[llvm] [KnownBits] Make nuw and nsw support in computeForAddSub optimal (PR #83382)

[Simon Pilgrim via llvm-commits]

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@@ -62,6 +62,11 @@ struct KnownBits {
   /// Returns true if we don't know any bits.
   bool isUnknown() const { return Zero.isZero() && One.isZero(); }
 
+  /// Returns true if we don't know the sign bit.
+  bool isSignUnknown() const {
+    return !Zero.isSignBitSet() && !One.isSignBitSet();
+  }
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RKSimon wrote:

Add unit-test coverage?

https://github.com/llvm/llvm-project/pull/83382