2 * branch-opts.c: Branch optimizations support
5 * Patrik Torstensson (Patrik.Torstesson at gmail.com)
7 * (C) 2005 Ximian, Inc. http://www.ximian.com
8 * Copyright 2011 Xamarin Inc. http://www.xamarin.com
9 * Licensed under the MIT license. See LICENSE file in the project root for full license information.
17 * Returns true if @bb is a basic block which falls through the next block.
18 * TODO verify if it helps to check if the bb last ins is a branch to its successor.
21 mono_bb_is_fall_through (MonoCompile *cfg, MonoBasicBlock *bb)
23 return bb->next_bb && bb->next_bb->region == bb->region && /*fall throught between regions is not really interesting or useful*/
24 (bb->last_ins == NULL || !MONO_IS_BRANCH_OP (bb->last_ins)); /*and the last op can't be a branch too*/
28 * Used by the arch code to replace the exception handling
29 * with a direct branch. This is safe to do if the
30 * exception object isn't used, no rethrow statement and
31 * no filter statement (verify).
35 mono_branch_optimize_exception_target (MonoCompile *cfg, MonoBasicBlock *bb, const char * exname)
37 MonoMethodHeader *header = cfg->header;
38 MonoExceptionClause *clause;
42 if (!(cfg->opt & MONO_OPT_EXCEPTION))
45 if (bb->region == -1 || !MONO_BBLOCK_IS_IN_REGION (bb, MONO_REGION_TRY))
48 exclass = mono_class_load_from_name (mono_get_corlib (), "System", exname);
49 /* search for the handler */
50 for (i = 0; i < header->num_clauses; ++i) {
51 clause = &header->clauses [i];
52 if (MONO_OFFSET_IN_CLAUSE (clause, bb->real_offset)) {
53 if (clause->flags == MONO_EXCEPTION_CLAUSE_NONE && clause->data.catch_class && mono_class_is_assignable_from (clause->data.catch_class, exclass)) {
56 /* get the basic block for the handler and
57 * check if the exception object is used.
58 * Flag is set during method_to_ir due to
59 * pop-op is optmized away in codegen (burg).
61 tbb = cfg->cil_offset_to_bb [clause->handler_offset];
62 if (tbb && tbb->flags & BB_EXCEPTION_DEAD_OBJ && !(tbb->flags & BB_EXCEPTION_UNSAFE)) {
63 MonoBasicBlock *targetbb = tbb;
64 gboolean unsafe = FALSE;
66 /* Check if this catch clause is ok to optimize by
67 * looking for the BB_EXCEPTION_UNSAFE in every BB that
68 * belongs to the same region.
70 * UNSAFE flag is set during method_to_ir (OP_RETHROW)
72 while (!unsafe && tbb->next_bb && tbb->region == tbb->next_bb->region) {
73 if (tbb->next_bb->flags & BB_EXCEPTION_UNSAFE) {
83 /* Create dummy inst to allow easier integration in
84 * arch dependent code (opcode ignored)
86 MONO_INST_NEW (cfg, jump, OP_BR);
88 /* Allocate memory for our branch target */
89 jump->inst_i1 = (MonoInst *)mono_mempool_alloc0 (cfg->mempool, sizeof (MonoInst));
90 jump->inst_true_bb = targetbb;
92 if (cfg->verbose_level > 2)
93 g_print ("found exception to optimize - returning branch to BB%d (%s) (instead of throw) for method %s:%s\n", targetbb->block_num, clause->data.catch_class->name, cfg->method->klass->name, cfg->method->name);
100 /* Branching to an outer clause could skip inner clauses */
104 /* Branching to an outer clause could skip inner clauses */
113 static const int int_cmov_opcodes [] = {
126 static const int long_cmov_opcodes [] = {
139 static G_GNUC_UNUSED int
140 br_to_br_un (int opcode)
156 g_assert_not_reached ();
164 * Replace INS with its decomposition which is stored in a series of bblocks starting
165 * at FIRST_BB and ending at LAST_BB. On enter, PREV points to the predecessor of INS.
166 * On return, it will be set to the last ins of the decomposition.
169 mono_replace_ins (MonoCompile *cfg, MonoBasicBlock *bb, MonoInst *ins, MonoInst **prev, MonoBasicBlock *first_bb, MonoBasicBlock *last_bb)
171 MonoInst *next = ins->next;
173 if (next && next->opcode == OP_NOP) {
174 /* Avoid NOPs following branches */
175 ins->next = next->next;
179 if (first_bb == last_bb) {
181 * Only one replacement bb, merge the code into
185 /* Delete links between the first_bb and its successors */
186 while (first_bb->out_count)
187 mono_unlink_bblock (cfg, first_bb, first_bb->out_bb [0]);
191 (*prev)->next = first_bb->code;
192 first_bb->code->prev = (*prev);
194 bb->code = first_bb->code;
198 last_bb->last_ins->next = next;
200 next->prev = last_bb->last_ins;
202 bb->last_ins = last_bb->last_ins;
203 *prev = last_bb->last_ins;
204 bb->has_array_access |= first_bb->has_array_access;
207 MonoBasicBlock **tmp_bblocks, *tmp;
213 for (tmp = first_bb; tmp; tmp = tmp->next_bb)
214 tmp->region = bb->region;
216 /* Split the original bb */
218 ins->next->prev = NULL;
222 /* Merge the second part of the original bb into the last bb */
223 if (last_bb->last_ins) {
224 last_bb->last_ins->next = next;
226 next->prev = last_bb->last_ins;
228 last_bb->code = next;
230 last_bb->has_array_access |= bb->has_array_access;
233 for (last = next; last->next != NULL; last = last->next)
235 last_bb->last_ins = last;
238 for (i = 0; i < bb->out_count; ++i)
239 mono_link_bblock (cfg, last_bb, bb->out_bb [i]);
241 /* Merge the first (dummy) bb to the original bb */
243 (*prev)->next = first_bb->code;
244 first_bb->code->prev = (*prev);
246 bb->code = first_bb->code;
248 bb->last_ins = first_bb->last_ins;
249 bb->has_array_access |= first_bb->has_array_access;
251 /* Delete the links between the original bb and its successors */
252 tmp_bblocks = bb->out_bb;
253 count = bb->out_count;
254 for (i = 0; i < count; ++i)
255 mono_unlink_bblock (cfg, bb, tmp_bblocks [i]);
257 /* Add links between the original bb and the first_bb's successors */
258 for (i = 0; i < first_bb->out_count; ++i) {
259 MonoBasicBlock *out_bb = first_bb->out_bb [i];
261 mono_link_bblock (cfg, bb, out_bb);
263 /* Delete links between the first_bb and its successors */
264 for (i = 0; i < bb->out_count; ++i) {
265 MonoBasicBlock *out_bb = bb->out_bb [i];
267 mono_unlink_bblock (cfg, first_bb, out_bb);
269 last_bb->next_bb = bb->next_bb;
270 bb->next_bb = first_bb->next_bb;
277 mono_if_conversion (MonoCompile *cfg)
279 #ifdef MONO_ARCH_HAVE_CMOV_OPS
281 gboolean changed = FALSE;
282 int filter = FILTER_NOP | FILTER_IL_SEQ_POINT;
284 if (!(cfg->opt & MONO_OPT_CMOV))
287 // FIXME: Make this work with extended bblocks
290 * This pass requires somewhat optimized IR code so it should be run after
291 * local cprop/deadce. Also, it should be run before dominator computation, since
292 * it changes control flow.
