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25 #include "main/compiler.h"
26 #include "glsl_types.h"
27 #include "loop_analysis.h"
28 #include "ir_hierarchical_visitor.h"
31 * Find an initializer of a variable outside a loop
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
37 * \param loop Loop where \c var is an induction variable
38 * \param var Variable whose initializer is to be found
41 * The \c ir_rvalue assigned to the variable outside the loop. May return
42 * \c NULL if no initializer can be found.
45 find_initial_value(ir_loop *loop, ir_variable *var)
47 for (exec_node *node = loop->prev;
48 !node->is_head_sentinel();
50 ir_instruction *ir = (ir_instruction *) node;
52 switch (ir->ir_type) {
55 case ir_type_loop_jump:
60 case ir_type_function:
61 case ir_type_function_signature:
62 assert(!"Should not get here.");
65 case ir_type_assignment: {
66 ir_assignment *assign = ir->as_assignment();
67 ir_variable *assignee = assign->lhs->whole_variable_referenced();
70 return (assign->condition != NULL) ? NULL : assign->rhs;
85 calculate_iterations(ir_rvalue *from, ir_rvalue *to, ir_rvalue *increment,
86 enum ir_expression_operation op)
88 if (from == NULL || to == NULL || increment == NULL)
91 void *mem_ctx = ralloc_context(NULL);
93 ir_expression *const sub =
94 new(mem_ctx) ir_expression(ir_binop_sub, from->type, to, from);
96 ir_expression *const div =
97 new(mem_ctx) ir_expression(ir_binop_div, sub->type, sub, increment);
99 ir_constant *iter = div->constant_expression_value();
104 if (!iter->type->is_integer()) {
106 new(mem_ctx) ir_expression(ir_unop_f2i, glsl_type::int_type, iter,
109 iter = cast->constant_expression_value();
112 int iter_value = iter->get_int_component(0);
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.
119 * for (float x = 0.0; x != 0.9; x += 0.2)
122 const int bias[] = { -1, 0, 1 };
123 bool valid_loop = false;
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]));
130 ir_expression *const mul =
131 new(mem_ctx) ir_expression(ir_binop_mul, increment->type, iter,
134 ir_expression *const add =
135 new(mem_ctx) ir_expression(ir_binop_add, mul->type, mul, from);
137 ir_expression *const cmp =
138 new(mem_ctx) ir_expression(op, glsl_type::bool_type, add, to);
140 ir_constant *const cmp_result = cmp->constant_expression_value();
142 assert(cmp_result != NULL);
143 if (cmp_result->get_bool_component(0)) {
144 iter_value += bias[i];
150 ralloc_free(mem_ctx);
151 return (valid_loop) ? iter_value : -1;
155 class loop_control_visitor : public ir_hierarchical_visitor {
157 loop_control_visitor(loop_state *state)
160 this->progress = false;
163 virtual ir_visitor_status visit_leave(ir_loop *ir);
172 loop_control_visitor::visit_leave(ir_loop *ir)
174 loop_variable_state *const ls = this->state->get(ir);
176 /* If we've entered a loop that hasn't been analyzed, something really,
177 * really bad has happened.
181 return visit_continue;
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
188 int max_iterations = ls->max_iterations;
190 if(ir->from && ir->to && ir->increment)
191 max_iterations = calculate_iterations(ir->from, ir->to, ir->increment, (ir_expression_operation)ir->cmp);
193 if(max_iterations < 0)
194 max_iterations = INT_MAX;
196 foreach_list(node, &ls->terminators) {
197 loop_terminator *t = (loop_terminator *) node;
198 ir_if *if_stmt = t->ir;
200 /* If-statements can be either 'if (expr)' or 'if (deref)'. We only care
201 * about the former here.
203 ir_expression *cond = if_stmt->condition->as_expression();
207 switch (cond->operation) {
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
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;
221 counter = cond->operands[1]->as_dereference_variable();
222 limit = cond->operands[0]->as_constant();
225 case ir_binop_less: cmp = ir_binop_greater; break;
226 case ir_binop_greater: cmp = ir_binop_less; break;
227 case ir_binop_lequal: cmp = ir_binop_gequal; break;
228 case ir_binop_gequal: cmp = ir_binop_lequal; break;
229 default: assert(!"Should not get here.");
233 if ((counter == NULL) || (limit == NULL))
236 ir_variable *var = counter->variable_referenced();
238 ir_rvalue *init = find_initial_value(ir, var);
240 foreach_list(iv_node, &ls->induction_variables) {
241 loop_variable *lv = (loop_variable *) iv_node;
243 if (lv->var == var) {
244 const int iterations = calculate_iterations(init, limit,
247 if (iterations >= 0) {
248 /* If the new iteration count is lower than the previously
249 * believed iteration count, update the loop control values.
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;
258 max_iterations = iterations;
261 /* Remove the conditional break statement. The loop
262 * controls are now set such that the exit condition will be
267 assert(ls->num_loop_jumps > 0);
268 ls->num_loop_jumps--;
270 this->progress = true;
284 /* If we have proven the one of the loop exit conditions is satisifed before
285 * running the loop once, remove the loop.
287 if (max_iterations == 0)
290 ls->max_iterations = max_iterations;
292 return visit_continue;
297 set_loop_controls(exec_list *instructions, loop_state *ls)
299 loop_control_visitor v(ls);