opt_if_simplification.cpp revision 9a3bd5e0452c9c791ba94155d3c9ddba42abd114 
1/*
2 * Copyright © 2010 Intel Corporation
3 *
4 * Permission is hereby granted, free of charge, to any person obtaining a
5 * copy of this software and associated documentation files (the "Software"),
6 * to deal in the Software without restriction, including without limitation
7 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
8 * and/or sell copies of the Software, and to permit persons to whom the
9 * Software is furnished to do so, subject to the following conditions:
10 *
11 * The above copyright notice and this permission notice (including the next
12 * paragraph) shall be included in all copies or substantial portions of the
13 * Software.
14 *
15 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
16 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
17 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
18 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
19 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
20 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
21 * DEALINGS IN THE SOFTWARE.
22 */
23
24/**
25 * \file opt_if_simplification.cpp
26 *
27 * Moves constant branches of if statements out to the surrounding
28 * instruction stream.
29 */
30
31#include "ir.h"
32
33class ir_if_simplification_visitor : public ir_hierarchical_visitor {
34public:
35   ir_if_simplification_visitor()
36   {
37      this->made_progress = false;
38   }
39
40   ir_visitor_status visit_leave(ir_if *);
41   ir_visitor_status visit_enter(ir_assignment *);
42
43   bool made_progress;
44};
45
46/* We only care about the top level "if" instructions, so don't
47 * descend into expressions.
48 */
49ir_visitor_status
50ir_if_simplification_visitor::visit_enter(ir_assignment *ir)
51{
52   (void) ir;
53   return visit_continue_with_parent;
54}
55
56bool
57do_if_simplification(exec_list *instructions)
58{
59   ir_if_simplification_visitor v;
60
61   v.run(instructions);
62   return v.made_progress;
63}
64
65
66ir_visitor_status
67ir_if_simplification_visitor::visit_leave(ir_if *ir)
68{
69   /* FINISHME: Ideally there would be a way to note that the condition results
70    * FINISHME: in a constant before processing both of the other subtrees.
71    * FINISHME: This can probably be done with some flags, but it would take
72    * FINISHME: some work to get right.
73    */
74   ir_constant *condition_constant = ir->condition->constant_expression_value();
75   if (condition_constant) {
76      /* Move the contents of the one branch of the conditional
77       * that matters out.
78       */
79      if (condition_constant->value.b[0]) {
80	 foreach_iter(exec_list_iterator, then_iter, ir->then_instructions) {
81	    ir_instruction *then_ir = (ir_instruction *)then_iter.get();
82	    ir->insert_before(then_ir);
83	 }
84      } else {
85	 foreach_iter(exec_list_iterator, else_iter, ir->else_instructions) {
86	    ir_instruction *else_ir = (ir_instruction *)else_iter.get();
87	    ir->insert_before(else_ir);
88	 }
89      }
90      ir->remove();
91      this->made_progress = true;
92   }
93
94   return visit_continue;
95}
96