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
16 * Returns true if @bb is a basic block which falls through the next block.
17 * TODO verify if it helps to check if the bb last ins is a branch to its successor.
20 mono_bb_is_fall_through (MonoCompile *cfg, MonoBasicBlock *bb)
22 return bb->next_bb && bb->next_bb->region == bb->region && /*fall throught between regions is not really interesting or useful*/
23 (bb->last_ins == NULL || !MONO_IS_BRANCH_OP (bb->last_ins)); /*and the last op can't be a branch too*/
27 * Used by the arch code to replace the exception handling
28 * with a direct branch. This is safe to do if the
29 * exception object isn't used, no rethrow statement and
30 * no filter statement (verify).
34 mono_branch_optimize_exception_target (MonoCompile *cfg, MonoBasicBlock *bb, const char * exname)
36 MonoMethodHeader *header = cfg->header;
37 MonoExceptionClause *clause;
41 if (!(cfg->opt & MONO_OPT_EXCEPTION))
44 if (bb->region == -1 || !MONO_BBLOCK_IS_IN_REGION (bb, MONO_REGION_TRY))
47 exclass = mono_class_from_name (mono_get_corlib (), "System", exname);
48 /* search for the handler */
49 for (i = 0; i < header->num_clauses; ++i) {
50 clause = &header->clauses [i];
51 if (MONO_OFFSET_IN_CLAUSE (clause, bb->real_offset)) {
52 if (clause->flags == MONO_EXCEPTION_CLAUSE_NONE && clause->data.catch_class && mono_class_is_assignable_from (clause->data.catch_class, exclass)) {
55 /* get the basic block for the handler and
56 * check if the exception object is used.
57 * Flag is set during method_to_ir due to
58 * pop-op is optmized away in codegen (burg).
60 tbb = cfg->cil_offset_to_bb [clause->handler_offset];
61 if (tbb && tbb->flags & BB_EXCEPTION_DEAD_OBJ && !(tbb->flags & BB_EXCEPTION_UNSAFE)) {
62 MonoBasicBlock *targetbb = tbb;
63 gboolean unsafe = FALSE;
65 /* Check if this catch clause is ok to optimize by
66 * looking for the BB_EXCEPTION_UNSAFE in every BB that
67 * belongs to the same region.
69 * UNSAFE flag is set during method_to_ir (OP_RETHROW)
71 while (!unsafe && tbb->next_bb && tbb->region == tbb->next_bb->region) {
72 if (tbb->next_bb->flags & BB_EXCEPTION_UNSAFE) {
82 /* Create dummy inst to allow easier integration in
83 * arch dependent code (opcode ignored)
85 MONO_INST_NEW (cfg, jump, OP_BR);
87 /* Allocate memory for our branch target */
88 jump->inst_i1 = mono_mempool_alloc0 (cfg->mempool, sizeof (MonoInst));
89 jump->inst_true_bb = targetbb;
91 if (cfg->verbose_level > 2)
92 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);
99 /* Branching to an outer clause could skip inner clauses */
103 /* Branching to an outer clause could skip inner clauses */
112 static const int int_cmov_opcodes [] = {
125 static const int long_cmov_opcodes [] = {
138 static G_GNUC_UNUSED int
139 br_to_br_un (int opcode)
155 g_assert_not_reached ();
163 * Replace INS with its decomposition which is stored in a series of bblocks starting
164 * at FIRST_BB and ending at LAST_BB. On enter, PREV points to the predecessor of INS.
165 * On return, it will be set to the last ins of the decomposition.
168 mono_replace_ins (MonoCompile *cfg, MonoBasicBlock *bb, MonoInst *ins, MonoInst **prev, MonoBasicBlock *first_bb, MonoBasicBlock *last_bb)
170 MonoInst *next = ins->next;
172 if (next && next->opcode == OP_NOP) {
173 /* Avoid NOPs following branches */
174 ins->next = next->next;
178 if (first_bb == last_bb) {
180 * Only one replacement bb, merge the code into
184 /* Delete links between the first_bb and its successors */
185 while (first_bb->out_count)
186 mono_unlink_bblock (cfg, first_bb, first_bb->out_bb [0]);
190 (*prev)->next = first_bb->code;
191 first_bb->code->prev = (*prev);
193 bb->code = first_bb->code;
197 last_bb->last_ins->next = next;
199 next->prev = last_bb->last_ins;
201 bb->last_ins = last_bb->last_ins;
202 *prev = last_bb->last_ins;
203 bb->has_array_access |= first_bb->has_array_access;
206 MonoBasicBlock **tmp_bblocks, *tmp;
212 for (tmp = first_bb; tmp; tmp = tmp->next_bb)
213 tmp->region = bb->region;
215 /* Split the original bb */
217 ins->next->prev = NULL;
221 /* Merge the second part of the original bb into the last bb */
222 if (last_bb->last_ins) {
223 last_bb->last_ins->next = next;
225 next->prev = last_bb->last_ins;
227 last_bb->code = next;
229 last_bb->has_array_access |= bb->has_array_access;
232 for (last = next; last->next != NULL; last = last->next)
234 last_bb->last_ins = last;
237 for (i = 0; i < bb->out_count; ++i)
238 mono_link_bblock (cfg, last_bb, bb->out_bb [i]);
240 /* Merge the first (dummy) bb to the original bb */
242 (*prev)->next = first_bb->code;
243 first_bb->code->prev = (*prev);
245 bb->code = first_bb->code;
247 bb->last_ins = first_bb->last_ins;
248 bb->has_array_access |= first_bb->has_array_access;
250 /* Delete the links between the original bb and its successors */
251 tmp_bblocks = bb->out_bb;
252 count = bb->out_count;
253 for (i = 0; i < count; ++i)
254 mono_unlink_bblock (cfg, bb, tmp_bblocks [i]);
256 /* Add links between the original bb and the first_bb's successors */
257 for (i = 0; i < first_bb->out_count; ++i) {
258 MonoBasicBlock *out_bb = first_bb->out_bb [i];
260 mono_link_bblock (cfg, bb, out_bb);
262 /* Delete links between the first_bb and its successors */
263 for (i = 0; i < bb->out_count; ++i) {
264 MonoBasicBlock *out_bb = bb->out_bb [i];
266 mono_unlink_bblock (cfg, first_bb, out_bb);
268 last_bb->next_bb = bb->next_bb;
269 bb->next_bb = first_bb->next_bb;
276 mono_if_conversion (MonoCompile *cfg)
278 #ifdef MONO_ARCH_HAVE_CMOV_OPS
280 gboolean changed = FALSE;
281 int filter = FILTER_NOP | FILTER_IL_SEQ_POINT;
283 if (!(cfg->opt & MONO_OPT_CMOV))
286 // FIXME: Make this work with extended bblocks
289 * This pass requires somewhat optimized IR code so it should be run after
290 * local cprop/deadce. Also, it should be run before dominator computation, since
291 * it changes control flow.