294 for (bb = cfg->bb_entry; bb; bb = bb->next_bb) {
295 MonoBasicBlock *bb1, *bb2;
298 /* Look for the IR code generated from cond ? a : b
309 if (!(bb->out_count == 2 && !bb->extended))
312 bb1 = bb->out_bb [0];
313 bb2 = bb->out_bb [1];
315 if (bb1->in_count == 1 && bb2->in_count == 1 && bb1->out_count == 1 && bb2->out_count == 1 && bb1->out_bb [0] == bb2->out_bb [0]) {
316 MonoInst *compare, *branch, *ins1, *ins2, *cmov, *move, *tmp;
317 MonoBasicBlock *true_bb, *false_bb;
318 gboolean simple, ret;
322 branch = mono_bb_last_inst (bb, filter);
324 if (!branch || branch->opcode == OP_BR_REG || branch->opcode == OP_BR)
327 /* Find the compare instruction */
328 compare = mono_inst_prev (branch, filter);
332 if (!MONO_IS_COND_BRANCH_OP (branch))
333 /* This can happen if a cond branch is optimized away */
336 true_bb = branch->inst_true_bb;
337 false_bb = branch->inst_false_bb;
340 * Check that bb1 and bb2 are 'simple' and both assign to the same
343 /* FIXME: Get rid of the nops earlier */
344 ins1 = mono_bb_first_inst (true_bb, filter);
345 ins2 = mono_bb_first_inst (false_bb, filter);
347 if (!(ins1 && ins2 && ins1->dreg == ins2->dreg && ins1->dreg != -1))
351 for (tmp = ins1->next; tmp; tmp = tmp->next)
352 if (!((tmp->opcode == OP_NOP) || (tmp->opcode == OP_IL_SEQ_POINT) || (tmp->opcode == OP_BR)))
355 for (tmp = ins2->next; tmp; tmp = tmp->next)
356 if (!((tmp->opcode == OP_NOP) || (tmp->opcode == OP_IL_SEQ_POINT) || (tmp->opcode == OP_BR)))
362 /* We move ins1/ins2 before the compare so they should have no side effect */
363 if (!(MONO_INS_HAS_NO_SIDE_EFFECT (ins1) && MONO_INS_HAS_NO_SIDE_EFFECT (ins2)))
366 /* Moving ins1/ins2 could change the comparison */
368 if (!((compare->sreg1 != ins1->dreg) && (compare->sreg2 != ins1->dreg)))
372 comp_type = mono_opcode_to_type (branch->opcode, compare->opcode);
373 if (!((comp_type == CMP_TYPE_I) || (comp_type == CMP_TYPE_L)))
377 /* ins->type might not be set */
378 if (INS_INFO (ins1->opcode) [MONO_INST_DEST] != 'i')
381 if (cfg->verbose_level > 2) {
382 printf ("\tBranch -> CMove optimization in BB%d on\n", bb->block_num);
383 printf ("\t\t"); mono_print_ins (compare);
384 printf ("\t\t"); mono_print_ins (mono_inst_next (compare, filter));
385 printf ("\t\t"); mono_print_ins (ins1);
386 printf ("\t\t"); mono_print_ins (ins2);
393 /* Assignments to the return register must remain at the end of bbs */
395 ret = ins1->dreg == cfg->ret->dreg;
399 tmp_reg = mono_alloc_dreg (cfg, STACK_I4);
402 /* Rewrite ins1 to emit to tmp_reg */
403 ins1->dreg = tmp_reg;
406 dreg = mono_alloc_dreg (cfg, STACK_I4);
410 /* Remove ins1/ins2 from bb1/bb2 */
411 MONO_REMOVE_INS (true_bb, ins1);
412 MONO_REMOVE_INS (false_bb, ins2);
414 /* Move ins1 and ins2 before the comparison */
415 /* ins1 comes first to avoid ins1 overwriting an argument of ins2 */
416 mono_bblock_insert_before_ins (bb, compare, ins2);
417 mono_bblock_insert_before_ins (bb, ins2, ins1);
419 /* Add cmov instruction */
420 MONO_INST_NEW (cfg, cmov, OP_NOP);
423 cmov->sreg2 = tmp_reg;
424 switch (mono_opcode_to_type (branch->opcode, compare->opcode)) {
426 cmov->opcode = int_cmov_opcodes [mono_opcode_to_cond (branch->opcode)];
429 cmov->opcode = long_cmov_opcodes [mono_opcode_to_cond (branch->opcode)];
432 g_assert_not_reached ();
434 mono_bblock_insert_after_ins (bb, compare, cmov);
437 /* Add an extra move */
438 MONO_INST_NEW (cfg, move, OP_MOVE);
439 move->dreg = cfg->ret->dreg;
441 mono_bblock_insert_after_ins (bb, cmov, move);
444 /* Rewrite the branch */
445 branch->opcode = OP_BR;
446 branch->inst_target_bb = true_bb->out_bb [0];
447 mono_link_bblock (cfg, bb, branch->inst_target_bb);
449 /* Reorder bblocks */
450 mono_unlink_bblock (cfg, bb, true_bb);
451 mono_unlink_bblock (cfg, bb, false_bb);
452 mono_unlink_bblock (cfg, true_bb, true_bb->out_bb [0]);
453 mono_unlink_bblock (cfg, false_bb, false_bb->out_bb [0]);
454 mono_remove_bblock (cfg, true_bb);
455 mono_remove_bblock (cfg, false_bb);
457 /* Merge bb and its successor if possible */
