i965/vs: Add virtual function make_reg_for_system_value().

The system values handled by vec4_visitor::visit(ir_variable *) are
VS-specific (vertex ID and instance ID).  This patch moves the
handling of those values into a new virtual function,
make_reg_for_system_value(), so that this VS-specific code won't be
inherited by geomtry shaders.

Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/mesa/drivers/dri/i965/brw_vec4.h

@@ -482,6 +482,7 @@ public:
    void dump_instructions();
 
 protected:
+   virtual dst_reg *make_reg_for_system_value(ir_variable *ir) = 0;
    virtual int setup_attributes(int payload_reg) = 0;
    virtual void emit_prolog() = 0;
    virtual void emit_program_code() = 0;
@@ -499,6 +500,7 @@ public:
                    void *mem_ctx);
 
 protected:
+   virtual dst_reg *make_reg_for_system_value(ir_variable *ir);
    virtual int setup_attributes(int payload_reg);
    virtual void emit_prolog();
    virtual void emit_program_code();

src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp

@@ -1015,6 +1015,33 @@ vec4_vs_visitor::emit_prolog()
    }
 }
 
+
+dst_reg *
+vec4_vs_visitor::make_reg_for_system_value(ir_variable *ir)
+{
+   /* VertexID is stored by the VF as the last vertex element, but
+    * we don't represent it with a flag in inputs_read, so we call
+    * it VERT_ATTRIB_MAX, which setup_attributes() picks up on.
+    */
+   dst_reg *reg = new(mem_ctx) dst_reg(ATTR, VERT_ATTRIB_MAX);
+   prog_data->uses_vertexid = true;
+
+   switch (ir->location) {
+   case SYSTEM_VALUE_VERTEX_ID:
+      reg->writemask = WRITEMASK_X;
+      break;
+   case SYSTEM_VALUE_INSTANCE_ID:
+      reg->writemask = WRITEMASK_Y;
+      break;
+   default:
+      assert(!"not reached");
+      break;
+   }
+
+   return reg;
+}
+
+
 void
 vec4_visitor::visit(ir_variable *ir)
 {
@@ -1068,24 +1095,7 @@ vec4_visitor::visit(ir_variable *ir)
       break;
 
    case ir_var_system_value:
-      /* VertexID is stored by the VF as the last vertex element, but
-       * we don't represent it with a flag in inputs_read, so we call
-       * it VERT_ATTRIB_MAX, which setup_attributes() picks up on.
-       */
-      reg = new(mem_ctx) dst_reg(ATTR, VERT_ATTRIB_MAX);
-      prog_data->uses_vertexid = true;
-
-      switch (ir->location) {
-      case SYSTEM_VALUE_VERTEX_ID:
-	 reg->writemask = WRITEMASK_X;
-	 break;
-      case SYSTEM_VALUE_INSTANCE_ID:
-	 reg->writemask = WRITEMASK_Y;
-	 break;
-      default:
-	 assert(!"not reached");
-	 break;
-      }
+      reg = make_reg_for_system_value(ir);
       break;
 
    default:

src/mesa/drivers/dri/i965/test_vec4_register_coalesce.cpp

@@ -54,6 +54,12 @@ public:
    }
 
 protected:
+   virtual dst_reg *make_reg_for_system_value(ir_variable *ir)
+   {
+      assert(!"Not reached");
+      return NULL;
+   }
+
    virtual int setup_attributes(int payload_reg)
    {
       assert(!"Not reached");