================
Comment at: lib/CodeGen/ItaniumCXXABI.cpp:1599
@@ +1598,3 @@
+ if (!isThreadLocalBackingVariableAlwaysReferenceable(VD, CGM))
+ return VD->hasDefinition() ? llvm::GlobalValue::WeakAnyLinkage
+ : llvm::GlobalValue::ExternalLinkage;
----------------
David Majnemer wrote:
> Richard Smith wrote:
> > Hmm, what's the motivation for making this weak? Should it be strong if the
> > `thread_local` variable is a strong definition?
> >
> > (I'm also not completely sure whether `WeakAny` or `WeakODR` is appropriate
> > for the case where the variable *is* weak; I *think* the intent is for the
> > underlying mechanism to be replaceable, which implies using `WeakAny`.)
> It's a strong definition but an internal one.
>
> `WeakODR` permits inlining of the thread-wrapper. This, in turn, allows
> references to the internal backing store of the variable to be proliferated
> if the thread-wrapper gets inlined.
I feel like I'm missing something here. Why doesn't this:
thread_local int n = f();
... get a non-weak, inlineable definition for its thread wrapper (in the
translation unit with the definition)?
================
Comment at: test/CodeGenCXX/tls-init-funcs.cpp:6-7
@@ -5,2 +5,4 @@
+// CHECK: call {{.*}} @_ZTW3ext()
+// CHECK: declare hidden {{.*}} @_ZTW3ext()
// CHECK: define weak hidden {{.*}} @_ZTW1a
----------------
David Majnemer wrote:
> Richard Smith wrote:
> > Why are these marked as `hidden`? Don't they need to be visible to support
> > cross-DSO linking of `thread_local` variables?
> ToT clang makes the thread-wrapper hidden. ItaniumCXXABI.cpp has the
> following comment in it:
> > Always resolve references to the wrapper at link time.
>
> It was added by you in r179858.
That works on the basis that every translation unit which references a TW
symbol provides a (weak) definition of that symbol. That's not true in the Mac
OS case (where they don't follow the Itanium ABI).
http://reviews.llvm.org/D4109
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