i965: Disable unlit-centroid workaround on Gen < 6.
authorMatt Turner <mattst88@gmail.com>
Tue, 9 Dec 2014 06:59:17 +0000 (22:59 -0800)
committerMatt Turner <mattst88@gmail.com>
Wed, 10 Dec 2014 18:18:39 +0000 (10:18 -0800)
commit1a2de7dce8fcff807a2b42b7197d11b28192fa3e
treee34b7ad9813e4a949e353b3fc892b1ab24338c2f
parent13e42fc025682bbead23012ec29499fb1502bea4
i965: Disable unlit-centroid workaround on Gen < 6.

Back to the original commit (8313f444) adding the workaround, we were
enabling it on gens <= 7, even though gens <= 5 can't do multisampling.

I cannot find documentation that says that Sandybridge needs this
workaround but in practice disabling it causes these piglit tests to
fail:

EXT_framebuffer_multisample/interpolation {2,4} centroid-deriv{,-disabled}

On Ironlake:

total instructions in shared programs: 4358478 -> 4349671 (-0.20%)
instructions in affected programs:     117680 -> 108873 (-7.48%)

A bunch of shaders in TF2, Portal 2, and L4D2 are cut by 25~30%.

Cc: "10.4" <mesa-stable@lists.freedesktop.org>
Reviewed-by: Chris Forbes <chrisf@ijw.co.nz>
src/mesa/drivers/dri/i965/brw_device_info.c