[Bug rtl-optimization/123786] [16 Regression] AArch64: Miscompile at -O3 -mtune=generic-armv9-a since r16-3628-g41b0c7a674e870

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123786

Alex Coplan <acoplan at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[16 Regression] AArch64:    |[16 Regression] AArch64:
                   |Miscompile at -O3           |Miscompile at -O3
                   |-mtune=generic-armv9-a      |-mtune=generic-armv9-a
                   |                            |since
                   |                            |r16-3628-g41b0c7a674e870

--- Comment #11 from Alex Coplan <acoplan at gcc dot gnu.org> ---
Just FTR, this started with the introduction of the dep_fusion pass, i.e.
r16-3628-g41b0c7a674e87074fdc8088479cb93f6fe1e070f.

Here is a slightly cleaned up testcase for the testsuite:

#include <arm_neon.h>

int g_36[3];
short g_s;
signed char g_82, g_179, g_x, g_101;

__attribute__((noipa))
void check(void)
{
  if (g_36[0] != 1)
    __builtin_abort ();
}

int main(void)
{
BS_LABEL_3:
  short l_65 = g_s;
  if (g_x) goto BS_LABEL_6;
  for (; g_101; g_101 = 5)
  {
  BS_LABEL_6:
  }
  for (; g_82 < 1; g_82++)
  {
    switch (vqadds_u32 (0, 0))
      {
        case 4: goto BS_LABEL_3;
        case 9: goto BS_LABEL_3;
      }
    short si1 = (l_65 &= 1) || (g_179 &= 0) != 6;
    g_36[0] = g_36[2] == 0 ? 1 : si1 / g_36[2];
  }

  check ();
}

or for a pre-processed testcase that works with just a cc1:

int g_36[3];
short g_s;
signed char g_82, g_179, g_x, g_101;

__attribute__((noipa))
void check(void)
{
  if (g_36[0] != 1)
    __builtin_abort ();
}

int main(void)
{
BS_LABEL_3:
  short l_65 = g_s;
  if (g_x) goto BS_LABEL_6;
  for (; g_101; g_101 = 5)
  {
  BS_LABEL_6:
  }
  for (; g_82 < 1; g_82++)
  {
    switch (__builtin_aarch64_usaddsi_uuu (0, 0))
      {
        case 4: goto BS_LABEL_3;
        case 9: goto BS_LABEL_3;
      }
    short si1 = (l_65 &= 1) || (g_179 &= 0) != 6;
    g_36[0] = g_36[2] == 0 ? 1 : si1 / g_36[2];
  }

  check ();
}