Re: [PATCH][amdgcn] Add runtime ISA check for amdgcn offloading

[Jakub Jelinek <jakub at redhat dot com>]

On Mon, Jan 20, 2020 at 11:00:58AM +0000, Andrew Stubbs wrote:
> Indeed, fat binaries would be a good solution.
> 
> Presumably it's possible, but I'm not sure how we'd go about getting the
> offload mechanism to launch the backend multiple times? Having got that far,
> the libgomp and mkoffload changes to select the right variant would probably
> be fairly straight-forward.

I'd say easiest would be to do that in the gcn specific mkoffload.
But there needs to be a way for the user to specify that he wants only a
particular variant and not all of them (perhaps look for -march= in the
offload options?)?

Or, for the 8 vs. 16 regs, have -march=generic or whatever that would try to
generate something that will work everywhere or on as many chips as
possible, e.g. by using mostly fiji, but try to use 16 adjacent regs instead
of 8?  I admit I don't know anything about the hw, just worried because if
we have already 4 variants now when the port is almost new, won't we have 30
later on, which could be prohibitive for the fat binaries?

	Jakub