[Bug c++/49949] New: wrong sign for product of complex<double> and double with -O2

[Bug c++/49949] New: wrong sign for product of complex<double> and double with -O2

[begovic79 at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49949

           Summary: wrong sign for product of complex<double> and double
                    with -O2
           Product: gcc
           Version: 4.5.2
            Status: UNCONFIRMED
          Severity: minor
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: begovic79@gmail.com


With the -O2 flag and in a very specialized circumstance, the product of a
complex<double> and a double has the wrong sign.

The problem arises when the blitz++ array library is used.
(http://www.oonumerics.org/blitz/) Unfortunately, I could not prune out all the
references to the unnecessary C++ standard libraries. The size of the .ii file
is therefore pretty big. I hope the report will still be useful.

The output of the executable gcc_complex_bug should be

(-0.0,-1.0)x100.0=(0.0,100.0)

which shows the wrong sign for the product.

The following is the output of "g++ -v -save-temps -I. -O2 -o gcc_complex_bug
gcc_complex_bug.cpp"

Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/lib/x86_64-linux-gnu/gcc/x86_64-linux-gnu/4.5.2/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro
4.5.2-8ubuntu4' --with-bugurl=file:///usr/share/doc/gcc-4.5/README.Bugs
--enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr
--program-suffix=-4.5 --enable-shared --enable-multiarch
--with-multiarch-defaults=x86_64-linux-gnu --enable-linker-build-id
--with-system-zlib --libexecdir=/usr/lib/x86_64-linux-gnu
--without-included-gettext --enable-threads=posix
--with-gxx-include-dir=/usr/include/c++/4.5 --libdir=/usr/lib/x86_64-linux-gnu
--enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug
--enable-libstdcxx-time=yes --enable-plugin --enable-gold --enable-ld=default
--with-plugin-ld=ld.gold --enable-objc-gc --disable-werror --with-arch-32=i686
--with-tune=generic --enable-checking=release --build=x86_64-linux-gnu
--host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 4.5.2 (Ubuntu/Linaro 4.5.2-8ubuntu4) 
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-I.' '-O2' '-o' 'gcc_complex_bug'
'-shared-libgcc' '-mtune=generic' '-march=x86-64'
 /usr/lib/x86_64-linux-gnu/gcc/x86_64-linux-gnu/4.5.2/cc1plus -E -quiet -v -I.
-D_GNU_SOURCE gcc_complex_bug.cpp -D_FORTIFY_SOURCE=2 -mtune=generic
-march=x86-64 -O2 -fpch-preprocess -fstack-protector -o gcc_complex_bug.ii
ignoring nonexistent directory "/usr/local/include/x86_64-linux-gnu"
ignoring nonexistent directory
"/usr/lib/x86_64-linux-gnu/gcc/x86_64-linux-gnu/4.5.2/../../../../../x86_64-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:
 .
 /usr/include/c++/4.5
 /usr/include/c++/4.5/x86_64-linux-gnu
 /usr/include/c++/4.5/backward
 /usr/local/include
 /usr/lib/x86_64-linux-gnu/gcc/x86_64-linux-gnu/4.5.2/include
 /usr/lib/x86_64-linux-gnu/gcc/x86_64-linux-gnu/4.5.2/include-fixed
 /usr/include/x86_64-linux-gnu
 /usr/include
End of search list.
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-I.' '-O2' '-o' 'gcc_complex_bug'
'-shared-libgcc' '-mtune=generic' '-march=x86-64'
 /usr/lib/x86_64-linux-gnu/gcc/x86_64-linux-gnu/4.5.2/cc1plus -fpreprocessed
gcc_complex_bug.ii -quiet -dumpbase gcc_complex_bug.cpp -mtune=generic
-march=x86-64 -auxbase gcc_complex_bug -O2 -version -fstack-protector -o
gcc_complex_bug.s
GNU C++ (Ubuntu/Linaro 4.5.2-8ubuntu4) version 4.5.2 (x86_64-linux-gnu)
    compiled by GNU C version 4.5.2, GMP version 4.3.2, MPFR version 3.0.0-p8,
MPC version 0.9
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
GNU C++ (Ubuntu/Linaro 4.5.2-8ubuntu4) version 4.5.2 (x86_64-linux-gnu)
    compiled by GNU C version 4.5.2, GMP version 4.3.2, MPFR version 3.0.0-p8,
MPC version 0.9
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: 1a8763bcd4db37297f4ae8b8aab36cf0
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-I.' '-O2' '-o' 'gcc_complex_bug'
'-shared-libgcc' '-mtune=generic' '-march=x86-64'
 as -V -Qy --64 -o gcc_complex_bug.o gcc_complex_bug.s
GNU assembler version 2.21.0 (x86_64-linux-gnu) using BFD version (GNU Binutils
for Ubuntu) 2.21.0.20110327
COMPILER_PATH=/usr/lib/x86_64-linux-gnu/gcc/x86_64-linux-gnu/4.5.2/:/usr/lib/x86_64-linux-gnu/gcc/x86_64-linux-gnu/4.5.2/:/usr/lib/x86_64-linux-gnu/gcc/x86_64-linux-gnu/:/usr/lib/x86_64-linux-gnu/gcc/x86_64-linux-gnu/4.5.2/:/usr/lib/x86_64-linux-gnu/gcc/x86_64-linux-gnu/
LIBRARY_PATH=/usr/lib/x86_64-linux-gnu/gcc/x86_64-linux-gnu/4.5.2/:/usr/lib/x86_64-linux-gnu/gcc/x86_64-linux-gnu/4.5.2/../../../:/lib/:/usr/lib/:/usr/lib/x86_64-linux-gnu/
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-I.' '-O2' '-o' 'gcc_complex_bug'
'-shared-libgcc' '-mtune=generic' '-march=x86-64'
 /usr/lib/x86_64-linux-gnu/gcc/x86_64-linux-gnu/4.5.2/collect2 --build-id
--eh-frame-hdr -m elf_x86_64 --hash-style=gnu -dynamic-linker
/lib64/ld-linux-x86-64.so.2 -z relro -o gcc_complex_bug
/usr/lib/x86_64-linux-gnu/gcc/x86_64-linux-gnu/4.5.2/../../../crt1.o
/usr/lib/x86_64-linux-gnu/gcc/x86_64-linux-gnu/4.5.2/../../../crti.o
/usr/lib/x86_64-linux-gnu/gcc/x86_64-linux-gnu/4.5.2/crtbegin.o
-L/usr/lib/x86_64-linux-gnu/gcc/x86_64-linux-gnu/4.5.2
-L/usr/lib/x86_64-linux-gnu/gcc/x86_64-linux-gnu/4.5.2/../../..
-L/usr/lib/x86_64-linux-gnu gcc_complex_bug.o -lstdc++ -lm -lgcc_s -lgcc -lc
-lgcc_s -lgcc /usr/lib/x86_64-linux-gnu/gcc/x86_64-linux-gnu/4.5.2/crtend.o
/usr/lib/x86_64-linux-gnu/gcc/x86_64-linux-gnu/4.5.2/../../../crtn.o

