[PATCH] D20907: [IfConversion] Bugfix: don't add Undef flag on use if reg is live.

[Krzysztof Parzyszek via llvm-commits]

kparzysz added a comment.

In http://reviews.llvm.org/D20907#461968, @jonpa wrote:

> My question was regarding design issues, but this is still a needed bugfix.


In terms of complexity there is no benefit of adding tied uses, since you'd need to keep track of their liveness the same way as with implicit uses.  If you have a predicated instruction that defines a register that has already been defined prior to that point, the implicit use/tied use would have to be "not undef", otherwise it could get reordered with the prior definition.


http://reviews.llvm.org/D20907