Re: [PATCH 1/2] drm/i915: Cache elsp submit register

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On 22/03/16 17:29, Ville Syrjälä wrote:
On Tue, Mar 22, 2016 at 05:16:52PM +0000, Tvrtko Ursulin wrote:
From: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>

Since we write four times to the same register, caching
the mmio register saves a tiny amount of generated code.

The compiler can't figure this out on its own?

Nope, at least gcc 4.84 I am running here can't. :(

And this only solves one part of the things it can't figure out in that code. It still recalculates one part, can't remember which one is which now without revisiting the generated assembly. It used to be for times in a row: load register, add 0x230, displace 0x78, store[0-4]. This only solves the add 0x230 redundancy. But working around that would possibly be a bit too low level.

Regards,

Tvrtko
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