i965/fs: Expose "urb_setup" as part of brw_wm_prog_data.

At the moment, for Gen6+, the FS assumes that all varying inputs are
delivered to it in the order in which they appear in the
gl_program::InputsRead bitfield, and the SF/SBE setup code ensures
that they are delivered in this order.

When we add support for more than 64 varying components, this will no
longer always be possible, because the Gen6+ SF/SBE stage is only
capable of performing arbitrary reorderings of 16 varying slots.

To allow extra flexibility in the ordering of FS varyings, this patch
causes the FS to advertise exactly what ordering it expects.
i965/fs: Change brw_wm_prog_data::urb_read_length to num_varying_inputs.

On gen4-5, the FS stage reads varying inputs from URB entries that
were output by the SF thread, where each register stores the
interpolation setup for two components of a vec4, therefore the FS
urb_read_length is twice the number of FS input varyings.  On gen6+,
varying inputs are directly deposited in the FS payload by the SF/SBE
fixed function logic, so urb_read_length is irrelevant.

However, in future patches, it will be nice to be able to consult
brw_wm_prog_data to determine how many varying inputs the FS expects
(rather than inferring it from gl_program::InputsRead).  So instead of
storing urb_read_length, we simply store num_varying_inputs in
brw_wm_prog_data.  On gen4-5, we simply multiply this by 2 to recover
the URB read length.
i965/fs: Consult brw_wm_prog_data::num_varying_inputs when setting up WM state.

Previously, we assumed that the number of varying inputs consumed by
the fragment shader was equal to the number of bits set in
gl_program::InputsRead.  However, we'll soon be making two changes
that will cause that not to be true:

- We'll stop wasting varying input space for gl_FragCoord and
  gl_FrontFacing, which aren't varyings.

- For fragment shaders that have more than 16 varying inputs, we'll
  adjust the layout of the inputs to account for the fact that the
  SF/SBE pipeline stage can't reorder inputs beyond the first 16; if
  there are GS outputs that the FS doens't use (or vice versa) this
  may cause the number of FS varying inputs to change.

So, instead of trying to guess the number of FS inputs from
gl_program::InputsRead, simply read it from
brw_wm_prog_data:num_varying_inputs, which is guaranteed to be correct
since it's populated by fs_visitor::calculate_urb_setup().
i965/sf: Use BRW_SF_URB_ENTRY_READ_OFFSET rather than hardcoded values.

We always program the SF unit to start reading the vertex URB entry at
offset 1.  In the next patch, we'll be adding FS code that relies on
this.  So consistently use the constant BRW_SF_URB_ENTRY_READ_OFFSET
rather than hardcoding a 1.
i965/sf: Consolidate common code for setting up gen6-7 attribute overrides.
i965/sf: Consult brw_wm_prog_data when setting up SF/SBE state.

Previously, the SF/SBE setup code delivered varying inputs to the FS
in the order in which they appear in the gl_program::InputsRead
bitfield, since that's what the FS expects.

When we add support for more than 64 varying components, this will no
longer always be the case, because the Gen6+ SF/SBE stage is only
capable of performing arbitrary reorderings of 16 varyings slots.  So,
when there are more than 16 vec4's worth of varying inputs, the FS
will have to adjust the order its input varyings in order to partially
match the order of outputs from the geometry or vertex shader.

To allow extra flexibility in the ordering of FS varyings, this causes
the SF/SBE to deliver varying inputs to the FS in exactly the order
that the FS requests using brw_wm_prog_data::urb_setup and
brw_wm_prog_data::num_varying_inputs.
i965/fs: Stop wasting input attribute space on gl_FragCoord and gl_FrontFacing.

Previously, if a fragment shader accessed gl_FragCoord or
gl_FrontFacing, we would assign them their own slots in the fragment
shader input attribute array, using up space that could be made
available to real varyings.  This was not strictly necessary (since
these values are not true varyings, and are instead computed from
other data available in the FS payload).  But we had to do it anyway
because the SF/SBE setup code assumed that every 1 bit in the
gl_program::InputsRead bitfield corresponded to a genuine varying
variable.

Now that the SF/SBE code consults brw_wm_prog_data and only sets up
the attributes that the fragment shader actually needs, we don't have
to do this anymore.
i965/gen6+: Remove VUE map dependency on userclip_active.

Previously, on Gen6+, we laid out the vertex (or geometry) shader VUE
map differently depending whether user clipping was active.  If it was
active, we put the clip distances in slots 2 and 3 (where the clipper
expects them); if it was inactive, we assigned them in the order of
the gl_varying_slot enum.

