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, 6 insertions, 0 deletions

diff --git a/clang/lib/AST/Decl.cpp b/clang/lib/AST/Decl.cpp
index 8ce960ff5ff..b6d35f4260c 100644
--- a/clang/lib/AST/Decl.cpp
+++ b/clang/lib/AST/Decl.cpp
@@ -2449,6 +2449,12 @@ bool VarDecl::isKnownToBeDefined() const {
   return hasDefinition();
 }
 
+bool VarDecl::isNoDestroy(const ASTContext &Ctx) const {
+  return hasGlobalStorage() && (hasAttr<NoDestroyAttr>() ||
+                                (!Ctx.getLangOpts().RegisterStaticDestructors &&
+                                 !hasAttr<AlwaysDestroyAttr>()));
+}
+
 MemberSpecializationInfo *VarDecl::getMemberSpecializationInfo() const {
   if (isStaticDataMember())
     // FIXME: Remove ?