by distributing the
innermost loop:

mad_synth_mute (struct mad_synth * synth)
{
  long unsigned int D.2739;
  long unsigned int D.2740;
  long unsigned int D.2741;
  long unsigned int D.2742;
  long unsigned int D.2743;
  struct mad_synth * D.2744;
  long unsigned int D.2730;
  long unsigned int D.2731;
  long unsigned int D.2732;
  long unsigned int D.2733;
  <unnamed-signed:64> D.2734;
  <unnamed-signed:64> D.2735;
  <unnamed-signed:64> D.2736;
  long unsigned int D.2737;
  struct mad_synth * D.2738;
  long unsigned int D.2721;
  long unsigned int D.2722;
  long unsigned int D.2723;
  long unsigned int D.2724;
  <unnamed-signed:64> D.2725;
  <unnamed-signed:64> D.2726;
  <unnamed-signed:64> D.2727;
  long unsigned int D.2728;
  struct mad_synth * D.2729;
  long unsigned int D.2712;
  long unsigned int D.2713;
  long unsigned int D.2714;
  long unsigned int D.2715;
  <unnamed-signed:64> D.2716;
  <unnamed-signed:64> D.2717;
  <unnamed-signed:64> D.2718;
  long unsigned int D.2719;
  struct mad_synth * D.2720;
  unsigned int pretmp.2;
  unsigned int v;
  unsigned int s;
  unsigned int ch;

<bb 2>:
  goto <bb 10>;

<bb 5>:
Invalid sum of incoming frequencies 139, should be 1111
  s_9 = s_29 + 1;
  if (s_9 != 16)
    goto <bb 6>;
  else
    goto <bb 8>;

<bb 6>:

<bb 7>:
Invalid sum of outgoing probabilities 12.5%
  # s_29 = PHI <0(10), s_9(6)>
  D.2712_25 = (long unsigned int) s_29;
  D.2713_22 = (long unsigned int) ch_28;
  D.2714_1 = D.2713_22 * 64;
  D.2715_2 = D.2712_25 + D.2714_1;
  D.2716_3 = (<unnamed-signed:64>) D.2715_2;
  D.2717_26 = D.2716_3 + 48;
  D.2718_27 = D.2717_26 * 32;
  D.2719_24 = (long unsigned int) D.2718_27;
  D.2720_23 = synth_7(D) + D.2719_24;
  __builtin_memset (D.2720_23, 0, 32);
  D.2721_13 = (long unsigned int) s_29;
  D.2722_12 = (long unsigned int) ch_28;
  D.2723_11 = D.2722_12 * 64;
  D.2724_6 = D.2721_13 + D.2723_11;
  D.2725_20 = (<unnamed-signed:64>) D.2724_6;
  D.2726_32 = D.2725_20 + 32;
  D.2727_33 = D.2726_32 * 32;
  D.2728_34 = (long unsigned int) D.2727_33;
  D.2729_35 = synth_7(D) + D.2728_34;
  __builtin_memset (D.2729_35, 0, 32);
  D.2730_36 = (long unsigned int) s_29;
  D.2731_37 = (long unsigned int) ch_28;
  D.2732_38 = D.2731_37 * 64;
  D.2733_39 = D.2730_36 + D.2732_38;
  D.2734_40 = (<unnamed-signed:64>) D.2733_39;
  D.2735_41 = D.2734_40 + 16;
  D.2736_42 = D.2735_41 * 32;
  D.2737_43 = (long unsigned int) D.2736_42;
  D.2738_44 = synth_7(D) + D.2737_43;
  __builtin_memset (D.2738_44, 0, 32);
  D.2739_45 = (long unsigned int) ch_28;
  D.2740_46 = D.2739_45 * 64;
  D.2741_47 = (long unsigned int) s_29;
  D.2742_48 = D.2740_46 + D.2741_47;
  D.2743_49 = D.2742_48 * 32;
  D.2744_50 = synth_7(D) + D.2743_49;
  __builtin_memset (D.2744_50, 0, 32);
  goto <bb 5>;

<bb 8>:
  ch_10 = ch_28 + 1;
  if (ch_10 != 2)
    goto <bb 9>;
  else
    goto <bb 11>;

<bb 9>:

<bb 10>:
  # ch_28 = PHI <0(2), ch_10(9)>
  goto <bb 7>;

<bb 11>:
  return;

}

and the assembler:

mad_synth_mute:
.LFB0:
    .cfi_startproc
    movq    %rdi, %r9
    xorl    %r8d, %r8d
.L2:
    leaq    16(%r8), %rsi
    movq    %r9, %rdx
    movq    %r8, %rax
    .p2align 4,,10
    .p2align 3
.L3:
    leaq    48(%rax), %rcx
    salq    $5, %rcx
    addq    %rdi, %rcx
    movq    $0, (%rcx)
    movq    $0, 8(%rcx)
    movq    $0, 16(%rcx)
    movq    $0, 24(%rcx)
    leaq    32(%rax), %rcx
    salq    $5, %rcx
    addq    %rdi, %rcx
    movq    $0, (%rcx)
    movq    $0, 8(%rcx)
    movq    $0, 16(%rcx)
    movq    $0, 24(%rcx)
    leaq    16(%rax), %rcx
    addq    $1, %rax
    salq    $5, %rcx
    addq    %rdi, %rcx
    movq    $0, (%rcx)
    movq    $0, 8(%rcx)
    movq    $0, 16(%rcx)
    movq    $0, 24(%rcx)
    movq    $0, (%rdx)
    movq    $0, 8(%rdx)
    movq    $0, 16(%rdx)
    movq    $0, 24(%rdx)
    addq    $32, %rdx
    cmpq    %rsi, %rax
    jne    .L3
    addq    $64, %r8
    addq    $2048, %r9
    cmpq    $128, %r8
    jne    .L2
    rep
    ret