[Bug c/12108] New: wrong code generated in the presence of asm("...")

["anton at mips dot complang dot tuwien dot ac dot at" <gcc-bugzilla at gcc dot gnu dot org>]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12108

           Summary: wrong code generated in the presence of asm("...")
           Product: gcc
           Version: 3.3.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: anton at mips dot complang dot tuwien dot ac dot at
                CC: gcc-bugs at gcc dot gnu dot org
  GCC host triplet: hppa-linux

The 3.3.2 version is the one distributed with Debian.

Also shows up on gcc-3.2 on hppa2.0n-hp-hpux11.00, but not on
gcc-2.95.2 on hppa2.0n-hp-hpux11.00, nor on a number of non-hppa
platforms.

Command line:

gcc -o conftest -g -O2 conftest.c -L/lib/pa1.1/

conftest.c is:

int foo(int);
main()
{
  exit(foo(0)!=16);
}
int foo(int x)
{
  if (x) {
  label1:
    asm(".skip 16"); /* or ".space 16" or somesuch */
  label2:
  }
  return (&&label2)-(&&label1);
}

(The purpose of this program is a test for autoconf: test if .skip
works as we expect).

This program crashes, because the code in the asm statement is
executed even though x is 0.

A small variation is to insert some code before label1:

int foo(int);
main()
{
  exit(foo(0)!=16);
}
int y;
int foo(int x)
{
  if (x) {
    y++;
  label1:
    asm(".skip 16"); /* or ".space 16" or somesuch */
  label2:
  }
  return (&&label2)-(&&label1);
}

This time the program finishes, but produces the wrong result, because
(interpreting the disassembled code) "&&label1" is computed as if it was
placed before the "y++":

(gdb) disass foo
Dump of assembler code for function foo:
;;; File: conftest.c
;;;   if (x) {
0x2648 <foo>:   cmpib,= 0,%r26,0x266c <foo+36>
0x264c <foo+4>: addil L'0,%dp,%r1
;;;     y++;
0x2650 <foo+8>: ldw 0x20(%r1),%r19
0x2654 <foo+12>:        ldo 1(%r19),%r19
0x2658 <foo+16>:        stw %r19,0x20(%r1)
;;;     asm(".skip 16"); /* or ".space 16" or somesuch */
0x265c <foo+20>:        break 0,0
0x2660 <foo+24>:        break 0,0
0x2664 <foo+28>:        break 0,0
0x2668 <foo+32>:        break 0,0
;;;   return (&&label2)-(&&label1);
0x266c <foo+36>:        ldil L'0x2000,%ret0
0x2670 <foo+40>:        ldil L'0x2000,%r19
0x2674 <foo+44>:        ldo 0x650(%r19),%r19
0x2678 <foo+48>:        ldo 0x66c(%ret0),%ret0
;;; }
0x267c <foo+52>:        bv %r0(%rp)
0x2680 <foo+56>:        sub %ret0,%r19,%ret0
0x2684 <foo+60>:        break 0,0

I.e., &&label1 (%r19 at the end) is computed as 0x2650, but it should
be 0x265c.