SIL: add a lazy_property_getter flag to SILFunction

It is set on getter-functions for lazy properties.

include/swift/SIL/SILFunction.h

@@ -118,6 +118,13 @@ class SILFunction
 public:
   using BlockListType = llvm::iplist<SILBasicBlock>;
 
+  // For more information see docs/SIL.rst
+  enum class Purpose : uint8_t {
+    None,
+    GlobalInit,
+    LazyPropertyGetter
+  };
+
 private:
   friend class SILBasicBlock;
   friend class SILModule;
@@ -183,6 +190,8 @@ private:
   /// should use weak linking.
   AvailabilityContext Availability;
 
+  Purpose specialPurpose = Purpose::None;
+
   /// This is the number of uses of this SILFunction inside the SIL.
   /// It does not include references from debug scopes.
   unsigned RefCount = 0;
@@ -806,6 +815,8 @@ public:
   void setEffectsKind(EffectsKind E) {
     EffectsKindAttr = unsigned(E);
   }
+  
+  Purpose getSpecialPurpose() const { return specialPurpose; }
 
   /// Get this function's global_init attribute.
   ///
@@ -819,8 +830,13 @@ public:
   /// generated from a global variable access. Note that the initialization
   /// function itself does not need this attribute. It is private and only
   /// called within the addressor.
-  bool isGlobalInit() const { return GlobalInitFlag; }
-  void setGlobalInit(bool isGI) { GlobalInitFlag = isGI; }
+  bool isGlobalInit() const { return specialPurpose == Purpose::GlobalInit; }
+
+  bool isLazyPropertyGetter() const {
+    return specialPurpose == Purpose::LazyPropertyGetter;
+  }
+
+  void setSpecialPurpose(Purpose purpose) { specialPurpose = purpose; }
 
   /// Return whether this function has a foreign implementation which can
   /// be emitted on demand.