2 * Copyright © 2010 Intel Corporation
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5 * copy of this software and associated documentation files (the "Software"),
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9 * Software is furnished to do so, subject to the following conditions:
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
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
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21 * DEALINGS IN THE SOFTWARE.
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
*);
37 * Record the fact that the given loop variable was referenced inside the loop.
39 * \arg in_assignee is true if the reference was on the LHS of an assignment.
41 * \arg in_conditional_code_or_nested_loop is true if the reference occurred
42 * inside an if statement or a nested loop.
44 * \arg current_assignment is the ir_assignment node that the loop variable is
45 * on the LHS of, if any (ignored if \c in_assignee is false).
48 loop_variable::record_reference(bool in_assignee
,
49 bool in_conditional_code_or_nested_loop
,
50 ir_assignment
*current_assignment
)
53 assert(current_assignment
!= NULL
);
55 this->conditional_or_nested_assignment
=
56 in_conditional_code_or_nested_loop
57 || current_assignment
->condition
!= NULL
;
59 if (this->first_assignment
== NULL
) {
60 assert(this->num_assignments
== 0);
62 this->first_assignment
= current_assignment
;
65 this->num_assignments
++;
66 } else if (this->first_assignment
== current_assignment
) {
67 /* This catches the case where the variable is used in the RHS of an
68 * assignment where it is also in the LHS.
70 this->read_before_write
= true;
75 loop_state::loop_state()
77 this->ht
= hash_table_ctor(0, hash_table_pointer_hash
,
78 hash_table_pointer_compare
);
79 this->mem_ctx
= ralloc_context(NULL
);
80 this->loop_found
= false;
84 loop_state::~loop_state()
86 hash_table_dtor(this->ht
);
87 ralloc_free(this->mem_ctx
);
92 loop_state::insert(ir_loop
*ir
)
94 loop_variable_state
*ls
= new(this->mem_ctx
) loop_variable_state
;
96 hash_table_insert(this->ht
, ls
, ir
);
97 this->loop_found
= true;
103 loop_variable_state
*
104 loop_state::get(const ir_loop
*ir
)
106 return (loop_variable_state
*) hash_table_find(this->ht
, ir
);
111 loop_variable_state::get(const ir_variable
*ir
)
113 return (loop_variable
*) hash_table_find(this->var_hash
, ir
);
118 loop_variable_state::insert(ir_variable
*var
)
120 void *mem_ctx
= ralloc_parent(this);
121 loop_variable
*lv
= rzalloc(mem_ctx
, loop_variable
);
125 hash_table_insert(this->var_hash
, lv
, lv
->var
);
126 this->variables
.push_tail(lv
);
133 loop_variable_state::insert(ir_if
*if_stmt
)
135 void *mem_ctx
= ralloc_parent(this);
136 loop_terminator
*t
= rzalloc(mem_ctx
, loop_terminator
);
139 this->terminators
.push_tail(t
);
146 * If the given variable already is recorded in the state for this loop,
147 * return the corresponding loop_variable object that records information
150 * Otherwise, create a new loop_variable object to record information about
151 * the variable, and set its \c read_before_write field appropriately based on
154 * \arg in_assignee is true if this variable was encountered on the LHS of an
158 loop_variable_state::get_or_insert(ir_variable
*var
, bool in_assignee
)
160 loop_variable
*lv
= this->get(var
);
163 lv
= this->insert(var
);
164 lv
->read_before_write
= !in_assignee
;
173 class loop_analysis
: public ir_hierarchical_visitor
{
175 loop_analysis(loop_state
*loops
);
177 virtual ir_visitor_status
visit(ir_loop_jump
*);
178 virtual ir_visitor_status
visit(ir_dereference_variable
*);
180 virtual ir_visitor_status
visit_enter(ir_call
*);
182 virtual ir_visitor_status
visit_enter(ir_loop
*);
183 virtual ir_visitor_status
visit_leave(ir_loop
*);
184 virtual ir_visitor_status
visit_enter(ir_assignment
*);
185 virtual ir_visitor_status
visit_leave(ir_assignment
*);
186 virtual ir_visitor_status
visit_enter(ir_if
*);
187 virtual ir_visitor_status
visit_leave(ir_if
*);
191 int if_statement_depth
;
193 ir_assignment
*current_assignment
;
198 } /* anonymous namespace */
200 loop_analysis::loop_analysis(loop_state
*loops
)
201 : loops(loops
), if_statement_depth(0), current_assignment(NULL
)
208 loop_analysis::visit(ir_loop_jump
*ir
)
212 assert(!this->state
.is_empty());
214 loop_variable_state
*const ls
=
215 (loop_variable_state
*) this->state
.get_head();
217 ls
->num_loop_jumps
++;
219 return visit_continue
;
224 loop_analysis::visit_enter(ir_call
*ir
)
226 /* Mark every loop that we're currently analyzing as containing an ir_call
227 * (even those at outer nesting levels).
