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> 1. copyRegToReg() won't be able to use register classes to pick a copy opcode. For instance, an XMM register will no longer be copied by MOVSS or MOVSD. Given just the physical register, MOVAPS will be used. Is that a problem? I haven't had time to really look into it, but have been playing around with the idea that instead of two register classes copyRegToReg and some of the load

I am considering adding a new target independent codegen-only COPY instruction to our MachineInstr representation. It would be used to replace INSERT_SUBREG, EXTRACT_SUBREG, and virtual register copies after instruction selection. Selection DAG still needs {INSERT,EXTRACT}_SUBREG, but they would not appear as MachineInstrs any longer. The COPY instruction handles subreg operations with less