458 if ((bb->out_bb [0]->in_count == 1) && (bb->out_bb [0] != cfg->bb_exit) &&
459 (bb->region == bb->out_bb [0]->region)) {
460 mono_merge_basic_blocks (cfg, bb, bb->out_bb [0]);
465 /* Look for the IR code generated from if (cond) <var> <- <a>
474 if ((bb2->in_count == 1 && bb2->out_count == 1 && bb2->out_bb [0] == bb1) ||
475 (bb1->in_count == 1 && bb1->out_count == 1 && bb1->out_bb [0] == bb2)) {
476 MonoInst *compare, *branch, *ins1, *cmov, *tmp;
481 MonoBasicBlock *next_bb, *code_bb;
483 /* code_bb is the bblock containing code, next_bb is the successor bblock */
484 if (bb2->in_count == 1 && bb2->out_count == 1 && bb2->out_bb [0] == bb1) {
492 ins1 = mono_bb_first_inst (code_bb, filter);
497 /* Check that code_bb is simple */
499 for (tmp = ins1; tmp; tmp = tmp->next)
500 if (!((tmp->opcode == OP_NOP) || (tmp->opcode == OP_IL_SEQ_POINT) || (tmp->opcode == OP_BR)))
506 /* We move ins1 before the compare so it should have no side effect */
507 if (!MONO_INS_HAS_NO_SIDE_EFFECT (ins1))
510 branch = mono_bb_last_inst (bb, filter);
512 if (!branch || branch->opcode == OP_BR_REG)
515 /* Find the compare instruction */
516 compare = mono_inst_prev (branch, filter);
520 if (!MONO_IS_COND_BRANCH_OP (branch))
521 /* This can happen if a cond branch is optimized away */
525 comp_type = mono_opcode_to_type (branch->opcode, compare->opcode);
526 if (!((comp_type == CMP_TYPE_I) || (comp_type == CMP_TYPE_L)))
530 /* ins->type might not be set */
531 if (INS_INFO (ins1->opcode) [MONO_INST_DEST] != 'i')
535 if (cfg->ret && ins1->dreg == cfg->ret->dreg)
538 if (!(cfg->opt & MONO_OPT_DEADCE))
540 * It is possible that dreg is never set before, so we can't use
541 * it as an sreg of the cmov instruction (#582322).
545 if (cfg->verbose_level > 2) {
546 printf ("\tBranch -> CMove optimization (2) in BB%d on\n", bb->block_num);
547 printf ("\t\t"); mono_print_ins (compare);
548 printf ("\t\t"); mono_print_ins (mono_inst_next (compare, filter));
549 printf ("\t\t"); mono_print_ins (ins1);
556 tmp_reg = mono_alloc_dreg (cfg, STACK_I4);
559 /* Rewrite ins1 to emit to tmp_reg */
560 ins1->dreg = tmp_reg;
562 /* Remove ins1 from code_bb */
563 MONO_REMOVE_INS (code_bb, ins1);
565 /* Move ins1 before the comparison */
566 mono_bblock_insert_before_ins (bb, compare, ins1);
568 /* Add cmov instruction */
569 MONO_INST_NEW (cfg, cmov, OP_NOP);
572 cmov->sreg2 = tmp_reg;
573 cond = mono_opcode_to_cond (branch->opcode);
574 if (branch->inst_false_bb == code_bb)
575 cond = mono_negate_cond (cond);
576 switch (mono_opcode_to_type (branch->opcode, compare->opcode)) {
578 cmov->opcode = int_cmov_opcodes [cond];
581 cmov->opcode = long_cmov_opcodes [cond];
584 g_assert_not_reached ();
586 mono_bblock_insert_after_ins (bb, compare, cmov);
588 /* Rewrite the branch */
589 branch->opcode = OP_BR;
590 branch->inst_target_bb = next_bb;
591 mono_link_bblock (cfg, bb, branch->inst_target_bb);
593 /* Nullify the branch at the end of code_bb */
595 branch = code_bb->code;
596 MONO_DELETE_INS (code_bb, branch);
599 /* Reorder bblocks */
600 mono_unlink_bblock (cfg, bb, code_bb);
601 mono_unlink_bblock (cfg, code_bb, next_bb);
603 /* Merge bb and its successor if possible */
604 if ((bb->out_bb [0]->in_count == 1) && (bb->out_bb [0] != cfg->bb_exit) &&
605 (bb->region == bb->out_bb [0]->region)) {
606 mono_merge_basic_blocks (cfg, bb, bb->out_bb [0]);
609 * bbn might have fallen through to the next bb without a branch,
610 * have to add one now (#474718).
611 * FIXME: Maybe need to do this more generally in
612 * merge_basic_blocks () ?
614 if (!(bb->last_ins && MONO_IS_BRANCH_OP (bb->last_ins)) && bb->out_count) {
615 MONO_INST_NEW (cfg, ins1, OP_BR);
616 ins1->inst_target_bb = bb->out_bb [0];
617 MONO_ADD_INS (bb, ins1);
625 * Optimize checks like: if (v < 0 || v > limit) by changing then to unsigned
626 * compares. This isn't really if conversion, but it easier to do here than in
627 * optimize_branches () since the IR is already optimized.
