[LLVMdev] RFC: Are we ready to completely move away from the optionality of a DataLayout?

[Eric Christopher]

On Wed Oct 22 2014 at 12:33:53 PM Chris Lattner <clattner at apple.com> wrote:

> On Oct 20, 2014, at 10:41 PM, Eric Christopher <echristo at gmail.com> wrote:
> >>> So the storage for DataLayout right now is on a per-subtarget basis.
> >>> I.e. if you don't construct one in the module the backend will make
> >>> one up based on information in the subtarget (everything from
> >>
> >> I think this is what Chandler is proposing to fix: every module will
> have a DataLayout string.
> >>
> >
> > Right. I was figuring there'd be some way of having the backend
> > specify it if there isn't one in the module IR - or a way of calling
> > into the backend to generate one up since memorizing all of the
> > possible target layouts for all of the targets would probably be a
> > pain. These bits would probably be off of the TargetMachine right now.
> > It'd make moving the DataLayout string onto the TargetMachine easier
> > later if we decide to do that.
>
> I think I see what you’re saying: you’re saying that it doesn’t make sense
> for each target to know the DL string *and* to require each frontend to
> know the DL string for each target it supports.
>
> If that’s the problem you’re trying to solve, the approach I would take is
> to have Clang (and other frontends) query the TargetMachine directly when
> it is setting up the module.  This will give you the layering that you’re
> looking for, and avoid duplicating the magic strings.
>
>
Yep. That's basically what I was suggesting. :)

Go total agreement!

-eric
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