[clang] [llvm] [ValueTracking] use KnownBits to compute fpclass from bitcast (PR #97762)

[Matt Arsenault via cfe-commits]

arsenm wrote:

> Don't do this. It is a trap of code coverage. We need to strike a balance between optimizations, compilation time and maintainability.

I think just about any of these can appear in math library code. Comprehensively modeling operations can find surprising optimizations you might not have manually noticed 

https://github.com/llvm/llvm-project/pull/97762