Consider expression "0.0 - X" as the negation of X if

- this expression is explicitly marked no-signed-zero, or
  - no-signed-zero of this expression can be derived from some context.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@171922 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/IR/Constant.h

@@ -61,6 +61,9 @@ public:
   /// by getZeroValueForNegation.
   bool isNegativeZeroValue() const;
 
+  /// Return true if the value is negative zero or null value.
+  bool isZeroValue() const;
+
   /// canTrap - Return true if evaluation of this constant could trap.  This is
   /// true for things like constant expressions that could divide by zero.
   bool canTrap() const;