[llvm] [Don't merge][LLVM] Refine undef to null values (PR #96375)

[Yingwei Zheng via llvm-commits]

dtcxzyw wrote:

> Suspicious how many benchmarks improve...

See the result on llvm-test-suite: https://github.com/dtcxzyw/llvm-ci/pull/1158.


https://github.com/llvm/llvm-project/pull/96375