[llvm] [InstCombine] Avoid Allocating Arrays Too Large For the Target (PR #70980)

[Qiongsi Wu via llvm-commits]

qiongsiwu wrote:

@arsenm @nikic Could you comment on what is the defined behaviour for an `alloca` when NumElements is negative? Is it an undefined behaviour? If so, can we replace such `alloca`s with a poison value? 

Thanks so much! 

https://github.com/llvm/llvm-project/pull/70980