A decl never becomes unused. Make that explicit in the API.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@193248 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Sema/SemaDecl.cpp b/lib/Sema/SemaDecl.cpp
index bc7be6d..ba78928 100644
--- a/lib/Sema/SemaDecl.cpp
+++ b/lib/Sema/SemaDecl.cpp
@@ -2801,7 +2801,8 @@
     New->setPure();
 
   // Merge "used" flag.
-  New->setIsUsed(Old->getMostRecentDecl()->isUsed(false));
+  if (Old->getMostRecentDecl()->isUsed(false))
+    New->setIsUsed();
 
   // Merge attributes from the parameters.  These can mismatch with K&R
   // declarations.
@@ -3114,7 +3115,8 @@
   }
 
   // Merge "used" flag.
-  New->setIsUsed(Old->getMostRecentDecl()->isUsed(false));
+  if (Old->getMostRecentDecl()->isUsed(false))
+    New->setIsUsed();
 
   // Keep a chain of previous declarations.
   New->setPreviousDecl(Old);
diff --git a/lib/Sema/SemaTemplateInstantiateDecl.cpp b/lib/Sema/SemaTemplateInstantiateDecl.cpp
index 3989c56..f5c4c72 100644
--- a/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -3378,7 +3378,8 @@
   NewVar->setAccess(OldVar->getAccess());
 
   if (!OldVar->isStaticDataMember()) {
-    NewVar->setIsUsed(OldVar->isUsed(false));
+    if (OldVar->isUsed(false))
+      NewVar->setIsUsed();
     NewVar->setReferenced(OldVar->isReferenced());
   }