[Bug c++/20729] New: Bitwise operations work wrong with -O2 or -O3 optimization

[evgeny at nowecom dot ru]

I wrote the following testcase:

#include <iostream>

using namespace std;

inline bool sign(double x){return !((*(((unsigned int*)&(x)) + 1))&0x80000000);}
inline bool sign1(double x){return (x>=0.0);}

inline bool cmp(double x,double y){
return ((*(((unsigned int*)&(x)) + 1))&0x80000000)^((*(((unsigned int*)&(y)) +
1))&0x80000000);
}

inline bool cmp1(double x,double y){
return ((x>=0.0)!=(y>=0.0));
}

int main(void){
double a(1.0),b(1.0);

cout << sign(a) << " " << sign(b) << " " << sign1(a) << " " << sign1(b) << endl;
cout << cmp(a,b) << " " << cmp1(a,b) << endl;
cout << a << " " << b << endl;
}

Its output is:
g++-3.4 test.cpp -O3 && ./a.out
0 1 1 1
1 0
1 1

g++ test.cpp -O3 && ./a.out
1 1 1 1
1 0
1 1

g++-3.4 -v
Reading specs from /usr/local/lib/gcc/i686-pc-linux-gnu/3.4.3/specs
Configured with: ./configure --prefix=/usr/local --program-suffix=-3.4
--enable-threads=posix --with-cpu=i686 --with-arch=i686 --disable-nls
Thread model: posix
gcc version 3.4.3

g++ -v
Reading specs from /usr/lib/gcc-lib/i586-suse-linux/3.3.2/specs
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
Thread model: posix
gcc version 3.3.2 20031216 (prerelease) (SuSE Linux)

But the right output is:
1 1 1 1
0 0
1 1 

It can be reached at any optimization level by using flag -fno-schedule-insns2.

-- 
           Summary: Bitwise operations work wrong with -O2 or -O3
                    optimization
           Product: gcc
           Version: 3.4.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: evgeny at nowecom dot ru
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20729