PPC: Teach FMA mutate to respect register classes.

This was causing bad code gen and assembly that won't assemble, as
mixed altivec and vsx code would end up with a vsx high register
assigned to an altivec instruction, which won't work. Constraining the
classes allows the optimization to proceed.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@255299 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed