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24 #include "glsl_types.h"
25 #include "loop_analysis.h"
26 #include "ir_hierarchical_visitor.h"
28 static bool is_loop_terminator(ir_if *ir);
30 static bool all_expression_operands_are_loop_constant(ir_rvalue *,
33 static ir_rvalue *get_basic_induction_increment(ir_assignment *, hash_table *);
36 loop_state::loop_state()
38 this->ht = hash_table_ctor(0, hash_table_pointer_hash,
39 hash_table_pointer_compare);
40 this->mem_ctx = talloc_init("loop state");
44 loop_state::~loop_state()
46 hash_table_dtor(this->ht);
47 talloc_free(this->mem_ctx);
52 loop_state::insert(ir_loop *ir)
54 loop_variable_state *ls = new(this->mem_ctx) loop_variable_state;
55 hash_table_insert(this->ht, ls, ir);
62 loop_state::get(const ir_loop *ir)
64 return (loop_variable_state *) hash_table_find(this->ht, ir);
69 loop_variable_state::get(const ir_variable *ir)
71 return (loop_variable *) hash_table_find(this->var_hash, ir);
76 loop_variable_state::insert(ir_variable *var)
78 void *mem_ctx = talloc_parent(this);
79 loop_variable *lv = talloc_zero(mem_ctx, loop_variable);
83 hash_table_insert(this->var_hash, lv, lv->var);
84 this->variables.push_tail(lv);
91 loop_variable_state::insert(ir_if *if_stmt)
93 void *mem_ctx = talloc_parent(this);
94 loop_terminator *t = talloc_zero(mem_ctx, loop_terminator);
97 this->terminators.push_tail(t);
103 class loop_analysis : public ir_hierarchical_visitor {
107 virtual ir_visitor_status visit(ir_loop_jump *);
108 virtual ir_visitor_status visit(ir_dereference_variable *);
110 virtual ir_visitor_status visit_enter(ir_loop *);
111 virtual ir_visitor_status visit_leave(ir_loop *);
112 virtual ir_visitor_status visit_enter(ir_assignment *);
113 virtual ir_visitor_status visit_leave(ir_assignment *);
114 virtual ir_visitor_status visit_enter(ir_if *);
115 virtual ir_visitor_status visit_leave(ir_if *);
119 int if_statement_depth;
121 ir_assignment *current_assignment;
127 loop_analysis::loop_analysis()
129 this->loops = new loop_state;
131 this->if_statement_depth = 0;
132 this->current_assignment = NULL;
137 loop_analysis::visit(ir_loop_jump *ir)
141 assert(!this->state.is_empty());
143 loop_variable_state *const ls =
144 (loop_variable_state *) this->state.get_head();
146 ls->num_loop_jumps++;
148 return visit_continue;
153 loop_analysis::visit(ir_dereference_variable *ir)
155 /* If we're not somewhere inside a loop, there's nothing to do.
157 if (this->state.is_empty())
158 return visit_continue;
160 loop_variable_state *const ls =
161 (loop_variable_state *) this->state.get_head();
163 ir_variable *var = ir->variable_referenced();
164 loop_variable *lv = ls->get(var);
167 lv = ls->insert(var);
168 lv->read_before_write = !this->in_assignee;
171 if (this->in_assignee) {
172 assert(this->current_assignment != NULL);
174 lv->conditional_assignment = (this->if_statement_depth > 0)
175 || (this->current_assignment->condition != NULL);
177 if (lv->first_assignment == NULL) {
178 assert(lv->num_assignments == 0);
180 lv->first_assignment = this->current_assignment;
183 lv->num_assignments++;
184 } else if (lv->first_assignment == this->current_assignment) {
185 /* This catches the case where the variable is used in the RHS of an
186 * assignment where it is also in the LHS.
188 lv->read_before_write = true;
191 return visit_continue;
195 loop_analysis::visit_enter(ir_loop *ir)
197 loop_variable_state *ls = this->loops->insert(ir);
198 this->state.push_head(ls);
200 return visit_continue;
204 loop_analysis::visit_leave(ir_loop *ir)
206 loop_variable_state *const ls =
207 (loop_variable_state *) this->state.pop_head();
210 foreach_list(node, &ir->body_instructions) {
211 /* Skip over declarations at the start of a loop.
213 if (((ir_instruction *) node)->as_variable())
216 ir_if *if_stmt = ((ir_instruction *) node)->as_if();
218 if ((if_stmt != NULL) && is_loop_terminator(if_stmt))
225 foreach_list_safe(node, &ls->variables) {
226 loop_variable *lv = (loop_variable *) node;
228 /* Move variables that are already marked as being loop constant to
229 * a separate list. These trivially don't need to be tested.
231 if (lv->is_loop_constant()) {
233 ls->constants.push_tail(lv);
237 /* Each variable assigned in the loop that isn't already marked as being loop
238 * constant might still be loop constant. The requirements at this point
241 * - Variable is written before it is read.
243 * - Only one assignment to the variable.
245 * - All operands on the RHS of the assignment are also loop constants.
247 * The last requirement is the reason for the progress loop. A variable
248 * marked as a loop constant on one pass may allow other variables to be
249 * marked as loop constant on following passes.