629 for (bb = cfg->bb_entry; bb; bb = bb->next_bb) {
630 MonoBasicBlock *bb1, *bb2, *next_bb;
631 MonoInst *branch1, *branch2, *compare1, *ins, *next;
633 /* Look for the IR code generated from if (<var> < 0 || v > <limit>)
634 * after branch opts which is:
639 * icompare_imm R [<limit>]
642 if (!(bb->out_count == 2 && !bb->extended))
645 bb1 = bb->out_bb [0];
646 bb2 = bb->out_bb [1];
648 // FIXME: Add more cases
650 /* Check structure */
651 if (!(bb1->in_count == 2 && bb1->in_bb [0] == bb && bb1->in_bb [1] == bb2 && bb2->in_count == 1 && bb2->out_count == 2))
656 /* Check first branch */
657 branch1 = mono_bb_last_inst (bb, filter);
658 if (!(branch1 && ((branch1->opcode == OP_IBLT) || (branch1->opcode == OP_LBLT)) && (branch1->inst_false_bb == next_bb)))
661 /* Check second branch */
662 branch2 = mono_bb_last_inst (next_bb, filter);
666 /* mcs sometimes generates inverted branches */
667 if (((branch2->opcode == OP_IBGT) || (branch2->opcode == OP_LBGT)) && branch2->inst_true_bb == branch1->inst_true_bb)
669 else if (((branch2->opcode == OP_IBLE) || (branch2->opcode == OP_LBLE)) && branch2->inst_false_bb == branch1->inst_true_bb)
674 /* Check first compare */
675 compare1 = mono_inst_prev (mono_bb_last_inst (bb, filter), filter);
676 if (!(compare1 && ((compare1->opcode == OP_ICOMPARE_IMM) || (compare1->opcode == OP_LCOMPARE_IMM)) && compare1->inst_imm == 0))
679 /* Check second bblock */
680 ins = mono_bb_first_inst (next_bb, filter);
683 next = mono_inst_next (ins, filter);
684 if (((ins->opcode == OP_ICOMPARE_IMM) || (ins->opcode == OP_LCOMPARE_IMM)) && ins->sreg1 == compare1->sreg1 && next == branch2) {
685 /* The second arg must be positive */
686 if (ins->inst_imm < 0)
688 } else if (((ins->opcode == OP_LDLEN) || (ins->opcode == OP_STRLEN)) && ins->dreg != compare1->sreg1 && next && next->opcode == OP_ICOMPARE && next->sreg1 == compare1->sreg1 && next->sreg2 == ins->dreg && mono_inst_next (next, filter) == branch2) {
689 /* Another common case: if (index < 0 || index > arr.Length) */
694 if (cfg->verbose_level > 2) {
695 printf ("\tSigned->unsigned compare optimization in BB%d on\n", bb->block_num);
696 printf ("\t\t"); mono_print_ins (compare1);
697 printf ("\t\t"); mono_print_ins (mono_inst_next (compare1, filter));
698 printf ("\t\t"); mono_print_ins (ins);
701 /* Rewrite the first compare+branch */
702 MONO_DELETE_INS (bb, compare1);
703 branch1->opcode = OP_BR;
704 mono_unlink_bblock (cfg, bb, branch1->inst_true_bb);
705 mono_unlink_bblock (cfg, bb, branch1->inst_false_bb);
706 branch1->inst_target_bb = next_bb;
707 mono_link_bblock (cfg, bb, next_bb);
709 /* Rewrite the second branch */
710 branch2->opcode = br_to_br_un (branch2->opcode);
712 mono_merge_basic_blocks (cfg, bb, next_bb);
716 for (bb = cfg->bb_entry; bb; bb = bb->next_bb) {
717 MonoBasicBlock *bb1, *bb2;
718 MonoInst *prev, *compare, *branch, *ins1, *ins2, *cmov, *move, *tmp;
719 gboolean simple, ret;
723 /* Look for the IR code generated from if (cond) <var> <- <a>
724 * after branch opts which is:
731 if (!(bb->out_count == 1 && bb->extended && bb->code && bb->code->next && bb->code->next->next))
734 mono_print_bb (bb, "");
736 /* Find the compare instruction */
740 while (compare->next->next && compare->next->next != bb->last_ins) {
742 compare = compare->next;
744 branch = compare->next;
745 if (!MONO_IS_COND_BRANCH_OP (branch))
751 if (cfg->opt & MONO_OPT_BRANCH)
752 mono_optimize_branches (cfg);
753 /* Merging bblocks could make some variables local */
754 mono_handle_global_vregs (cfg);
755 if (cfg->opt & (MONO_OPT_CONSPROP | MONO_OPT_COPYPROP))
756 mono_local_cprop (cfg);
757 if (cfg->opt & MONO_OPT_DEADCE)
758 mono_local_deadce (cfg);
764 mono_nullify_basic_block (MonoBasicBlock *bb)
771 bb->code = bb->last_ins = NULL;
776 replace_out_block (MonoBasicBlock *bb, MonoBasicBlock *orig, MonoBasicBlock *repl)
780 for (i = 0; i < bb->out_count; i++) {
781 MonoBasicBlock *ob = bb->out_bb [i];
784 if (bb->out_count > 1) {
785 bb->out_bb [i] = bb->out_bb [bb->out_count - 1];
789 bb->out_bb [i] = repl;
796 replace_in_block (MonoBasicBlock *bb, MonoBasicBlock *orig, MonoBasicBlock *repl)
800 for (i = 0; i < bb->in_count; i++) {
801 MonoBasicBlock *ib = bb->in_bb [i];
804 if (bb->in_count > 1) {
805 bb->in_bb [i] = bb->in_bb [bb->in_count - 1];
809 bb->in_bb [i] = repl;
816 replace_out_block_in_code (MonoBasicBlock *bb, MonoBasicBlock *orig, MonoBasicBlock *repl) {
819 #if defined(__native_client_codegen__)
820 /* Need to maintain this flag for the new block because */
821 /* we can't jump indirectly to a non-aligned block. */
822 if (orig->flags & BB_INDIRECT_JUMP_TARGET)
824 repl->flags |= BB_INDIRECT_JUMP_TARGET;
828 for (ins = bb->code; ins != NULL; ins = ins->next) {
829 switch (ins->opcode) {
831 if (ins->inst_target_bb == orig)
832 ins->inst_target_bb = repl;
834 case OP_CALL_HANDLER:
835 if (ins->inst_target_bb == orig)
836 ins->inst_target_bb = repl;
840 int n = GPOINTER_TO_INT (ins->klass);
841 for (i = 0; i < n; i++ ) {
842 if (ins->inst_many_bb [i] == orig)
843 ins->inst_many_bb [i] = repl;
848 if (MONO_IS_COND_BRANCH_OP (ins)) {
849 if (ins->inst_true_bb == orig)
850 ins->inst_true_bb = repl;
851 if (ins->inst_false_bb == orig)
852 ins->inst_false_bb = repl;
853 } else if (MONO_IS_JUMP_TABLE (ins)) {
855 MonoJumpInfoBBTable *table = (MonoJumpInfoBBTable *)MONO_JUMP_TABLE_FROM_INS (ins);
856 for (i = 0; i < table->table_size; i++ ) {
857 if (table->table [i] == orig)
858 table->table [i] = repl;
868 * Check if a bb is useless (is just made of NOPs and ends with an
869 * unconditional branch, or nothing).