[Bug c++/49949] wrong sign for product of complex<double> and double with -O2

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49949

Richard Guenther <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |WAITING
   Last reconfirmed|                            |2011.08.03 09:40:46
     Ever Confirmed|0                           |1

--- Comment #1 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-08-03 09:40:46 UTC ---
An attachment is missing.  Please try to create a small self-contained
testcase using <complex>.

[Bug c++/49949] wrong sign for product of complex<double> and double with -O2

[begovic79 at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49949

--- Comment #2 from Ilker R Capoglu <begovic79 at gmail dot com> 2011-08-03 16:20:53 UTC ---
(In reply to comment #1)
> An attachment is missing.  Please try to create a small self-contained
> testcase using <complex>.

Sorry, I think it didn't get uploaded because it was above 1000k. I'll try and
get a smaller .ii file.

Thanks!

[Bug c++/49949] wrong sign for product of complex<double> and double with -O2

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49949

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-08-03 16:27:23 UTC ---
http://gcc.gnu.org/wiki/A_guide_to_testcase_reduction is useful

if you can't reduce it then using gzip or bzip2 might make it small enough to
attach

[Bug c++/49949] wrong sign for product of complex<double> and double with -O2

[begovic79 at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49949

--- Comment #4 from Ilker R Capoglu <begovic79 at gmail dot com> 2011-08-03 16:32:47 UTC ---
(In reply to comment #3)
> http://gcc.gnu.org/wiki/A_guide_to_testcase_reduction is useful
> 
> if you can't reduce it then using gzip or bzip2 might make it small enough to
> attach

I actually read the instructions very carefully and managed to go through a lot
of it. The problem is that (a) I'm not so familiar with the internals of the
blitz++ library to prune out the crud effectively (b) the STL headers are
buried so deep into blitz++ that it takes a blitz++ developer to take them out.

I'll try to gzip the file and resubmit, though.

