1 files changed, 246 insertions, 0 deletions
diff --git a/src/glsl/ir_if_return.cpp b/src/glsl/ir_if_return.cpp
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+++ b/src/glsl/ir_if_return.cpp
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+/*
+ * 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 ir_if_return.cpp
+ *
+ * This pass tries to normalize functions to always return from one
+ * place by moving around blocks of code in if statements.
+ *
+ * This helps on hardware with no branching support, and may even be a
+ * useful transform on hardware supporting control flow by turning
+ * masked returns into normal returns.
+ */
+
+#include <string.h>
+#include "glsl_types.h"
+#include "ir.h"
+
+class ir_if_return_visitor : public ir_hierarchical_visitor {
+public:
+   ir_if_return_visitor()
+   {
+      this->progress = false;
+   }
+
+   ir_visitor_status visit_enter(ir_function_signature *);
+   ir_visitor_status visit_leave(ir_if *);
+
+   ir_visitor_status move_outer_block_inside(ir_instruction *ir,
+					     exec_list *inner_block);
+   void move_returns_after_block(ir_instruction *ir,
+				 ir_return *then_return,
+				 ir_return *else_return);
+   bool progress;
+};
+
+bool
+do_if_return(exec_list *instructions)
+{
+   ir_if_return_visitor v;
+
+   do {
+      v.progress = false;
+      visit_list_elements(&v, instructions);
+   } while (v.progress);
+
+   return v.progress;
+}
+
+/**
+ * Removes any instructions after a (unconditional) return, since they will
+ * never be executed.
+ */
+static void
+truncate_after_instruction(ir_instruction *ir)
+{
+   if (!ir)
+      return;
+
+   while (!ir->get_next()->is_tail_sentinel())
+      ((ir_instruction *)ir->get_next())->remove();
+}
+
+/**
+ * Returns an ir_instruction of the first ir_return in the exec_list, or NULL.
+ */
+static ir_return *
+find_return_in_block(exec_list *instructions)
+{
+   foreach_iter(exec_list_iterator, iter, *instructions) {
+      ir_instruction *ir = (ir_instruction *)iter.get();
+      if (ir->ir_type == ir_type_return)
+	 return (ir_return *)ir;
+   }
+
+   return NULL;
+}
+
+void
+ir_if_return_visitor::move_returns_after_block(ir_instruction *ir,
+					       ir_return *then_return,
+					       ir_return *else_return)
+{
+
+   if (!then_return->value) {
+      then_return->remove();
+      else_return->remove();
+      ir->insert_after(new(ir) ir_return(NULL));
+   } else {
+      ir_assignment *assign;
+      ir_variable *new_var = new(ir) ir_variable(then_return->value->type,
+						 "if_return_tmp",
+						 ir_var_temporary);
+      ir->insert_before(new_var);
+
+      assign = new(ir) ir_assignment(new(ir) ir_dereference_variable(new_var),
+				     then_return->value, NULL);
+      then_return->replace_with(assign);
+
+      assign = new(ir) ir_assignment(new(ir) ir_dereference_variable(new_var),
+				     else_return->value, NULL);
+      else_return->replace_with(assign);
+
+      ir_dereference_variable *deref = new(ir) ir_dereference_variable(new_var);
+      ir->insert_after(new(ir) ir_return(deref));
+   }
+   this->progress = true;
+}
+
+ir_visitor_status
+ir_if_return_visitor::move_outer_block_inside(ir_instruction *ir,
+					      exec_list *inner_block)
+{
+   if (!ir->get_next()->is_tail_sentinel()) {
+      while (!ir->get_next()->is_tail_sentinel()) {
+	 ir_instruction *move_ir = (ir_instruction *)ir->get_next();
+
+	 move_ir->remove();
+	 inner_block->push_tail(move_ir);
+      }
+
+      /* If we move the instructions following ir inside the block, it
+       * will confuse the exec_list iteration in the parent that visited
+       * us.  So stop the visit at this point.
+       */
+      return visit_stop;
+   } else {
+      return visit_continue;
+   }
+}
+
+/* Normalize a function to always have a return statement at the end.
+ *
+ * This avoids the ir_if handler needing to know whether it is at the
+ * top level of the function to know if there's an implicit return at
+ * the end of the outer block.
+ */
+ir_visitor_status
+ir_if_return_visitor::visit_enter(ir_function_signature *ir)
+{
+   ir_return *ret;
+
+   if (!ir->is_defined)
+      return visit_continue_with_parent;
+   if (strcmp(ir->function_name(), "main") == 0)
+      return visit_continue_with_parent;
+
+   ret = find_return_in_block(&ir->body);
+
+   if (ret) {
+      truncate_after_instruction(ret);
+   } else {
+      if (ir->return_type->is_void()) {
+	 ir->body.push_tail(new(ir) ir_return(NULL));
+      } else {
+	 /* Probably, if we've got a function with a return value
+	  * hitting this point, it's something like:
+	  *
+	  * float reduce_below_half(float val)
+	  * {
+	  *         while () {
+	  *                 if (val >= 0.5)
+	  *                         val /= 2.0;
+	  *                 else
+	  *                         return val;
+	  *         }
+	  * }
+	  *
+	  * So we gain a junk return statement of an undefined value
+	  * at the end that never gets executed.  However, a backend
+	  * using this pass is probably desperate to get rid of
+	  * function calls, so go ahead and do it for their sake in
+	  * case it fixes apps.
+	  */
+	 ir_variable *undef = new(ir) ir_variable(ir->return_type,
+						  "if_return_undef",
+						  ir_var_temporary);
+	 ir->body.push_tail(undef);
+
+	 ir_dereference_variable *deref = new(ir) ir_dereference_variable(undef);
+	 ir->body.push_tail(new(ir) ir_return(deref));
+      }
+   }
+
+   return visit_continue;
+}
+
+ir_visitor_status
+ir_if_return_visitor::visit_leave(ir_if *ir)
+{
+   ir_return *then_return;
+   ir_return *else_return;
+
+   then_return = find_return_in_block(&ir->then_instructions);
+   else_return = find_return_in_block(&ir->else_instructions);
+   if (!then_return && !else_return)
+      return visit_continue;
+
+   /* Trim off any trailing instructions after the return statements
+    * on both sides.
+    */
+   truncate_after_instruction(then_return);
+   truncate_after_instruction(else_return);
+
+   /* If both sides return, then we can move the returns to a single
+    * one outside the if statement.
+    */
+   if (then_return && else_return) {
+      move_returns_after_block(ir, then_return, else_return);
+      return visit_continue;
+   }
+
+   /* If only one side returns, then the block of code after the "if"
+    * is only executed by the other side, so those instructions don't
+    * need to be anywhere but that other side.
+    *
+    * This will usually pull a return statement up into the other
+    * side, so we'll trigger the above case on the next pass.
+    */
+   if (then_return) {
+      return move_outer_block_inside(ir, &ir->else_instructions);
+   } else {
+      assert(else_return);
+      return move_outer_block_inside(ir, &ir->then_instructions);
+   }
+}