Re: optimization/10877: [3.3/3.4 regression] miscompilation with -O3 -fPIC on x86

[Andrew Pinski <pinskia@physics.uc.edu>]

The following reply was made to PR optimization/10877; it has been noted by GNATS.

From: Andrew Pinski <pinskia@physics.uc.edu>
To: Wolfgang Bangerth <bangerth@ices.utexas.edu>
Cc: Andrew Pinski <pinskia@physics.uc.edu>,
   Christian Ehrhardt <ehrhardt@mathematik.uni-ulm.de>, <gcc-bugs@gcc.gnu.org>,
   <lloyd@acm.jhu.edu>, <gcc-gnats@gcc.gnu.org>
Subject: Re: optimization/10877: [3.3/3.4 regression] miscompilation with -O3 -fPIC on x86
Date: Tue, 20 May 2003 15:19:43 -0400

 Here is the differences between -O2 (works ---) and -O3 (does not work  
 +++):
 
 --- testpic.O2.s        Tue May 20 15:12:01 2003
 +++ testpic.s   Tue May 20 15:12:16 2003
 @@ -12,13 +12,13 @@
   .globl _Z5get_xv
          .type   _Z5get_xv, @function
   _Z5get_xv:
 -       call    __i686.get_pc_thunk.cx
 -       addl    $_GLOBAL_OFFSET_TABLE_, %ecx
 +       call    __i686.get_pc_thunk.ax
 +       addl    $_GLOBAL_OFFSET_TABLE_, %eax
          pushl   %ebp
 -       movl    i@GOT(%ecx), %eax
 +       movl    i@GOT(%eax), %edx
          movl    %esp, %ebp
          popl    %ebp
 -       movl    (%eax), %eax
 +       movl    (%edx), %eax
          ret
          .size   _Z5get_xv, .-_Z5get_xv
          .align 2
 @@ -28,26 +28,26 @@
   main:
          pushl   %ebp
          movl    %esp, %ebp
 -       leal    -8(%ebp), %edx
 +       leal    -8(%ebp), %eax
          pushl   %ebx
          subl    $4, %esp
          andl    $-16, %esp
          call    __i686.get_pc_thunk.bx
          addl    $_GLOBAL_OFFSET_TABLE_, %ebx
 -       movl    i@GOT(%ebx), %eax
 -       movl    %edx, (%eax)
 +       movl    i@GOT(%ebx), %ecx
 +       movl    %eax, (%ecx)
          call    _Z5get_xv@PLT
          movl    -4(%ebp), %ebx
          xorl    %eax, %eax
          leave
          ret
          .size   main, .-main
 -       .section         
 .gnu.linkonce.t.__i686.get_pc_thunk.cx,"ax",@progbits
 -.globl __i686.get_pc_thunk.cx
 -       .hidden __i686.get_pc_thunk.cx
 -       .type   __i686.get_pc_thunk.cx, @function
 -__i686.get_pc_thunk.cx:
 -       movl    (%esp), %ecx
 +       .section         
 .gnu.linkonce.t.__i686.get_pc_thunk.ax,"ax",@progbits
 +.globl __i686.get_pc_thunk.ax
 +       .hidden __i686.get_pc_thunk.ax
 +       .type   __i686.get_pc_thunk.ax, @function
 +__i686.get_pc_thunk.ax:
 +       movl    (%esp), %eax
          ret
          .section         
 .gnu.linkonce.t.__i686.get_pc_thunk.bx,"ax",@progbits
   .globl __i686.get_pc_thunk.bx
 
 looks like putting the pc_thunk into eax is the problem.
 
 Thanks,
 Andrew Pinski
 
 
 
 On Tuesday, May 20, 2003, at 15:10 US/Eastern, Wolfgang Bangerth wrote:
 
 >
 >> I can reproduce it with `GNU assembler 2.11.93.0.2 20020207' tough so
 >> it looks like it binutils fault but it has already been fixed.
 >
 > So what do we do with this, then? Since we silently generate  
 > non-working
 > code, I'd prefer gcc work around the problem, but then I'm not in a
 > position to contribute anything reasonable to this aim...
 >
 > W.
 >
 > ----------------------------------------------------------------------- 
 > --
 > Wolfgang Bangerth              email:             
 > bangerth@ices.utexas.edu
 >                                www:  
 > http://www.ices.utexas.edu/~bangerth/
 >
 >
 >
 >