[Bug c++/49949] wrong sign for product of complex<double> and double with -O2

[begovic79 at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49949

--- Comment #5 from Ilker R Capoglu <begovic79 at gmail dot com> 2011-08-03 16:34:31 UTC ---
Created attachment 24906
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=24906
The preprocessed file with the STL and blitz++ headers. (bzip2'd)

[Bug c++/49949] wrong sign for product of complex<double> and double with -O2

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49949

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|WAITING                     |NEW

--- Comment #6 from Paolo Carlini <paolo.carlini at oracle dot com> 2011-09-28 14:57:26 UTC ---
I can reproduce the problem with gcc4.5.x and 4.6.x, but mainline (would be
4.7.0) is fine. Did it ever work for you with older compilers? Because if isn't
a regression, I'm afraid that not much will happen. But would be still
interesting to understand what fixed the problem in mainline...

[Bug c++/49949] wrong sign for product of complex<double> and double with -O2

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49949

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |hjl.tools at gmail dot com
           Severity|minor                       |normal

--- Comment #7 from Paolo Carlini <paolo.carlini at oracle dot com> 2011-09-28 15:10:47 UTC ---
HJ, any chance you can find what fixed this? Doesn't seem a regression, but
it's an annoying issue anyway, if the patch is simple...

[Bug c++/49949] wrong sign for product of complex<double> and double with -O2

[hjl.tools at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49949

--- Comment #8 from H.J. Lu <hjl.tools at gmail dot com> 2011-09-28 15:54:09 UTC ---
(In reply to comment #0)
> With the -O2 flag and in a very specialized circumstance, the product of a
> complex<double> and a double has the wrong sign.
> 
> The problem arises when the blitz++ array library is used.
> (http://www.oonumerics.org/blitz/) Unfortunately, I could not prune out all the
> references to the unnecessary C++ standard libraries. The size of the .ii file
> is therefore pretty big. I hope the report will still be useful.
> 
> The output of the executable gcc_complex_bug should be
> 
> (-0.0,-1.0)x100.0=(0.0,100.0)
> 

I also got

(-0.0,-1.0)x100.0=(-0.0,-100.0)

with GCC 4.7.0 revision 179164.  Why should we get (0.0,100.0)?

[Bug c++/49949] wrong sign for product of complex<double> and double with -O2

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49949

--- Comment #9 from Paolo Carlini <paolo.carlini at oracle dot com> 2011-09-28 16:02:05 UTC ---
HJ, I think the correct output, showing that we are *not* miscompiling or
something is:

(-0.0,-1.0)x100.0=(-0.0,-100.0)

exactly what you are seeing. The problem is, with 4.6 we get:

(-0.0,-1.0)x100.0=(0.0,100.0)

which is wrong. When that changed?

[Bug c++/49949] wrong sign for product of complex<double> and double with -O2

[hjl.tools at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49949

--- Comment #10 from H.J. Lu <hjl.tools at gmail dot com> 2011-09-28 18:03:50 UTC ---
It is fixed by revision 172430:

http://gcc.gnu.org/ml/gcc-cvs/2011-04/msg00625.html

[Bug c++/49949] wrong sign for product of complex<double> and double with -O2

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49949

--- Comment #11 from Paolo Carlini <paolo.carlini at oracle dot com> 2011-09-29 15:26:30 UTC ---
Doesn't seem to make much sense, but thanks, anyway.

[Bug c++/49949] wrong sign for product of complex<double> and double with -O2

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49949

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |hubicka at gcc dot gnu.org

--- Comment #12 from Paolo Carlini <paolo.carlini at oracle dot com> 2011-09-29 15:27:56 UTC ---
Maybe Honza has ideas about this...

[Bug c++/49949] wrong sign for product of complex<double> and double with -O2

[hubicka at ucw dot cz]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49949

--- Comment #13 from Jan Hubicka <hubicka at ucw dot cz> 2011-09-30 16:26:46 UTC ---
> Maybe Honza has ideas about this...
That patch affect inlining decisions, but should not affect correctness. So it
seems that the bug whatever it is just gone latent.

Honza

[Bug c++/49949] wrong sign for product of complex<double> and double with -O2

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49949

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org,
                   |                            |paolo.carlini at oracle dot
                   |                            |com

--- Comment #14 from Paolo Carlini <paolo.carlini at oracle dot com> 2011-09-30 20:27:36 UTC ---
Hug :( We should really distill a much, much smaller snippet and analyze what
is really going wrong. Maybe Jakub could help?