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

[Yingwei Zheng via llvm-commits]

dtcxzyw wrote:

Compile-time impact:
```
Top 5 improvements:
  faiss/HNSW.cpp.ll 3445921402 3333911686 -3.25%
  php/jis0208.ll 308288236 299253584 -2.93%
  spike/regnames.ll 488153333 475353793 -2.62%
  faiss/IndexAdditiveQuantizerFastScan.cpp.ll 434431627 423208324 -2.58%
  lightgbm/boosting.cpp.ll 2999781046 2927390287 -2.41%
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%
Overall: 0.00777903
```

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