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29 /** @file brw_vec4_cse.cpp
31 * Support for local common subexpression elimination.
33 * See Muchnick's Advanced Compiler Design and Implementation, section
38 struct aeb_entry : public exec_node {
39 /** The instruction that generates the expression value. */
40 vec4_instruction *generator;
42 /** The temporary where the value is stored. */
48 is_expression(const vec4_instruction *const inst)
50 switch (inst->opcode) {
73 case SHADER_OPCODE_RCP:
74 case SHADER_OPCODE_RSQ:
75 case SHADER_OPCODE_SQRT:
76 case SHADER_OPCODE_EXP2:
77 case SHADER_OPCODE_LOG2:
78 case SHADER_OPCODE_POW:
79 case SHADER_OPCODE_INT_QUOTIENT:
80 case SHADER_OPCODE_INT_REMAINDER:
81 case SHADER_OPCODE_SIN:
82 case SHADER_OPCODE_COS:
83 return inst->mlen == 0;
90 is_expression_commutative(enum opcode op)
105 operands_match(enum opcode op, src_reg *xs, src_reg *ys)
107 if (!is_expression_commutative(op)) {
108 return xs[0].equals(ys[0]) && xs[1].equals(ys[1]) && xs[2].equals(ys[2]);
110 return (xs[0].equals(ys[0]) && xs[1].equals(ys[1])) ||
111 (xs[1].equals(ys[0]) && xs[0].equals(ys[1]));
116 instructions_match(vec4_instruction *a, vec4_instruction *b)
118 return a->opcode == b->opcode &&
119 a->saturate == b->saturate &&
120 a->conditional_mod == b->conditional_mod &&
121 a->dst.type == b->dst.type &&
122 a->dst.writemask == b->dst.writemask &&
123 operands_match(a->opcode, a->src, b->src);
127 vec4_visitor::opt_cse_local(bblock_t *block)
129 bool progress = false;
132 void *cse_ctx = ralloc_context(NULL);
134 int ip = block->start_ip;
135 foreach_inst_in_block (vec4_instruction, inst, block) {
136 /* Skip some cases. */
137 if (is_expression(inst) && !inst->predicate && inst->mlen == 0 &&
138 (inst->dst.file != HW_REG || inst->dst.is_null()))
142 foreach_in_list_use_after(aeb_entry, entry, &aeb) {
143 /* Match current instruction's expression against those in AEB. */
144 if (instructions_match(inst, entry->generator)) {
152 /* Our first sighting of this expression. Create an entry. */
153 aeb_entry *entry = ralloc(cse_ctx, aeb_entry);
154 entry->tmp = src_reg(); /* file will be BAD_FILE */
155 entry->generator = inst;
156 aeb.push_tail(entry);
158 /* This is at least our second sighting of this expression.
159 * If we don't have a temporary already, make one.
161 bool no_existing_temp = entry->tmp.file == BAD_FILE;
162 if (no_existing_temp && !entry->generator->dst.is_null()) {
163 entry->tmp = src_reg(this, glsl_type::float_type);
164 entry->tmp.type = inst->dst.type;
165 entry->tmp.swizzle = BRW_SWIZZLE_XYZW;
167 vec4_instruction *copy = MOV(entry->generator->dst, entry->tmp);
168 entry->generator->insert_after(block, copy);
169 entry->generator->dst = dst_reg(entry->tmp);
173 if (!inst->dst.is_null()) {
174 assert(inst->dst.type == entry->tmp.type);
175 vec4_instruction *copy = MOV(inst->dst, entry->tmp);
176 copy->force_writemask_all = inst->force_writemask_all;
177 inst->insert_before(block, copy);
180 /* Set our iterator so that next time through the loop inst->next
181 * will get the instruction in the basic block after the one we've
184 vec4_instruction *prev = (vec4_instruction *)inst->prev;
188 /* Appending an instruction may have changed our bblock end. */
189 if (inst == block->end) {
197 foreach_in_list_safe(aeb_entry, entry, &aeb) {
198 /* Kill all AEB entries that write a different value to or read from
199 * the flag register if we just wrote it.
201 if (inst->writes_flag()) {
202 if (entry->generator->reads_flag() ||
203 (entry->generator->writes_flag() &&
204 !instructions_match(inst, entry->generator))) {
211 for (int i = 0; i < 3; i++) {
212 src_reg *src = &entry->generator->src[i];
214 /* Kill all AEB entries that use the destination we just
217 if (inst->dst.file == entry->generator->src[i].file &&
218 inst->dst.reg == entry->generator->src[i].reg) {
224 /* Kill any AEB entries using registers that don't get reused any
225 * more -- a sure sign they'll fail operands_match().
227 int last_reg_use = MAX2(MAX2(virtual_grf_end[src->reg * 4 + 0],
228 virtual_grf_end[src->reg * 4 + 1]),
229 MAX2(virtual_grf_end[src->reg * 4 + 2],
230 virtual_grf_end[src->reg * 4 + 3]));
231 if (src->file == GRF && last_reg_use < ip) {
242 ralloc_free(cse_ctx);
248 vec4_visitor::opt_cse()
250 bool progress = false;
252 calculate_live_intervals();
254 foreach_block (block, cfg) {
255 progress = opt_cse_local(block) || progress;
259 invalidate_live_intervals(false);