870 * If it is so, unlink it from the CFG and nullify it, and return TRUE.
871 * Otherwise, return FALSE;
874 remove_block_if_useless (MonoCompile *cfg, MonoBasicBlock *bb, MonoBasicBlock *previous_bb) {
875 MonoBasicBlock *target_bb = NULL;
878 /* Do not touch handlers */
879 if (bb->region != -1) {
880 bb->not_useless = TRUE;
884 MONO_BB_FOR_EACH_INS (bb, inst) {
885 switch (inst->opcode) {
887 case OP_IL_SEQ_POINT:
890 target_bb = inst->inst_target_bb;
893 bb->not_useless = TRUE;
898 if (target_bb == NULL) {
899 if ((bb->out_count == 1) && (bb->out_bb [0] == bb->next_bb)) {
900 target_bb = bb->next_bb;
902 /* Do not touch empty BBs that do not "fall through" to their next BB (like the exit BB) */
907 /* Do not touch BBs following a switch (they are the "default" branch) */
908 if ((previous_bb->last_ins != NULL) && (previous_bb->last_ins->opcode == OP_SWITCH)) {
912 /* Do not touch BBs following the entry BB and jumping to something that is not */
913 /* thiry "next" bb (the entry BB cannot contain the branch) */
914 if ((previous_bb == cfg->bb_entry) && (bb->next_bb != target_bb)) {
919 * Do not touch BBs following a try block as the code in
920 * mini_method_compile needs them to compute the length of the try block.
922 if (MONO_BBLOCK_IS_IN_REGION (previous_bb, MONO_REGION_TRY))
925 /* Check that there is a target BB, and that bb is not an empty loop (Bug 75061) */
926 if ((target_bb != NULL) && (target_bb != bb)) {
929 if (cfg->verbose_level > 1) {
930 printf ("remove_block_if_useless, removed BB%d\n", bb->block_num);
933 /* unlink_bblock () modifies the bb->in_bb array so can't use a for loop here */
934 while (bb->in_count) {
935 MonoBasicBlock *in_bb = bb->in_bb [0];
936 mono_unlink_bblock (cfg, in_bb, bb);
937 mono_link_bblock (cfg, in_bb, target_bb);
938 replace_out_block_in_code (in_bb, bb, target_bb);
941 mono_unlink_bblock (cfg, bb, target_bb);
942 if (previous_bb != cfg->bb_entry && mono_bb_is_fall_through (cfg, previous_bb)) {
943 for (i = 0; i < previous_bb->out_count; i++) {
944 if (previous_bb->out_bb [i] == target_bb) {
946 MONO_INST_NEW (cfg, jump, OP_BR);
947 MONO_ADD_INS (previous_bb, jump);
948 jump->cil_code = previous_bb->cil_code;
949 jump->inst_target_bb = target_bb;
955 previous_bb->next_bb = bb->next_bb;
956 mono_nullify_basic_block (bb);
965 mono_merge_basic_blocks (MonoCompile *cfg, MonoBasicBlock *bb, MonoBasicBlock *bbn)
968 MonoBasicBlock *prev_bb;
971 bb->has_array_access |= bbn->has_array_access;
972 bb->extended |= bbn->extended;
974 /* Compute prev_bb if possible to avoid the linear search below */
976 for (i = 0; i < bbn->in_count; ++i)
977 if (bbn->in_bb [0]->next_bb == bbn)
978 prev_bb = bbn->in_bb [0];
980 mono_unlink_bblock (cfg, bb, bbn);
981 for (i = 0; i < bbn->out_count; ++i)
982 mono_link_bblock (cfg, bb, bbn->out_bb [i]);
983 while (bbn->out_count)
984 mono_unlink_bblock (cfg, bbn, bbn->out_bb [0]);
986 /* Handle the branch at the end of the bb */
987 if (bb->has_call_handler) {
988 for (inst = bb->code; inst != NULL; inst = inst->next) {
989 if (inst->opcode == OP_CALL_HANDLER) {
990 g_assert (inst->inst_target_bb == bbn);
995 if (bb->has_jump_table) {
996 for (inst = bb->code; inst != NULL; inst = inst->next) {
997 if (MONO_IS_JUMP_TABLE (inst)) {
999 MonoJumpInfoBBTable *table = (MonoJumpInfoBBTable *)MONO_JUMP_TABLE_FROM_INS (inst);
1000 for (i = 0; i < table->table_size; i++ ) {
1001 /* Might be already NULL from a previous merge */
1002 if (table->table [i])
1003 g_assert (table->table [i] == bbn);
1004 table->table [i] = NULL;
1006 /* Can't nullify this as later instructions depend on it */
1010 if (bb->last_ins && MONO_IS_COND_BRANCH_OP (bb->last_ins)) {
1011 g_assert (bb->last_ins->inst_false_bb == bbn);
1012 bb->last_ins->inst_false_bb = NULL;
1013 bb->extended = TRUE;
1014 } else if (bb->last_ins && MONO_IS_BRANCH_OP (bb->last_ins)) {
1015 NULLIFY_INS (bb->last_ins);
1018 bb->has_call_handler |= bbn->has_call_handler;
1019 bb->has_jump_table |= bbn->has_jump_table;
1023 bb->last_ins->next = bbn->code;
1024 bbn->code->prev = bb->last_ins;
1025 bb->last_ins = bbn->last_ins;
1028 bb->code = bbn->code;
1029 bb->last_ins = bbn->last_ins;
1033 for (prev_bb = cfg->bb_entry; prev_bb && prev_bb->next_bb != bbn; prev_bb = prev_bb->next_bb)
1037 prev_bb->next_bb = bbn->next_bb;
1039 /* bbn might not be in the bb list yet */
1040 if (bb->next_bb == bbn)
1041 bb->next_bb = bbn->next_bb;
1043 mono_nullify_basic_block (bbn);
1046 * If bbn fell through to its next bblock, have to add a branch, since bb
1047 * will not fall though to the same bblock (#513931).
