* Move branch-local register and stack allocation metadata to the
function-local struct. Conditional branches clone this data in order
to restore it after generating machine code for a branch.
Branch-local data is now only the instruction table mapping *ir.Inst
to MCValue.
* Implement conditional branching
- Process operand deaths
- Handle register and stack allocation metadata
* Avoid storing unreferenced or void typed instructions into
the branch-local instruction table.
* Fix integer types reporting the wrong value for hasCodeGenBits.
* Remove the codegen optimization for eliding length-0 jumps. I need to
reexamine how this works because it was causing invalid jumps to be
emitted.
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