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

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

[Wolfgang Bangerth]

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

From: Wolfgang Bangerth <bangerth@ices.utexas.edu>
To: Andrew Pinski <pinskia@physics.uc.edu>
Cc: 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 08:47:58 -0500 (CDT)

 > It does not fail for me though on i686-pc-linux-gnu with GCC: 3.4  
 > 20030517 (experimental).
 > Or on i686-unkown-openbsd3.1 with gcc version 3.4 20030519  
 > (experimental).
 
 That's pretty weird. I can reproduce this with most a 3.4 snapshot from 
 2003-05-15 as well as a 3.3 snapshot from 2003-05-16. I compared the 
 assembler output, and instructionwise they are equal, but there are some 
 additional linkonce things in your output. I don't know enough about this 
 stuff to tell whether that's relevant.
 
 I'll update now to present HEAD and check+report again once the bootstrap 
 is done.
 
 W.
 
 -------------------------------------------------------------------------
 Wolfgang Bangerth              email:            bangerth@ices.utexas.edu
                                www: http://www.ices.utexas.edu/~bangerth/
 
 

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

[Christian Ehrhardt]

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

From: "Christian Ehrhardt" <ehrhardt@mathematik.uni-ulm.de>
To: Wolfgang Bangerth <bangerth@ices.utexas.edu>, ebotcazou@libertysurf.fr
Cc: Andrew Pinski <pinskia@physics.uc.edu>, 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: Wed, 21 May 2003 14:39:38 +0200

 [ Added Eric to cc because his patch might have triggered this gas bug. ]
 
 On Tue, May 20, 2003 at 12:05:35PM -0500, Wolfgang Bangerth wrote:
 > > Feeding this assembler file into gcc 3.2 on an Intel box works for me
 > > and the program doesn't crash! This might mean that we have an
 > > assembler/binutils problem here.
 > 
 > Whereas if I do the same, it crashes. So you seem to have a point :-)
 
 This is definitely a gas Bug! The problem is the following instruction:
 
 	addl    $_GLOBAL_OFFSET_TABLE_, %eax
 
 This tells the assembler that we want the difference between the adress
 of this addl instruction and the start of the global offset table to be
 added to %eax. When translating this request into relocation records an
 R_386_GOTPC relocation is used.
 However, this relocation calculates the difference between the place where
 the relocation takes place and the start of the global offset table.
 Hence the assembler must add an addend to fix up the difference between
 the address of the addl instruction and the address of its immediate
 operand (the latter is the place of the relocation).
 
 Now in the %eax case gas emmits the 0x05 opcode for addl imm32,%eax
 with a length of 1 byte. If the register isn't %eax the assembler
 has to use the longer 0x81 0xc3 opcode. Both opcodes are followed by
 the immediate 32bit Operand.
 
 I.e. if %eax is used the addend for the R_386_GOTPC relocation must be 1
 but for all other registers it must be 2 due to the different length of
 the opcode. This is what some gas versions seem to get wrong.
 
 So what should we do with this report? Do we want to work around
 this bug in gcc or should we close it and tell people to upgrade
 binutils. The bug is fixed at least since 2.12.90.0.15 20020717 (SuSE).
 
    regards   Christian
 
 -- 
 THAT'S ALL FOLKS!

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

[Christian Ehrhardt]

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

From: "Christian Ehrhardt" <ehrhardt@mathematik.uni-ulm.de>
To: Eric Botcazou <ebotcazou@libertysurf.fr>
Cc: janis187@us.ibm.com, gcc-bugs@gcc.gnu.org, gcc-gnats@gcc.gnu.org,
  lloyd@acm.jhu.edu
Subject: Re: optimization/10877: [3.3/3.4 regression] miscompilation with -O3  -fPIC on x86
Date: Wed, 21 May 2003 13:15:13 +0200

 On Wed, May 21, 2003 at 10:42:30AM +0200, Eric Botcazou wrote:
 > Is it illegal for the pc_thunk to go into %eax instead of %ecx in that case?
 
 I don't know but there are apparently some gas/ld versions that make
 a mess of it (see the rest of this thread). Even if it is a gas Bug we
 may want to work around it.
 
    regards  Christian
 
 -- 
 THAT'S ALL FOLKS!

