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25 * \file opt_array_splitting.cpp
27 * If an array is always dereferenced with a constant index, then
28 * split it apart into its elements, making it more amenable to other
29 * optimization passes.
31 * This skips uniform/varying arrays, which would need careful
32 * handling due to their ir->location fields tying them to the GL API
33 * and other shader stages.
37 #include "ir_visitor.h"
38 #include "ir_rvalue_visitor.h"
39 #include "compiler/glsl_types.h"
41 static bool debug
= false;
45 namespace opt_array_splitting
{
47 class variable_entry
: public exec_node
50 variable_entry(ir_variable
*var
)
54 this->declaration
= false;
55 this->components
= NULL
;
57 if (var
->type
->is_array())
58 this->size
= var
->type
->length
;
60 this->size
= var
->type
->matrix_columns
;
63 ir_variable
*var
; /* The key: the variable's pointer. */
64 unsigned size
; /* array length or matrix columns */
66 /** Whether this array should be split or not. */
69 /* If the variable had a decl we can work with in the instruction
70 * stream. We can't do splitting on function arguments, which
71 * don't get this variable set.
75 ir_variable
**components
;
77 /** ralloc_parent(this->var) -- the shader's talloc context. */
83 using namespace opt_array_splitting
;
86 * This class does a walk over the tree, coming up with the set of
87 * variables that could be split by looking to see if they are arrays
88 * that are only ever constant-index dereferenced.
90 class ir_array_reference_visitor
: public ir_hierarchical_visitor
{
92 ir_array_reference_visitor(void)
94 this->mem_ctx
= ralloc_context(NULL
);
95 this->variable_list
.make_empty();
96 this->in_whole_array_copy
= false;
99 ~ir_array_reference_visitor(void)
101 ralloc_free(mem_ctx
);
104 bool get_split_list(exec_list
*instructions
, bool linked
);
106 virtual ir_visitor_status
visit(ir_variable
*);
107 virtual ir_visitor_status
visit(ir_dereference_variable
*);
108 virtual ir_visitor_status
visit_enter(ir_assignment
*);
109 virtual ir_visitor_status
visit_leave(ir_assignment
*);
110 virtual ir_visitor_status
visit_enter(ir_dereference_array
*);
111 virtual ir_visitor_status
visit_enter(ir_function_signature
*);
113 variable_entry
*get_variable_entry(ir_variable
*var
);
115 /* List of variable_entry */
116 exec_list variable_list
;
120 bool in_whole_array_copy
;
126 ir_array_reference_visitor::get_variable_entry(ir_variable
*var
)
130 if (var
->data
.mode
!= ir_var_auto
&&
131 var
->data
.mode
!= ir_var_temporary
)
134 if (!(var
->type
->is_array() || var
->type
->is_matrix()))
137 /* If the array hasn't been sized yet, we can't split it. After
138 * linking, this should be resolved.
140 if (var
->type
->is_unsized_array())
143 foreach_in_list(variable_entry
, entry
, &this->variable_list
) {
144 if (entry
->var
== var
)
148 variable_entry
*entry
= new(mem_ctx
) variable_entry(var
);
149 this->variable_list
.push_tail(entry
);
155 ir_array_reference_visitor::visit(ir_variable
*ir
)
157 variable_entry
*entry
= this->get_variable_entry(ir
);
160 entry
->declaration
= true;
162 return visit_continue
;
166 ir_array_reference_visitor::visit_enter(ir_assignment
*ir
)
168 in_whole_array_copy
=
169 ir
->lhs
->type
->is_array() && ir
->whole_variable_written();
171 return visit_continue
;
175 ir_array_reference_visitor::visit_leave(ir_assignment
*ir
)
177 in_whole_array_copy
= false;
179 return visit_continue
;
183 ir_array_reference_visitor::visit(ir_dereference_variable
*ir
)
185 variable_entry
*entry
= this->get_variable_entry(ir
->var
);
187 /* Allow whole-array assignments on the LHS. We can split those
188 * by "unrolling" the assignment into component-wise assignments.