293 for (bb = cfg->bb_entry; bb; bb = bb->next_bb) {
294 MonoBasicBlock *bb1, *bb2;
297 /* Look for the IR code generated from cond ? a : b
308 if (!(bb->out_count == 2 && !bb->extended))
311 bb1 = bb->out_bb [0];
312 bb2 = bb->out_bb [1];
314 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]) {
315 MonoInst *compare, *branch, *ins1, *ins2, *cmov, *move, *tmp;
316 MonoBasicBlock *true_bb, *false_bb;
317 gboolean simple, ret;
321 branch = mono_bb_last_inst (bb, filter);
323 if (!branch || branch->opcode == OP_BR_REG || branch->opcode == OP_BR)
326 /* Find the compare instruction */
327 compare = mono_inst_prev (branch, filter);
331 if (!MONO_IS_COND_BRANCH_OP (branch))
332 /* This can happen if a cond branch is optimized away */
335 true_bb = branch->inst_true_bb;
336 false_bb = branch->inst_false_bb;
339 * Check that bb1 and bb2 are 'simple' and both assign to the same
342 /* FIXME: Get rid of the nops earlier */
343 ins1 = mono_bb_first_inst (true_bb, filter);
344 ins2 = mono_bb_first_inst (false_bb, filter);
346 if (!(ins1 && ins2 && ins1->dreg == ins2->dreg && ins1->dreg != -1))
350 for (tmp = ins1->next; tmp; tmp = tmp->next)
351 if (!((tmp->opcode == OP_NOP) || (tmp->opcode == OP_IL_SEQ_POINT) || (tmp->opcode == OP_BR)))
354 for (tmp = ins2->next; tmp; tmp = tmp->next)
355 if (!((tmp->opcode == OP_NOP) || (tmp->opcode == OP_IL_SEQ_POINT) || (tmp->opcode == OP_BR)))
361 /* We move ins1/ins2 before the compare so they should have no side effect */
362 if (!(MONO_INS_HAS_NO_SIDE_EFFECT (ins1) && MONO_INS_HAS_NO_SIDE_EFFECT (ins2)))
365 /* Moving ins1/ins2 could change the comparison */
367 if (!((compare->sreg1 != ins1->dreg) && (compare->sreg2 != ins1->dreg)))
371 comp_type = mono_opcode_to_type (branch->opcode, compare->opcode);
372 if (!((comp_type == CMP_TYPE_I) || (comp_type == CMP_TYPE_L)))
376 /* ins->type might not be set */
377 if (INS_INFO (ins1->opcode) [MONO_INST_DEST] != 'i')
380 if (cfg->verbose_level > 2) {
381 printf ("\tBranch -> CMove optimization in BB%d on\n", bb->block_num);
382 printf ("\t\t"); mono_print_ins (compare);
383 printf ("\t\t"); mono_print_ins (mono_inst_next (compare, filter));
384 printf ("\t\t"); mono_print_ins (ins1);
385 printf ("\t\t"); mono_print_ins (ins2);
392 /* Assignments to the return register must remain at the end of bbs */
394 ret = ins1->dreg == cfg->ret->dreg;
398 tmp_reg = mono_alloc_dreg (cfg, STACK_I4);
401 /* Rewrite ins1 to emit to tmp_reg */
402 ins1->dreg = tmp_reg;
405 dreg = mono_alloc_dreg (cfg, STACK_I4);
409 /* Remove ins1/ins2 from bb1/bb2 */
410 MONO_REMOVE_INS (true_bb, ins1);
411 MONO_REMOVE_INS (false_bb, ins2);
413 /* Move ins1 and ins2 before the comparison */
414 /* ins1 comes first to avoid ins1 overwriting an argument of ins2 */
415 mono_bblock_insert_before_ins (bb, compare, ins2);
416 mono_bblock_insert_before_ins (bb, ins2, ins1);
418 /* Add cmov instruction */
419 MONO_INST_NEW (cfg, cmov, OP_NOP);
422 cmov->sreg2 = tmp_reg;
423 switch (mono_opcode_to_type (branch->opcode, compare->opcode)) {
425 cmov->opcode = int_cmov_opcodes [mono_opcode_to_cond (branch->opcode)];
428 cmov->opcode = long_cmov_opcodes [mono_opcode_to_cond (branch->opcode)];
431 g_assert_not_reached ();
433 mono_bblock_insert_after_ins (bb, compare, cmov);
436 /* Add an extra move */
437 MONO_INST_NEW (cfg, move, OP_MOVE);
438 move->dreg = cfg->ret->dreg;
440 mono_bblock_insert_after_ins (bb, cmov, move);
443 /* Rewrite the branch */
444 branch->opcode = OP_BR;
445 branch->inst_target_bb = true_bb->out_bb [0];
446 mono_link_bblock (cfg, bb, branch->inst_target_bb);
448 /* Reorder bblocks */
449 mono_unlink_bblock (cfg, bb, true_bb);
450 mono_unlink_bblock (cfg, bb, false_bb);
451 mono_unlink_bblock (cfg, true_bb, true_bb->out_bb [0]);
452 mono_unlink_bblock (cfg, false_bb, false_bb->out_bb [0]);
453 mono_remove_bblock (cfg, true_bb);
454 mono_remove_bblock (cfg, false_bb);
456 /* Merge bb and its successor if possible */
