Summary:
The comments in the code said
// Remove <def,read-undef> flags. This def is now a partial redef.
but the code didn't just remove read-undef, it could introduce new ones which
could cause errors.
E.g. if we have something like
%vreg1<def> = IMPLICIT_DEF
%vreg2:subreg1<def, read-undef> = op %vreg3, %vreg4
%vreg2:subreg2<def> = op %vreg6, %vreg7
and we merge %vreg1 and %vreg2 then we should not set undef on the second subreg
def, which the old code did.
Now we solve this by actually do what the code comment says. We remove
read-undef flags rather than remove or introduce them.
Reviewers: qcolombet, MatzeB
Reviewed By: MatzeB
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D38616
llvm-svn: 315564
a079ef68e3