Add a new flag and attributes to control static destructor registration

This commit adds the flag -fno-c++-static-destructors and the attributes
[[clang::no_destroy]] and [[clang::always_destroy]]. no_destroy specifies that a
specific static or thread duration variable shouldn't have it's destructor
registered, and is the default in -fno-c++-static-destructors mode.
always_destroy is the opposite, and is the default in -fc++-static-destructors
mode.

A variable whose destructor is disabled (either because of
-fno-c++-static-destructors or [[clang::no_destroy]]) doesn't count as a use of
the destructor, so we don't do any access checking or mark it referenced. We
also don't emit -Wexit-time-destructors for these variables.

rdar://21734598

Differential revision: https://reviews.llvm.org/D50994

llvm-svn: 340306

1 files changed, 19 insertions, 0 deletions

diff --git a/clang/lib/Sema/SemaDeclAttr.cpp b/clang/lib/Sema/SemaDeclAttr.cpp
index 39d7019b259..27eb533360c 100644
--- a/clang/lib/Sema/SemaDeclAttr.cpp
+++ b/clang/lib/Sema/SemaDeclAttr.cpp
@@ -5917,6 +5917,20 @@ static void handleOpenCLAccessAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
       AL.getRange(), S.Context, AL.getAttributeSpellingListIndex()));
 }
 
+static void handleDestroyAttr(Sema &S, Decl *D, const ParsedAttr &A) {
+  if (!isa<VarDecl>(D) || !cast<VarDecl>(D)->hasGlobalStorage()) {
+    S.Diag(D->getLocation(), diag::err_destroy_attr_on_non_static_var)
+        << (A.getKind() == ParsedAttr::AT_AlwaysDestroy);
+    return;
+  }
+
+  if (A.getKind() == ParsedAttr::AT_AlwaysDestroy) {
+    handleSimpleAttributeWithExclusions<AlwaysDestroyAttr, NoDestroyAttr>(S, D, A);
+  } else {
+    handleSimpleAttributeWithExclusions<NoDestroyAttr, AlwaysDestroyAttr>(S, D, A);
+  }
+}
+
 //===----------------------------------------------------------------------===//
 // Top Level Sema Entry Points
 //===----------------------------------------------------------------------===//
@@ -6587,6 +6601,11 @@ static void ProcessDeclAttribute(Sema &S, Scope *scope, Decl *D,
   case ParsedAttr::AT_Reinitializes:
     handleSimpleAttribute<ReinitializesAttr>(S, D, AL);
     break;
+
+  case ParsedAttr::AT_AlwaysDestroy:
+  case ParsedAttr::AT_NoDestroy:
+    handleDestroyAttr(S, D, AL);
+    break;
   }
 }