457 if ((bb->out_bb [0]->in_count == 1) && (bb->out_bb [0] != cfg->bb_exit) &&
458 (bb->region == bb->out_bb [0]->region)) {
459 mono_merge_basic_blocks (cfg, bb, bb->out_bb [0]);
464 /* Look for the IR code generated from if (cond) <var> <- <a>
473 if ((bb2->in_count == 1 && bb2->out_count == 1 && bb2->out_bb [0] == bb1) ||
474 (bb1->in_count == 1 && bb1->out_count == 1 && bb1->out_bb [0] == bb2)) {
475 MonoInst *compare, *branch, *ins1, *cmov, *tmp;
480 MonoBasicBlock *next_bb, *code_bb;
482 /* code_bb is the bblock containing code, next_bb is the successor bblock */
483 if (bb2->in_count == 1 && bb2->out_count == 1 && bb2->out_bb [0] == bb1) {
491 ins1 = mono_bb_first_inst (code_bb, filter);
496 /* Check that code_bb is simple */
498 for (tmp = ins1; tmp; tmp = tmp->next)
499 if (!((tmp->opcode == OP_NOP) || (tmp->opcode == OP_IL_SEQ_POINT) || (tmp->opcode == OP_BR)))
505 /* We move ins1 before the compare so it should have no side effect */
506 if (!MONO_INS_HAS_NO_SIDE_EFFECT (ins1))
509 branch = mono_bb_last_inst (bb, filter);
511 if (!branch || branch->opcode == OP_BR_REG)
514 /* Find the compare instruction */
515 compare = mono_inst_prev (branch, filter);
519 if (!MONO_IS_COND_BRANCH_OP (branch))
520 /* This can happen if a cond branch is optimized away */
524 comp_type = mono_opcode_to_type (branch->opcode, compare->opcode);
525 if (!((comp_type == CMP_TYPE_I) || (comp_type == CMP_TYPE_L)))
529 /* ins->type might not be set */
530 if (INS_INFO (ins1->opcode) [MONO_INST_DEST] != 'i')
534 if (cfg->ret && ins1->dreg == cfg->ret->dreg)
537 if (!(cfg->opt & MONO_OPT_DEADCE))
539 * It is possible that dreg is never set before, so we can't use
540 * it as an sreg of the cmov instruction (#582322).
544 if (cfg->verbose_level > 2) {
545 printf ("\tBranch -> CMove optimization (2) in BB%d on\n", bb->block_num);
546 printf ("\t\t"); mono_print_ins (compare);
547 printf ("\t\t"); mono_print_ins (mono_inst_next (compare, filter));
548 printf ("\t\t"); mono_print_ins (ins1);
555 tmp_reg = mono_alloc_dreg (cfg, STACK_I4);
558 /* Rewrite ins1 to emit to tmp_reg */
559 ins1->dreg = tmp_reg;
561 /* Remove ins1 from code_bb */
562 MONO_REMOVE_INS (code_bb, ins1);
564 /* Move ins1 before the comparison */
565 mono_bblock_insert_before_ins (bb, compare, ins1);
567 /* Add cmov instruction */
568 MONO_INST_NEW (cfg, cmov, OP_NOP);
571 cmov->sreg2 = tmp_reg;
572 cond = mono_opcode_to_cond (branch->opcode);
573 if (branch->inst_false_bb == code_bb)
574 cond = mono_negate_cond (cond);
575 switch (mono_opcode_to_type (branch->opcode, compare->opcode)) {
577 cmov->opcode = int_cmov_opcodes [cond];
580 cmov->opcode = long_cmov_opcodes [cond];
583 g_assert_not_reached ();
585 mono_bblock_insert_after_ins (bb, compare, cmov);
587 /* Rewrite the branch */
588 branch->opcode = OP_BR;
589 branch->inst_target_bb = next_bb;
590 mono_link_bblock (cfg, bb, branch->inst_target_bb);
592 /* Nullify the branch at the end of code_bb */
594 branch = code_bb->code;
595 MONO_DELETE_INS (code_bb, branch);
598 /* Reorder bblocks */
599 mono_unlink_bblock (cfg, bb, code_bb);
600 mono_unlink_bblock (cfg, code_bb, next_bb);
602 /* Merge bb and its successor if possible */
603 if ((bb->out_bb [0]->in_count == 1) && (bb->out_bb [0] != cfg->bb_exit) &&
604 (bb->region == bb->out_bb [0]->region)) {
605 mono_merge_basic_blocks (cfg, bb, bb->out_bb [0]);
608 * bbn might have fallen through to the next bb without a branch,
609 * have to add one now (#474718).
610 * FIXME: Maybe need to do this more generally in
611 * merge_basic_blocks () ?
613 if (!(bb->last_ins && MONO_IS_BRANCH_OP (bb->last_ins)) && bb->out_count) {
614 MONO_INST_NEW (cfg, ins1, OP_BR);
615 ins1->inst_target_bb = bb->out_bb [0];
616 MONO_ADD_INS (bb, ins1);
624 * Optimize checks like: if (v < 0 || v > limit) by changing then to unsigned
625 * compares. This isn't really if conversion, but it easier to do here than in
626 * optimize_branches () since the IR is already optimized.
