As long as you avoid unspecified instructions (reciprocal square-root estimate, fsin) and avoid library functions or code-gen that takes different paths when SSE2/AVX/whatever are available and as long as you run the same binary on every machine (compatibility between PowerPC and x86 is much harder) you can definitely do it. Many games have.
So, if you can restrict yourself to x86 CPUs it's manageable, at least for modest sized chunks of code.
https://randomascii.wordpress.com/2013/07/16/floating-point-...
As long as you avoid unspecified instructions (reciprocal square-root estimate, fsin) and avoid library functions or code-gen that takes different paths when SSE2/AVX/whatever are available and as long as you run the same binary on every machine (compatibility between PowerPC and x86 is much harder) you can definitely do it. Many games have.
So, if you can restrict yourself to x86 CPUs it's manageable, at least for modest sized chunks of code.