i965: Push most TES inputs in vec4 mode.

i965: Push most TES inputs in vec4 mode.

(This is commit 4a1c8a3037cd29938b2a6e2c680c341e9903cfbe for vec4 mode.)

Using the push model for inputs is much more efficient than pulling
inputs - the hardware can simply copy a large chunk into URB registers
at thread creation time, rather than having the thread send messages to
request data from the L3 cache.  Unfortunately, it's possible to have
more TES inputs than fit in registers, so we have to fall back to the
pull model in some cases.

However, it turns out that most tessellation evaluation shaders are
fairly simple, and don't use many inputs.  An arbitrary cut-off of
24 vec4 slots (12 registers) should suffice.  (I chose this instead of
the 32 vec4 slots used in the scalar backend to avoid regressing a few
Piglit tests due to the vec4 register allocator being too stupid to
figure out what to do.  We probably ought to fix that, but it's a
separate issue.)

Improves performance in GPUTest's tessmark_x64 microbenchmark by
41.5394% +/- 0.288519% (n = 115) at 1024x768 on my Clevo W740SU
(with Iris Pro 5200).

Improves performance in Synmark's Gl40TerrainFlyTess microbenchmark by
38.3576% +/- 0.759748% (n = 42).

v2: Simplify abs/negate handling, as requested by Matt.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Chris Forbes <chrisf@ijw.co.nz>
Reviewed-by: Matt Turner <mattst88@gmail.com>