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.

llvm-svn: 129794

2 files changed, 3 insertions, 0 deletions

diff --git a/clang/lib/Serialization/ASTReaderDecl.cpp b/clang/lib/Serialization/ASTReaderDecl.cpp
index 5b4a64eeb5c..889ef7324c8 100644
--- a/clang/lib/Serialization/ASTReaderDecl.cpp
+++ b/clang/lib/Serialization/ASTReaderDecl.cpp
@@ -214,6 +214,7 @@ void ASTDeclReader::VisitDecl(Decl *D) {
   }
   D->setImplicit(Record[Idx++]);
   D->setUsed(Record[Idx++]);
+  D->setReferenced(Record[Idx++]);
   D->setAccess((AccessSpecifier)Record[Idx++]);
   D->setPCHLevel(Record[Idx++] + (F.Type <= ASTReader::PCH));
 }
diff --git a/clang/lib/Serialization/ASTWriterDecl.cpp b/clang/lib/Serialization/ASTWriterDecl.cpp
index 1306ffda6dd..b3b55f584ae 100644
--- a/clang/lib/Serialization/ASTWriterDecl.cpp
+++ b/clang/lib/Serialization/ASTWriterDecl.cpp
@@ -141,6 +141,7 @@ void ASTDeclWriter::VisitDecl(Decl *D) {
     Writer.WriteAttributes(D->getAttrs(), Record);
   Record.push_back(D->isImplicit());
   Record.push_back(D->isUsed(false));
+  Record.push_back(D->isReferenced());
   Record.push_back(D->getAccess());
   Record.push_back(D->getPCHLevel());
 }
@@ -1133,6 +1134,7 @@ void ASTWriter::WriteDeclsBlockAbbrevs() {
   Abv->Add(BitCodeAbbrevOp(0));                       // HasAttrs
   Abv->Add(BitCodeAbbrevOp(0));                       // isImplicit
   Abv->Add(BitCodeAbbrevOp(0));                       // isUsed
+  Abv->Add(BitCodeAbbrevOp(0));                       // isReferenced
   Abv->Add(BitCodeAbbrevOp(AS_none));                 // C++ AccessSpecifier
   Abv->Add(BitCodeAbbrevOp(0));                       // PCH level