[Bug target/48348] New: incorrect loongson builtin pcmpgtb_u

[hp at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48348

           Summary: incorrect loongson builtin pcmpgtb_u
           Product: gcc
           Version: 4.6.1
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: target
        AssignedTo: unassig...@gcc.gnu.org
        ReportedBy: h...@gcc.gnu.org
            Target: mips64el-unknown-linux-gnu


There's no such instruction.  The GCC intrinsic pcmpgtb_u maps to a *signed*
compare insn, the same as pcmpgtb_s. To wit:

#include <loongson.h>
#include <stdio.h>

static void vdump(const char *s, void *v)
{
  unsigned char *r = v;
  int i;

  printf("%04s:", s);
  for (i = 0; i < sizeof (uint8x8_t); i++)
    printf (" %02x", r[i]);
  printf("\n");
}

int main(void)
{
  uint8x8_t v1 = {2, 3, 0,    0xff,    1,    0x80, 0x40, 0xfe};
  uint8x8_t v2 = {3, 2, 0xff, 0,    0xff,    0x81, 0xc0, 0xff};
  uint8x8_t res;

  res = pcmpgtb_u (v1, v2);
  vdump("v1", &v1);
  vdump("v2", &v2);
  vdump("res", &res);
}

gcc51%  ./xgcc -O2 -B./ -march=loongson2f ~/pcmpgtu.c -o a
gcc51% ./a
  v1: 02 03 00 ff 01 80 40 fe
  v2: 03 02 ff 00 ff 81 c0 ff
 res: 00 ff ff 00 ff 00 ff 00

I suggest the builtin either removed or changed to emit multiple instructions
(you'd need only a pmaxub and a pcmpeqb) to implement the correct comparison
operator.

gcc version 4.6.0 20110309 (experimental) [trunk revision 170836] (GCC)