190 if (in_assignee
&& in_whole_array_copy
)
191 return visit_continue
;
193 /* If we made it to here without seeing an ir_dereference_array,
194 * then the dereference of this array didn't have a constant index
195 * (see the visit_continue_with_parent below), so we can't split
199 entry
->split
= false;
201 return visit_continue
;
205 ir_array_reference_visitor::visit_enter(ir_dereference_array
*ir
)
207 ir_dereference_variable
*deref
= ir
->array
->as_dereference_variable();
209 return visit_continue
;
211 variable_entry
*entry
= this->get_variable_entry(deref
->var
);
213 /* If the access to the array has a variable index, we wouldn't
214 * know which split variable this dereference should go to.
216 if (!ir
->array_index
->as_constant()) {
218 entry
->split
= false;
219 /* This variable indexing could come from a different array dereference
220 * that also has variable indexing, that is, something like a[b[a[b[0]]]].
221 * If we return visit_continue_with_parent here for the first appearence
222 * of a, then we can miss that b also has indirect indexing (if this is
223 * the only place in the program where such indirect indexing into b
224 * happens), so keep going.
226 return visit_continue
;
229 /* If the index is also array dereference, visit index. */
230 if (ir
->array_index
->as_dereference_array())
231 visit_enter(ir
->array_index
->as_dereference_array());
233 return visit_continue_with_parent
;
237 ir_array_reference_visitor::visit_enter(ir_function_signature
*ir
)
239 /* We don't have logic for array-splitting function arguments,
240 * so just look at the body instructions and not the parameter
243 visit_list_elements(this, &ir
->body
);
244 return visit_continue_with_parent
;
248 ir_array_reference_visitor::get_split_list(exec_list
*instructions
,
251 visit_list_elements(this, instructions
);
253 /* If the shaders aren't linked yet, we can't mess with global
254 * declarations, which need to be matched by name across shaders.
257 foreach_in_list(ir_instruction
, node
, instructions
) {
258 ir_variable
*var
= node
->as_variable();
260 variable_entry
*entry
= get_variable_entry(var
);
267 /* Trim out variables we found that we can't split. */
268 foreach_in_list_safe(variable_entry
, entry
, &variable_list
) {
270 printf("array %s@%p: decl %d, split %d\n",
271 entry
->var
->name
, (void *) entry
->var
, entry
->declaration
,
275 if (!(entry
->declaration
&& entry
->split
)) {
280 return !variable_list
.is_empty();
284 * This class rewrites the dereferences of arrays that have been split
285 * to use the newly created ir_variables for each component.
287 class ir_array_splitting_visitor
: public ir_rvalue_visitor
{
289 ir_array_splitting_visitor(exec_list
*vars
)
291 this->variable_list
= vars
;
294 virtual ~ir_array_splitting_visitor()
298 virtual ir_visitor_status
visit_leave(ir_assignment
*);
300 void split_deref(ir_dereference
**deref
);
301 void handle_rvalue(ir_rvalue
**rvalue
);
302 variable_entry
*get_splitting_entry(ir_variable
*var
);
304 exec_list
*variable_list
;
308 ir_array_splitting_visitor::get_splitting_entry(ir_variable
*var
)
312 foreach_in_list(variable_entry
, entry
, this->variable_list
) {
313 if (entry
->var
== var
) {
322 ir_array_splitting_visitor::split_deref(ir_dereference
**deref
)
324 ir_dereference_array
*deref_array
= (*deref
)->as_dereference_array();
328 ir_dereference_variable
*deref_var
= deref_array
->array
->as_dereference_variable();
331 ir_variable
*var
= deref_var
->var
;
333 variable_entry
*entry
= get_splitting_entry(var
);
337 ir_constant
*constant
= deref_array
->array_index
->as_constant();
340 if (constant
->value
.i
[0] >= 0 && constant
->value
.i
[0] < (int)entry
->size
) {
341 *deref
= new(entry
->mem_ctx
)
342 ir_dereference_variable(entry
->components
[constant
->value
.i
[0]]);
344 /* There was a constant array access beyond the end of the
345 * array. This might have happened due to constant folding
346 * after the initial parse. This produces an undefined value,
347 * but shouldn't crash. Just give them an uninitialized
350 ir_variable
*temp
= new(entry
->mem_ctx
) ir_variable(deref_array
->type
,
353 entry
->components
[0]->insert_before(temp
);
354 *deref
= new(entry
->mem_ctx
) ir_dereference_variable(temp
);
359 ir_array_splitting_visitor::handle_rvalue(ir_rvalue
**rvalue
)
364 ir_dereference
*deref
= (*rvalue
)->as_dereference();
374 ir_array_splitting_visitor::visit_leave(ir_assignment
*ir
)
376 /* The normal rvalue visitor skips the LHS of assignments, but we
377 * need to process those just the same.