628 for (bb = cfg->bb_entry; bb; bb = bb->next_bb) {
629 MonoBasicBlock *bb1, *bb2, *next_bb;
630 MonoInst *branch1, *branch2, *compare1, *ins, *next;
632 /* Look for the IR code generated from if (<var> < 0 || v > <limit>)
633 * after branch opts which is:
638 * icompare_imm R [<limit>]
641 if (!(bb->out_count == 2 && !bb->extended))
644 bb1 = bb->out_bb [0];
645 bb2 = bb->out_bb [1];
647 // FIXME: Add more cases
649 /* Check structure */
650 if (!(bb1->in_count == 2 && bb1->in_bb [0] == bb && bb1->in_bb [1] == bb2 && bb2->in_count == 1 && bb2->out_count == 2))
655 /* Check first branch */
656 branch1 = mono_bb_last_inst (bb, filter);
657 if (!(branch1 && ((branch1->opcode == OP_IBLT) || (branch1->opcode == OP_LBLT)) && (branch1->inst_false_bb == next_bb)))
660 /* Check second branch */
661 branch2 = mono_bb_last_inst (next_bb, filter);
665 /* mcs sometimes generates inverted branches */
666 if (((branch2->opcode == OP_IBGT) || (branch2->opcode == OP_LBGT)) && branch2->inst_true_bb == branch1->inst_true_bb)
668 else if (((branch2->opcode == OP_IBLE) || (branch2->opcode == OP_LBLE)) && branch2->inst_false_bb == branch1->inst_true_bb)
673 /* Check first compare */
674 compare1 = mono_inst_prev (mono_bb_last_inst (bb, filter), filter);
675 if (!(compare1 && ((compare1->opcode == OP_ICOMPARE_IMM) || (compare1->opcode == OP_LCOMPARE_IMM)) && compare1->inst_imm == 0))
678 /* Check second bblock */
679 ins = mono_bb_first_inst (next_bb, filter);
682 next = mono_inst_next (ins, filter);
683 if (((ins->opcode == OP_ICOMPARE_IMM) || (ins->opcode == OP_LCOMPARE_IMM)) && ins->sreg1 == compare1->sreg1 && next == branch2) {
684 /* The second arg must be positive */
685 if (ins->inst_imm < 0)
687 } 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) {
688 /* Another common case: if (index < 0 || index > arr.Length) */
693 if (cfg->verbose_level > 2) {
694 printf ("\tSigned->unsigned compare optimization in BB%d on\n", bb->block_num);
695 printf ("\t\t"); mono_print_ins (compare1);
696 printf ("\t\t"); mono_print_ins (mono_inst_next (compare1, filter));
697 printf ("\t\t"); mono_print_ins (ins);
700 /* Rewrite the first compare+branch */
701 MONO_DELETE_INS (bb, compare1);
702 branch1->opcode = OP_BR;
703 mono_unlink_bblock (cfg, bb, branch1->inst_true_bb);
704 mono_unlink_bblock (cfg, bb, branch1->inst_false_bb);
705 branch1->inst_target_bb = next_bb;
706 mono_link_bblock (cfg, bb, next_bb);
708 /* Rewrite the second branch */
709 branch2->opcode = br_to_br_un (branch2->opcode);
711 mono_merge_basic_blocks (cfg, bb, next_bb);
715 for (bb = cfg->bb_entry; bb; bb = bb->next_bb) {
716 MonoBasicBlock *bb1, *bb2;
717 MonoInst *prev, *compare, *branch, *ins1, *ins2, *cmov, *move, *tmp;
718 gboolean simple, ret;
722 /* Look for the IR code generated from if (cond) <var> <- <a>
723 * after branch opts which is:
730 if (!(bb->out_count == 1 && bb->extended && bb->code && bb->code->next && bb->code->next->next))
733 mono_print_bb (bb, "");
735 /* Find the compare instruction */
739 while (compare->next->next && compare->next->next != bb->last_ins) {
741 compare = compare->next;
743 branch = compare->next;
744 if (!MONO_IS_COND_BRANCH_OP (branch))
750 if (cfg->opt & MONO_OPT_BRANCH)
751 mono_optimize_branches (cfg);
752 /* Merging bblocks could make some variables local */
753 mono_handle_global_vregs (cfg);
754 if (cfg->opt & (MONO_OPT_CONSPROP | MONO_OPT_COPYPROP))
755 mono_local_cprop (cfg);
756 if (cfg->opt & MONO_OPT_DEADCE)
757 mono_local_deadce (cfg);
763 mono_nullify_basic_block (MonoBasicBlock *bb)
770 bb->code = bb->last_ins = NULL;
775 replace_out_block (MonoBasicBlock *bb, MonoBasicBlock *orig, MonoBasicBlock *repl)
779 for (i = 0; i < bb->out_count; i++) {
780 MonoBasicBlock *ob = bb->out_bb [i];
783 if (bb->out_count > 1) {
784 bb->out_bb [i] = bb->out_bb [bb->out_count - 1];
788 bb->out_bb [i] = repl;
795 replace_in_block (MonoBasicBlock *bb, MonoBasicBlock *orig, MonoBasicBlock *repl)
799 for (i = 0; i < bb->in_count; i++) {
800 MonoBasicBlock *ib = bb->in_bb [i];
803 if (bb->in_count > 1) {
804 bb->in_bb [i] = bb->in_bb [bb->in_count - 1];
808 bb->in_bb [i] = repl;
815 replace_out_block_in_code (MonoBasicBlock *bb, MonoBasicBlock *orig, MonoBasicBlock *repl) {
818 #if defined(__native_client_codegen__)
819 /* Need to maintain this flag for the new block because */
820 /* we can't jump indirectly to a non-aligned block. */
821 if (orig->flags & BB_INDIRECT_JUMP_TARGET)
823 repl->flags |= BB_INDIRECT_JUMP_TARGET;
827 for (ins = bb->code; ins != NULL; ins = ins->next) {
828 switch (ins->opcode) {
830 if (ins->inst_target_bb == orig)
831 ins->inst_target_bb = repl;
833 case OP_CALL_HANDLER:
834 if (ins->inst_target_bb == orig)
835 ins->inst_target_bb = repl;
839 int n = GPOINTER_TO_INT (ins->klass);
840 for (i = 0; i < n; i++ ) {
841 if (ins->inst_many_bb [i] == orig)
842 ins->inst_many_bb [i] = repl;
847 if (MONO_IS_COND_BRANCH_OP (ins)) {
848 if (ins->inst_true_bb == orig)
849 ins->inst_true_bb = repl;
850 if (ins->inst_false_bb == orig)
851 ins->inst_false_bb = repl;
852 } else if (MONO_IS_JUMP_TABLE (ins)) {
854 MonoJumpInfoBBTable *table = MONO_JUMP_TABLE_FROM_INS (ins);
855 for (i = 0; i < table->table_size; i++ ) {
856 if (table->table [i] == orig)
857 table->table [i] = repl;
867 * Check if a bb is useless (is just made of NOPs and ends with an
868 * unconditional branch, or nothing).
