[Bug inline-asm/18450] New: Wrong code generated by gcc from inline assembler

[Bug inline-asm/18450] New: Wrong code generated by gcc from inline assembler

[thalakan at technologist dot com]

I wrote an x86 specific program that uses inline assembler to set and unset the
alignment check bit in the EFLAGS register.  In between setting and unsetting
the bit, I use more inline assembler to save the state of the EFLAGS register.

The problem is that I get different results depending on whether optimization is
turned on or not.  Further inspection reveals that when optimization is turned
on, gcc decides to optimize out the chunk of inline assembler I use to verify
the AC bit was turned off.  When optimization is disabled, the chunk of inline
assembler re-appears.

The Intel C compiler v8.1 on the same machine does not exhibit this problem.

-- 
           Summary: Wrong code generated by gcc from inline assembler
           Product: gcc
           Version: 3.3.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: inline-asm
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: thalakan at technologist dot com
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: i386-portbld-freebsd5.1
  GCC host triplet: i386-portbld-freebsd5.1
GCC target triplet: i386-portbld-freebsd5.1


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18450

[Bug inline-asm/18450] Wrong code generated by gcc from inline assembler

[thalakan at technologist dot com]

------- Additional Comments From thalakan at technologist dot com  2004-11-12 11:08 -------
Created an attachment (id=7529)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=7529&action=view)
Preprocessed source of program

This is the preprocessed source of the program.  Compile and run it with and
without optimization.  When optimization is turned on, the program will output
a nonzero value in the second line; this is wrong.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18450

[Bug inline-asm/18450] Wrong code generated by gcc from inline assembler

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-11-12 12:46 -------
Since the asm is not violate or have outputs which are used they are removed, this is not a bug:
  asm("	pushf\n"
      " orl %0, (%%esp)\n"
      "	popf\n"
      : : "i" (0x00040000));

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
   GCC host triplet|i386-portbld-freebsd5.1     |i386-portbld-freebsd5.1
         Resolution|                            |INVALID


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18450