[Bug 86469] Unreal Engine demo doesn't run

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=86469

--- Comment #4 from Tapani Pälli <lemody at gmail.com> ---
(In reply to Matt Turner from comment #3)
> (In reply to Tapani Pälli from comment #2)
> > (In reply to Kenneth Graunke from comment #1)
> > > This should actually be pretty easy to fix.  Sandybridge has more than 16
> > > MRFs, so we could just adjust the spilling code to use the higher numbered
> > > ones which aren't used for anything else.
> > > 
> > > The check also seems a bit heavy handed...it may not actually conflict...
> > 
> > I've checked that Effects works on SNB by simply setting spill_base_mrf 15
> > (as 14 is used). I did not find documentation that would indicate more than
> > 16 MRFs available though. Docs indicate there are 16 from which 1 .. 15 can
> > be used.
> 
> SNB PRM Vol4 Part2's "Table 5-4. MRF Registers Available in Device Hardware"
> says "Number per Thread" - "24 registers"
> 
> This would be an easy experiment for someone with a Sandybridge -- modify
> the fs_visitor::spill_reg() function in
> src/mesa/drivers/dri/i965/brw_fs_reg_allocate.cpp

Yep, I saw this but bspec states that it might not be safe to use MRFs other
than 1 .. 15. It feels a bit risky to go change this just because of one demo.

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