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

[Christian Ehrhardt]

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

From: "Christian Ehrhardt" <ehrhardt@mathematik.uni-ulm.de>
To: Wolfgang Bangerth <bangerth@ices.utexas.edu>
Cc: Andrew Pinski <pinskia@physics.uc.edu>, 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: Wed, 21 May 2003 10:30:33 +0200

 On Tue, May 20, 2003 at 12:05:35PM -0500, Wolfgang Bangerth wrote:
 > 
 > > Feeding this assembler file into gcc 3.2 on an Intel box works for me
 > > and the program doesn't crash! This might mean that we have an
 > > assembler/binutils problem here.
 > 
 > Whereas if I do the same, it crashes. So you seem to have a point :-)
 > 
 > My binutils are
 >   2.11.92.0.10 20011021 (SuSE)
 > (this is what SuSE shipped with 8.0). What do you have?
 
 Mine is 
     2.12.90.0.15 20020717 (SuSE)
 and it works with this version.
 
     regards  Christian
 -- 
 THAT'S ALL FOLKS!

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

[Janis Johnson]

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

From: Janis Johnson <janis187@us.ibm.com>
To: gcc-prs@gcc.gnu.org, gcc-bugs@gcc.gnu.org, gcc-gnats@gcc.gnu.org,
   lloyd@acm.jhu.edu, nobody@gcc.gnu.org, ebotcazou@libertysurf.fr
Cc:  
Subject: Re: optimization/10877: [3.3/3.4 regression] miscompilation with -O3 
 -fPIC on x86
Date: Tue, 20 May 2003 15:32:32 -0700

 The pc_thunk started going into %eax with this patch:
 
 > 2003-03-12  Eric Botcazou  <ebotcazou@libertysurf.fr>
 >
 >       PR optimization/9888
 >       * config/i386/i386.md (jcc_1): Fix range.
 >       (jcc_2): Likewise.
 >       (jump): LIkewise.
 >       (doloop_end_internal): Likewise.
 >
 > 2003-03-12  Eric Botcazou  <ebotcazou@libertysurf.fr>
 >
 >       PR optimization/9888
 >       * config/i386/i386.md (movsi_1): Remove special alternatives
 >       for %eax register.
 >       (movsi_1_nointernunit): Likewise.
 >       (movhi_1): Likewise.
 >       * config/i386/i386.c (memory_address_length): Do not use
 >       short displacement when there is no base.
 >       (ix86_attr_length_address_default): Handle LEA instructions.
 
 This was tested using Wolfgang's smaller testcase and
 searching for '_GLOBAL_OFFSET_TABLE_, %eax' in the .s file.
 
 http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=10877
 
 
 

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

[Andrew Pinski]

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

From: Andrew Pinski <pinskia@physics.uc.edu>
To: Andrew Pinski <pinskia@physics.uc.edu>
Cc: Wolfgang Bangerth <bangerth@ices.utexas.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 15:28:18 -0400

 The differences in the rtl shows up in testpic.cc.30.rnreg.
 The work around in this case is to run with -fno-rename-registers, but 
 this might not work in all cases.
 
 Thanks,
 Andrew Pinski
 

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

[Andrew Pinski]

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/
 >
 >
 >
 >
 

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

[Wolfgang Bangerth]

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

From: Wolfgang Bangerth <bangerth@ices.utexas.edu>
To: Andrew Pinski <pinskia@physics.uc.edu>
Cc: 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 14:10:17 -0500 (CDT)

 > 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/
 
 

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

[Andrew Pinski]

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

From: Andrew Pinski <pinskia@physics.uc.edu>
To: Andrew Pinski <pinskia@physics.uc.edu>
Cc: Wolfgang Bangerth <bangerth@ices.utexas.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 13:14:22 -0400

 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.
 
 Thanks,
 Andrew Pinski
 
 On Tuesday, May 20, 2003, at 13:08 US/Eastern, Andrew Pinski wrote:
 
 > Mine is the top of the tree from the fsf's tree:
 > GNU assembler 2.14.90 20030520
 >
 > Thanks,
 > Andrew Pinski
 >
 > On Tuesday, May 20, 2003, at 13:05 US/Eastern, Wolfgang Bangerth wrote:
 >
 >>
 >>> Feeding this assembler file into gcc 3.2 on an Intel box works for me
 >>> and the program doesn't crash! This might mean that we have an
 >>> assembler/binutils problem here.
 >>
 >> Whereas if I do the same, it crashes. So you seem to have a point :-)
 >>
 >> My binutils are
 >>   2.11.92.0.10 20011021 (SuSE)
 >> (this is what SuSE shipped with 8.0). What do you have?
 >>
 >> W.
 >>
 >> ---------------------------------------------------------------------- 
 >> ---
 >> Wolfgang Bangerth              email:             
 >> bangerth@ices.utexas.edu
 >>                                www:  
 >> http://www.ices.utexas.edu/~bangerth/
 >>
 >>
 >>
 >>
 >
 >
 >
 

