[PATCH] D148533: ValueTracking: Improve trunc handling in computeKnownFPClass

[Jay Foad via Phabricator via llvm-commits]

foad added inline comments.


================
Comment at: llvm/lib/Analysis/ValueTracking.cpp:4606
+        if (KnownSrc.isKnownNever(fcPosSubnormal | fcPosNormal))
+          Known.knownNot(fcPosZero);
+
----------------
This seems wrong - the result could be poszero if the input is poszero.

Same for negzero below.


================
Comment at: llvm/lib/Analysis/ValueTracking.cpp:4612
+        // Sign should be preserved
+        Known.SignBit = KnownSrc.SignBit;
         break;
----------------
Seems reasonable but is this actually documented anywhere (when the result is zero)?


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D148533/new/

https://reviews.llvm.org/D148533