[Mesa-dev] [PATCH 1/2] i965: Extract depctrl hazards

[Ben Widawsky]

Move this to a separate function so that we can begin to add other little
caveats without making too big a mess.

NOTE: There is some desire to improve this function eventually, but we need to
fix a bug first.

Signed-off-by: Ben Widawsky <ben at bwidawsk.net>
---
 src/mesa/drivers/dri/i965/brw_vec4.cpp | 42 ++++++++++++++++------------------
 1 file changed, 20 insertions(+), 22 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_vec4.cpp b/src/mesa/drivers/dri/i965/brw_vec4.cpp
index df589b8..0c2bbe9 100644
--- a/src/mesa/drivers/dri/i965/brw_vec4.cpp
+++ b/src/mesa/drivers/dri/i965/brw_vec4.cpp
@@ -840,6 +840,25 @@ vec4_visitor::move_push_constants_to_pull_constants()
    pack_uniform_registers();
 }
 
+/* Conditions for which we want to avoid setting the dependency control bits */
+static bool
+is_dep_ctrl_safe(vec4_instruction *inst)
+{
+   /*
+    * In the presence of send messages, totally interrupt dependency
+    * control. They're long enough that the chance of dependency
+    * control around them just doesn't matter.
+    *
+    * It looks like setting dependency control on a predicated
+    * instruction hangs the GPU.
+    * NB: I can find no evidence of this in modern specs.
+    *
+    * Dependency control does not work well over math instructions.
+    * NB: I can find no evidence of this in modern specs.
+    */
+   return !(inst->mlen || inst->predicate || inst->is_math());
+}
+
 /**
  * Sets the dependency control fields on instructions after register
  * allocation and before the generator is run.
@@ -885,28 +904,7 @@ vec4_visitor::opt_set_dependency_control()
             assert(inst->src[i].file != MRF);
          }
 
-         /* In the presence of send messages, totally interrupt dependency
-          * control.  They're long enough that the chance of dependency
-          * control around them just doesn't matter.
-          */
-         if (inst->mlen) {
-            memset(last_grf_write, 0, sizeof(last_grf_write));
-            memset(last_mrf_write, 0, sizeof(last_mrf_write));
-            continue;
-         }
-
-         /* It looks like setting dependency control on a predicated
-          * instruction hangs the GPU.
-          */
-         if (inst->predicate) {
-            memset(last_grf_write, 0, sizeof(last_grf_write));
-            memset(last_mrf_write, 0, sizeof(last_mrf_write));
-            continue;
-         }
-
-         /* Dependency control does not work well over math instructions.
-          */
-         if (inst->is_math()) {
+         if (!is_dep_ctrl_safe(inst)) {
             memset(last_grf_write, 0, sizeof(last_grf_write));
             memset(last_mrf_write, 0, sizeof(last_mrf_write));
             continue;
-- 
2.1.3