255 foreach_list_safe(node, &ls->variables) {
256 loop_variable *lv = (loop_variable *) node;
258 if (lv->conditional_assignment || (lv->num_assignments > 1))
261 /* Process the RHS of the assignment. If all of the variables
262 * accessed there are loop constants, then add this
264 ir_rvalue *const rhs = lv->first_assignment->rhs;
265 if (all_expression_operands_are_loop_constant(rhs, ls->var_hash)) {
266 lv->rhs_clean = true;
268 if (lv->is_loop_constant()) {
272 ls->constants.push_tail(lv);
278 /* The remaining variables that are not loop invariant might be loop
279 * induction variables.
281 foreach_list_safe(node, &ls->variables) {
282 loop_variable *lv = (loop_variable *) node;
284 /* If there is more than one assignment to a variable, it cannot be a
285 * loop induction variable. This isn't strictly true, but this is a
286 * very simple induction variable detector, and it can't handle more
289 if (lv->num_assignments > 1)
292 /* All of the variables with zero assignments in the loop are loop
293 * invariant, and they should have already been filtered out.
295 assert(lv->num_assignments == 1);
296 assert(lv->first_assignment != NULL);
298 /* The assignmnet to the variable in the loop must be unconditional.
300 if (lv->conditional_assignment)
303 /* Basic loop induction variables have a single assignment in the loop
304 * that has the form 'VAR = VAR + i' or 'VAR = VAR - i' where i is a
307 ir_rvalue *const inc =
308 get_basic_induction_increment(lv->first_assignment, ls->var_hash);
315 ls->induction_variables.push_tail(lv);
319 return visit_continue;
323 loop_analysis::visit_enter(ir_if *ir)
327 if (!this->state.is_empty())
328 this->if_statement_depth++;
330 return visit_continue;
334 loop_analysis::visit_leave(ir_if *ir)
338 if (!this->state.is_empty())
339 this->if_statement_depth--;
341 return visit_continue;
345 loop_analysis::visit_enter(ir_assignment *ir)
347 /* If we're not somewhere inside a loop, there's nothing to do.
349 if (this->state.is_empty())
350 return visit_continue_with_parent;
352 this->current_assignment = ir;
354 return visit_continue;
358 loop_analysis::visit_leave(ir_assignment *ir)
360 /* Since the visit_enter exits with visit_continue_with_parent for this
361 * case, the loop state stack should never be empty here.
363 assert(!this->state.is_empty());
365 assert(this->current_assignment == ir);
366 this->current_assignment = NULL;
368 return visit_continue;
372 class examine_rhs : public ir_hierarchical_visitor {
374 examine_rhs(hash_table *loop_variables)
376 this->only_uses_loop_constants = true;
377 this->loop_variables = loop_variables;
380 virtual ir_visitor_status visit(ir_dereference_variable *ir)
383 (loop_variable *) hash_table_find(this->loop_variables, ir->var);
387 if (lv->is_loop_constant()) {
388 return visit_continue;
390 this->only_uses_loop_constants = false;
395 hash_table *loop_variables;
396 bool only_uses_loop_constants;
401 all_expression_operands_are_loop_constant(ir_rvalue *ir, hash_table *variables)
403 examine_rhs v(variables);
407 return v.only_uses_loop_constants;
412 get_basic_induction_increment(ir_assignment *ir, hash_table *var_hash)
414 /* The RHS must be a binary expression.
416 ir_expression *const rhs = ir->rhs->as_expression();
418 || ((rhs->operation != ir_binop_add)
419 && (rhs->operation != ir_binop_sub)))
422 /* One of the of operands of the expression must be the variable assigned.
423 * If the operation is subtraction, the variable in question must be the
426 ir_variable *const var = ir->lhs->variable_referenced();
428 ir_variable *const op0 = rhs->operands[0]->variable_referenced();
429 ir_variable *const op1 = rhs->operands[1]->variable_referenced();
431 if (((op0 != var) && (op1 != var))
432 || ((op1 == var) && (rhs->operation == ir_binop_sub)))
435 ir_rvalue *inc = (op0 == var) ? rhs->operands[1] : rhs->operands[0];
437 if (inc->as_constant() == NULL) {
438 ir_variable *const inc_var = inc->variable_referenced();
439 if (inc_var != NULL) {
441 (loop_variable *) hash_table_find(var_hash, inc_var);
443 if (!lv->is_loop_constant())
449 if ((inc != NULL) && (rhs->operation == ir_binop_sub)) {
450 void *mem_ctx = talloc_parent(ir);
452 inc = new(mem_ctx) ir_expression(ir_unop_neg,
454 inc->clone(mem_ctx, NULL),
463 * Detect whether an if-statement is a loop terminating condition
465 * Detects if-statements of the form
467 * (if (expression bool ...) (break))
470 is_loop_terminator(ir_if *ir)
472 if (!ir->else_instructions.is_empty())
475 ir_instruction *const inst =
476 (ir_instruction *) ir->then_instructions.get_head();
477 assert(inst != NULL);
479 if (inst->ir_type != ir_type_loop_jump)
482 ir_loop_jump *const jump = (ir_loop_jump *) inst;
483 if (jump->mode != ir_loop_jump::jump_break)
491 analyze_loop_variables(exec_list *instructions)