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#include <limits.h>
25#include "main/compiler.h"
26#include "glsl_types.h"
27#include "loop_analysis.h"
28#include "ir_hierarchical_visitor.h"
29
30/**
31 * Find an initializer of a variable outside a loop
32 *
33 * Works backwards from the loop to find the pre-loop value of the variable.
34 * This is used, for example, to find the initial value of loop induction
35 * variables.
36 *
37 * \param loop  Loop where \c var is an induction variable
38 * \param var   Variable whose initializer is to be found
39 *
40 * \return
41 * The \c ir_rvalue assigned to the variable outside the loop.  May return
42 * \c NULL if no initializer can be found.
43 */
44ir_rvalue *
45find_initial_value(ir_loop *loop, ir_variable *var)
46{
47   for (exec_node *node = loop->prev;
48	!node->is_head_sentinel();
49	node = node->prev) {
50      ir_instruction *ir = (ir_instruction *) node;
51
52      switch (ir->ir_type) {
53      case ir_type_call:
54      case ir_type_loop:
55      case ir_type_loop_jump:
56      case ir_type_return:
57      case ir_type_if:
58	 return NULL;
59
60      case ir_type_function:
61      case ir_type_function_signature:
62	 assert(!"Should not get here.");
63	 return NULL;
64
65      case ir_type_assignment: {
66	 ir_assignment *assign = ir->as_assignment();
67	 ir_variable *assignee = assign->lhs->whole_variable_referenced();
68
69	 if (assignee == var)
70	    return (assign->condition != NULL) ? NULL : assign->rhs;
71
72	 break;
73      }
74
75      default:
76	 break;
77      }
78   }
79
80   return NULL;
81}
82
83
84int
85calculate_iterations(ir_rvalue *from, ir_rvalue *to, ir_rvalue *increment,
86		     enum ir_expression_operation op)
87{
88   if (from == NULL || to == NULL || increment == NULL)
89      return -1;
90
91   void *mem_ctx = ralloc_context(NULL);
92
93   ir_expression *const sub =
94      new(mem_ctx) ir_expression(ir_binop_sub, from->type, to, from);
95
96   ir_expression *const div =
97      new(mem_ctx) ir_expression(ir_binop_div, sub->type, sub, increment);
98
99   ir_constant *iter = div->constant_expression_value();
100
101   if (iter == NULL)
102      return -1;
103
104   if (!iter->type->is_integer()) {
105      ir_rvalue *cast =
106	 new(mem_ctx) ir_expression(ir_unop_f2i, glsl_type::int_type, iter,
107				    NULL);
108
109      iter = cast->constant_expression_value();
110   }
111
112   int iter_value = iter->get_int_component(0);
113
114   /* Make sure that the calculated number of iterations satisfies the exit
115    * condition.  This is needed to catch off-by-one errors and some types of
116    * ill-formed loops.  For example, we need to detect that the following
117    * loop does not have a maximum iteration count.
118    *
119    *    for (float x = 0.0; x != 0.9; x += 0.2)
120    *        ;
121    */
122   const int bias[] = { -1, 0, 1 };
123   bool valid_loop = false;
124
125   for (unsigned i = 0; i < Elements(bias); i++) {
126      iter = (increment->type->is_integer())
127	 ? new(mem_ctx) ir_constant(iter_value + bias[i])
128	 : new(mem_ctx) ir_constant(float(iter_value + bias[i]));
129
130      ir_expression *const mul =
131	 new(mem_ctx) ir_expression(ir_binop_mul, increment->type, iter,
132				    increment);
133
134      ir_expression *const add =
135	 new(mem_ctx) ir_expression(ir_binop_add, mul->type, mul, from);
136
137      ir_expression *const cmp =
138	 new(mem_ctx) ir_expression(op, glsl_type::bool_type, add, to);
139
140      ir_constant *const cmp_result = cmp->constant_expression_value();
141
142      assert(cmp_result != NULL);
143      if (cmp_result->get_bool_component(0)) {
144	 iter_value += bias[i];
145	 valid_loop = true;
146	 break;
147      }
148   }
149
150   ralloc_free(mem_ctx);
151   return (valid_loop) ? iter_value : -1;
152}
153
154
155class loop_control_visitor : public ir_hierarchical_visitor {
156public:
157   loop_control_visitor(loop_state *state)
158   {
159      this->state = state;
160      this->progress = false;
161   }
162
163   virtual ir_visitor_status visit_leave(ir_loop *ir);
164
165   loop_state *state;
166
167   bool progress;
168};
169
170
171ir_visitor_status
172loop_control_visitor::visit_leave(ir_loop *ir)
173{
174   loop_variable_state *const ls = this->state->get(ir);
175
176   /* If we've entered a loop that hasn't been analyzed, something really,
177    * really bad has happened.
