[llvm] [ValueTracking] Compute knownbits from known fp classes (PR #86409)

[Yingwei Zheng via llvm-commits]

dtcxzyw wrote:

Reduced test case:
```
define i32 @test(double %x) {
  %cmp = fcmp oeq double %x, 0xFFF0000000000000
  br i1 %cmp, label %if.then, label %if.else

if.then:
  %cast = bitcast double %x to i64
  %trunc = trunc i64 %cast to i32
  ret i32 %trunc

if.else:
  ret i32 0
}
```

I will post a fix.


https://github.com/llvm/llvm-project/pull/86409