[Bug 93840] [i965] Compiler backend uses too much stack with Alien: Isolation

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=93840

--- Comment #29 from Darius Spitznagel <d.spitznagel at goodbytez.de> ---
> Are you forcing GL 4.3 / compute on, like earlier? [1]
> 
> If not, which Mesa version do you use?  Haswell officially provides GL 4.2
> in Mesa 17.0.0 (required FP64 came on Jan 12th), which was released 2 days
> ago.    Only with latest Mesa git version Haswell officially supports GL 4.5
> (Jan 16th commit).  Compute shaders come in GL 4.3.
> 
> [1] Game will start, but doesn't render correctly if compute shader support
> is missing:
>   https://bugs.freedesktop.org/show_bug.cgi?id=93144#c31

I use Mesa 17.0.0 with no override.
Mesa 17.0.0 exposes OpenGL 4.5 for Haswell. The release notes at
http://mesa3d.org are totally WRONG!!!
Look here...
https://cgit.freedesktop.org/mesa/mesa/commit/?id=d2590eb65ff28a9cbd592353d15d7e6cbd2c6fc6

Clone branch mesa-17.0.0 and search for "Haswell" and you will see it.

IMPORTANT: You also need a newer kernel otherwise CS will not be exposed due to
missing "pipelined register writes" support (see intel_extensions.c)
Kernel 4.8 should be fine.

So I use no magic but Matts patch and some others for Divinity: OS.

> Also, which exact CPU model do you have?

Intel(R) Core(TM) i7-4770R CPU @ 3.20GHz

> Game needs to know when the parallel shader compilation has finished. 
> That's an extension on top of GL 4.5:
> https://www.khronos.org/registry/OpenGL/extensions/ARB/
> ARB_parallel_shader_compile.txt
> 
> Game needs to specifically have support for that.

AHA, very interesting! Thanks for this info.

> That uses gallium / LLVM backend.  Maybe it uses less stack, or used at that
> point, and would now also run out of stack.

I know.

> 300-400 KB of stack is ridiculously low amount of stack if there's something
> that actually uses it.  Game cannot assume that driver will use less than
> that (game itself will use some of that stack too).

A good point to look what others do.

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