Re: nvptx offloading patches [3/n], i386 bits RFD

[Bernd Schmidt <bernds@codesourcery.com>]

On 11/05/2014 01:19 AM, Bernd Schmidt wrote:
> On 11/04/2014 10:50 PM, Jeff Law wrote:
>> No, I don't think it's terminology.  It's really that in effect we have
>> two targets.  One is a normal CPU, the other is a GPU.
>>
>> ie, there's nothing that says we won't have a GPU that's being driven by
>> an ARM or PPC.  What I want to avoid is GPU-isms getting sprinkled into
>> the x86 (or any other) backend.
>>
>> The problem is we don't have any infrastructure in place for this kind
>> of situation.  So we start off with a few hacks and hopefully we're able
>> to see some commonality and start to see how to handle the
>> multi-architecture target issues a bit better.
>
> FWIW the three non-ptx patches I sent plus the -foffload-abi stuff are
> the only ones necessary to make offloading through the LTO path work
> (this was against the gomp-4_0-branch with earlier versions of the
> offload patches Ilya's been posting; I haven't had a chance to test
> everything together in trunk yet). That doesn't seem like a large amount
> of changes.
>
> For other targets I don't expect the situation to be too different. ARM
> has a similar float mode issue for HFmode, and things like
> m{big,little}-endian may have to be handled. I expect these can be
> handled with -foffload-abi machinery.
>
> So, looking ahead - I'm imagining extra switches along the lines of
>   -foffload-abi-hflt={arm,ieee,...}
>   -foffload-abi-ldbl={64,x86,128}
>   -foffload-abi-endian={big,little}
>
> On some targets it might make sense to disallow offloading if certain
> switches are used. Uros seems to agree that on x86 the -mlong-double-128
> switch isn't very interesting. I'm thinking about how to deal with such
> a situation - maybe an offload_abi_valid hook that gets called whenever
> we find that we want to stream out offloaded functions. That would then
> sorry out (or maybe just warn) if the hook returns false.
>
> I can do either or both, whatever the consensus turns out to be.

The discussion on these patches kind of stalled, so a gentle ping - it 
would be nice to integrate these now that Ilya's offload patches are in.


Bernd