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
33namespace {
34
35class ir_if_simplification_visitor : public ir_hierarchical_visitor {
36public:
37   ir_if_simplification_visitor()
38   {
39      this->made_progress = false;
40   }
41
42   ir_visitor_status visit_leave(ir_if *);
43   ir_visitor_status visit_enter(ir_assignment *);
44
45   bool made_progress;
46};
47
48} /* unnamed namespace */
49
50/* We only care about the top level "if" instructions, so don't
51 * descend into expressions.
52 */
53ir_visitor_status
54ir_if_simplification_visitor::visit_enter(ir_assignment *ir)
55{
56   (void) ir;
57   return visit_continue_with_parent;
58}
59
60bool
61do_if_simplification(exec_list *instructions)
62{
63   ir_if_simplification_visitor v;
64
65   v.run(instructions);
66   return v.made_progress;
67}
68
69
70ir_visitor_status
71ir_if_simplification_visitor::visit_leave(ir_if *ir)
72{
73   /* If the if statement has nothing on either side, remove it. */
74   if (ir->then_instructions.is_empty() &&
75       ir->else_instructions.is_empty()) {
76      ir->remove();
77      this->made_progress = true;
78      return visit_continue;
79   }
80
81   /* FINISHME: Ideally there would be a way to note that the condition results
82    * FINISHME: in a constant before processing both of the other subtrees.
83    * FINISHME: This can probably be done with some flags, but it would take
84    * FINISHME: some work to get right.
85    */
86   ir_constant *condition_constant = ir->condition->constant_expression_value();
87   if (condition_constant) {
88      /* Move the contents of the one branch of the conditional
89       * that matters out.
90       */
91      if (condition_constant->value.b[0]) {
92	 foreach_iter(exec_list_iterator, then_iter, ir->then_instructions) {
93	    ir_instruction *then_ir = (ir_instruction *)then_iter.get();
94	    ir->insert_before(then_ir);
95	 }
96      } else {
97	 foreach_iter(exec_list_iterator, else_iter, ir->else_instructions) {
98	    ir_instruction *else_ir = (ir_instruction *)else_iter.get();
99	    ir->insert_before(else_ir);
100	 }
101      }
102      ir->remove();
103      this->made_progress = true;
104   }
105
106   return visit_continue;
107}
108