i965/vs: Add simple dead code elimination.

This is copied right from the fragment shader.  It is needed for real
register allocation to work correctly.

diff --git a/src/mesa/drivers/dri/i965/brw_vec4.cpp b/src/mesa/drivers/dri/i965/brw_vec4.cpp
index a3ed31a9da0a8a171903f0c9d48e4b47ebd4c3bc..760bc1f7acdea9adb5c15a051256e65989fe0670 100644 (file)
--- a/src/mesa/drivers/dri/i965/brw_vec4.cpp
+++ b/src/mesa/drivers/dri/i965/brw_vec4.cpp
@@ -127,4 +127,35 @@ vec4_visitor::virtual_grf_interferes(int a, int b)
    return start < end;
 }
 
+/**
+ * Must be called after calculate_live_intervales() to remove unused
+ * writes to registers -- register allocation will fail otherwise
+ * because something deffed but not used won't be considered to
+ * interfere with other regs.
+ */
+bool
+vec4_visitor::dead_code_eliminate()
+{
+   bool progress = false;
+   int pc = 0;
+
+   calculate_live_intervals();
+
+   foreach_list_safe(node, &this->instructions) {
+      vec4_instruction *inst = (vec4_instruction *)node;
+
+      if (inst->dst.file == GRF && this->virtual_grf_use[inst->dst.reg] <= pc) {
+        inst->remove();
+        progress = true;
+      }
+
+      pc++;
+   }
+
+   if (progress)
+      live_intervals_valid = false;
+
+   return progress;
+}
+
 } /* namespace brw */

diff --git a/src/mesa/drivers/dri/i965/brw_vec4.h b/src/mesa/drivers/dri/i965/brw_vec4.h
index 77a28c7cda7e68336ef690397083f50ab9f3b7ec..1db910e2b9913858e3432d209a7e79a4456127df 100644 (file)
--- a/src/mesa/drivers/dri/i965/brw_vec4.h
+++ b/src/mesa/drivers/dri/i965/brw_vec4.h
@@ -381,6 +381,7 @@ public:
    void reg_allocate();
    void move_grf_array_access_to_scratch();
    void calculate_live_intervals();
+   bool dead_code_eliminate();
    bool virtual_grf_interferes(int a, int b);
 
    vec4_instruction *emit(enum opcode opcode);

diff --git a/src/mesa/drivers/dri/i965/brw_vec4_emit.cpp b/src/mesa/drivers/dri/i965/brw_vec4_emit.cpp
index 011af6f2d3eedfd8d4465bce97f034bbc26f95fa..65ac7d9dc09778ff9bb5b48bf9d05c9bb4bc977e 100644 (file)
--- a/src/mesa/drivers/dri/i965/brw_vec4_emit.cpp
+++ b/src/mesa/drivers/dri/i965/brw_vec4_emit.cpp
@@ -558,6 +558,12 @@ vec4_visitor::run()
     */
    move_grf_array_access_to_scratch();
 
+   bool progress;
+   do {
+      progress = false;
+      progress = dead_code_eliminate() || progress;
+   } while (progress);
+
    if (failed)
       return false;