Merge of HSA branch

[Thomas Schwinge]

Hi!

On Fri, 6 Nov 2015 12:03:25 +0100, Bernd Schmidt <bschmidt@redhat.com> wrote:
> On 11/06/2015 11:30 AM, Richard Biener wrote:
> > On Fri, 6 Nov 2015, Bernd Schmidt wrote:
> >>
> >> Realistically we're probably not going to reject this work, but I still want
> >> to ask whether the approach was acked by the community before you started. I'm
> >> really not exactly thrilled about having two different classes of backends in
> >> the compiler, and two different ways of handling offloading.
> >
> > Realistically the other approaches werent acked either (well, implicitely
> > by review).
> 
> I think the LTO approach was discussed beforehand. As far as I remember 
> (and Jakub may correct me) it was considered for intelmic, and Jakub had 
> considerable input on it. I heard that it came up at the 2013 Cauldron.
> Writing an rtl backend is the default thing to do for gcc and I would 
> expect any other approach to be discussed beforehand.
> 
> > Not doing an RTL backend for NVPTX would have simplified
> > your life as well.
> 
> I'm not convinced about this. At least I just had to turn off the 
> register allocator, not write a new one.

From the notes of the Accelerator BoF at the GNU Tools Cauldron 2013,
<http://news.gmane.org/find-root.php?message_id=%3C1375103926.7129.7694.camel%40triegel.csb%3E>:

| The main issue we discussed in the backend category was how to target
| more than one ISA when generating code (i.e., we need code in the host's
| ISA and in the accelerator(s)' (virtual) ISA(s)).  Multi-target support
| in GCC might be one option, but would probably need quite some time and
| thus depending on it would probably delay the accelerator efforts.  It
| might be simpler to stream code several times to different backends
| using the LTO infrastructure.  [...] A third
| option that SuSE is experimenting with is not writing a new backend but
| instead generating code right after the last GIMPLE pass; however, HSAIL
| needs register allocation, so it was noted that writing a light-weight
| backend might be
| easier.


Grüße
 Thomas
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