[ValueTracking] Clarify comments on CannotBeOrderedLessThanZero and SignBitMustBeZero.

Reviewers: hfinkel, efriedma, sanjoy

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D28926

llvm-svn: 292691

Author: Justin Lebar

llvm/include/llvm/Analysis/ValueTracking.h

@@ -167,13 +167,25 @@ template <typename T> class ArrayRef;
   bool CannotBeNegativeZero(const Value *V, const TargetLibraryInfo *TLI,
                             unsigned Depth = 0);
 
-  /// Return true if we can prove that the specified FP value is either a NaN or
-  /// never less than 0.0.
-  /// If \p IncludeNeg0 is false, -0.0 is considered less than 0.0.
+  /// Return true if we can prove that the specified FP value is either NaN or
+  /// never less than -0.0.
+  ///
+  ///      NaN --> true
+  ///       +0 --> true
+  ///       -0 --> true
+  ///   x > +0 --> true
+  ///   x < -0 --> false
+  ///
   bool CannotBeOrderedLessThanZero(const Value *V, const TargetLibraryInfo *TLI);
 
-  /// \returns true if we can prove that the specified FP value has a 0 sign
-  /// bit.
+  /// Return true if we can prove that the specified FP value's sign bit is 0.
+  ///
+  ///      NaN --> true/false (depending on the NaN's sign bit)
+  ///       +0 --> true
+  ///       -0 --> false
+  ///   x > +0 --> true
+  ///   x < -0 --> false
+  ///
   bool SignBitMustBeZero(const Value *V, const TargetLibraryInfo *TLI);
 
   /// If the specified value can be set by repeating the same byte in memory,