i965/fs: Disable CSE optimization for untyped & typed surface reads

An untyped surface read is volatile because it might be affected by a
write.

In the ES31-CTS.compute_shader.resources-max test, two back to back
read/modify/writes of an SSBO variable looked something like this:

  r1 = untyped_surface_read(ssbo_float)
  r2 = r1 + 1
  untyped_surface_write(ssbo_float, r2)
  r3 = untyped_surface_read(ssbo_float)
  r4 = r3 + 1
  untyped_surface_write(ssbo_float, r4)

And after CSE, we had:

  r1 = untyped_surface_read(ssbo_float)
  r2 = r1 + 1
  untyped_surface_write(ssbo_float, r2)
  r4 = r1 + 1
  untyped_surface_write(ssbo_float, r4)

Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/src/mesa/drivers/dri/i965/brw_fs_cse.cpp b/src/mesa/drivers/dri/i965/brw_fs_cse.cpp
index c7628dc..3a28c8d 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_cse.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_cse.cpp
@@ -93,7 +93,8 @@ is_expression(const fs_visitor *v, const fs_inst *const inst)
    case SHADER_OPCODE_LOAD_PAYLOAD:
       return !inst->is_copy_payload(v->alloc);
    default:
-      return inst->is_send_from_grf() && !inst->has_side_effects();
+      return inst->is_send_from_grf() && !inst->has_side_effects() &&
+         !inst->is_volatile();
    }
 }