1 files changed, 126 insertions, 0 deletions
diff --git a/src/compiler/glsl/opt_if_simplification.cpp b/src/compiler/glsl/opt_if_simplification.cpp
new file mode 100644
index 00000000000..e05f03190aa
--- /dev/null
+++ b/src/compiler/glsl/opt_if_simplification.cpp
@@ -0,0 +1,126 @@
+/*
+ * Copyright © 2010 Intel Corporation
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+
+/**
+ * \file opt_if_simplification.cpp
+ *
+ * Moves constant branches of if statements out to the surrounding
+ * instruction stream, and inverts if conditionals to avoid empty
+ * "then" blocks.
+ */
+
+#include "ir.h"
+
+namespace {
+
+class ir_if_simplification_visitor : public ir_hierarchical_visitor {
+public:
+   ir_if_simplification_visitor()
+   {
+      this->made_progress = false;
+   }
+
+   ir_visitor_status visit_leave(ir_if *);
+   ir_visitor_status visit_enter(ir_assignment *);
+
+   bool made_progress;
+};
+
+} /* unnamed namespace */
+
+/* We only care about the top level "if" instructions, so don't
+ * descend into expressions.
+ */
+ir_visitor_status
+ir_if_simplification_visitor::visit_enter(ir_assignment *ir)
+{
+   (void) ir;
+   return visit_continue_with_parent;
+}
+
+bool
+do_if_simplification(exec_list *instructions)
+{
+   ir_if_simplification_visitor v;
+
+   v.run(instructions);
+   return v.made_progress;
+}
+
+
+ir_visitor_status
+ir_if_simplification_visitor::visit_leave(ir_if *ir)
+{
+   /* If the if statement has nothing on either side, remove it. */
+   if (ir->then_instructions.is_empty() &&
+       ir->else_instructions.is_empty()) {
+      ir->remove();
+      this->made_progress = true;
+      return visit_continue;
+   }
+
+   /* FINISHME: Ideally there would be a way to note that the condition results
+    * FINISHME: in a constant before processing both of the other subtrees.
+    * FINISHME: This can probably be done with some flags, but it would take
+    * FINISHME: some work to get right.
+    */
+   ir_constant *condition_constant = ir->condition->constant_expression_value();
+   if (condition_constant) {
+      /* Move the contents of the one branch of the conditional
+       * that matters out.
+       */
+      if (condition_constant->value.b[0]) {
+         ir->insert_before(&ir->then_instructions);
+      } else {
+         ir->insert_before(&ir->else_instructions);
+      }
+      ir->remove();
+      this->made_progress = true;
+      return visit_continue;
+   }
+
+   /* Turn:
+    *
+    *     if (cond) {
+    *     } else {
+    *         do_work();
+    *     }
+    *
+    * into :
+    *
+    *     if (!cond)
+    *         do_work();
+    *
+    * which avoids control flow for "else" (which is usually more
+    * expensive than normal operations), and the "not" can usually be
+    * folded into the generation of "cond" anyway.
+    */
+   if (ir->then_instructions.is_empty()) {
+      ir->condition = new(ralloc_parent(ir->condition))
+	 ir_expression(ir_unop_logic_not, ir->condition);
+      ir->else_instructions.move_nodes_to(&ir->then_instructions);
+      this->made_progress = true;
+   }
+
+   return visit_continue;
+}