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* [Bug tree-optimization/26144] New: with -O3 and pointer casts, gcc skips if
@ 2006-02-07 0:42 gcc-bugzilla at gcc dot gnu dot org
2006-02-07 0:53 ` [Bug tree-optimization/26144] " pinskia at gcc dot gnu dot org
` (2 more replies)
0 siblings, 3 replies; 4+ messages in thread
From: gcc-bugzilla at gcc dot gnu dot org @ 2006-02-07 0:42 UTC (permalink / raw)
To: gcc-bugs
When casting a pointer and checking for == NULL, the check is skipped
when -O3 is enabled. I found this problem while compiling bind with
uClibc,
but could reproduce the problem with the debian version of gcc and this
simple
test file.
Environment:
System: Linux dungeon2 2.6.11-1-k7-smp #1 SMP Mon Jun 20 22:34:51 MDT 2005 i686
GNU/Linux
Architecture: i686
host: i486-pc-linux-gnu
build: i486-pc-linux-gnu
target: i486-pc-linux-gnu
configured with: ../src/configure -v
--enable-languages=c,c++,java,f95,objc,ada,treelang --prefix=/usr
--enable-shared --with-system-zlib --libexecdir=/usr/lib
--without-included-gettext --enable-threads=posix --enable-nls
--program-suffix=-4.0 --enable-__cxa_atexit --enable-clocale=gnu
--enable-libstdcxx-debug --enable-java-awt=gtk-default --enable-gtk-cairo
--with-java-home=/usr/lib/jvm/java-1.4.2-gcj-4.0-1.4.2.0/jre --enable-mpfr
--disable-werror --with-tune=i686 --enable-checking=release i486-linux-gnu
How-To-Repeat:
Compile this file:
#include <stdio.h>
void foo(char **dee) { *dee = ""; }
int main(int argc, char *argv[])
{
struct blah *ptr = argv[1];
if(ptr == NULL)
foo(&ptr);
printf("%p", ptr); // output: (nil) expected: 0xADDRESS
return 0;
}
--
Summary: with -O3 and pointer casts, gcc skips if
Product: gcc
Version: 4.0.3
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: devin at dungeon2 dot cainetworks dot com
GCC build triplet: i486-pc-linux-gnu
GCC host triplet: i486-pc-linux-gnu
GCC target triplet: i486-pc-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26144
^ permalink raw reply [flat|nested] 4+ messages in thread* [Bug tree-optimization/26144] with -O3 and pointer casts, gcc skips if 2006-02-07 0:42 [Bug tree-optimization/26144] New: with -O3 and pointer casts, gcc skips if gcc-bugzilla at gcc dot gnu dot org @ 2006-02-07 0:53 ` pinskia at gcc dot gnu dot org 2006-02-07 17:07 ` devin at freeshell dot org 2006-02-09 1:02 ` pinskia at gcc dot gnu dot org 2 siblings, 0 replies; 4+ messages in thread From: pinskia at gcc dot gnu dot org @ 2006-02-07 0:53 UTC (permalink / raw) To: gcc-bugs ------- Comment #1 from pinskia at gcc dot gnu dot org 2006-02-07 00:53 ------- I cannot reproduce this at all with 4.0.3 20051105. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26144 ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug tree-optimization/26144] with -O3 and pointer casts, gcc skips if 2006-02-07 0:42 [Bug tree-optimization/26144] New: with -O3 and pointer casts, gcc skips if gcc-bugzilla at gcc dot gnu dot org 2006-02-07 0:53 ` [Bug tree-optimization/26144] " pinskia at gcc dot gnu dot org @ 2006-02-07 17:07 ` devin at freeshell dot org 2006-02-09 1:02 ` pinskia at gcc dot gnu dot org 2 siblings, 0 replies; 4+ messages in thread From: devin at freeshell dot org @ 2006-02-07 17:07 UTC (permalink / raw) To: gcc-bugs ------- Comment #2 from devin at freeshell dot org 2006-02-07 17:07 ------- I could reproduce it with that dated build. And it isn't just debian but also the buildroot gcc. Here is the assembly produced from -O3. Following that is the assembly from -O2. What seems to happen is that with -O3 foo() is optimized out and in it's place .LC0 is stored on the stack. Seems fine. But then the original value of "ptr" is used for calling printf instead of the updated value from the stack. .file "test.c" .section .rodata.str1.1,"aMS",@progbits,1 .LC0: .string "" .text .p2align 4,,15 .globl foo .type foo, @function foo: pushl %ebp movl %esp, %ebp movl 8(%ebp), %eax movl $.LC0, (%eax) popl %ebp ret .size foo, .