[SIL] Add getProperty to AssignOrInit instruction

This aim to compensate the fact that not all of the changes
were cherry-picked to 5.9.

Author: xedin

include/swift/SIL/SILInstruction.h

@@ -4962,6 +4962,8 @@ class AssignOrInitInst
   SILValue getInitializer() const { return Operands[2].get(); }
   SILValue getSetter() { return  Operands[3].get(); }
 
+  VarDecl *getProperty() const;
+
   Mode getMode() const {
     return Mode(sharedUInt8().AssignOrInitInst.mode);
   }

lib/SIL/IR/SILInstructions.cpp

@@ -1283,6 +1283,12 @@ bool AssignOrInitInst::isPropertyAlreadyInitialized(unsigned propertyIdx) {
   return Assignments.test(propertyIdx);
 }
 
+VarDecl *AssignOrInitInst::getProperty() const {
+  auto *accessor = getReferencedInitAccessor();
+  assert(accessor);
+  return cast<VarDecl>(accessor->getStorage());
+}
+
 StringRef AssignOrInitInst::getPropertyName() const {
   auto *accessor = getReferencedInitAccessor();
   assert(accessor);