229 foreach_list(node
, &this->state
) {
230 loop_variable_state
*const ls
= (loop_variable_state
*) node
;
231 ls
->contains_calls
= true;
234 return visit_continue_with_parent
;
239 loop_analysis::visit(ir_dereference_variable
*ir
)
241 /* If we're not somewhere inside a loop, there's nothing to do.
243 if (this->state
.is_empty())
244 return visit_continue
;
248 foreach_list(node
, &this->state
) {
249 loop_variable_state
*const ls
= (loop_variable_state
*) node
;
251 ir_variable
*var
= ir
->variable_referenced();
252 loop_variable
*lv
= ls
->get_or_insert(var
, this->in_assignee
);
254 lv
->record_reference(this->in_assignee
,
255 nested
|| this->if_statement_depth
> 0,
256 this->current_assignment
);
260 return visit_continue
;
264 loop_analysis::visit_enter(ir_loop
*ir
)
266 loop_variable_state
*ls
= this->loops
->insert(ir
);
267 this->state
.push_head(ls
);
269 return visit_continue
;
273 loop_analysis::visit_leave(ir_loop
*ir
)
275 loop_variable_state
*const ls
=
276 (loop_variable_state
*) this->state
.pop_head();
278 /* Function calls may contain side effects. These could alter any of our
279 * variables in ways that cannot be known, and may even terminate shader
280 * execution (say, calling discard in the fragment shader). So we can't
281 * rely on any of our analysis about assignments to variables.
283 * We could perform some conservative analysis (prove there's no statically
284 * possible assignment, etc.) but it isn't worth it for now; function
285 * inlining will allow us to unroll loops anyway.
287 if (ls
->contains_calls
)
288 return visit_continue
;
290 foreach_list(node
, &ir
->body_instructions
) {
291 /* Skip over declarations at the start of a loop.
293 if (((ir_instruction
*) node
)->as_variable())
296 ir_if
*if_stmt
= ((ir_instruction
*) node
)->as_if();
298 if ((if_stmt
!= NULL
) && is_loop_terminator(if_stmt
))
305 foreach_list_safe(node
, &ls
->variables
) {
306 loop_variable
*lv
= (loop_variable
*) node
;
308 /* Move variables that are already marked as being loop constant to
309 * a separate list. These trivially don't need to be tested.
311 if (lv
->is_loop_constant()) {
313 ls
->constants
.push_tail(lv
);
317 /* Each variable assigned in the loop that isn't already marked as being loop
318 * constant might still be loop constant. The requirements at this point
321 * - Variable is written before it is read.
323 * - Only one assignment to the variable.
325 * - All operands on the RHS of the assignment are also loop constants.
327 * The last requirement is the reason for the progress loop. A variable
328 * marked as a loop constant on one pass may allow other variables to be
329 * marked as loop constant on following passes.
335 foreach_list_safe(node
, &ls
->variables
) {
336 loop_variable
*lv
= (loop_variable
*) node
;
338 if (lv
->conditional_or_nested_assignment
|| (lv
->num_assignments
> 1))
341 /* Process the RHS of the assignment. If all of the variables
342 * accessed there are loop constants, then add this
344 ir_rvalue
*const rhs
= lv
->first_assignment
->rhs
;
345 if (all_expression_operands_are_loop_constant(rhs
, ls
->var_hash
)) {
346 lv
->rhs_clean
= true;
348 if (lv
->is_loop_constant()) {
352 ls
->constants
.push_tail(lv
);
358 /* The remaining variables that are not loop invariant might be loop
359 * induction variables.
361 foreach_list_safe(node
, &ls
->variables
) {
362 loop_variable
*lv
= (loop_variable
*) node
;
364 /* If there is more than one assignment to a variable, it cannot be a
365 * loop induction variable. This isn't strictly true, but this is a
366 * very simple induction variable detector, and it can't handle more
369 if (lv
->num_assignments
> 1)
372 /* All of the variables with zero assignments in the loop are loop
373 * invariant, and they should have already been filtered out.
375 assert(lv
->num_assignments
== 1);
376 assert(lv
->first_assignment
!= NULL
);
378 /* The assignment to the variable in the loop must be unconditional and
379 * not inside a nested loop.