178    */
179   if (ls == NULL) {
180      assert(ls != NULL);
181      return visit_continue;
182   }
183
184   /* Search the loop terminating conditions for one of the form 'i < c' where
185    * i is a loop induction variable, c is a constant, and < is any relative
186    * operator.
187    */
188   int max_iterations = ls->max_iterations;
189
190   if(ir->from && ir->to && ir->increment)
191      max_iterations = calculate_iterations(ir->from, ir->to, ir->increment, (ir_expression_operation)ir->cmp);
192
193   if(max_iterations < 0)
194      max_iterations = INT_MAX;
195
196   foreach_list(node, &ls->terminators) {
197      loop_terminator *t = (loop_terminator *) node;
198      ir_if *if_stmt = t->ir;
199
200      /* If-statements can be either 'if (expr)' or 'if (deref)'.  We only care
201       * about the former here.
202       */
203      ir_expression *cond = if_stmt->condition->as_expression();
204      if (cond == NULL)
205	 continue;
206
207      switch (cond->operation) {
208      case ir_binop_less:
209      case ir_binop_greater:
210      case ir_binop_lequal:
211      case ir_binop_gequal: {
212	 /* The expressions that we care about will either be of the form
213	  * 'counter < limit' or 'limit < counter'.  Figure out which is
214	  * which.
215	  */
216	 ir_rvalue *counter = cond->operands[0]->as_dereference_variable();
217	 ir_constant *limit = cond->operands[1]->as_constant();
218	 enum ir_expression_operation cmp = cond->operation;
219
220	 if (limit == NULL) {
221	    counter = cond->operands[1]->as_dereference_variable();
222	    limit = cond->operands[0]->as_constant();
223
224	    switch (cmp) {
225	    case ir_binop_less:    cmp = ir_binop_gequal;  break;
226	    case ir_binop_greater: cmp = ir_binop_lequal;  break;
227	    case ir_binop_lequal:  cmp = ir_binop_greater; break;
228	    case ir_binop_gequal:  cmp = ir_binop_less;    break;
229	    default: assert(!"Should not get here.");
230	    }
231	 }
232
233	 if ((counter == NULL) || (limit == NULL))
234	    break;
235
236	 ir_variable *var = counter->variable_referenced();
237
238	 ir_rvalue *init = find_initial_value(ir, var);
239
240	 foreach_list(iv_node, &ls->induction_variables) {
241	    loop_variable *lv = (loop_variable *) iv_node;
242
243	    if (lv->var == var) {
244	       const int iterations = calculate_iterations(init, limit,
245							   lv->increment,
246							   cmp);
247	       if (iterations >= 0) {
248		  /* If the new iteration count is lower than the previously
249		   * believed iteration count, update the loop control values.
250		   */
251		  if (iterations < max_iterations) {
252		     ir->from = init->clone(ir, NULL);
253		     ir->to = limit->clone(ir, NULL);
254		     ir->increment = lv->increment->clone(ir, NULL);
255		     ir->counter = lv->var;
256		     ir->cmp = cmp;
257
258		     max_iterations = iterations;
259		  }
260
261		  /* Remove the conditional break statement.  The loop
262		   * controls are now set such that the exit condition will be
263		   * satisfied.
264		   */
265		  if_stmt->remove();
266
267		  assert(ls->num_loop_jumps > 0);
268		  ls->num_loop_jumps--;
269
270		  this->progress = true;
271	       }
272
273	       break;
274	    }
275	 }
276	 break;
277      }
278
279      default:
280	 break;
281      }
282   }
283
284   /* If we have proven the one of the loop exit conditions is satisifed before
285    * running the loop once, remove the loop.
286    */
287   if (max_iterations == 0)
288      ir->remove();
289   else
290      ls->max_iterations = max_iterations;
291
292   return visit_continue;
293}
294
295
296bool
297set_loop_controls(exec_list *instructions, loop_state *ls)
298{
299   loop_control_visitor v(ls);
300
301   v.run(instructions);
302
303   return v.progress;
304}
305