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* [Bug optimization/14938] New: bug with global register variables and function pointer calls
@ 2004-04-13 11:17 gcc-bugzilla at gcc dot gnu dot org
2004-04-13 11:19 ` [Bug optimization/14938] " pinskia at gcc dot gnu dot org
0 siblings, 1 reply; 2+ messages in thread
From: gcc-bugzilla at gcc dot gnu dot org @ 2004-04-13 11:17 UTC (permalink / raw)
To: gcc-bugs
In a function using a global register variable, that calls a function
through a function pointer, the -O optimization omits the last update
of the register variable before the call.
Environment:
System: Linux linuix 2.4.21-99-default #1 Wed Sep 24 13:30:51 UTC 2003 i686 athlon i386 GNU/Linux
Architecture: i686
<machine, os, target, libraries (multiple lines)>
host: i586-suse-linux-gnu
build: i586-suse-linux-gnu
target: i586-suse-linux-gnu
configured with: ../configure --enable-threads=posix --prefix=/usr --with-local-prefix=/usr/local --infodir=/usr/share/info --mandir=/usr/share/man --libdir=/usr/lib --enable-languages=c,c++,f77,objc,java,ada --disable-checking --enable-libgcj --with-gxx-include-dir=/usr/include/g++ --with-slibdir=/lib --with-system-zlib --enable-shared --enable-__cxa_atexit i586-suse-linux
How-To-Repeat:
================================== bug.c ===================================
register void** STACK __asm__("%ebx");
extern void** saved_STACK;
extern unsigned int func (void);
extern unsigned int (*func_pointer) (void);
void lisp_completion_indirect ()
{
STACK[0] = (void*)0;
STACK++;
func_pointer();
saved_STACK = STACK;
STACK--;
}
void lisp_completion_direct ()
{
STACK[0] = (void*)0;
STACK++;
func();
saved_STACK = STACK;
STACK--;
}
============================================================================
$ gcc -Wall -O -S bug.c
In the resulting bug.s, you see that the increment of %ebx before the call
is omitted in the lisp_completion_indirect function.
================================== bug.s ===================================
.file "bug.c"
.text
.globl lisp_completion_indirect
.type lisp_completion_indirect, @function
lisp_completion_indirect:
pushl %ebp
movl %esp, %ebp
subl $8, %esp
movl $0, (%ebx)
call *func_pointer
movl %ebx, saved_STACK
subl $4, %ebx
leave
ret
.size lisp_completion_indirect, .-lisp_completion_indirect
.globl lisp_completion_direct
.type lisp_completion_direct, @function
lisp_completion_direct:
pushl %ebp
movl %esp, %ebp
subl $8, %esp
movl $0, (%ebx)
addl $4, %ebx
call func
movl %ebx, saved_STACK
subl $4, %ebx
leave
ret
.size lisp_completion_direct, .-lisp_completion_direct
.ident "GCC: (GNU) 3.3.1 (SuSE Linux)"
============================================================================
------- Additional Comments From bruno at clisp dot org 2004-04-13 10:11 -------
Fix:
The bug goes away if -O is not passed to gcc.
--
Summary: bug with global register variables and function pointer
calls
Product: gcc
Version: 3.3.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: optimization
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: bruno at clisp dot org
CC: gcc-bugs at gcc dot gnu dot org
GCC build triplet: i586-suse-linux-gnu
GCC host triplet: i586-suse-linux-gnu
GCC target triplet: i586-suse-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14938
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2004-04-13 11:17 [Bug optimization/14938] New: bug with global register variables and function pointer calls gcc-bugzilla at gcc dot gnu dot org
2004-04-13 11:19 ` [Bug optimization/14938] " pinskia at gcc dot gnu dot org
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