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

[Christian Ehrhardt]

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

From: "Christian Ehrhardt" <ehrhardt@mathematik.uni-ulm.de>
To: Wolfgang Bangerth <bangerth@ices.utexas.edu>
Cc: Andrew Pinski <pinskia@physics.uc.edu>, 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 19:00:33 +0200

 On Tue, May 20, 2003 at 10:26:37AM -0500, Wolfgang Bangerth wrote:
 > OK, I made the experiment -- and my small snippet still segfaults with 
 > both 3.3 and 3.4 checked out an hour or so ago. This is the assembler 
 > output I get on my system with present 3.4. I think I'm at a loss for 
 > further explanations, but feel free to ask me if you think you have a 
 > theory...
 
 Feeding this assembler file into gcc 3.2 on an Intel box works for me
 and the program doesn't crash! This might mean that we have an
 assembler/binutils problem here.
 
    Gruesse  Christian
 
 -- 
 THAT'S ALL FOLKS!

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

[Wolfgang Bangerth]

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

From: Wolfgang Bangerth <bangerth@ices.utexas.edu>
To: Christian Ehrhardt <ehrhardt@mathematik.uni-ulm.de>
Cc: Andrew Pinski <pinskia@physics.uc.edu>, <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 12:05:35 -0500 (CDT)

 > Feeding this assembler file into gcc 3.2 on an Intel box works for me
 > and the program doesn't crash! This might mean that we have an
 > assembler/binutils problem here.
 
 Whereas if I do the same, it crashes. So you seem to have a point :-)
 
 My binutils are
   2.11.92.0.10 20011021 (SuSE)
 (this is what SuSE shipped with 8.0). What do you have?
 
 W.
 
 -------------------------------------------------------------------------
 Wolfgang Bangerth              email:            bangerth@ices.utexas.edu
                                www: http://www.ices.utexas.edu/~bangerth/
 
 

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

[Wolfgang Bangerth]

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

From: Wolfgang Bangerth <bangerth@ices.utexas.edu>
To: Andrew Pinski <pinskia@physics.uc.edu>
Cc: 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 10:26:37 -0500 (CDT)

 > It does not fail for me though on i686-pc-linux-gnu with GCC: 3.4  
 > 20030517 (experimental).
 > Or on i686-unkown-openbsd3.1 with gcc version 3.4 20030519  
 > (experimental).
 
 OK, I made the experiment -- and my small snippet still segfaults with 
 both 3.3 and 3.4 checked out an hour or so ago. This is the assembler 
 output I get on my system with present 3.4. I think I'm at a loss for 
 further explanations, but feel free to ask me if you think you have a 
 theory...
 
   W.
 
 
 	.file	"y.cc"
 .globl i
 	.bss
 	.align 4
 	.type	i, @object
 	.size	i, 4
 i:
 	.zero	4
 	.text
 	.align 2
 	.p2align 4,,15
 .globl _Z5get_xv
 	.type	_Z5get_xv, @function
 _Z5get_xv:
 .LFB4:
 	call	.LPR0
 	addl	$_GLOBAL_OFFSET_TABLE_, %eax
 	pushl	%ebp
 .LCFI0:
 	movl	i@GOT(%eax), %edx
 	movl	%esp, %ebp
 .LCFI1:
 	popl	%ebp
 	movl	(%edx), %eax
 	ret
 .LFE4:
 	.size	_Z5get_xv, .-_Z5get_xv
 	.align 2
 	.p2align 4,,15
 .globl main
 	.type	main, @function
 main:
 .LFB5:
 	pushl	%ebp
 .LCFI2:
 	movl	%esp, %ebp
 .LCFI3:
 	leal	-8(%ebp), %eax
 	pushl	%ebx
 .LCFI4:
 	subl	$4, %esp
 .LCFI5:
 	andl	$-16, %esp
 	call	.LPR3
 	addl	$_GLOBAL_OFFSET_TABLE_, %ebx
 	movl	i@GOT(%ebx), %ecx
 	movl	%eax, (%ecx)
 	call	_Z5get_xv@PLT
 	movl	-4(%ebp), %ebx
 	xorl	%eax, %eax
 	leave
 	ret
 .LFE5:
 	.size	main, .-main
 .LPR0:
 	movl	(%esp), %eax
 	ret
 .LPR3:
 	movl	(%esp), %ebx
 	ret
 	.ident	"GCC: (GNU) 3.4 20030520 (experimental)"
 

