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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);