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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug rtl-optimization/61673] New: [4.9/4.10 Regression] Miscompilation of _gnutls_hostname_compare on s390
Date: Wed, 02 Jul 2014 14:53:00 -0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: rtl-optimization
X-Bugzilla-Version: 4.9.1
X-Bugzilla-Keywords: wrong-code
X-Bugzilla-Severity: normal
X-Bugzilla-Who: jakub at gcc dot gnu.org
X-Bugzilla-Status: UNCONFIRMED
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: jakub at gcc dot gnu.org
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61673

            Bug ID: 61673
           Summary: [4.9/4.10 Regression] Miscompilation of
                    _gnutls_hostname_compare on s390
           Product: gcc
           Version: 4.9.1
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: jakub at gcc dot gnu.org
          Reporter: jakub at gcc dot gnu.org
            Target: s390-linux

char e;

__attribute__((noinline, noclone)) void
foo (const char *x)
{
  char d = x[0];
  int c = d;
  if ((c >= 0 && c <= 0x7f) == 0)
    e = d;
}

int
main ()
{
  const char c[] = { 0x54, 0x87 };
  e = 0x21;
  foo (c);
  if (e != 0x21)
    __builtin_abort ();
  foo (c + 1);
  if (e != 0x87)
    __builtin_abort ();
  return 0;
}

is miscompiled supposedly starting with r202393.  Before combine we have:
(insn 7 6 8 2 (parallel [
            (set (reg:SI 47 [ D.1404 ])
                (and:SI (subreg:SI (reg/v:QI 44 [ d ]) 0)
                    (const_int 255 [0xff])))
            (clobber (reg:CC 33 %cc))
        ]) gnutls2.c:8 455 {*andsi3_esa}
     (expr_list:REG_UNUSED (reg:CC 33 %cc)
        (nil)))
(insn 8 7 9 2 (set (reg:CCU 33 %cc)
        (compare:CCU (reg:SI 47 [ D.1404 ])
            (const_int 127 [0x7f]))) gnutls2.c:8 39 {*cmpsi_ccu}
     (expr_list:REG_DEAD (reg:SI 47 [ D.1404 ])
        (nil)))
(jump_insn 9 8 10 2 (set (pc)
        (if_then_else (leu (reg:CCU 33 %cc)
                (const_int 0 [0]))
            (label_ref:SI 15)
            (pc))) gnutls2.c:8 599 {*cjump_31}
     (expr_list:REG_DEAD (reg:CCU 33 %cc)
        (int_list:REG_BR_PROB 3900 (nil)))
 -> 15)
and combine turns this into:
(note 7 6 8 2 NOTE_INSN_DELETED)
(insn 8 7 9 2 (parallel [
            (set (reg:CCZ 33 %cc)
                (compare:CCZ (and:SI (subreg:SI (reg/v:QI 44 [ d ]) 0)
                        (const_int -128 [0xffffffffffffff80]))
                    (const_int 0 [0])))
            (clobber (scratch:SI))
        ]) gnutls2.c:8 453 {*andsi3_cconly}
     (nil))
(jump_insn 9 8 10 2 (set (pc)
        (if_then_else (eq (reg:CCZ 33 %cc)
                (const_int 0 [0]))
            (label_ref:SI 15)
            (pc))) gnutls2.c:8 599 {*cjump_31}
     (expr_list:REG_DEAD (reg:CCU 33 %cc)
        (int_list:REG_BR_PROB 3900 (nil)))
 -> 15)

The -128 should have been 128, we want to test the sign bit of QImode rather
than also any of the higher bits that contain garbage.