Ian Lance Taylor wrote:
"Liu, Lei"<lei.liu2@xxxxxxxxxxxxx> writes:
Here is my program.
#include<stdio.h>
struct s1 {
unsigned int a,b,c;
};
struct s2 {
unsigned int b,c;
};
int main(void)
{
struct s1 s;
s.c = 0xdead;
struct s2 *p = (struct s2*)&s.b;
p->c = 0xbeef;
printf("s.c=%04x\n", s.c);
return 0;
}
I compile this code with '-O2' flag and get a 's.c=dead'. It's
reasonable under strict aliasing rule. But when I recompile it with
-O2 -fno-strict-aliasing', the output is still 's.c=dead'.
I don't see this when I use -fno-strict-aliasing. I see the "s.c=beef"
as you expect. That is with gcc 4.4.3 on x86_64. What version of gcc
are you using?
Ian
I'm using gcc 4.3.3.
Using built-in specs.
Target: i486-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu
4.3.3-5ubuntu4' --with-bugurl=file:///usr/share/doc/gcc-4.3/README.Bugs
--enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr
--enable-shared --with-system-zlib --libexecdir=/usr/lib
--without-included-gettext --enable-threads=posix --enable-nls
--with-gxx-include-dir=/usr/include/c++/4.3 --program-suffix=-4.3
--enable-clocale=gnu --enable-libstdcxx-debug --enable-objc-gc
--enable-mpfr --enable-targets=all --with-tune=generic
--enable-checking=release --build=i486-linux-gnu --host=i486-linux-gnu
--target=i486-linux-gnu
Thread model: posix
gcc version 4.3.3 (Ubuntu 4.3.3-5ubuntu4)
Is it a fixed bug of gcc?
Lei
