Summary:
Consider an instruction that has multiple defs of the same
vreg, but defining different subregs:
%7.sub1:rc, dead %7.sub2:rc = inst
Calling checkLivenessAtDef for the live interval associated
with %7 incorrectly reported "live range continues after a
dead def". The live range for %7 has a dead def at the slot
index for "inst" even if the live range continues (given that
there are later uses of %7.sub1).
This patch adjusts MachineVerifier::checkLivenessAtDef
to allow dead subregister definitions, unless we are checking
a subrange (when tracking subregister liveness).
A limitation is that we do not detect the situation when the
live range continues past an instruction that defines the
full virtual register by multiple dead subreg defines.
I also removed some dead code related to physical register
in checkLivenessAtDef. Wwe only call that method for virtual
registers, so I added an assertion instead.
Reviewers: kparzysz
Reviewed By: kparzysz
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D52237
llvm-svn: 342618