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

[Andrew Pinski]

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

From: Andrew Pinski <pinskia@physics.uc.edu>
To: bangerth@dealii.org, gcc-bugs@gcc.gnu.org, gcc-prs@gcc.gnu.org,
   lloyd@acm.jhu.edu, nobody@gcc.gnu.org, gcc-gnats@gcc.gnu.org
Cc: Andrew Pinski <pinskia@physics.uc.edu>
Subject: Re: optimization/10877: [3.3/3.4 regression] miscompilation with -O3 -fPIC on x86
Date: Mon, 19 May 2003 21:58:26 -0400

 It does not fail for me though on i686-pc-linux-gnu with GCC: 3.4  
 20030517 (experimental).
 Or on i686-unkown-openbsd3.1 with gcc version 3.4 20030519  
 (experimental).
 
 tin:~/src/gnu/gcc>g++ -O3 -fPIC ../gcctest/testpic.cc
 tin:~/src/gnu/gcc>./a.out
 tin:~/src/gnu/gcc>more ../gcctest/testpic.cc
      int* i;
 
      int& get_x() {
        return *i;
      }
 
      int main() {
        int j;
        i = &j;
        get_x();
      }
 
 Thanks,
 Andrew Pinski
 
 PS here is the asm from a working version:
 
          .file   "testpic.cc"
 .globl i
          .bss
          .align 4
          .type   i, @object
          .size   i, 4
 i:
          .zero   4
          .text
          .align 2
          .p2align 4,,15
 .globl _Z5get_xv
          .type   _Z5get_xv, @function
 _Z5get_xv:
 .LFB4:
          call    __i686.get_pc_thunk.ax
          addl    $_GLOBAL_OFFSET_TABLE_, %eax
          pushl   %ebp
 .LCFI0:
          movl    i@GOT(%eax), %edx
          movl    %esp, %ebp
 .LCFI1:
          popl    %ebp
          movl    (%edx), %eax
          ret
 .LFE4:
          .size   _Z5get_xv, .-_Z5get_xv
          .align 2
          .p2align 4,,15
 .globl main
          .type   main, @function
 main:
 .LFB5:
          pushl   %ebp
 .LCFI2:
          movl    %esp, %ebp
 .LCFI3:
          leal    -8(%ebp), %eax
          pushl   %ebx
 .LCFI4:
          subl    $4, %esp
 .LCFI5:
          andl    $-16, %esp
          call    __i686.get_pc_thunk.bx
          addl    $_GLOBAL_OFFSET_TABLE_, %ebx
          movl    i@GOT(%ebx), %ecx
          movl    %eax, (%ecx)
          call    _Z5get_xv@PLT
          movl    -4(%ebp), %ebx
          xorl    %eax, %eax
          leave
          ret
 .LFE5:
          .size   main, .-main
          .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
          .hidden __i686.get_pc_thunk.bx
          .type   __i686.get_pc_thunk.bx, @function
 __i686.get_pc_thunk.bx:
          movl    (%esp), %ebx
          ret
          .ident  "GCC: (GNU) 3.4 20030517 (experimental)"
 
 
 http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit- 
 trail&database=gcc&pr=10877
 

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

[bangerth]

Old Synopsis: GCC 3.3 miscompiles code with -O3 -fPIC on x86
New Synopsis: [3.3/3.4 regression] miscompilation with -O3 -fPIC on x86

State-Changed-From-To: open->analyzed
State-Changed-By: bangerth
State-Changed-When: Tue May 20 01:16:37 2003
State-Changed-Why:
    Confirmed. This is a smaller snippet (it has nothing to
    do with namespaces):
    ----------------------------
    int* i;
    
    int& get_x() {
      return *i;
    }
    
    int main() {
      int j;
      i = &j;
      get_x();
    }
    --------------------------
    It crashed in get_x:
    
    g/x> /home/bangerth/bin/gcc-3.3-pre/bin/c++ -O3 -fPIC x.cc
    g/x> ./a.out
    Segmentation fault
    
    Note that we really need both -fPIC and -O3.
    
    This crashes with both 3.3 and present mainline. It
    doesn't with 2.95 and 3.2.3, so it's definitely a
    regression worth fixing!
    
    W.

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=10877