[PATCH] D82602: [SelectionDAG] don't split branch on logic-of-vector-compares

[Ulrich Weigand via Phabricator via llvm-commits]

uweigand added a comment.

In D82602#2116747 <https://reviews.llvm.org/D82602#2116747>, @spatel wrote:

> 2. I missed a SystemZ test change in the earlier draft; adding SystemZ reviewers to confirm if that's an improvement.


Interesting.   The compiler now completely optimizes out all operations on one of the two vector lanes, apparently because it recognizes their value is constant and computable at compile time.  So that's an improvement (even though not one this test case was expecting to happen ...).

On the other hand, in the operations on the remaining lane, it seems the compiler is now no longer able to perform the known-bits optimization that this test is actually written for -- see the comment that says we should optimize out a redundant AND to get a compare instead of a TM (test-under-mask), but the code now actually does contain a TM (tmll).  That seems a regression at first glance.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D82602/new/

https://reviews.llvm.org/D82602