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25 * \file opt_dead_code_local.cpp
27 * Eliminates local dead assignments from the code.
29 * This operates on basic blocks, tracking assignments and finding if
30 * they're used before the variable is completely reassigned.
32 * Compare this to ir_dead_code.cpp, which operates globally looking
33 * for assignments to variables that are never read.
37 #include "ir_basic_block.h"
38 #include "ir_optimization.h"
39 #include "glsl_types.h"
41 static bool debug
= false;
45 class assignment_entry
: public exec_node
48 assignment_entry(ir_variable
*lhs
, ir_assignment
*ir
)
54 this->available
= ir
->write_mask
;
60 /* bitmask of xyzw channels written that haven't been used so far. */
64 class kill_for_derefs_visitor
: public ir_hierarchical_visitor
{
66 kill_for_derefs_visitor(exec_list
*assignments
)
68 this->assignments
= assignments
;
71 void kill_channels(ir_variable
*const var
, int used
)
73 foreach_iter(exec_list_iterator
, iter
, *this->assignments
) {
74 assignment_entry
*entry
= (assignment_entry
*)iter
.get();
76 if (entry
->lhs
== var
) {
77 if (var
->type
->is_scalar() || var
->type
->is_vector()) {
79 printf("kill %s (0x%01x - 0x%01x)\n", entry
->lhs
->name
,
80 entry
->available
, used
);
81 entry
->available
&= ~used
;
82 if (!entry
->available
)
86 printf("kill %s\n", entry
->lhs
->name
);
93 virtual ir_visitor_status
visit(ir_dereference_variable
*ir
)
95 kill_channels(ir
->var
, ~0);
97 return visit_continue
;
100 virtual ir_visitor_status
visit(ir_swizzle
*ir
)
102 ir_dereference_variable
*deref
= ir
->val
->as_dereference_variable();
104 return visit_continue
;
107 used
|= 1 << ir
->mask
.x
;
108 used
|= 1 << ir
->mask
.y
;
109 used
|= 1 << ir
->mask
.z
;
110 used
|= 1 << ir
->mask
.w
;
112 kill_channels(deref
->var
, used
);
114 return visit_continue_with_parent
;
118 exec_list
*assignments
;
121 class array_index_visit
: public ir_hierarchical_visitor
{
123 array_index_visit(ir_hierarchical_visitor
*v
)
128 virtual ir_visitor_status
visit_enter(class ir_dereference_array
*ir
)
130 ir
->array_index
->accept(visitor
);
131 return visit_continue
;
134 static void run(ir_instruction
*ir
, ir_hierarchical_visitor
*v
)
136 array_index_visit
top_visit(v
);
137 ir
->accept(& top_visit
);
140 ir_hierarchical_visitor
*visitor
;
143 } /* unnamed namespace */
146 * Adds an entry to the available copy list if it's a plain assignment
147 * of a variable to a variable.
150 process_assignment(void *ctx
, ir_assignment
*ir
, exec_list
*assignments
)
152 ir_variable
*var
= NULL
;
153 bool progress
= false;
154 kill_for_derefs_visitor
v(assignments
);
156 /* Kill assignment entries for things used to produce this assignment. */
159 ir
->condition
->accept(&v
);
162 /* Kill assignment enties used as array indices.
164 array_index_visit::run(ir
->lhs
, &v
);
165 var
= ir
->lhs
->variable_referenced();
168 /* Now, check if we did a whole-variable assignment. */
169 if (!ir
->condition
) {
170 ir_dereference_variable
*deref_var
= ir
->lhs
->as_dereference_variable();
172 /* If it's a vector type, we can do per-channel elimination of
175 if (deref_var
&& (deref_var
->var
->type
->is_scalar() ||
176 deref_var
->var
->type
->is_vector())) {
179 printf("looking for %s.0x%01x to remove\n", var
->name
,
182 foreach_iter(exec_list_iterator
, iter
, *assignments
) {
183 assignment_entry
*entry
= (assignment_entry
*)iter
.get();
185 if (entry
->lhs
!= var
)
188 int remove
= entry
->available
& ir
->write_mask
;
190 printf("%s 0x%01x - 0x%01x = 0x%01x\n",
192 entry
->ir
->write_mask
,
193 remove
, entry
->ir
->write_mask
& ~remove
);
199 printf("rewriting:\n ");
204 entry
->ir
->write_mask
&= ~remove
;
205 entry
->available
&= ~remove
;
206 if (entry
->ir
->write_mask
== 0) {
207 /* Delete the dead assignment. */
211 void *mem_ctx
= ralloc_parent(entry
->ir
);
212 /* Reswizzle the RHS arguments according to the new
215 unsigned components
[4];
216 unsigned channels
= 0;
219 for (int i
= 0; i
< 4; i
++) {
220 if ((entry
->ir
->write_mask
| remove
) & (1 << i
)) {
221 if (!(remove
& (1 << i
)))
222 components
[channels
++] = next
;
227 entry
->ir
->rhs
= new(mem_ctx
) ir_swizzle(entry
->ir
->rhs
,
238 } else if (ir
->whole_variable_written() != NULL
) {
239 /* We did a whole-variable assignment. So, any instruction in
240 * the assignment list with the same LHS is dead.
243 printf("looking for %s to remove\n", var
->name
);
244 foreach_iter(exec_list_iterator
, iter
, *assignments
) {
245 assignment_entry
*entry
= (assignment_entry
*)iter
.get();
247 if (entry
->lhs
== var
) {
249 printf("removing %s\n", var
->name
);
258 /* Add this instruction to the assignment list available to be removed. */
259 assignment_entry
*entry
= new(ctx
) assignment_entry(var
, ir
);
260 assignments
->push_tail(entry
);
263 printf("add %s\n", var
->name
);
265 printf("current entries\n");
266 foreach_iter(exec_list_iterator
, iter
, *assignments
) {
267 assignment_entry
*entry
= (assignment_entry
*)iter
.get();
269 printf(" %s (0x%01x)\n", entry
->lhs
->name
, entry
->available
);
277 dead_code_local_basic_block(ir_instruction
*first
,
278 ir_instruction
*last
,
281 ir_instruction
*ir
, *ir_next
;
282 /* List of avaialble_copy */
283 exec_list assignments
;
284 bool *out_progress
= (bool *)data
;
285 bool progress
= false;
287 void *ctx
= ralloc_context(NULL
);
288 /* Safe looping, since process_assignment */
289 for (ir
= first
, ir_next
= (ir_instruction
*)first
->next
;;
290 ir
= ir_next
, ir_next
= (ir_instruction
*)ir
->next
) {
291 ir_assignment
*ir_assign
= ir
->as_assignment();
299 progress
= process_assignment(ctx
, ir_assign
, &assignments
) || progress
;
301 kill_for_derefs_visitor
kill(&assignments
);
308 *out_progress
= progress
;
313 * Does a copy propagation pass on the code present in the instruction stream.
316 do_dead_code_local(exec_list
*instructions
)
318 bool progress
= false;
320 call_for_basic_blocks(instructions
, dead_code_local_basic_block
, &progress
);