-foo .section .rodata.str1.1 .LC1: .string "%p" .text .p2align 4,,15 .globl main .type main, @function main: pushl %ebp movl %esp, %ebp subl $24, %esp movl 12(%ebp), %eax andl $-16, %esp subl $16, %esp movl 4(%eax), %eax testl %eax, %eax movl %eax, -4(%ebp) je .L8 movl %eax, 4(%esp) movl $.LC1, (%esp) call printf xorl %eax, %eax leave ret .p2align 4,,7 .L8: movl $.LC0, -4(%ebp) movl %eax, 4(%esp) movl $.LC1, (%esp) call printf xorl %eax, %eax leave ret .size main, .-main .ident "GCC: (GNU) 4.0.3 20060128 (prerelease) (Debian 4.0.2-8)" .section .note.GNU-stack,"",@progbits ############## Correct Version ######################### .file "test.c" .section .rodata.str1.1,"aMS",@progbits,1 .LC0: .string "" .text .p2align 4,,15 .globl foo .type foo, @function foo: pushl %ebp movl %esp, %ebp movl 8(%ebp), %eax movl $.LC0, (%eax) popl %ebp ret .size foo, .-foo .section .rodata.str1.1 .LC1: .string "%p" .text .p2align 4,,15 .globl main .type main, @function main: pushl %ebp movl %esp, %ebp subl $24, %esp movl 12(%ebp), %eax andl $-16, %esp subl $16, %esp movl 4(%eax), %eax testl %eax, %eax movl %eax, -4(%ebp) je .L8 movl -4(%ebp), %eax movl $.LC1, (%esp) movl %eax, 4(%esp) call printf xorl %eax, %eax leave ret .p2align 4,,7 .L8: leal -4(%ebp), %eax movl %eax, (%esp) call foo movl -4(%ebp), %eax movl $.LC1, (%esp) movl %eax, 4(%esp) call printf xorl %eax, %eax leave ret .size main, .-main .ident "GCC: (GNU) 4.0.3 20060128 (prerelease) (Debian 4.0.2-8)" .section .note.GNU-stack,"",@progbits -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26144 ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug tree-optimization/26144] with -O3 and pointer casts, gcc skips if 2006-02-07 0:42 [Bug tree-optimization/26144] New: with -O3 and pointer casts, gcc skips if gcc-bugzilla at gcc dot gnu dot org 2006-02-07 0:53 ` [Bug tree-optimization/26144] " pinskia at gcc dot gnu dot org 2006-02-07 17:07 ` devin at freeshell dot org @ 2006-02-09 1:02 ` pinskia at gcc dot gnu dot org 2 siblings, 0 replies; 4+ messages in thread From: pinskia at gcc dot gnu dot org @ 2006-02-09 1:02 UTC (permalink / raw) To: gcc-bugs ------- Comment #3 from pinskia at gcc dot gnu dot org 2006-02-09 01:02 ------- You are violating aliasing rules which is why this does not work at -O3. Either access the variable ptr as a "struct blah *" or use -fno-strict-aliasing. *** This bug has been marked as a duplicate of 21920 *** -- pinskia at gcc dot gnu dot org changed: What |Removed |Added ---------------------------------------------------------------------------- Status|UNCONFIRMED |RESOLVED Resolution| |DUPLICATE http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26144 ^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2006-02-09 1:02 UTC | newest] Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2006-02-07 0:42 [Bug tree-optimization/26144] New: with -O3 and pointer casts, gcc skips if gcc-bugzilla at gcc dot gnu dot org 2006-02-07 0:53 ` [Bug tree-optimization/26144] " pinskia at gcc dot gnu dot org 2006-02-07 17:07 ` devin at freeshell dot org 2006-02-09 1:02 ` pinskia at gcc dot gnu dot org
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