869 * If it is so, unlink it from the CFG and nullify it, and return TRUE.
870 * Otherwise, return FALSE;
873 remove_block_if_useless (MonoCompile *cfg, MonoBasicBlock *bb, MonoBasicBlock *previous_bb) {
874 MonoBasicBlock *target_bb = NULL;
877 /* Do not touch handlers */
878 if (bb->region != -1) {
879 bb->not_useless = TRUE;
883 MONO_BB_FOR_EACH_INS (bb, inst) {
884 switch (inst->opcode) {
886 case OP_IL_SEQ_POINT:
889 target_bb = inst->inst_target_bb;
892 bb->not_useless = TRUE;
897 if (target_bb == NULL) {
898 if ((bb->out_count == 1) && (bb->out_bb [0] == bb->next_bb)) {
899 target_bb = bb->next_bb;
901 /* Do not touch empty BBs that do not "fall through" to their next BB (like the exit BB) */
906 /* Do not touch BBs following a switch (they are the "default" branch) */
907 if ((previous_bb->last_ins != NULL) && (previous_bb->last_ins->opcode == OP_SWITCH)) {
911 /* Do not touch BBs following the entry BB and jumping to something that is not */
912 /* thiry "next" bb (the entry BB cannot contain the branch) */
913 if ((previous_bb == cfg->bb_entry) && (bb->next_bb != target_bb)) {
918 * Do not touch BBs following a try block as the code in
919 * mini_method_compile needs them to compute the length of the try block.
921 if (MONO_BBLOCK_IS_IN_REGION (previous_bb, MONO_REGION_TRY))
924 /* Check that there is a target BB, and that bb is not an empty loop (Bug 75061) */
925 if ((target_bb != NULL) && (target_bb != bb)) {
928 if (cfg->verbose_level > 1) {
929 printf ("remove_block_if_useless, removed BB%d\n", bb->block_num);
932 /* unlink_bblock () modifies the bb->in_bb array so can't use a for loop here */
933 while (bb->in_count) {
934 MonoBasicBlock *in_bb = bb->in_bb [0];
935 mono_unlink_bblock (cfg, in_bb, bb);
936 mono_link_bblock (cfg, in_bb, target_bb);
937 replace_out_block_in_code (in_bb, bb, target_bb);
940 mono_unlink_bblock (cfg, bb, target_bb);
941 if (previous_bb != cfg->bb_entry && mono_bb_is_fall_through (cfg, previous_bb)) {
942 for (i = 0; i < previous_bb->out_count; i++) {
943 if (previous_bb->out_bb [i] == target_bb) {
945 MONO_INST_NEW (cfg, jump, OP_BR);
946 MONO_ADD_INS (previous_bb, jump);
947 jump->cil_code = previous_bb->cil_code;
948 jump->inst_target_bb = target_bb;
954 previous_bb->next_bb = bb->next_bb;
955 mono_nullify_basic_block (bb);
964 mono_merge_basic_blocks (MonoCompile *cfg, MonoBasicBlock *bb, MonoBasicBlock *bbn)
967 MonoBasicBlock *prev_bb;
970 bb->has_array_access |= bbn->has_array_access;
971 bb->extended |= bbn->extended;
973 /* Compute prev_bb if possible to avoid the linear search below */
975 for (i = 0; i < bbn->in_count; ++i)
976 if (bbn->in_bb [0]->next_bb == bbn)
977 prev_bb = bbn->in_bb [0];
979 mono_unlink_bblock (cfg, bb, bbn);
980 for (i = 0; i < bbn->out_count; ++i)
981 mono_link_bblock (cfg, bb, bbn->out_bb [i]);
982 while (bbn->out_count)
983 mono_unlink_bblock (cfg, bbn, bbn->out_bb [0]);
985 /* Handle the branch at the end of the bb */
986 if (bb->has_call_handler) {
987 for (inst = bb->code; inst != NULL; inst = inst->next) {
988 if (inst->opcode == OP_CALL_HANDLER) {
989 g_assert (inst->inst_target_bb == bbn);
994 if (bb->has_jump_table) {
995 for (inst = bb->code; inst != NULL; inst = inst->next) {
996 if (MONO_IS_JUMP_TABLE (inst)) {
998 MonoJumpInfoBBTable *table = MONO_JUMP_TABLE_FROM_INS (inst);
999 for (i = 0; i < table->table_size; i++ ) {
1000 /* Might be already NULL from a previous merge */
1001 if (table->table [i])
1002 g_assert (table->table [i] == bbn);
1003 table->table [i] = NULL;
1005 /* Can't nullify this as later instructions depend on it */
1009 if (bb->last_ins && MONO_IS_COND_BRANCH_OP (bb->last_ins)) {
1010 g_assert (bb->last_ins->inst_false_bb == bbn);
1011 bb->last_ins->inst_false_bb = NULL;
1012 bb->extended = TRUE;
1013 } else if (bb->last_ins && MONO_IS_BRANCH_OP (bb->last_ins)) {
1014 NULLIFY_INS (bb->last_ins);
1017 bb->has_call_handler |= bbn->has_call_handler;
1018 bb->has_jump_table |= bbn->has_jump_table;
1022 bb->last_ins->next = bbn->code;
1023 bbn->code->prev = bb->last_ins;
1024 bb->last_ins = bbn->last_ins;
1027 bb->code = bbn->code;
1028 bb->last_ins = bbn->last_ins;
1032 for (prev_bb = cfg->bb_entry; prev_bb && prev_bb->next_bb != bbn; prev_bb = prev_bb->next_bb)
1036 prev_bb->next_bb = bbn->next_bb;
1038 /* bbn might not be in the bb list yet */
1039 if (bb->next_bb == bbn)
1040 bb->next_bb = bbn->next_bb;
1042 mono_nullify_basic_block (bbn);
1045 * If bbn fell through to its next bblock, have to add a branch, since bb
1046 * will not fall though to the same bblock (#513931).
