[llvm] [MachineLICM] Relax overlay conservative PHI check (PR #67186)

[Nikita Popov via llvm-commits]

nikic wrote:

Due to the merge we have some compile-time numbers: http://llvm-compile-time-tracker.com/compare.php?from=7b3bbd83c0c24087072ec5b22a76799ab31f87d5&to=71a8d2e3064fcb3ff76565e6e8529613f90aa51b&stat=instructions%3Au

This causes significant overhead in some cases, e.g. libclamav_autoit.c goes up by 3.5% and libclamav_htmlnorm.c goes up by 6%. Please mitigate compile-time regressions before resubmitting this.

https://github.com/llvm/llvm-project/pull/67186