[Bug c/57080] New: Invalid optimization (-O2) when doing double -> int conversion (on big endian archs(?))

["ondrej at sury dot org" <gcc-bugzilla@gcc.gnu.org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57080

             Bug #: 57080
           Summary: Invalid optimization (-O2) when doing double -> int
                    conversion (on big endian archs(?))
    Classification: Unclassified
           Product: gcc
           Version: 4.7.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: ondrej@sury.org


Reproduceable on:

Using built-in specs.
COLLECT_GCC=gcc-4.6
COLLECT_LTO_WRAPPER=/usr/lib/gcc/ia64-linux-gnu/4.6/lto-wrapper
Target: ia64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Debian 4.6.3-15'
--with-bugurl=file:///usr/share/doc/gcc-4.6/README.Bugs
--enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr
--program-suffix=-4.6 --enable-shared --enable-linker-build-id
--with-system-zlib --libexecdir=/usr/lib --without-included-gettext
--enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.6
--libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu
--enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-gnu-unique-object
--disable-libssp --enable-plugin --enable-objc-gc --with-system-libunwind
--enable-checking=release --build=ia64-linux-gnu --host=ia64-linux-gnu
--target=ia64-linux-gnu
Thread model: posix
gcc version 4.6.3 (Debian 4.6.3-15) 

and

Using built-in specs.
COLLECT_GCC=gcc-4.7
COLLECT_LTO_WRAPPER=/usr/lib/gcc/ia64-linux-gnu/4.7/lto-wrapper
Target: ia64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Debian 4.7.2-5'
--with-bugurl=file:///usr/share/doc/gcc-4.7/README.Bugs
--enable-languages=c,c++,go,fortran,objc,obj-c++ --prefix=/usr
--program-suffix=-4.7 --enable-shared --enable-linker-build-id
--with-system-zlib --libexecdir=/usr/lib --without-included-gettext
--enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.7
--libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu
--enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-gnu-unique-object
--disable-libssp --disable-libitm --enable-plugin --enable-objc-gc
--with-system-libunwind --enable-checking=release --build=ia64-linux-gnu
--host=ia64-linux-gnu --target=ia64-linux-gnu
Thread model: posix
gcc version 4.7.2 (Debian 4.7.2-5) 


This bug manifest itself on ia64, powerpc and s390x (all Big Endian[1]) where
gcc-4.6 is used and the optmized code (-O2) fails to produce correct math
results.

This code from libgd2:src/gd.c:clip_1d:

  *y1 -= m * (*x1 - mindim);

where

  m = (double) -0.050000
  *x1 = -200
  mindim = 0
  *y1 = 15

results in *y1 = 4, which is incorrect value, since it should be 5.

Most simple workaround, which allows gcc to produce correct value:

  *y1 -= (int)(m * (*x1 - mindim));

Assigning to some other variable also works ok:

  int t;
  t = m * (*x1 - mindim);
  *y1 -= t;

Compiling with -O0 also produces correct value.

1. Although SPARC, which should be B-E too, was built correctly.