[Bug tree-optimization/123002] [15/16 regression] WIDEN_MULT_EXPR are incorrectly vectorized since r15-3189-gd3e71b99194bff

[rguenth at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123002

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |needs-bisection

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
Note I cannot reproduce the issue on trunk where we no longer recognize a
widen_mult pattern, but the principle issue is still there IMO.  I wonder what
fixed it on trunk.

Better testcase:

static unsigned int const enc_table_32[8][3] = {
    {513735U, 77223048U, 437087610U },
    {0U,      78508U,    646269101U },
    {0U,      0U,        11997U,    },
    {0U,      0U,        0U,        },
    {0U,      0U,        0U,        },
    {0U,      0U,        0U,        },
    {0U,      0U,        0U,        },
    {0U,      0U,        0U,        }};

int __attribute__((noipa)) foo()
{
  unsigned long intermediate[3] = {0};

  for (unsigned long i = 0UL; i < 8; i++) {
      intermediate[0] += 2 * (unsigned long)(enc_table_32)[i][0];
      intermediate[1] += 2 * (unsigned long)(enc_table_32)[i][1];
      intermediate[2] += 2 * (unsigned long)(enc_table_32)[i][2];
  }

  if (intermediate[0] == 0xfad8e &&
      intermediate[1] == 0x9370e68 && intermediate[2] == 0x8125ca08) {
      return 0;
  } else {
      return 1;
  }
}
int main()
{
  if (foo ())
    __builtin_abort ();
  return 0;
}