1049 if (bb->last_ins && bb->out_count == 1 && bb->out_bb [0] != bb->next_bb && !MONO_IS_BRANCH_OP (bb->last_ins)) {
1050 MONO_INST_NEW (cfg, inst, OP_BR);
1051 inst->inst_target_bb = bb->out_bb [0];
1052 MONO_ADD_INS (bb, inst);
1057 move_basic_block_to_end (MonoCompile *cfg, MonoBasicBlock *bb)
1059 MonoBasicBlock *bbn, *next;
1063 /* Find the previous */
1064 for (bbn = cfg->bb_entry; bbn->next_bb && bbn->next_bb != bb; bbn = bbn->next_bb)
1067 bbn->next_bb = bb->next_bb;
1071 for (bbn = cfg->bb_entry; bbn->next_bb; bbn = bbn->next_bb)
1077 if (next && (!bb->last_ins || ((bb->last_ins->opcode != OP_NOT_REACHED) && (bb->last_ins->opcode != OP_BR) && (bb->last_ins->opcode != OP_BR_REG) && (!MONO_IS_COND_BRANCH_OP (bb->last_ins))))) {
1080 MONO_INST_NEW (cfg, ins, OP_BR);
1081 MONO_ADD_INS (bb, ins);
1082 mono_link_bblock (cfg, bb, next);
1083 ins->inst_target_bb = next;
1088 * mono_remove_block:
1090 * Remove BB from the control flow graph
1093 mono_remove_bblock (MonoCompile *cfg, MonoBasicBlock *bb)
1095 MonoBasicBlock *tmp_bb;
1097 for (tmp_bb = cfg->bb_entry; tmp_bb && tmp_bb->next_bb != bb; tmp_bb = tmp_bb->next_bb)
1101 tmp_bb->next_bb = bb->next_bb;
1105 mono_remove_critical_edges (MonoCompile *cfg)
1108 MonoBasicBlock *previous_bb;
1110 if (cfg->verbose_level > 3) {
1111 for (bb = cfg->bb_entry; bb; bb = bb->next_bb) {
1113 printf ("remove_critical_edges, BEFORE BB%d (in:", bb->block_num);
1114 for (i = 0; i < bb->in_count; i++) {
1115 printf (" %d", bb->in_bb [i]->block_num);
1118 for (i = 0; i < bb->out_count; i++) {
1119 printf (" %d", bb->out_bb [i]->block_num);
1122 if (bb->last_ins != NULL) {
1124 mono_print_ins (bb->last_ins);
1130 for (previous_bb = cfg->bb_entry, bb = previous_bb->next_bb; bb != NULL; previous_bb = previous_bb->next_bb, bb = bb->next_bb) {
1131 if (bb->in_count > 1) {
1133 for (in_bb_index = 0; in_bb_index < bb->in_count; in_bb_index++) {
1134 MonoBasicBlock *in_bb = bb->in_bb [in_bb_index];
1136 * Have to remove non-critical edges whose source ends with a BR_REG
1137 * ins too, since inserting a computation before the BR_REG could
1138 * overwrite the sreg1 of the ins.
1140 if ((in_bb->out_count > 1) || (in_bb->out_count == 1 && in_bb->last_ins && in_bb->last_ins->opcode == OP_BR_REG)) {
1141 MonoBasicBlock *new_bb = (MonoBasicBlock *)mono_mempool_alloc0 ((cfg)->mempool, sizeof (MonoBasicBlock));
1142 new_bb->block_num = cfg->num_bblocks++;
1143 // new_bb->real_offset = bb->real_offset;
1144 new_bb->region = bb->region;
1146 /* Do not alter the CFG while altering the BB list */
1147 if (mono_bb_is_fall_through (cfg, previous_bb)) {
1148 if (previous_bb != cfg->bb_entry) {
1150 /* Make sure previous_bb really falls through bb */
1151 for (i = 0; i < previous_bb->out_count; i++) {
1152 if (previous_bb->out_bb [i] == bb) {
1154 MONO_INST_NEW (cfg, jump, OP_BR);
1155 MONO_ADD_INS (previous_bb, jump);
1156 jump->cil_code = previous_bb->cil_code;
1157 jump->inst_target_bb = bb;
1162 /* We cannot add any inst to the entry BB, so we must */
1163 /* put a new BB in the middle to hold the OP_BR */
1165 MonoBasicBlock *new_bb_after_entry = (MonoBasicBlock *)mono_mempool_alloc0 ((cfg)->mempool, sizeof (MonoBasicBlock));
1166 new_bb_after_entry->block_num = cfg->num_bblocks++;
1167 // new_bb_after_entry->real_offset = bb->real_offset;
1168 new_bb_after_entry->region = bb->region;
1170 MONO_INST_NEW (cfg, jump, OP_BR);
1171 MONO_ADD_INS (new_bb_after_entry, jump);
1172 jump->cil_code = bb->cil_code;
1173 jump->inst_target_bb = bb;
1175 mono_unlink_bblock (cfg, previous_bb, bb);
1176 mono_link_bblock (cfg, new_bb_after_entry, bb);
1177 mono_link_bblock (cfg, previous_bb, new_bb_after_entry);
1179 previous_bb->next_bb = new_bb_after_entry;
1180 previous_bb = new_bb_after_entry;
1182 if (cfg->verbose_level > 2) {
1183 printf ("remove_critical_edges, added helper BB%d jumping to BB%d\n", new_bb_after_entry->block_num, bb->block_num);
1188 /* Insert new_bb in the BB list */
1189 previous_bb->next_bb = new_bb;
1190 new_bb->next_bb = bb;
1191 previous_bb = new_bb;
1193 /* Setup in_bb and out_bb */
1194 new_bb->in_bb = (MonoBasicBlock **)mono_mempool_alloc ((cfg)->mempool, sizeof (MonoBasicBlock*));
1195 new_bb->in_bb [0] = in_bb;
1196 new_bb->in_count = 1;
1197 new_bb->out_bb = (MonoBasicBlock **)mono_mempool_alloc ((cfg)->mempool, sizeof (MonoBasicBlock*));
1198 new_bb->out_bb [0] = bb;
1199 new_bb->out_count = 1;
1201 /* Relink in_bb and bb to (from) new_bb */
1202 replace_out_block (in_bb, bb, new_bb);
1203 replace_out_block_in_code (in_bb, bb, new_bb);
1204 replace_in_block (bb, in_bb, new_bb);
1206 if (cfg->verbose_level > 2) {
1207 printf ("remove_critical_edges, removed critical edge from BB%d to BB%d (added BB%d)\n", in_bb->block_num, bb->block_num, new_bb->block_num);
1214 if (cfg->verbose_level > 3) {
1215 for (bb = cfg->bb_entry; bb; bb = bb->next_bb) {
