[Attributor] Clamp operator to extend known state

Summary:
Similar to `^=` operator for IntegerState, this patch introduces a `+=` operator to "clamp" known information.

Reviewers: jdoerfert, sstefan1

Reviewed By: jdoerfert

Subscribers: llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D66635

llvm-svn: 370015

llvm/include/llvm/Transforms/IPO/Attributor.h

@@ -940,6 +940,13 @@ struct IntegerState : public AbstractState {
     return *this;
   }
 
+  /// "Clamp" this state with \p R. The result is the maximum of the known
+  /// information but not more than what was assumed before.
+  IntegerState operator+=(const IntegerState &R) {
+    takeKnownMaximum(R.Known);
+    return *this;
+  }
+
   /// Make this the minimum, known and assumed, of this state and \p R.
   IntegerState operator&=(const IntegerState &R) {
     Known = std::min(Known, R.Known);
@@ -1445,6 +1452,13 @@ struct DerefState : AbstractState {
     return *this;
   }
 
+  /// See IntegerState::operator+=
+  DerefState operator+=(const DerefState &R) {
+    DerefBytesState += R.DerefBytesState;
+    GlobalState += R.GlobalState;
+    return *this;
+  }
+
   /// See IntegerState::operator&=
   DerefState operator&=(const DerefState &R) {
     DerefBytesState &= R.DerefBytesState;