diff --git a/include/llvm/Analysis/ValueTracking.h b/include/llvm/Analysis/ValueTracking.h
index 6bb3b3c..212b5d1 100644
--- a/include/llvm/Analysis/ValueTracking.h
+++ b/include/llvm/Analysis/ValueTracking.h
@@ -29,6 +29,12 @@
   /// known to be either zero or one and return them in the KnownZero/KnownOne
   /// bit sets.  This code only analyzes bits in Mask, in order to short-circuit
   /// processing.
+  ///
+  /// This function is defined on values with integer type, values with pointer
+  /// type (but only if TD is non-null), and vectors of integers.  In the case
+  /// where V is a vector, the mask, known zero, and known one values are the
+  /// same width as the vector element, and the bit is set only if it is true
+  /// for all of the elements in the vector.
   void ComputeMaskedBits(Value *V, const APInt &Mask, APInt &KnownZero,
                          APInt &KnownOne, const TargetData *TD = 0,
                          unsigned Depth = 0);
@@ -36,6 +42,12 @@
   /// MaskedValueIsZero - Return true if 'V & Mask' is known to be zero.  We use
   /// this predicate to simplify operations downstream.  Mask is known to be
   /// zero for bits that V cannot have.
+  ///
+  /// This function is defined on values with integer type, values with pointer
+  /// type (but only if TD is non-null), and vectors of integers.  In the case
+  /// where V is a vector, the mask, known zero, and known one values are the
+  /// same width as the vector element, and the bit is set only if it is true
+  /// for all of the elements in the vector.
   bool MaskedValueIsZero(Value *V, const APInt &Mask, 
                          const TargetData *TD = 0, unsigned Depth = 0);
 
diff --git a/lib/Analysis/ValueTracking.cpp b/lib/Analysis/ValueTracking.cpp
index aa71f1d..78bb3db 100644
--- a/lib/Analysis/ValueTracking.cpp
+++ b/lib/Analysis/ValueTracking.cpp
@@ -35,6 +35,12 @@
 /// optimized based on the contradictory assumption that it is non-zero.
 /// Because instcombine aggressively folds operations with undef args anyway,
 /// this won't lose us code quality.
+///
+/// This function is defined on values with integer type, values with pointer
+/// type (but only if TD is non-null), and vectors of integers.  In the case
+/// where V is a vector, the mask, known zero, and known one values are the
+/// same width as the vector element, and the bit is set only if it is true
+/// for all of the elements in the vector.
 void llvm::ComputeMaskedBits(Value *V, const APInt &Mask,
                              APInt &KnownZero, APInt &KnownOne,
                              const TargetData *TD, unsigned Depth) {
@@ -608,6 +614,12 @@
 /// MaskedValueIsZero - Return true if 'V & Mask' is known to be zero.  We use
 /// this predicate to simplify operations downstream.  Mask is known to be zero
 /// for bits that V cannot have.
+///
+/// This function is defined on values with integer type, values with pointer
+/// type (but only if TD is non-null), and vectors of integers.  In the case
+/// where V is a vector, the mask, known zero, and known one values are the
+/// same width as the vector element, and the bit is set only if it is true
+/// for all of the elements in the vector.
 bool llvm::MaskedValueIsZero(Value *V, const APInt &Mask,
                              const TargetData *TD, unsigned Depth) {
   APInt KnownZero(Mask.getBitWidth(), 0), KnownOne(Mask.getBitWidth(), 0);