[llvm] [ConstantFPRange][UnitTests] Disable exhaustive testing in debug builds (PR #111276)

[Arthur Eubanks via llvm-commits]

aeubanks wrote:

I ran IRTests and makeAllowedFCmpRegion is the longest test at 7183 ms, second is MismatchedSemantics at 1131 ms, then after that is some random death test at 472 ms.

7s in an optimized build is still non-trivial. is it possible to do some basic checks in a normal build, and exhaustive in an expensive checks build?

https://github.com/llvm/llvm-project/pull/111276