This made for unnecessary recompiles, since turning clipping on/off
for a shader that used gl_ClipDistance might rearrange the varyings.
It also required extra bookkeeping, since it required the user
clipping flag to be provided to brw_compute_vue_map() as a parameter.

With this patch, we always put clip distances at in slots 2 and 3 if
they are written to.  do_vs_prog() and do_gs_prog() are responsible
for ensuring that clip distances are written to when user clipping is
enabled (as do_vs_prog() previously did for gen4-5).

This makes the only input to brw_compute_vue_map() a bitfield of which
varyings the shader writes to, a fact that we'll take advantage of in
forthcoming patches.
i965/gs: Stop storing an input VUE map in the GS program key.

Now that the vertex shader output VUE map is determined solely by a
64-bit bitfield, we don't have to store it in its entirety in the
geometry shader program key; instead, we can just store the bitfield,
and let the geometry shader infer the VUE map at compile time.

This dramatically reduces the size of the geometry shader program key,
which we want to keep small since it gets recomputed whenever the
active program changes.
i965/fs: Simplify computation of key.input_slots_valid during precompile.

The for loop was rather silly.  In addition to checking brw->gen < 6
on each loop iteration, it took pains to exclude bits from
fp->Base.InputsRead that don't correspond to fragment shader inputs.
But those bits would never have been set in the first place, since the
only bits that are ever set in fp->Base.InputsRead are fragment shader
inputs.
i965/fs: When >64 input components, order them to match prev pipeline stage.

Since the SF/SBE stage is only capable of performing arbitrary
reorderings of 16 varying slots, we can't arrange the fragment shader
inputs in an arbitrary order if there are more than 16 input varying
slots in use.  We need to make sure that slots 16-31 match the
corresponding outputs of the previous pipeline stage.

The easiest way to accomplish this is to just make all varying slots
match up with the previous pipeline stage.
i965/vec4: Generate URB writes using a loop.

Previously we only ever did 1 or 2 URB writes, since the maximum
number of varyings we support is small enough to fit in 2 URB writes.
But GL 3.2 requires the geometry shader to support 128 output varying
components, and this could require up to 3 URB writes.
i965/gen6: Fix assertions on VS/GS URB size.

The "{VS,GS} URB Entry Allocation Size" fields of 3DSTATE_URB allow
values in the range 0-4, but they are U8-1 fields, so the range of
possible allocation sizes is 1-5.  We were erroneously prohibiting a
size of 5.
i965/ff_gs: Generate URB writes using a loop.

Previously we only ever did 1 URB write, since the maximum number of
varyings we support is small enough to fit in 1 URB write (when using
BRW_URB_SWIZZLE_NONE, which is what the pre-Gen7 GS always uses).  But
we're about to increase the number of varying components we support
from 64 to 128.

With 128 varyings, the most URB writes we'll have to do is 2, but it's
just as easy to write a general-purpose loop.
i965/gen6+: Support 128 varying components.

GL 3.2 requires us to support 128 varying components for geometry
shader outputs and fragment shader inputs, and 64 varying components
otherwise.  But there's no hardware limitation that restricts us to 64
varying components, and core Mesa doesn't currently allow different
stages to have different maximum values, so just go ahead and enable
128 varying components for all stages.  This gets us better test
coverage anyway.

Even though we are only working on GL 3.2 support for gen7 right now,
gen6 also supports 128 varying components, so go ahead and switch it
on there too.
i965/gs: Don't assign gl_Layer its own slot in the VUE map.
i965: Add some missing bits to {mesa,brw,cache}_bits[].

These data structures are used for debug output, so it wasn't hurting
anything that there were missing bits.  But it's good to keep things
up to date.

This patch also adds static asserts so that the {brw,cache}_bits[]
arrays are the proper size, so that we don't forget to add to them in
the future.  Unfortunately there's no convenient way to assert that
mesa_bits[] is the proper size.
i965/vs: Move vs-specific code out of brw_vec4.h.

Now brw_vec4.h contains only code that is shared between the vertex
and geometry shaders.
i965/vec4: Make with_writemask() non-static.

This will allow it to be shared between brw_vec4_visitor.cpp and
brw_vec4_vs_visitor.cpp (which will be created in the next patch).
i965/vs: Move vs-specific code out of brw_vec4_visitor.cpp.

This patch creates a new file brw_vec4_vs_visitor.cpp, to contain code
that is specific to the vertex shader.  Now the organization of vertex
shader and geometry shader visitor code is symmetric: vs-specific code
is in brw_vec4_vs_visitor.cpp, gs-specific code is in
brw_vec4_gs_visitor.cpp, and code shared between vs and gs is in
brw_vec4_visitor.cpp.