[PATCH] D143195: ValueTracking: Add start of computeKnownFPClass API

[Matt Arsenault via Phabricator via llvm-commits]

arsenm added inline comments.


================
Comment at: llvm/include/llvm/Analysis/ValueTracking.h:234
+    else if (SignBit)
+      *SignBit &= *RHS.SignBit;
+
----------------
nikic wrote:
> I don't understand your logic here. If `&` is supposed to be (doc comments?) an intersection, then if one side knows the sign bit and the other doesn't, shouldn't we be using the known sign bit?
> 
> It doesn't look like `operator&=` or `commonBits()` is actually used though. It may be worthwhile to split out this class into a separate header (like KnownBits) and unit test it.
If you don't know one of the sign bits you don't know anything. & should only return true if we know both sign bits must be true


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  https://reviews.llvm.org/D143195/new/

https://reviews.llvm.org/D143195