[Bug 92760] Add FP64 support to the i965 shader backends

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=92760

--- Comment #50 from Connor Abbott <cwabbott0 at gmail.com> ---
(In reply to Connor Abbott from comment #49)
> (In reply to Iago Toral from comment #48)
> > Connor, I think there is a problem with the implementation of d2f and f2d in
> > the vec4 backend. These use a generator opcode that switches to scalar mode
> > like this (for d2f):
> > 
> > brw_set_default_access_mode(p, BRW_ALIGN_1);
> > dst.hstride = BRW_HORIZONTAL_STRIDE_2;
> > dst.width = BRW_WIDTH_4;
> > brw_MOV(p, dst, src[0]);
> > brw_set_default_access_mode(p, BRW_ALIGN_16);
> > 
> > The problem with this is that scalar mode does not consider the swizzle in
> > src[0] and because of copy-propagation, we can end up with a swizzle like
> > zwzw here.
> > 
> > In the case of d2f, it seems that  I can just do a normal MOV in align16
> > mode and that seems to work, but f2d is not so easy and we probably need
> > align1 mode there.
> > 
> > Of course, we can fix this by disabling copy-propagation for the generator
> > opcodes we use for this, I suppose that should be alright, but I wonder if
> > you think there is a better approach.
> 
> Yeah, I think that my plan was just to disable copy propagation into those.
> We already do this for other opcodes where we use align1 mode, and I thought
> I had already disabled it, although I could be mis-remembering. If we try
> and handle the swizzle in the generator by emitting another MOV, we would
> just be undoing the copy propagation which seems a little silly.

Err, disable copy propagation with swizzles of course...

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