I am happily using compilers for just register allocation, spills, and scheduling in these use cases, but my impression is that compiler authors don't really consider compilers to be especially good at inputs like this where the user has already chosen the instructions and just wants register allocation, spills, and scheduling. The problem is known to be hard and the solutions we have are mostly heuristics tuned for very small numbers of live variables, which is the opposite of what you have if you want to do anything while you wait for your multiplies to be done.

Instruction selection as you said is mostly absent. Compilers will not substitute or for blend or shift for shuffle even in cases where they are trivially equivalent, so the programmer has to know what execution ports are available anyway =/