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 lower_if_to_cond_assign.cpp
26 *
27 * This attempts to flatten if-statements to conditional assignments for
28 * GPUs with limited or no flow control support.
29 *
30 * It can't handle other control flow being inside of its block, such
31 * as calls or loops.  Hopefully loop unrolling and inlining will take
32 * care of those.
33 *
34 * Drivers for GPUs with no control flow support should simply call
35 *
36 *    lower_if_to_cond_assign(instructions)
37 *
38 * to attempt to flatten all if-statements.
39 *
40 * Some GPUs (such as i965 prior to gen6) do support control flow, but have a
41 * maximum nesting depth N.  Drivers for such hardware can call
42 *
43 *    lower_if_to_cond_assign(instructions, N)
44 *
45 * to attempt to flatten any if-statements appearing at depth > N.
46 */
47
48#include "glsl_types.h"
49#include "ir.h"
50
51class ir_if_to_cond_assign_visitor : public ir_hierarchical_visitor {
52public:
53   ir_if_to_cond_assign_visitor(unsigned max_depth)
54   {
55      this->progress = false;
56      this->max_depth = max_depth;
57      this->depth = 0;
58   }
59
60   ir_visitor_status visit_enter(ir_if *);
61   ir_visitor_status visit_leave(ir_if *);
62
63   bool progress;
64   unsigned max_depth;
65   unsigned depth;
66};
67
68bool
69lower_if_to_cond_assign(exec_list *instructions, unsigned max_depth)
70{
71   ir_if_to_cond_assign_visitor v(max_depth);
72
73   visit_list_elements(&v, instructions);
74
75   return v.progress;
76}
77
78void
79check_control_flow(ir_instruction *ir, void *data)
80{
81   bool *found_control_flow = (bool *)data;
82   switch (ir->ir_type) {
83   case ir_type_call:
84   case ir_type_discard:
85   case ir_type_loop:
86   case ir_type_loop_jump:
87   case ir_type_return:
88      *found_control_flow = true;
89      break;
90   default:
91      break;
92   }
93}
94
95void
96move_block_to_cond_assign(void *mem_ctx,
97			  ir_if *if_ir, ir_variable *cond_var, bool then)
98{
99   exec_list *instructions;
100
101   if (then) {
102      instructions = &if_ir->then_instructions;
103   } else {
104      instructions = &if_ir->else_instructions;
105   }
106
107   foreach_iter(exec_list_iterator, iter, *instructions) {
108      ir_instruction *ir = (ir_instruction *)iter.get();
109
110      if (ir->ir_type == ir_type_assignment) {
111	 ir_assignment *assign = (ir_assignment *)ir;
112	 ir_rvalue *cond_expr;
113	 ir_dereference *deref = new(mem_ctx) ir_dereference_variable(cond_var);
114
115	 if (then) {
116	    cond_expr = deref;
117	 } else {
118	    cond_expr = new(mem_ctx) ir_expression(ir_unop_logic_not,
119						   glsl_type::bool_type,
120						   deref,
121						   NULL);
122	 }
123
124	 if (!assign->condition) {
125	    assign->condition = cond_expr;
126	 } else {
127	    assign->condition = new(mem_ctx) ir_expression(ir_binop_logic_and,
128							   glsl_type::bool_type,
129							   cond_expr,
130							   assign->condition);
131	 }
132      }
133
134      /* Now, move from the if block to the block surrounding it. */
135      ir->remove();
136      if_ir->insert_before(ir);
137   }
138}
139
140ir_visitor_status
141ir_if_to_cond_assign_visitor::visit_enter(ir_if *ir)
142{
143   (void) ir;
144   this->depth++;
145   return visit_continue;
146}
147
148ir_visitor_status
149ir_if_to_cond_assign_visitor::visit_leave(ir_if *ir)
150{
151   /* Only flatten when beyond the GPU's maximum supported nesting depth. */
152   if (this->depth <= this->max_depth)
153      return visit_continue;
154
155   this->depth--;
156
157   bool found_control_flow = false;
158   ir_variable *cond_var;
159   ir_assignment *assign;
160   ir_dereference_variable *deref;
161
162   /* Check that both blocks don't contain anything we can't support. */
163   foreach_iter(exec_list_iterator, then_iter, ir->then_instructions) {
164      ir_instruction *then_ir = (ir_instruction *)then_iter.get();
165      visit_tree(then_ir, check_control_flow, &found_control_flow);
166   }
167   foreach_iter(exec_list_iterator, else_iter, ir->else_instructions) {
168      ir_instruction *else_ir = (ir_instruction *)else_iter.get();
169      visit_tree(else_ir, check_control_flow, &found_control_flow);
170   }
171   if (found_control_flow)
172      return visit_continue;
173
174   void *mem_ctx = hieralloc_parent(ir);
175
176   /* Store the condition to a variable so the assignment conditions are
177    * simpler.
178    */
179   cond_var = new(mem_ctx) ir_variable(glsl_type::bool_type,
180				       "if_to_cond_assign_condition",
181				       ir_var_temporary);
182   ir->insert_before(cond_var);
183
184   deref = new(mem_ctx) ir_dereference_variable(cond_var);
185   assign = new(mem_ctx) ir_assignment(deref,
186				       ir->condition, NULL);
187   ir->insert_before(assign);
188
189   /* Now, move all of the instructions out of the if blocks, putting
190    * conditions on assignments.
191    */
192   move_block_to_cond_assign(mem_ctx, ir, cond_var, true);
193   move_block_to_cond_assign(mem_ctx, ir, cond_var, false);
194
195   ir->remove();
196
197   this->progress = true;
198
199   return visit_continue;
200}
201