Reapply "[VPlan] Use predicate from VPValue VPWidenSelectR::computeCost." (#173170)
This reverts commit f42af14073228 and re-applies
https://github.com/llvm/llvm-project/pull/172915.
It has an additional check if the condition is a live-in,
which makes sure we preserve the original behavior in that case.
This should fix the crash that caused the revert.
Original commit message:
Instead of looking up the predicate from the VPValue condition instead
of the underlying IR.
This improves cost modeling in some cases, e.g. when we can fold
operations like negations in compares. On AArch64, this leads to
additional vectorization in a few cases in practice.
Example lowering for the modified test case:
https://llvm.godbolt.org/z/6nc6jo5eG
llvm-project
44a8d9c1 - Reapply "[VPlan] Use predicate from VPValue VPWidenSelectR::computeCost." (#173170)