1048 if (bb->last_ins && bb->out_count == 1 && bb->out_bb [0] != bb->next_bb && !MONO_IS_BRANCH_OP (bb->last_ins)) {
1049 MONO_INST_NEW (cfg, inst, OP_BR);
1050 inst->inst_target_bb = bb->out_bb [0];
1051 MONO_ADD_INS (bb, inst);
1056 move_basic_block_to_end (MonoCompile *cfg, MonoBasicBlock *bb)
1058 MonoBasicBlock *bbn, *next;
1062 /* Find the previous */
1063 for (bbn = cfg->bb_entry; bbn->next_bb && bbn->next_bb != bb; bbn = bbn->next_bb)
1066 bbn->next_bb = bb->next_bb;
1070 for (bbn = cfg->bb_entry; bbn->next_bb; bbn = bbn->next_bb)
1076 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))))) {
1079 MONO_INST_NEW (cfg, ins, OP_BR);
1080 MONO_ADD_INS (bb, ins);
1081 mono_link_bblock (cfg, bb, next);
1082 ins->inst_target_bb = next;
1087 * mono_remove_block:
1089 * Remove BB from the control flow graph
1092 mono_remove_bblock (MonoCompile *cfg, MonoBasicBlock *bb)
1094 MonoBasicBlock *tmp_bb;
1096 for (tmp_bb = cfg->bb_entry; tmp_bb && tmp_bb->next_bb != bb; tmp_bb = tmp_bb->next_bb)
1100 tmp_bb->next_bb = bb->next_bb;
1104 mono_remove_critical_edges (MonoCompile *cfg)
1107 MonoBasicBlock *previous_bb;
1109 if (cfg->verbose_level > 3) {
1110 for (bb = cfg->bb_entry; bb; bb = bb->next_bb) {
1112 printf ("remove_critical_edges, BEFORE BB%d (in:", bb->block_num);
1113 for (i = 0; i < bb->in_count; i++) {
1114 printf (" %d", bb->in_bb [i]->block_num);
1117 for (i = 0; i < bb->out_count; i++) {
1118 printf (" %d", bb->out_bb [i]->block_num);
1121 if (bb->last_ins != NULL) {
1123 mono_print_ins (bb->last_ins);
1129 for (previous_bb = cfg->bb_entry, bb = previous_bb->next_bb; bb != NULL; previous_bb = previous_bb->next_bb, bb = bb->next_bb) {
1130 if (bb->in_count > 1) {
1132 for (in_bb_index = 0; in_bb_index < bb->in_count; in_bb_index++) {
1133 MonoBasicBlock *in_bb = bb->in_bb [in_bb_index];
1135 * Have to remove non-critical edges whose source ends with a BR_REG
1136 * ins too, since inserting a computation before the BR_REG could
1137 * overwrite the sreg1 of the ins.
1139 if ((in_bb->out_count > 1) || (in_bb->out_count == 1 && in_bb->last_ins && in_bb->last_ins->opcode == OP_BR_REG)) {
1140 MonoBasicBlock *new_bb = mono_mempool_alloc0 ((cfg)->mempool, sizeof (MonoBasicBlock));
1141 new_bb->block_num = cfg->num_bblocks++;
1142 // new_bb->real_offset = bb->real_offset;
1143 new_bb->region = bb->region;
1145 /* Do not alter the CFG while altering the BB list */
1146 if (mono_bb_is_fall_through (cfg, previous_bb)) {
1147 if (previous_bb != cfg->bb_entry) {
1149 /* Make sure previous_bb really falls through bb */
1150 for (i = 0; i < previous_bb->out_count; i++) {
1151 if (previous_bb->out_bb [i] == bb) {
1153 MONO_INST_NEW (cfg, jump, OP_BR);
1154 MONO_ADD_INS (previous_bb, jump);
1155 jump->cil_code = previous_bb->cil_code;
1156 jump->inst_target_bb = bb;
1161 /* We cannot add any inst to the entry BB, so we must */
1162 /* put a new BB in the middle to hold the OP_BR */
1164 MonoBasicBlock *new_bb_after_entry = mono_mempool_alloc0 ((cfg)->mempool, sizeof (MonoBasicBlock));
1165 new_bb_after_entry->block_num = cfg->num_bblocks++;
1166 // new_bb_after_entry->real_offset = bb->real_offset;
1167 new_bb_after_entry->region = bb->region;
1169 MONO_INST_NEW (cfg, jump, OP_BR);
1170 MONO_ADD_INS (new_bb_after_entry, jump);
1171 jump->cil_code = bb->cil_code;
1172 jump->inst_target_bb = bb;
1174 mono_unlink_bblock (cfg, previous_bb, bb);
1175 mono_link_bblock (cfg, new_bb_after_entry, bb);
1176 mono_link_bblock (cfg, previous_bb, new_bb_after_entry);
1178 previous_bb->next_bb = new_bb_after_entry;
1179 previous_bb = new_bb_after_entry;
1181 if (cfg->verbose_level > 2) {
1182 printf ("remove_critical_edges, added helper BB%d jumping to BB%d\n", new_bb_after_entry->block_num, bb->block_num);
1187 /* Insert new_bb in the BB list */
1188 previous_bb->next_bb = new_bb;
1189 new_bb->next_bb = bb;
1190 previous_bb = new_bb;
1192 /* Setup in_bb and out_bb */
1193 new_bb->in_bb = mono_mempool_alloc ((cfg)->mempool, sizeof (MonoBasicBlock*));
1194 new_bb->in_bb [0] = in_bb;
1195 new_bb->in_count = 1;
1196 new_bb->out_bb = mono_mempool_alloc ((cfg)->mempool, sizeof (MonoBasicBlock*));
