We regard a function as 'unused' from the codegen perspective, so our warnings diverge from

gcc's unused warnings which don't get emitted if the function is referenced even in an unevaluated context
(e.g. in templates, sizeof, etc.). Also, saying that a function is 'unused' because it won't get codegen'ed
is somewhat misleading.

- Don't emit 'unused' warnings for functions that are referenced in any part of the user's code.
- A warning that an internal function/variable won't get emitted is useful though, so introduce
  -Wunneeded-internal-declaration which will warn if a function/variable with internal linkage is not
  "needed" ('used' from the codegen perspective), e.g:

  static void foo() { }

  template <int>
  void bar() {
    foo();
  }

test.cpp:1:13: warning: function 'foo' is not needed and will not be emitted
static void foo() { }
            ^

Addresses rdar://8733476.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@129794 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 13 insertions, 2 deletions

diff --git a/include/clang/AST/DeclBase.h b/include/clang/AST/DeclBase.h
index 1656240bc4..0473d1ca1f 100644
--- a/include/clang/AST/DeclBase.h
+++ b/include/clang/AST/DeclBase.h
@@ -227,6 +227,12 @@ private:
   /// required.
   unsigned Used : 1;
 
+  /// \brief Whether this declaration was "referenced".
+  /// The difference with 'Used' is whether the reference appears in a
+  /// evaluated context or not, e.g. functions used in uninstantiated templates
+  /// are regarded as "referenced" but not "used".
+  unsigned Referenced : 1;
+
 protected:
   /// Access - Used by C++ decls for the access specifier.
   // NOTE: VC++ treats enums as signed, avoid using the AccessSpecifier enum
@@ -261,7 +267,7 @@ protected:
   Decl(Kind DK, DeclContext *DC, SourceLocation L)
     : NextDeclInContext(0), DeclCtx(DC),
       Loc(L), DeclKind(DK), InvalidDecl(0),
-      HasAttrs(false), Implicit(false), Used(false),
+      HasAttrs(false), Implicit(false), Used(false), Referenced(false),
       Access(AS_none), PCHLevel(0), ChangedAfterLoad(false),
       IdentifierNamespace(getIdentifierNamespaceForKind(DK)),
       HasCachedLinkage(0) 
@@ -271,7 +277,7 @@ protected:
 
   Decl(Kind DK, EmptyShell Empty)
     : NextDeclInContext(0), DeclKind(DK), InvalidDecl(0),
-      HasAttrs(false), Implicit(false), Used(false),
+      HasAttrs(false), Implicit(false), Used(false), Referenced(false),
       Access(AS_none), PCHLevel(0), ChangedAfterLoad(false),
       IdentifierNamespace(getIdentifierNamespaceForKind(DK)),
       HasCachedLinkage(0)
@@ -408,6 +414,11 @@ public:
 
   void setUsed(bool U = true) { Used = U; }
 
+  /// \brief Whether this declaration was referenced.
+  bool isReferenced() const;
+
+  void setReferenced(bool R = true) { Referenced = R; }
+
   /// \brief Determine the availability of the given declaration.
   ///
   /// This routine will determine the most restrictive availability of