[Bug c++/18944] New: SSE ordered/unordered compare are either omitted or provoke an ICE, -ffast-math implied

[tbptbp at gmail dot com]

All versions of gcc and g++ i've tested have issues with SSE ordered/unordered
compare (vector or scalar) when -ffast-math is on; the result being either an
ICE, the instruction being omitted or rarely the Right Thing.

ie with gcc/g++ 4.0.0 20041205:
#include <xmmintrin.h>
int main() {
	__m128
		a = _mm_set1_ps(1.f/0.f),
		b = _mm_set1_ps(0),
		c = _mm_mul_ps(a,b),
		//z = _mm_setzero_ps(),
		comp = _mm_cmpunord_ps(c,c);	// ICE -O >= 1
		//comp = _mm_cmpord_ps(c,c);	// ok
		//comp = _mm_cmpord_ps(c,z);	// removed with -O >= 1
		//comp = _mm_cmpunord_ps(c,z);	// removed with -O >= 1
		//comp = _mm_cmpunord_ss(c,c);	// ok
		//comp = _mm_cmpord_ss(c,c);	// ok
		//comp = _mm_cmpord_ss(c,z);	// ok
		//comp = _mm_cmpunord_ss(c,z);	// ok

	return _mm_movemask_ps(comp);
}

$ /usr/local/gcc-405/bin/g++  sse.cpp -march=pentium4 -O1 -ffast-math
sse.cpp: In function 'int main()':
sse.cpp:7: warning: division by zero in '1.0e+0f / 0.'
sse.cpp:21: internal compiler error: in output_constant_pool_2, at varasm.c:3108
Please submit a full bug report,
with preprocessed source if appropriate.
See <URL:http://gcc.gnu.org/bugs.html> for instructions.

$ /usr/local/gcc-405/bin/gcc -v
Reading specs from /usr/local/gcc-405/lib/gcc/i686-pc-cygwin/4.0.0/specs
Configured with: ../configure --prefix=/usr/local/gcc-405
--enable-languages=c,c++ --enable-threads=posix --with-system-zlib
--disable-checking --disable-nls --disable-shared --disable-win32-registry
--verbose --with-gcc --with-gnu-ld --with-gnu-as
--with-as=/usr/local/binutils/bin/as --with-ld=/usr/local/binutils/bin/ld
Thread model: posix
gcc version 4.0.0 20041205 (experimental)

That 20041205 snapshot is the best at handling that particular issue, it's even
worse with other version. I've tried:
gcc version 3.3.3 (cygwin special)
gcc version 3.4.1 20040625 (prerelease)
gcc version 3.5.0 20040620 (experimental)

You get the same with -march=k8.
So it's not just a gcc4.0.0 problem, i don't have older version or other
platforms to test it but i guess it would be wise to check  it there too :)

-- 
           Summary: SSE ordered/unordered compare are either omitted or
                    provoke an ICE, -ffast-math implied
           Product: gcc
           Version: 4.0.0
            Status: UNCONFIRMED
          Severity: critical
          Priority: P2
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: tbptbp at gmail dot com
                CC: gcc-bugs at gcc dot gnu dot org
  GCC host triplet: cygwin


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18944