381 if (lv
->conditional_or_nested_assignment
)
384 /* Basic loop induction variables have a single assignment in the loop
385 * that has the form 'VAR = VAR + i' or 'VAR = VAR - i' where i is a
388 ir_rvalue
*const inc
=
389 get_basic_induction_increment(lv
->first_assignment
, ls
->var_hash
);
396 ls
->induction_variables
.push_tail(lv
);
400 return visit_continue
;
404 loop_analysis::visit_enter(ir_if
*ir
)
408 if (!this->state
.is_empty())
409 this->if_statement_depth
++;
411 return visit_continue
;
415 loop_analysis::visit_leave(ir_if
*ir
)
419 if (!this->state
.is_empty())
420 this->if_statement_depth
--;
422 return visit_continue
;
426 loop_analysis::visit_enter(ir_assignment
*ir
)
428 /* If we're not somewhere inside a loop, there's nothing to do.
430 if (this->state
.is_empty())
431 return visit_continue_with_parent
;
433 this->current_assignment
= ir
;
435 return visit_continue
;
439 loop_analysis::visit_leave(ir_assignment
*ir
)
441 /* Since the visit_enter exits with visit_continue_with_parent for this
442 * case, the loop state stack should never be empty here.
444 assert(!this->state
.is_empty());
446 assert(this->current_assignment
== ir
);
447 this->current_assignment
= NULL
;
449 return visit_continue
;
453 class examine_rhs
: public ir_hierarchical_visitor
{
455 examine_rhs(hash_table
*loop_variables
)
457 this->only_uses_loop_constants
= true;
458 this->loop_variables
= loop_variables
;
461 virtual ir_visitor_status
visit(ir_dereference_variable
*ir
)
464 (loop_variable
*) hash_table_find(this->loop_variables
, ir
->var
);
468 if (lv
->is_loop_constant()) {
469 return visit_continue
;
471 this->only_uses_loop_constants
= false;
476 hash_table
*loop_variables
;
477 bool only_uses_loop_constants
;
482 all_expression_operands_are_loop_constant(ir_rvalue
*ir
, hash_table
*variables
)
484 examine_rhs
v(variables
);
488 return v
.only_uses_loop_constants
;
493 get_basic_induction_increment(ir_assignment
*ir
, hash_table
*var_hash
)
495 /* The RHS must be a binary expression.
497 ir_expression
*const rhs
= ir
->rhs
->as_expression();
499 || ((rhs
->operation
!= ir_binop_add
)
500 && (rhs
->operation
!= ir_binop_sub
)))
503 /* One of the of operands of the expression must be the variable assigned.
504 * If the operation is subtraction, the variable in question must be the
507 ir_variable
*const var
= ir
->lhs
->variable_referenced();
509 ir_variable
*const op0
= rhs
->operands
[0]->variable_referenced();
510 ir_variable
*const op1
= rhs
->operands
[1]->variable_referenced();
512 if (((op0
!= var
) && (op1
!= var
))
513 || ((op1
== var
) && (rhs
->operation
== ir_binop_sub
)))
516 ir_rvalue
*inc
= (op0
== var
) ? rhs
->operands
[1] : rhs
->operands
[0];
518 if (inc
->as_constant() == NULL
) {
519 ir_variable
*const inc_var
= inc
->variable_referenced();
520 if (inc_var
!= NULL
) {
522 (loop_variable
*) hash_table_find(var_hash
, inc_var
);
524 if (!lv
->is_loop_constant())
530 if ((inc
!= NULL
) && (rhs
->operation
== ir_binop_sub
)) {
531 void *mem_ctx
= ralloc_parent(ir
);
533 inc
= new(mem_ctx
) ir_expression(ir_unop_neg
,
535 inc
->clone(mem_ctx
, NULL
),
544 * Detect whether an if-statement is a loop terminating condition
546 * Detects if-statements of the form
548 * (if (expression bool ...) (break))
551 is_loop_terminator(ir_if
*ir
)
553 if (!ir
->else_instructions
.is_empty())
556 ir_instruction
*const inst
=
557 (ir_instruction
*) ir
->then_instructions
.get_head();
561 if (inst
->ir_type
!= ir_type_loop_jump
)
564 ir_loop_jump
*const jump
= (ir_loop_jump
*) inst
;
565 if (jump
->mode
!= ir_loop_jump::jump_break
)
573 analyze_loop_variables(exec_list
*instructions
)
575 loop_state
*loops
= new loop_state
;
576 loop_analysis
v(loops
);