[Bug middle-end/118415] New: [15 Regression] crc optimization uses user accessible symbols

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118415

            Bug ID: 118415
           Summary: [15 Regression] crc optimization uses user accessible
                    symbols
           Product: gcc
           Version: 15.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jakub at gcc dot gnu.org
  Target Milestone: ---

unsigned char crc_table_for_crc_8_polynomial_0x7[2] = { 0xff, 0xff };

static unsigned char
foo (unsigned char byte, unsigned char crc)
{
  unsigned int i;
  crc ^= byte;
  for (i = 0; i < 8; i++)
    crc = (crc << 1) ^ ((crc >> 7) ? 0x07 : 0);
  return crc;
}

int
main ()
{
  volatile unsigned char byte = 1;
  volatile unsigned char crc = 0;
  crc = foo (byte, crc);
  if (crc != 7)
    __builtin_abort ();
}

is miscompiled starting with the introduction of the CRC optimization.
Using user accessible symbols should be only the last resort, I think in
any case the name should start with double underscore and have at least one of
the underscores replaced with . or $ if the target supports dot
(NO_DOT_IN_LABEL, NO_DOLLAR_IN_LABEL).

I think the symbol should be also hidden whenever target supports that, it is
fine to merge those across TUs within one executable or shared library, but the
optimization shouldn't add to the list of exported symbols.