1217 printf ("remove_critical_edges, AFTER BB%d (in:", bb->block_num);
1218 for (i = 0; i < bb->in_count; i++) {
1219 printf (" %d", bb->in_bb [i]->block_num);
1222 for (i = 0; i < bb->out_count; i++) {
1223 printf (" %d", bb->out_bb [i]->block_num);
1226 if (bb->last_ins != NULL) {
1228 mono_print_ins (bb->last_ins);
1236 * Optimizes the branches on the Control Flow Graph
1240 mono_optimize_branches (MonoCompile *cfg)
1242 int i, count = 0, changed = FALSE;
1243 MonoBasicBlock *bb, *bbn;
1244 guint32 niterations;
1245 MonoInst *bbn_first_inst;
1246 int filter = FILTER_IL_SEQ_POINT;
1249 * Some crazy loops could cause the code below to go into an infinite
1250 * loop, see bug #53003 for an example. To prevent this, we put an upper
1251 * bound on the number of iterations.
1253 if (cfg->num_bblocks > 1000)
1254 niterations = cfg->num_bblocks * 2;
1259 MonoBasicBlock *previous_bb;
1263 /* we skip the entry block (exit is handled specially instead ) */
1264 for (previous_bb = cfg->bb_entry, bb = cfg->bb_entry->next_bb; bb; previous_bb = bb, bb = bb->next_bb) {
1266 if (count == 1000) {
1267 mono_threads_safepoint ();
1270 /* dont touch code inside exception clauses */
1271 if (bb->region != -1)
1274 if (!bb->not_useless && remove_block_if_useless (cfg, bb, previous_bb)) {
1279 if ((bbn = bb->next_bb) && bbn->in_count == 0 && bbn != cfg->bb_exit && bb->region == bbn->region) {
1280 if (cfg->verbose_level > 2)
1281 g_print ("nullify block triggered %d\n", bbn->block_num);
1283 bb->next_bb = bbn->next_bb;
1285 for (i = 0; i < bbn->out_count; i++)
1286 replace_in_block (bbn->out_bb [i], bbn, NULL);
1288 mono_nullify_basic_block (bbn);
1292 if (bb->out_count == 1) {
1293 bbn = bb->out_bb [0];
1295 /* conditional branches where true and false targets are the same can be also replaced with OP_BR */
1296 if (bb->last_ins && (bb->last_ins->opcode != OP_BR) && MONO_IS_COND_BRANCH_OP (bb->last_ins)) {
1297 bb->last_ins->opcode = OP_BR;
1298 bb->last_ins->inst_target_bb = bb->last_ins->inst_true_bb;
1300 if (cfg->verbose_level > 2)
1301 g_print ("cond branch removal triggered in %d %d\n", bb->block_num, bb->out_count);
1304 if (bb->region == bbn->region && bb->next_bb == bbn) {
1305 /* the block are in sequence anyway ... */
1307 /* branches to the following block can be removed */
1308 if (bb->last_ins && bb->last_ins->opcode == OP_BR && !bbn->out_of_line) {
1309 NULLIFY_INS (bb->last_ins);
1311 if (cfg->verbose_level > 2)
1312 g_print ("br removal triggered %d -> %d\n", bb->block_num, bbn->block_num);
1315 if (bbn->in_count == 1 && !bb->extended) {
1316 if (bbn != cfg->bb_exit) {
1317 if (cfg->verbose_level > 2)
1318 g_print ("block merge triggered %d -> %d\n", bb->block_num, bbn->block_num);
1319 mono_merge_basic_blocks (cfg, bb, bbn);
1324 //mono_print_bb_code (bb);
1329 if ((bbn = bb->next_bb) && bbn->in_count == 0 && bbn != cfg->bb_exit && bb->region == bbn->region) {
1330 if (cfg->verbose_level > 2) {
1331 g_print ("nullify block triggered %d\n", bbn->block_num);
1333 bb->next_bb = bbn->next_bb;
1335 for (i = 0; i < bbn->out_count; i++)
1336 replace_in_block (bbn->out_bb [i], bbn, NULL);
1338 mono_nullify_basic_block (bbn);
1343 if (bb->out_count == 1) {
1344 bbn = bb->out_bb [0];
1346 if (bb->last_ins && bb->last_ins->opcode == OP_BR) {
1347 bbn = bb->last_ins->inst_target_bb;
1348 bbn_first_inst = mono_bb_first_inst (bbn, filter);
1349 if (bb->region == bbn->region && bbn_first_inst && bbn_first_inst->opcode == OP_BR &&
1350 bbn_first_inst->inst_target_bb != bbn &&
1351 bbn_first_inst->inst_target_bb->region == bb->region) {
1353 if (cfg->verbose_level > 2)
1354 g_print ("branch to branch triggered %d -> %d -> %d\n", bb->block_num, bbn->block_num, bbn_first_inst->inst_target_bb->block_num);
1356 replace_in_block (bbn, bb, NULL);
1357 replace_out_block (bb, bbn, bbn_first_inst->inst_target_bb);
1358 mono_link_bblock (cfg, bb, bbn_first_inst->inst_target_bb);
1359 bb->last_ins->inst_target_bb = bbn_first_inst->inst_target_bb;
1364 } else if (bb->out_count == 2) {
1365 if (bb->last_ins && MONO_IS_COND_BRANCH_NOFP (bb->last_ins)) {
1367 MonoBasicBlock *taken_branch_target = NULL, *untaken_branch_target = NULL;
1369 if (bb->last_ins->flags & MONO_INST_CFOLD_TAKEN)
1370 branch_result = BRANCH_TAKEN;
1371 else if (bb->last_ins->flags & MONO_INST_CFOLD_NOT_TAKEN)
1372 branch_result = BRANCH_NOT_TAKEN;
1374 branch_result = BRANCH_UNDEF;
1376 if (branch_result == BRANCH_TAKEN) {
1377 taken_branch_target = bb->last_ins->inst_true_bb;
1378 untaken_branch_target = bb->last_ins->inst_false_bb;
1379 } else if (branch_result == BRANCH_NOT_TAKEN) {
1380 taken_branch_target = bb->last_ins->inst_false_bb;
1381 untaken_branch_target = bb->last_ins->inst_true_bb;
1383 if (taken_branch_target) {
1384 /* if mono_eval_cond_branch () is ever taken to handle
1385 * non-constant values to compare, issue a pop here.
