Method to disable code SSE2 generation but still use -msse2

["David Mathog" <mathog at caltech dot edu>]

My software implementation of SSE2 now passes all the testsuite
programs. In case anybody else ever needs this, it is here: 

http://saf.bio.caltech.edu/pub/software/linux_or_unix_tools/soft_emmintrin.h

I compiled that with a target program and gprof showed
all the time in resulting binary in the inlined functions.  It ran about
4X slower than the SSE2 hardware version, which is about what I
expected.  So, so far so good.  What I am worried about now is that
since it was invoked with "-msse2" the compiler may still be generating
SSE2 calls within the inlined functions.  Is there a way to definitively
disable this but still retain -msse2 on the command line?  

For instance, here is one of the software version inline functions:

/*  vector subtract the two doubles in an __m128d  */
static __inline __m128d __attribute__((__always_inline__))
_mm_sub_pd (__m128d __A, __m128d __B)
{
  return (__m128d)((__v2df)__A - (__v2df)__B);
}

In the original gcc emmintrin.h that called a builtin _explicitly_.  I
also want to avoid having the compiler use the same builtin
_implicitly_.  If it uses SSE, 3DNOW or MMX implicitly, in this example,
that would be fine, it just cannot use any SSE2 hardware.

Actually, one thing I was never very clear on, do -msse2 -m3dnow
etc. only provide access to the corresponding machine operations through
the _mm* (or whatever) definitions in the header file, or does the
compiler also figure out vector operations by itself during the
optimization phase of compilation?

Thank you,

David Mathog
mathog@caltech.edu
Manager, Sequence Analysis Facility, Biology Division, Caltech