379 ir_rvalue
*lhs
= ir
->lhs
;
381 /* "Unroll" any whole array assignments, creating assignments for
382 * each array element. Then, do splitting on each new assignment.
384 if (lhs
->type
->is_array() && ir
->whole_variable_written() &&
385 get_splitting_entry(ir
->whole_variable_written())) {
386 void *mem_ctx
= ralloc_parent(ir
);
388 for (unsigned i
= 0; i
< lhs
->type
->length
; i
++) {
390 new(mem_ctx
) ir_dereference_array(ir
->lhs
->clone(mem_ctx
, NULL
),
391 new(mem_ctx
) ir_constant(i
));
393 new(mem_ctx
) ir_dereference_array(ir
->rhs
->clone(mem_ctx
, NULL
),
394 new(mem_ctx
) ir_constant(i
));
395 ir_rvalue
*condition_i
=
396 ir
->condition
? ir
->condition
->clone(mem_ctx
, NULL
) : NULL
;
398 ir_assignment
*assign_i
=
399 new(mem_ctx
) ir_assignment(lhs_i
, rhs_i
, condition_i
);
401 ir
->insert_before(assign_i
);
402 assign_i
->accept(this);
405 return visit_continue
;
409 ir
->lhs
= lhs
->as_dereference();
411 ir
->lhs
->accept(this);
413 handle_rvalue(&ir
->rhs
);
414 ir
->rhs
->accept(this);
417 handle_rvalue(&ir
->condition
);
418 ir
->condition
->accept(this);
421 return visit_continue
;
425 optimize_split_arrays(exec_list
*instructions
, bool linked
)
427 ir_array_reference_visitor refs
;
428 if (!refs
.get_split_list(instructions
, linked
))
431 void *mem_ctx
= ralloc_context(NULL
);
433 /* Replace the decls of the arrays to be split with their split
436 foreach_in_list(variable_entry
, entry
, &refs
.variable_list
) {
437 const struct glsl_type
*type
= entry
->var
->type
;
438 const struct glsl_type
*subtype
;
440 if (type
->is_matrix())
441 subtype
= type
->column_type();
443 subtype
= type
->fields
.array
;
445 entry
->mem_ctx
= ralloc_parent(entry
->var
);
447 entry
->components
= ralloc_array(mem_ctx
, ir_variable
*, entry
->size
);
449 for (unsigned int i
= 0; i
< entry
->size
; i
++) {
450 const char *name
= ralloc_asprintf(mem_ctx
, "%s_%d",
451 entry
->var
->name
, i
);
453 entry
->components
[i
] =
454 new(entry
->mem_ctx
) ir_variable(subtype
, name
, ir_var_temporary
);
455 entry
->var
->insert_before(entry
->components
[i
]);
458 entry
->var
->remove();
461 ir_array_splitting_visitor
split(&refs
.variable_list
);
462 visit_list_elements(&split
, instructions
);
465 _mesa_print_ir(stdout
, instructions
, NULL
);
467 ralloc_free(mem_ctx
);