Don't emit an available_externally vtable pointing to linkonce_odr funcs.
This fixes pr13124.
From the discussion at
http://lists.cs.uiuc.edu/pipermail/cfe-dev/2012-June/022606.html
we know that we cannot make funcions in a weak_odr vtable also weak_odr. They
should remain linkonce_odr.
The side effect is that we cannot emit a available_externally vtable unless we
also emit a copy of the function. This also has an issue: If codegen is going
to output a function, sema has to mark it used. Given llvm.org/pr9114, it looks
like sema cannot be more aggressive at marking functions used because
of vtables.
This leaves us with a few unpleasant options:
* Marking functions in vtables used if possible. This sounds a bit sloppy, so
we should avoid it.
* Producing available_externally vtables only when all the functions in it are
already used or weak_odr. This would cover cases like
--------------------
struct foo {
virtual ~foo();
};
struct bar : public foo {
virtual void zed();
};
void f() {
foo *x(new bar);
delete x;
}
void g(bar *x) {
x->~bar(); // force the destructor to be used
}
--------------------------
and
----------------------------------
template<typename T>
struct bar {
virtual ~bar();
};
template<typename T>
bar<T>::~bar() {
}
// make the destructor weak_odr instead of linkonce_odr
extern template class bar<int>;
void f() {
bar<int> *x(new bar<int>);
delete x;
}
----------------------------
These look like corner cases, so it is unclear if it is worth it.
* And finally: Just nuke this optimization. That is what this patch implements.
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@189852 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/CGVTables.cpp b/lib/CodeGen/CGVTables.cpp
index 26ebf91..3585c42 100644
--- a/lib/CodeGen/CGVTables.cpp
+++ b/lib/CodeGen/CGVTables.cpp
@@ -753,12 +753,7 @@
switch (keyFunction->getTemplateSpecializationKind()) {
case TSK_Undeclared:
case TSK_ExplicitSpecialization:
- // When compiling with optimizations turned on, we emit all vtables,
- // even if the key function is not defined in the current translation
- // unit. If this is the case, use available_externally linkage.
- if (!def && CodeGenOpts.OptimizationLevel)
- return llvm::GlobalVariable::AvailableExternallyLinkage;
-
+ assert(def && "Should not have been asked to emit this");
if (keyFunction->isInlined())
return !Context.getLangOpts().AppleKext ?
llvm::GlobalVariable::LinkOnceODRLinkage :
@@ -777,9 +772,7 @@
llvm::Function::InternalLinkage;
case TSK_ExplicitInstantiationDeclaration:
- return !Context.getLangOpts().AppleKext ?
- llvm::GlobalVariable::AvailableExternallyLinkage :
- llvm::Function::InternalLinkage;
+ llvm_unreachable("Should not have been asked to emit this");
}
}
@@ -795,7 +788,7 @@
return llvm::GlobalVariable::LinkOnceODRLinkage;
case TSK_ExplicitInstantiationDeclaration:
- return llvm::GlobalVariable::AvailableExternallyLinkage;
+ llvm_unreachable("Should not have been asked to emit this");
case TSK_ExplicitInstantiationDefinition:
return llvm::GlobalVariable::WeakODRLinkage;
@@ -897,16 +890,6 @@
/// we define that v-table?
static bool shouldEmitVTableAtEndOfTranslationUnit(CodeGenModule &CGM,
const CXXRecordDecl *RD) {
- // If we're building with optimization, we always emit v-tables
- // since that allows for virtual function calls to be devirtualized.
- // If the v-table is defined strongly elsewhere, this definition
- // will be emitted available_externally.
- //
- // However, we don't want to do this in -fapple-kext mode, because
- // kext mode does not permit devirtualization.
- if (CGM.getCodeGenOpts().OptimizationLevel && !CGM.getLangOpts().AppleKext)
- return true;
-
return !CGM.getVTables().isVTableExternal(RD);
}