Mesa (master): i965: Make emit_urb_writes() not produce an EOT message for GS.

[Kenneth Graunke]

Module: Mesa
Branch: master
Commit: 7e7e501acf3ea609e3e2e8bb4091a5a20ae3adc2
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=7e7e501acf3ea609e3e2e8bb4091a5a20ae3adc2

Author: Kenneth Graunke <kenneth at whitecape.org>
Date:   Sun Jun 26 00:39:19 2016 -0700

i965: Make emit_urb_writes() not produce an EOT message for GS.

emit_urb_writes() contains code to emit an EOT write with no actual
data when there are no output varyings.  This makes sense for the VS
and TES stages, where it's called once at the end of the program.

However, in the geometry shader stage, emit_urb_writes() is called once
for every EmitVertex().  We explicitly emit a URB write with EOT set at
the end of the shader, separately from this path.  So we'd better not
terminate the thread.  This could get us into trouble for shaders which
do EmitVertex() with no varyings followed by SSBO/image/atomic writes.

It also caused us to emit multiple sends with EOT set, which apparently
confuses the register allocator into not using g112-g127 for all but
the first one.  This caused EU validation failures in OglGSCloth
shaders in shader-db.  (The actual application was fine, but shader-db
thinks there are no outputs because it doesn't understand transform
feedback.)

Cc: mesa-stable at lists.freedesktop.org
Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
Reviewed-by: Iago Toral Quiroga <itoral at igalia.com>

---

 src/mesa/drivers/dri/i965/brw_fs_visitor.cpp | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
index 3a49794..17eba8d 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
@@ -594,6 +594,13 @@ fs_visitor::emit_urb_writes(const fs_reg &gs_vertex_count)
     *    "The write data payload can be between 1 and 8 message phases long."
     */
    if (vue_map->slots_valid == 0) {
+      /* For GS, just turn EmitVertex() into a no-op.  We don't want it to
+       * end the thread, and emit_gs_thread_end() already emits a SEND with
+       * EOT at the end of the program for us.
+       */
+      if (stage == MESA_SHADER_GEOMETRY)
+         return;
+
       fs_reg payload = fs_reg(VGRF, alloc.allocate(2), BRW_REGISTER_TYPE_UD);
       bld.exec_all().MOV(payload, urb_handle);