Behaviour of -msse -march=athlon

[Ryan Hill]

Are -march options expected to override any relevant options specified
previously on the command line?  It appears in GCC-4.2.0 that SSE movss
instructions will be generated when for example the following code is compiled
with -msse -march=athlon:

#include <mmintrin.h>
int main() {
  __m64 v = _mm_cvtsi32_si64(1);
  return 0;
}

$ gcc -msse -march=athlon conftest.c
$ ./a.out
Illegal instruction

I would expect this from -march=athlon -msse, but would also expect
-march=athlon to imply -mno-sse and therefore cancel the previous -msse option.

This was encountered in the pixman-0.9.5 configure script.
https://bugs.gentoo.org/192048


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