[Mesa-dev] [PATCH 07/15] i965/fs: Stop wasting input attribute space on gl_FragCoord and gl_FrontFacing.

[Paul Berry]

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.
---
 src/mesa/drivers/dri/i965/brw_context.h   | 9 +++++++++
 src/mesa/drivers/dri/i965/brw_fs.cpp      | 3 ++-
 src/mesa/drivers/dri/i965/gen6_sf_state.c | 8 --------
 3 files changed, 11 insertions(+), 9 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_context.h b/src/mesa/drivers/dri/i965/brw_context.h
index a0a8d4f..167ed4a 100644
--- a/src/mesa/drivers/dri/i965/brw_context.h
+++ b/src/mesa/drivers/dri/i965/brw_context.h
@@ -439,6 +439,15 @@ void brw_compute_vue_map(struct brw_context *brw, struct brw_vue_map *vue_map,
                          GLbitfield64 slots_valid, bool userclip_active);
 
 
+/**
+ * Bitmask indicating which fragment shader inputs represent varyings (and
+ * hence have to be delivered to the fragment shader by the SF/SBE stage).
+ */
+#define BRW_FS_VARYING_INPUT_MASK \
+   (BITFIELD64_RANGE(0, VARYING_SLOT_MAX) & \
+    ~VARYING_BIT_POS & ~VARYING_BIT_FACE)
+
+
 /*
  * Mapping of VUE map slots to interpolation modes.
  */
diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp b/src/mesa/drivers/dri/i965/brw_fs.cpp
index 444c2b5..013dc29 100644
--- a/src/mesa/drivers/dri/i965/brw_fs.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
@@ -1238,7 +1238,8 @@ fs_visitor::calculate_urb_setup()
    /* Figure out where each of the incoming setup attributes lands. */
    if (brw->gen >= 6) {
       for (unsigned int i = 0; i < VARYING_SLOT_MAX; i++) {
-	 if (fp->Base.InputsRead & BITFIELD64_BIT(i)) {
+	 if (fp->Base.InputsRead & BRW_FS_VARYING_INPUT_MASK &
+             BITFIELD64_BIT(i)) {
 	    c->prog_data.urb_setup[i] = urb_next++;
 	 }
       }
diff --git a/src/mesa/drivers/dri/i965/gen6_sf_state.c b/src/mesa/drivers/dri/i965/gen6_sf_state.c
index bcad5a4..a093dc1 100644
--- a/src/mesa/drivers/dri/i965/gen6_sf_state.c
+++ b/src/mesa/drivers/dri/i965/gen6_sf_state.c
@@ -56,14 +56,6 @@ static uint32_t
 get_attr_override(const struct brw_vue_map *vue_map, int urb_entry_read_offset,
                   int fs_attr, bool two_side_color, uint32_t *max_source_attr)
 {
-   if (fs_attr == VARYING_SLOT_POS) {
-      /* This attribute will be overwritten by the fragment shader's
-       * interpolation code (see emit_interp() in brw_wm_fp.c), so just let it
-       * reference the first available attribute.
-       */
-      return 0;
-   }
-
    /* Find the VUE slot for this attribute. */
    int slot = vue_map->varying_to_slot[fs_attr];
 
-- 
1.8.4