[llvm] [GlobalISel] Micro-optimize getConstantVRegValWithLookThrough (PR #91969)

[Pierre van Houtryve via llvm-commits]

Pierre-vh wrote:

> How are you benchmarking MatchTable for these changes? Not saying you have to do this, but I'd be curious to see if we still see gains with LTO builds of llvm.

I was writing a comment but then it got too long so I just added it to the thread, let's continue the discussion there: https://discourse.llvm.org/t/rfc-measuring-globalisel-compile-time-performance/78412/19

https://github.com/llvm/llvm-project/pull/91969