improve comments.

[oota-llvm.git] / include / llvm / Value.h

diff --git a/include/llvm/Value.h b/include/llvm/Value.h
index a38d8cb8d9846a895a210827b7ec217575453f37..7e7b415ffdeed671b1ba2ec26cf13a283633a236 100644 (file)
--- a/include/llvm/Value.h
+++ b/include/llvm/Value.h
@@ -62,6 +62,12 @@ class Value {
   const unsigned char SubclassID;   // Subclass identifier (for isa/dyn_cast)
   unsigned char HasValueHandle : 1; // Has a ValueHandle pointing to this?
 protected:
+  /// SubclassOptionalData - This member is similar to SubclassData, however it
+  /// is for holding information which may be used to aid optimization, but
+  /// which may be cleared to zero without affecting conservative
+  /// interpretation.
+  unsigned char SubclassOptionalData : 7;
+
   /// SubclassData - This member is defined by this class, but is not used for
   /// anything.  Subclasses can use it to hold whatever state they find useful.
   /// This field is initialized to zero by the ctor.
@@ -140,6 +146,12 @@ public:
   // Only use when in type resolution situations!
   void uncheckedReplaceAllUsesWith(Value *V);
 
+  /// clearOptionalData - Clear any optional optimization data from this Value.
+  /// Transformation passes must call this method whenever changing the IR
+  /// in a way that would affect the values produced by this Value, unless
+  /// it takes special care to ensure correctness in some other way.
+  void clearOptionalData() { SubclassOptionalData = 0; }
+
   //----------------------------------------------------------------------
   // Methods for handling the chain of uses of this Value.
   //