The initial switchover to regalloc2 retains the mechanism by which calls signal clobbered physical registers, namely, via phantom defs (defs that are immediately dead and are constrained to those regs). regalloc2 has an explicit mechanism for clobbers which is a bit more precise and possibly ever-so-slightly faster (skips liveness analysis); we should use that instead. No functional correctness implications either way.
The initial switchover to regalloc2 retains the mechanism by which calls signal clobbered physical registers, namely, via phantom defs (defs that are immediately dead and are constrained to those regs). regalloc2 has an explicit mechanism for clobbers which is a bit more precise and possibly ever-so-slightly faster (skips liveness analysis); we should use that instead. No functional correctness implications either way.