[PATCH] D105836: [AMDGPU] Add TII::isAmbientPhysRegUse() to allow VOP rematerialization

[Matt Arsenault via Phabricator via llvm-commits]

arsenm added a comment.

In D105836#2877763 <https://reviews.llvm.org/D105836#2877763>, @kparzysz wrote:

> Yes, that's what I meant.  I.e. not "it this register always rematerializable", but "it this register rematerializable in this situation".
>
> It will require more work, because we may need to insert instructions that restore the value of that physical register, and currently that's not happening.

We specifically do not want anything trying to manage the value of the register here. It's a predicate register and we want the value to be whatever it happens to be at that point. If the predicate was on for a lane at the def, it's fine if that bit is off at the use. The inverse would be an invalid situation to begin with


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