[llvm] [GVN] Look through select/phi when determining underlying object (PR #99509)

[Nikita Popov via llvm-commits]

nikic wrote:

> ```
> Top 5 regressions:
>   hermes/StackPromotion.cpp.ll 5074724986 5817835860 +14.64%
>   openjdk/ad_x86_gen.ll 18909114243 20121837367 +6.41%
>   postgres/strftime.ll 404414332 421153688 +4.14%
>   lightgbm/linear_tree_learner.cpp.ll 9902392573 10299377803 +4.01%
>   meshlab/filter_screened_poisson.cpp.ll 26246454218 27101073771 +3.26%
> ```
I checked all of these, and time spent in getUnderlyingObjectsAggressive() was always tiny (think sub-0.01% level). So any regressions here are due to second-order effects (i.e. pointer replacement enabling other optimizations that take more time etc).

https://github.com/llvm/llvm-project/pull/99509