1197 new_bb->out_bb [0] = bb;
1198 new_bb->out_count = 1;
1200 /* Relink in_bb and bb to (from) new_bb */
1201 replace_out_block (in_bb, bb, new_bb);
1202 replace_out_block_in_code (in_bb, bb, new_bb);
1203 replace_in_block (bb, in_bb, new_bb);
1205 if (cfg->verbose_level > 2) {
1206 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);
1213 if (cfg->verbose_level > 3) {
1214 for (bb = cfg->bb_entry; bb; bb = bb->next_bb) {
1216 printf ("remove_critical_edges, AFTER BB%d (in:", bb->block_num);
1217 for (i = 0; i < bb->in_count; i++) {
1218 printf (" %d", bb->in_bb [i]->block_num);
1221 for (i = 0; i < bb->out_count; i++) {
1222 printf (" %d", bb->out_bb [i]->block_num);
1225 if (bb->last_ins != NULL) {
1227 mono_print_ins (bb->last_ins);
1235 * Optimizes the branches on the Control Flow Graph
1239 mono_optimize_branches (MonoCompile *cfg)
1241 int i, changed = FALSE;
1242 MonoBasicBlock *bb, *bbn;
1243 guint32 niterations;
1244 MonoInst *bbn_first_inst;
1245 int filter = FILTER_IL_SEQ_POINT;
1248 * Some crazy loops could cause the code below to go into an infinite
1249 * loop, see bug #53003 for an example. To prevent this, we put an upper
1250 * bound on the number of iterations.
1252 if (cfg->num_bblocks > 1000)
1253 niterations = cfg->num_bblocks * 2;
1258 MonoBasicBlock *previous_bb;
1262 /* we skip the entry block (exit is handled specially instead ) */
1263 for (previous_bb = cfg->bb_entry, bb = cfg->bb_entry->next_bb; bb; previous_bb = bb, bb = bb->next_bb) {
1264 /* dont touch code inside exception clauses */
1265 if (bb->region != -1)
1268 if (!bb->not_useless && remove_block_if_useless (cfg, bb, previous_bb)) {
1273 if ((bbn = bb->next_bb) && bbn->in_count == 0 && bbn != cfg->bb_exit && bb->region == bbn->region) {
1274 if (cfg->verbose_level > 2)
1275 g_print ("nullify block triggered %d\n", bbn->block_num);
1277 bb->next_bb = bbn->next_bb;
1279 for (i = 0; i < bbn->out_count; i++)
1280 replace_in_block (bbn->out_bb [i], bbn, NULL);
1282 mono_nullify_basic_block (bbn);
1286 if (bb->out_count == 1) {
1287 bbn = bb->out_bb [0];
1289 /* conditional branches where true and false targets are the same can be also replaced with OP_BR */
1290 if (bb->last_ins && (bb->last_ins->opcode != OP_BR) && MONO_IS_COND_BRANCH_OP (bb->last_ins)) {
1291 bb->last_ins->opcode = OP_BR;
1292 bb->last_ins->inst_target_bb = bb->last_ins->inst_true_bb;
1294 if (cfg->verbose_level > 2)
1295 g_print ("cond branch removal triggered in %d %d\n", bb->block_num, bb->out_count);
1298 if (bb->region == bbn->region && bb->next_bb == bbn) {
1299 /* the block are in sequence anyway ... */
1301 /* branches to the following block can be removed */
1302 if (bb->last_ins && bb->last_ins->opcode == OP_BR && !bbn->out_of_line) {
1303 NULLIFY_INS (bb->last_ins);
1305 if (cfg->verbose_level > 2)
1306 g_print ("br removal triggered %d -> %d\n", bb->block_num, bbn->block_num);
1309 if (bbn->in_count == 1 && !bb->extended) {
1310 if (bbn != cfg->bb_exit) {
1311 if (cfg->verbose_level > 2)
1312 g_print ("block merge triggered %d -> %d\n", bb->block_num, bbn->block_num);
1313 mono_merge_basic_blocks (cfg, bb, bbn);
1318 //mono_print_bb_code (bb);
1323 if ((bbn = bb->next_bb) && bbn->in_count == 0 && bbn != cfg->bb_exit && bb->region == bbn->region) {
1324 if (cfg->verbose_level > 2) {
1325 g_print ("nullify block triggered %d\n", bbn->block_num);
1327 bb->next_bb = bbn->next_bb;
1329 for (i = 0; i < bbn->out_count; i++)
1330 replace_in_block (bbn->out_bb [i], bbn, NULL);
1332 mono_nullify_basic_block (bbn);
1337 if (bb->out_count == 1) {
1338 bbn = bb->out_bb [0];
1340 if (bb->last_ins && bb->last_ins->opcode == OP_BR) {
1341 bbn = bb->last_ins->inst_target_bb;
1342 bbn_first_inst = mono_bb_first_inst (bbn, filter);
1343 if (bb->region == bbn->region && bbn_first_inst && bbn_first_inst->opcode == OP_BR &&
1344 bbn_first_inst->inst_target_bb != bbn &&
1345 bbn_first_inst->inst_target_bb->region == bb->region) {
1347 if (cfg->verbose_level > 2)
1348 g_print ("branch to branch triggered %d -> %d -> %d\n", bb->block_num, bbn->block_num, bbn_first_inst->inst_target_bb->block_num);
1350 replace_in_block (bbn, bb, NULL);
