glsl: add ir_emit_vertex and ir_end_primitive instruction types

These correspond to the EmitVertex and EndPrimitive functions in GLSL.

v2 (Paul Berry <stereotype441@gmail.com>): Add stub implementations of
new pure visitor functions to i965's vec4_visitor and fs_visitor
classes.

v3 (Paul Berry <stereotype441@gmail.com>): Rename classes to be more
consistent with the names used in the GL spec.

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/glsl/opt_dead_code_local.cpp

@@ -114,6 +114,23 @@ public:
       return visit_continue_with_parent;
    }
 
+   virtual ir_visitor_status visit(ir_emit_vertex *ir)
+   {
+      /* For the purpose of dead code elimination, emitting a vertex counts as
+       * "reading" all of the currently assigned output variables.
+       */
+      foreach_iter(exec_list_iterator, iter, *this->assignments) {
+         assignment_entry *entry = (assignment_entry *)iter.get();
+         if (entry->lhs->mode == ir_var_shader_out) {
+            if (debug)
+               printf("kill %s\n", entry->lhs->name);
+            entry->remove();
+         }
+      }
+
+      return visit_continue;
+   }
+
 private:
    exec_list *assignments;
 };