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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->unused
= 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 use_channels(ir_variable
*const var
, int used
)
73 foreach_in_list_safe(assignment_entry
, entry
, this->assignments
) {
74 if (entry
->lhs
== var
) {
75 if (var
->type
->is_scalar() || var
->type
->is_vector()) {
77 printf("used %s (0x%01x - 0x%01x)\n", entry
->lhs
->name
,
78 entry
->unused
, used
& 0xf);
79 entry
->unused
&= ~used
;
84 printf("used %s\n", entry
->lhs
->name
);
91 virtual ir_visitor_status
visit(ir_dereference_variable
*ir
)
93 use_channels(ir
->var
, ~0);
95 return visit_continue
;
98 virtual ir_visitor_status
visit(ir_swizzle
*ir
)
100 ir_dereference_variable
*deref
= ir
->val
->as_dereference_variable();
102 return visit_continue
;
105 used
|= 1 << ir
->mask
.x
;
106 used
|= 1 << ir
->mask
.y
;
107 used
|= 1 << ir
->mask
.z
;
108 used
|= 1 << ir
->mask
.w
;
110 use_channels(deref
->var
, used
);
112 return visit_continue_with_parent
;
115 virtual ir_visitor_status
visit_leave(ir_emit_vertex
*)
117 /* For the purpose of dead code elimination, emitting a vertex counts as
118 * "reading" all of the currently assigned output variables.
120 foreach_in_list_safe(assignment_entry
, entry
, this->assignments
) {
121 if (entry
->lhs
->data
.mode
== ir_var_shader_out
) {
123 printf("kill %s\n", entry
->lhs
->name
);
128 return visit_continue
;
132 exec_list
*assignments
;
135 class array_index_visit
: public ir_hierarchical_visitor
{
137 array_index_visit(ir_hierarchical_visitor
*v
)
142 virtual ir_visitor_status
visit_enter(class ir_dereference_array
*ir
)
144 ir
->array_index
->accept(visitor
);
145 return visit_continue
;
148 static void run(ir_instruction
*ir
, ir_hierarchical_visitor
*v
)
150 array_index_visit
top_visit(v
);
151 ir
->accept(& top_visit
);
154 ir_hierarchical_visitor
*visitor
;
157 } /* unnamed namespace */
160 * Adds an entry to the available copy list if it's a plain assignment
161 * of a variable to a variable.
164 process_assignment(void *ctx
, ir_assignment
*ir
, exec_list
*assignments
)
166 ir_variable
*var
= NULL
;
167 bool progress
= false;
168 kill_for_derefs_visitor
v(assignments
);
170 /* Kill assignment entries for things used to produce this assignment. */
173 ir
->condition
->accept(&v
);
176 /* Kill assignment enties used as array indices.
178 array_index_visit::run(ir
->lhs
, &v
);
179 var
= ir
->lhs
->variable_referenced();
182 /* Now, check if we did a whole-variable assignment. */
183 if (!ir
->condition
) {
184 ir_dereference_variable
*deref_var
= ir
->lhs
->as_dereference_variable();
186 /* If it's a vector type, we can do per-channel elimination of
189 if (deref_var
&& (deref_var
->var
->type
->is_scalar() ||
190 deref_var
->var
->type
->is_vector())) {
193 printf("looking for %s.0x%01x to remove\n", var
->name
,
196 foreach_in_list_safe(assignment_entry
, entry
, assignments
) {
197 if (entry
->lhs
!= var
)
200 int remove
= entry
->unused
& ir
->write_mask
;
202 printf("%s 0x%01x - 0x%01x = 0x%01x\n",
204 entry
->ir
->write_mask
,
205 remove
, entry
->ir
->write_mask
& ~remove
);
211 printf("rewriting:\n ");
216 entry
->ir
->write_mask
&= ~remove
;
217 entry
->unused
&= ~remove
;
218 if (entry
->ir
->write_mask
== 0) {
219 /* Delete the dead assignment. */
223 void *mem_ctx
= ralloc_parent(entry
->ir
);
224 /* Reswizzle the RHS arguments according to the new
227 unsigned components
[4];
228 unsigned channels
= 0;
231 for (int i
= 0; i
< 4; i
++) {
232 if ((entry
->ir
->write_mask
| remove
) & (1 << i
)) {
233 if (!(remove
& (1 << i
)))
234 components
[channels
++] = next
;
239 entry
->ir
->rhs
= new(mem_ctx
) ir_swizzle(entry
->ir
->rhs
,
250 } else if (ir
->whole_variable_written() != NULL
) {
251 /* We did a whole-variable assignment. So, any instruction in
252 * the assignment list with the same LHS is dead.
255 printf("looking for %s to remove\n", var
->name
);
256 foreach_in_list_safe(assignment_entry
, entry
, assignments
) {
257 if (entry
->lhs
== var
) {
259 printf("removing %s\n", var
->name
);
268 /* Add this instruction to the assignment list available to be removed. */
269 assignment_entry
*entry
= new(ctx
) assignment_entry(var
, ir
);
270 assignments
->push_tail(entry
);
273 printf("add %s\n", var
->name
);
275 printf("current entries\n");
276 foreach_in_list(assignment_entry
, entry
, assignments
) {
277 printf(" %s (0x%01x)\n", entry
->lhs
->name
, entry
->unused
);
285 dead_code_local_basic_block(ir_instruction
*first
,
286 ir_instruction
*last
,
289 ir_instruction
*ir
, *ir_next
;
290 /* List of avaialble_copy */
291 exec_list assignments
;
292 bool *out_progress
= (bool *)data
;
293 bool progress
= false;
295 void *ctx
= ralloc_context(NULL
);
296 /* Safe looping, since process_assignment */
297 for (ir
= first
, ir_next
= (ir_instruction
*)first
->next
;;
298 ir
= ir_next
, ir_next
= (ir_instruction
*)ir
->next
) {
299 ir_assignment
*ir_assign
= ir
->as_assignment();
307 progress
= process_assignment(ctx
, ir_assign
, &assignments
) || progress
;
309 kill_for_derefs_visitor
kill(&assignments
);
316 *out_progress
= progress
;
321 * Does a copy propagation pass on the code present in the instruction stream.
324 do_dead_code_local(exec_list
*instructions
)
326 bool progress
= false;
328 call_for_basic_blocks(instructions
, dead_code_local_basic_block
, &progress
);