[MachineVerifier] Improve verification of live-in lists.

Authored by jonpa on Nov 4 2019, 6:59 AM.


[MachineVerifier] Improve verification of live-in lists.

MachineVerifier::visitMachineFunctionAfter() is extended to check the
live-through case for live-in lists. This is only done for registers without
aliases and that are neither allocatable or reserved, such as the SystemZ::CC

The MachineVerifier earlier only catched the case of a live-in use without
an entry in the live-in list (as "using an undefined physical register").

A comment in LivePhysRegs.h has been added stating a guarantee that
addLiveOuts() can be trusted for a full register both before and after
register allocation.

Review: Quentin Colombet