When building with optimizations, emit vtables where the key is not in the
current translation unit as available_externally.
This helps devirtualize the second example in PR3100, comment 18:
struct S { S() {}; virtual void xyzzy(); };
inline void foo(S *s) { s->xyzzy(); }
void bar() { S s; foo(&s); }
This involved four major changes:
1. In DefineUsedVTables, always mark virtual member functions as referenced for
non-template classes and class template specializations.
2. In CodeGenVTables::ShouldEmitVTableInThisTU return true if optimizations are
enabled, even if the key function is not implemented in this translation
unit. We don't ever do this for code compiled with -fapple-kext, because we
don't ever want to devirtualize virtual member function calls in that case.
3. Give the correct linkage for vtables where the key function is not defined.
4. Update the linkage for RTTI structures when necessary.
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@124565 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Sema/SemaDeclCXX.cpp b/lib/Sema/SemaDeclCXX.cpp
index 5da1035..c9c58b3 100644
--- a/lib/Sema/SemaDeclCXX.cpp
+++ b/lib/Sema/SemaDeclCXX.cpp
@@ -7110,6 +7110,13 @@
switch (KeyFunction->getTemplateSpecializationKind()) {
case TSK_Undeclared:
case TSK_ExplicitSpecialization:
+ // The key function is in another translation unit. Mark all of the
+ // virtual members of this class as referenced so that we can build a
+ // vtable anyway (in order to do devirtualization when optimizations
+ // are turned on for example.
+ MarkVirtualMembersReferenced(Loc, Class);
+ continue;
+
case TSK_ExplicitInstantiationDeclaration:
// The key function is in another translation unit.
continue;