1351 replace_out_block (bb, bbn, bbn_first_inst->inst_target_bb);
1352 mono_link_bblock (cfg, bb, bbn_first_inst->inst_target_bb);
1353 bb->last_ins->inst_target_bb = bbn_first_inst->inst_target_bb;
1358 } else if (bb->out_count == 2) {
1359 if (bb->last_ins && MONO_IS_COND_BRANCH_NOFP (bb->last_ins)) {
1361 MonoBasicBlock *taken_branch_target = NULL, *untaken_branch_target = NULL;
1363 if (bb->last_ins->flags & MONO_INST_CFOLD_TAKEN)
1364 branch_result = BRANCH_TAKEN;
1365 else if (bb->last_ins->flags & MONO_INST_CFOLD_NOT_TAKEN)
1366 branch_result = BRANCH_NOT_TAKEN;
1368 branch_result = BRANCH_UNDEF;
1370 if (branch_result == BRANCH_TAKEN) {
1371 taken_branch_target = bb->last_ins->inst_true_bb;
1372 untaken_branch_target = bb->last_ins->inst_false_bb;
1373 } else if (branch_result == BRANCH_NOT_TAKEN) {
1374 taken_branch_target = bb->last_ins->inst_false_bb;
1375 untaken_branch_target = bb->last_ins->inst_true_bb;
1377 if (taken_branch_target) {
1378 /* if mono_eval_cond_branch () is ever taken to handle
1379 * non-constant values to compare, issue a pop here.
1381 bb->last_ins->opcode = OP_BR;
1382 bb->last_ins->inst_target_bb = taken_branch_target;
1384 mono_unlink_bblock (cfg, bb, untaken_branch_target);
1388 bbn = bb->last_ins->inst_true_bb;
1389 bbn_first_inst = mono_bb_first_inst (bbn, filter);
1390 if (bb->region == bbn->region && bbn_first_inst && bbn_first_inst->opcode == OP_BR &&
1391 bbn_first_inst->inst_target_bb->region == bb->region) {
1392 if (cfg->verbose_level > 2)
1393 g_print ("cbranch1 to branch triggered %d -> (%d) %d (0x%02x)\n",
1394 bb->block_num, bbn->block_num, bbn_first_inst->inst_target_bb->block_num,
1395 bbn_first_inst->opcode);
1398 * Unlink, then relink bblocks to avoid various
1399 * tricky situations when the two targets of the branch
1400 * are equal, or will become equal after the change.
1402 mono_unlink_bblock (cfg, bb, bb->last_ins->inst_true_bb);
1403 mono_unlink_bblock (cfg, bb, bb->last_ins->inst_false_bb);
1405 bb->last_ins->inst_true_bb = bbn_first_inst->inst_target_bb;
1407 mono_link_bblock (cfg, bb, bb->last_ins->inst_true_bb);
1408 mono_link_bblock (cfg, bb, bb->last_ins->inst_false_bb);
1414 bbn = bb->last_ins->inst_false_bb;
1415 bbn_first_inst = mono_bb_first_inst (bbn, filter);
1416 if (bbn && bb->region == bbn->region && bbn_first_inst && bbn_first_inst->opcode == OP_BR &&
1417 bbn_first_inst->inst_target_bb->region == bb->region) {
1418 if (cfg->verbose_level > 2)
1419 g_print ("cbranch2 to branch triggered %d -> (%d) %d (0x%02x)\n",
1420 bb->block_num, bbn->block_num, bbn_first_inst->inst_target_bb->block_num,
1421 bbn_first_inst->opcode);
1423 mono_unlink_bblock (cfg, bb, bb->last_ins->inst_true_bb);
1424 mono_unlink_bblock (cfg, bb, bb->last_ins->inst_false_bb);
1426 bb->last_ins->inst_false_bb = bbn_first_inst->inst_target_bb;
1428 mono_link_bblock (cfg, bb, bb->last_ins->inst_true_bb);
1429 mono_link_bblock (cfg, bb, bb->last_ins->inst_false_bb);
1435 bbn = bb->last_ins->inst_false_bb;
1437 * If bb is an extended bb, it could contain an inside branch to bbn.
1438 * FIXME: Enable the optimization if that is not true.
1439 * If bblocks_linked () is true, then merging bb and bbn
1440 * would require addition of an extra branch at the end of bbn
1441 * slowing down loops.
1443 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)) {
1444 g_assert (bbn->in_bb [0] == bb);
1445 if (cfg->verbose_level > 2)
1446 g_print ("merge false branch target triggered BB%d -> BB%d\n", bb->block_num, bbn->block_num);
1447 mono_merge_basic_blocks (cfg, bb, bbn);
1453 if (bb->last_ins && MONO_IS_COND_BRANCH_NOFP (bb->last_ins)) {
1454 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) {
1455 /* Reverse the branch */
1456 bb->last_ins->opcode = mono_reverse_branch_op (bb->last_ins->opcode);
1457 bbn = bb->last_ins->inst_false_bb;
1458 bb->last_ins->inst_false_bb = bb->last_ins->inst_true_bb;
1459 bb->last_ins->inst_true_bb = bbn;
1461 move_basic_block_to_end (cfg, bb->last_ins->inst_true_bb);
1462 if (cfg->verbose_level > 2)
1463 g_print ("cbranch to throw block triggered %d.\n",
1469 } while (changed && (niterations > 0));
1472 #endif /* DISABLE_JIT */