[ms-cxxabi] Emit linkonce complete dtors in TUs that need them

Based on Peter Collingbourne's destructor patches.

Prior to this change, clang was considering ?1 to be the complete
destructor and the base destructor, which was wrong.  This lead to
crashes when clang tried to emit two LLVM functions with the same name.

In this ABI, TUs with non-inline dtors might not emit a complete
destructor.  They are emitted as inline thunks in TUs that need them,
and they always delegate to the base dtors of the complete class and its
virtual bases.  This change uses the DeferredDecls machinery to emit
complete dtors as needed.

Currently in clang try body destructors can catch exceptions thrown by
virtual base destructors.  In the Microsoft C++ ABI, clang may not have
the destructor definition, in which case clang won't wrap the virtual
virtual base destructor calls in a try-catch.  Diagnosing this in user
code is TODO.

Finally, for classes that don't use virtual inheritance, MSVC always
calls the base destructor (?1) directly.  This is a useful code size
optimization that avoids emitting lots of extra thunks or aliases.
Implementing it also means our existing tests continue to pass, and is
consistent with MSVC's output.

We can do the same for Itanium by tweaking GetAddrOfCXXDestructor, but
it will require further testing.

Reviewers: rjmccall

CC: cfe-commits

Differential Revision: http://llvm-reviews.chandlerc.com/D1066

llvm-svn: 186828

1 files changed, 8 insertions, 3 deletions

diff --git a/clang/lib/CodeGen/CGClass.cpp b/clang/lib/CodeGen/CGClass.cpp
index 2bb44552e26..dd75523d14a 100644
--- a/clang/lib/CodeGen/CGClass.cpp
+++ b/clang/lib/CodeGen/CGClass.cpp
@@ -1265,16 +1265,19 @@ void CodeGenFunction::EmitDestructorBody(FunctionArgList &Args) {
   // If this is the complete variant, just invoke the base variant;
   // the epilogue will destruct the virtual bases.  But we can't do
   // this optimization if the body is a function-try-block, because
-  // we'd introduce *two* handler blocks.
+  // we'd introduce *two* handler blocks.  In the Microsoft ABI, we 
+  // always delegate because we might not have a definition in this TU.
   switch (DtorType) {
   case Dtor_Deleting: llvm_unreachable("already handled deleting case");
 
   case Dtor_Complete:
+    assert((Body || getTarget().getCXXABI().isMicrosoft()) &&
+           "can't emit a dtor without a body for non-Microsoft ABIs");
+
     // Enter the cleanup scopes for virtual bases.
     EnterDtorCleanups(Dtor, Dtor_Complete);
 
-    if (!isTryBody &&
-        CGM.getTarget().getCXXABI().hasDestructorVariants()) {
+    if (!isTryBody) {
       EmitCXXDestructorCall(Dtor, Dtor_Base, /*ForVirtualBase=*/false,
                             /*Delegating=*/false, LoadCXXThis());
       break;
@@ -1282,6 +1285,8 @@ void CodeGenFunction::EmitDestructorBody(FunctionArgList &Args) {
     // Fallthrough: act like we're in the base variant.
       
   case Dtor_Base:
+    assert(Body);
+
     // Enter the cleanup scopes for fields and non-virtual bases.
     EnterDtorCleanups(Dtor, Dtor_Base);