[cfe-commits] [Patch] Support the tls_model attribute (PR9788)

[Chandler Carruth]

On Wed, Jun 6, 2012 at 9:01 AM, Hans Wennborg <hans at chromium.org> wrote:

> On Wed, Jun 6, 2012 at 10:57 AM, Chandler Carruth <chandlerc at google.com>
> wrote:
> > On Wed, Jun 6, 2012 at 2:17 AM, Hans Wennborg <hans at chromium.org> wrote:
> >>
> >> Hi all,
> >>
> >> Attached is the Clang-side patch for adding support for explicitly
> >> selected TLS models [1]. This adds support for the tls_model attribute
> >> [2].
> >
> >
> > Very cool.
>
> Thanks for looking! New patch attached.
>
> > Should support for these be documented somewhere? It should at least go
> into
> > the release notes for 3.2.
>
> I've added it to the ReleaseNotes.html. Is there any other place I
> should add it to? Maybe LanguageExtensions.html? I was hoping to add
> the "-ftls_model=" command-line flag too (in a later patch), and then
> document properly.
>

Yea, feel free to defer any/all docs changes until you're "done". =] This
comment wasn't about the patch specifically. Otherwise, your ideas for docs
seem fine. =]


>
> > This parsing is duplicated a lot:
> >
> > +    const TLSModelAttr *Attr = D.getAttr<TLSModelAttr>();
> > +    if (Attr->getModel() == "global-dynamic") {
> > +       TLM = llvm::GlobalVariable::GlobalDynamicTLSModel;
> > +    } else if (Attr->getModel() == "local-dynamic") {
> > +       TLM = llvm::GlobalVariable::LocalDynamicTLSModel;
> > +    } else if (Attr->getModel() == "initial-exec") {
> > +       TLM = llvm::GlobalVariable::InitialExecTLSModel;
> > +    } else if (Attr->getModel() == "local-exec") {
> > +       TLM = llvm::GlobalVariable::LocalExecTLSModel;
> > +    } else {
> > +      llvm_unreachable("unknown TLS model attribute");
> > +    }
> >
> > Could you pull this into helper function that returns the
> > llvm::GlobalVariable::ThreadLocalMode value? If you make it return
> > not-thread-local in the event that nothing parses, you can use it in both
> > the attribute checking code to diagnose invalid attributes, and in the
> rest
> > of Clang to interpret them.
>
> I've put a helper function in CodeGenModule for now; that way at least
> the codegen functions share the code.
>

Cool.


> To make the attribute checking codes share this, I'm unsure about what
> dependencies I'm allowed to add. If I put the helper in Sema, is Sema
> allowed to depend on LLVM's GlobalVariable? And is CodeGen allowed to
> depend on Sema? (I'm guessing introducing a dependency from Sema to
> CodeGen is right out?)
>

Bleh, yea skip this. I think the real solution is to bake support for a set
of string literal values into the attribute system, and have tablegen
generate the validation code, diagnostics, and mapping to/from an enum.
Then codegen can just do enum -> LLVM global variable mapping.

But none of that should block this patch, LGTM, submit whenever the LLVM
side is good-to-go.
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