1387 bb->last_ins->opcode = OP_BR;
1388 bb->last_ins->inst_target_bb = taken_branch_target;
1390 mono_unlink_bblock (cfg, bb, untaken_branch_target);
1394 bbn = bb->last_ins->inst_true_bb;
1395 bbn_first_inst = mono_bb_first_inst (bbn, filter);
1396 if (bb->region == bbn->region && bbn_first_inst && bbn_first_inst->opcode == OP_BR &&
1397 bbn_first_inst->inst_target_bb->region == bb->region) {
1398 if (cfg->verbose_level > 2)
1399 g_print ("cbranch1 to branch triggered %d -> (%d) %d (0x%02x)\n",
1400 bb->block_num, bbn->block_num, bbn_first_inst->inst_target_bb->block_num,
1401 bbn_first_inst->opcode);
1404 * Unlink, then relink bblocks to avoid various
1405 * tricky situations when the two targets of the branch
1406 * are equal, or will become equal after the change.
1408 mono_unlink_bblock (cfg, bb, bb->last_ins->inst_true_bb);
1409 mono_unlink_bblock (cfg, bb, bb->last_ins->inst_false_bb);
1411 bb->last_ins->inst_true_bb = bbn_first_inst->inst_target_bb;
1413 mono_link_bblock (cfg, bb, bb->last_ins->inst_true_bb);
1414 mono_link_bblock (cfg, bb, bb->last_ins->inst_false_bb);
1420 bbn = bb->last_ins->inst_false_bb;
1421 bbn_first_inst = mono_bb_first_inst (bbn, filter);
1422 if (bbn && bb->region == bbn->region && bbn_first_inst && bbn_first_inst->opcode == OP_BR &&
1423 bbn_first_inst->inst_target_bb->region == bb->region) {
1424 if (cfg->verbose_level > 2)
1425 g_print ("cbranch2 to branch triggered %d -> (%d) %d (0x%02x)\n",
1426 bb->block_num, bbn->block_num, bbn_first_inst->inst_target_bb->block_num,
1427 bbn_first_inst->opcode);
1429 mono_unlink_bblock (cfg, bb, bb->last_ins->inst_true_bb);
1430 mono_unlink_bblock (cfg, bb, bb->last_ins->inst_false_bb);
1432 bb->last_ins->inst_false_bb = bbn_first_inst->inst_target_bb;
1434 mono_link_bblock (cfg, bb, bb->last_ins->inst_true_bb);
1435 mono_link_bblock (cfg, bb, bb->last_ins->inst_false_bb);
1441 bbn = bb->last_ins->inst_false_bb;
1443 * If bb is an extended bb, it could contain an inside branch to bbn.
1444 * FIXME: Enable the optimization if that is not true.
1445 * If bblocks_linked () is true, then merging bb and bbn
1446 * would require addition of an extra branch at the end of bbn
1447 * slowing down loops.
1449 if (bbn && bb->region == bbn->region && bbn->in_count == 1 && cfg->enable_extended_bblocks && bbn != cfg->bb_exit && !bb->extended && !bbn->out_of_line && !mono_bblocks_linked (bbn, bb)) {
1450 g_assert (bbn->in_bb [0] == bb);
1451 if (cfg->verbose_level > 2)
1452 g_print ("merge false branch target triggered BB%d -> BB%d\n", bb->block_num, bbn->block_num);
1453 mono_merge_basic_blocks (cfg, bb, bbn);
1459 if (bb->last_ins && MONO_IS_COND_BRANCH_NOFP (bb->last_ins)) {
1460 if (bb->last_ins->inst_false_bb && bb->last_ins->inst_false_bb->out_of_line && (bb->region == bb->last_ins->inst_false_bb->region) && !cfg->disable_out_of_line_bblocks) {
1461 /* Reverse the branch */
1462 bb->last_ins->opcode = mono_reverse_branch_op (bb->last_ins->opcode);
1463 bbn = bb->last_ins->inst_false_bb;
1464 bb->last_ins->inst_false_bb = bb->last_ins->inst_true_bb;
1465 bb->last_ins->inst_true_bb = bbn;
1467 move_basic_block_to_end (cfg, bb->last_ins->inst_true_bb);
1468 if (cfg->verbose_level > 2)
1469 g_print ("cbranch to throw block triggered %d.\n",
1475 } while (changed && (niterations > 0));
1478 #endif /* DISABLE_JIT */