i965: Even if no VS inputs are set, still load some amount of URB as required.

See comment on Vertex URB Entry Read Length for VS_STATE.

This, combined with the previous three commits, fixes #22945.
(cherry picked from commit e340d4f9866db4bae391288e83a630a310b0dd2b)

1 files changed, 11 insertions, 0 deletions

diff --git a/src/mesa/drivers/dri/i965/brw_vs_emit.c b/src/mesa/drivers/dri/i965/brw_vs_emit.c
index 6792c3a34e..b95079a5d1 100644
--- a/src/mesa/drivers/dri/i965/brw_vs_emit.c
+++ b/src/mesa/drivers/dri/i965/brw_vs_emit.c
@@ -124,6 +124,11 @@ static void brw_vs_alloc_regs( struct brw_vs_compile *c )
 	 reg++;
       }
    }
+   /* If there are no inputs, we'll still be reading one attribute's worth
+    * because it's required -- see urb_read_length setting.
+    */
+   if (c->nr_inputs == 0)
+      reg++;
 
    /* Allocate outputs: TODO: could organize the non-position outputs
     * to go straight into message regs.
@@ -201,6 +206,12 @@ static void brw_vs_alloc_regs( struct brw_vs_compile *c )
     * vertex urb, so is half the amount:
     */
    c->prog_data.urb_read_length = (c->nr_inputs + 1) / 2;
+   /* Setting this field to 0 leads to undefined behavior according to the
+    * the VS_STATE docs.  Our VUEs will always have at least one attribute
+    * sitting in them, even if it's padding.
+    */
+   if (c->prog_data.urb_read_length == 0)
+      c->prog_data.urb_read_length = 1;
 
    /* The VS VUEs are shared by VF (outputting our inputs) and VS, so size
     * them to fit the biggest thing they need to.