i965/vec4: Let DCE eliminate dead writes in other basic blocks.

We previously stopped searching for unread writes after encountering
control flow, but we can instead just search backwards until we hit
control flow.

instructions in affected programs:     22854 -> 22194 (-2.89%)

diff --git a/src/mesa/drivers/dri/i965/brw_vec4.cpp b/src/mesa/drivers/dri/i965/brw_vec4.cpp
index 740d9ff60339507c86a3f30c3df82c8ffded103b..c34eec4d7dc71f6245641961d1dccf46fca69f63 100644 (file)
--- a/src/mesa/drivers/dri/i965/brw_vec4.cpp
+++ b/src/mesa/drivers/dri/i965/brw_vec4.cpp
@@ -378,7 +378,6 @@ bool
 vec4_visitor::dead_code_eliminate()
 {
    bool progress = false;
-   bool seen_control_flow = false;
    int pc = -1;
 
    calculate_live_intervals();
@@ -388,8 +387,6 @@ vec4_visitor::dead_code_eliminate()
 
       pc++;
 
-      seen_control_flow = inst->is_control_flow() || seen_control_flow;
-
       bool inst_writes_flag = false;
       if (inst->dst.file != GRF) {
          if (inst->dst.is_null() && inst->writes_flag()) {
@@ -415,7 +412,7 @@ vec4_visitor::dead_code_eliminate()
                     progress;
       }
 
-      if (seen_control_flow || inst->predicate || inst->prev == NULL)
+      if (inst->predicate || inst->prev == NULL)
          continue;
 
       int dead_channels;
@@ -443,6 +440,9 @@ vec4_visitor::dead_code_eliminate()
            node = prev, prev = prev->prev) {
          vec4_instruction *scan_inst = (vec4_instruction  *)node;
 
+         if (scan_inst->is_control_flow())
+            break;
+
          if (inst_writes_flag) {
             if (scan_inst->dst.is_null() && scan_inst->writes_flag()) {
                scan_inst->remove();