Add template <T> ValueBase::getSingleUserOfType.

Looping over all users and returning the only user of a specific type is a
common pattern in the compiler. This method just allows for the loop to be
eliminated.

include/swift/SIL/SILValue.h

@@ -198,6 +198,9 @@ public:
   /// otherwise.
   inline Operand *getSingleUse() const;
 
+  template <class T>
+  inline T *getSingleUserOfType();
+
   /// Pretty-print the value.
   void dump() const;
   void print(raw_ostream &OS) const;
@@ -527,6 +530,19 @@ inline Operand *ValueBase::getSingleUse() const {
   return Op;
 }
 
+template <class T>
+inline T *ValueBase::getSingleUserOfType() {
+  T *Result = nullptr;
+  for (auto *Op : getUses()) {
+    if (auto *Tmp = dyn_cast<T>(Op->getUser())) {
+      if (Result)
+        return nullptr;
+      Result = Tmp;
+    }
+  }
+  return Result;
+}
+
 /// A constant-size list of the operands of an instruction.
 template <unsigned N> class FixedOperandList {
   Operand Buffer[N];