[PATCH] D60333: [X86][SSE] SimplifyDemandedBitsForTargetNode - Add PACKSS support

[Simon Pilgrim via Phabricator via llvm-commits]

RKSimon marked an inline comment as done.
RKSimon added inline comments.


================
Comment at: lib/Target/X86/X86ISelLowering.cpp:33526
+                               KnownRHS, TLO, Depth + 1))
+        return true;
+    }
----------------
nikic wrote:
> Could use the known bits to determine the sign bit:
> 
> ```
> if (KnownLHS.isNegative() && KnownRHS.isNegative())
>   Known.makeNegative();
> else if (KnownLHS.isNonNegative() && KnownRHS.isNonNegative())
>   Known.makeNonNegative();
> ```
This needs test coverage which is proving tricky to create useful tests for - I'll add a TODO.


Repository:
  rL LLVM

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D60333/new/

https://reviews.llvm.org/D60333