[Bug tree-optimization/68786] New: Aligned masked store is generated for unaligned pointer

[ienkovich at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68786

            Bug ID: 68786
           Summary: Aligned masked store is generated for unaligned
                    pointer
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ienkovich at gcc dot gnu.org
  Target Milestone: ---

Here is a testcase:

double *a;
int b;

void
test (void)
{
  for (; b; b++)
    if (b < 7)
      a[b] = 1.0;
}

Produced assembler for that loop when compiled for AVX-512:

>gcc  -O2 -ftree-vectorize -march=skylake-avx512 small.i -S

.L4:
        vpcmpd  $2, %zmm2, %zmm0, %k1
        addl    $1, %r8d
        vpaddd  %zmm3, %zmm0, %zmm0
        vmovupd %zmm1, (%rsi){%k1}
        kshiftrw        $8, %k1, %k1
        vmovapd %zmm1, 64(%rsi){%k1}
        subq    $-128, %rsi
        cmpl    %edx, %r8d
        jb      .L4

We have two store using the same base.  One of them is unaligned and another
one is aligned.

The difference comes from GIMPLE.  Here is a vectorized loop:

  <bb 6>:
  # vect_vec_iv_.11_71 = PHI <vect_cst__69(5), vect_vec_iv_.11_72(6)>
  # ivtmp.26_87 = PHI <0(5), ivtmp.26_6(6)>
  # ivtmp.28_7 = PHI <ivtmp.28_24(5), ivtmp.28_8(6)>
  vectp.15_82 = (vector(8) double *) ivtmp.28_7;
  vect_vec_iv_.11_72 = vect_vec_iv_.11_71 + { 16, 16, 16, 16, 16, 16, 16, 16,
16, 16, 16, 16, 16, 16, 16, 16 };
  mask__24.12_74 = vect_vec_iv_.11_71 <= { 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
6, 6, 6, 6 };
  mask_patt_28.14_76 = [vec_unpack_lo_expr] mask__24.12_74;
  mask_patt_28.14_77 = [vec_unpack_hi_expr] mask__24.12_74;
  MASK_STORE (vectp.15_82, 0B, mask_patt_28.14_76, { 1.0e+0, 1.0e+0, 1.0e+0,
1.0e+0, 1.0e+0, 1.0e+0, 1.0e+0, 1.0e+0 });
  _25 = ivtmp.28_7 + 64;
  _88 = (vector(8) double *) _25;
  MASK_STORE (_88, 0B, mask_patt_28.14_77, { 1.0e+0, 1.0e+0, 1.0e+0, 1.0e+0,
1.0e+0, 1.0e+0, 1.0e+0, 1.0e+0 });
  ivtmp.26_6 = ivtmp.26_87 + 1;
  ivtmp.28_8 = ivtmp.28_7 + 128;
  if (ivtmp.26_6 < bnd.8_31)
    goto <bb 6>;

Pointers used for masked stores have different SSA_NAME_PTR_INFO

For vectp.15_82 we have

{pt = {anything = 0, nonlocal = 1, escaped = 1, ipa_escaped = 0, null = 0,
vars_contains_nonlocal = 0, vars_contains_escaped = 0,
vars_contains_escaped_heap = 0, vars = 0x7ffff7c13160}, align = 8, misalign =
0}

For _88 we have

{pt = {anything = 0, nonlocal = 1, escaped = 1, ipa_escaped = 0, null = 0,
vars_contains_nonlocal = 0, vars_contains_escaped = 0,
vars_contains_escaped_heap = 0, vars = 0x7ffff7c13160}, align = 0, misalign =
0}

Zero alignment here for _88 causes TYPE_ALIGN to be used for the second
MASK_STORE.  TYPE_ALIGN for vector types is its size and therefore we get
incorrect aligned memory access.