1 /* Tail call optimization on trees.
2 Copyright (C) 2003 Free Software Foundation, Inc.
4 This file is part of GCC.
6 GCC is free software; you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation; either version 2, or (at your option)
11 GCC is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with GCC; see the file COPYING. If not, write to
18 the Free Software Foundation, 59 Temple Place - Suite 330,
19 Boston, MA 02111-1307, USA. */
23 #include "coretypes.h"
28 #include "hard-reg-set.h"
29 #include "basic-block.h"
31 #include "tree-flow.h"
32 #include "tree-dump.h"
33 #include "diagnostic.h"
35 #include "tree-pass.h"
37 #include "langhooks.h"
39 /* The file implements the tail recursion elimination. It is also used to
40 analyze the tail calls in general, passing the results to the rtl level
41 where they are used for sibcall optimization.
43 In addition to the standard tail recursion elimination, we handle the most
44 trivial cases of making the call tail recursive by creating accumulators.
45 For example the following function
50 return n + sum (n - 1);
67 To do this, we maintain two accumulators (a_acc and m_acc) that indicate
68 when we reach the return x statement, we should return a_acc + x * m_acc
69 instead. They are initially initialized to 0 and 1, respectively,
70 so the semantics of the function is obviously preserved. If we are
71 guaranteed that the value of the accumulator never change, we
74 There are three cases how the function may exit. The first one is
75 handled in adjust_return_value, the other two in adjust_accumulator_values
76 (the second case is actually a special case of the third one and we
77 present it separately just for clarity):
79 1) Just return x, where x is not in any of the remaining special shapes.
80 We rewrite this to a gimple equivalent of return m_acc * x + a_acc.
82 2) return f (...), where f is the current function, is rewritten in a
83 classical tail-recursion elimination way, into assignment of arguments
84 and jump to the start of the function. Values of the accumulators
87 3) return a + m * f(...), where a and m do not depend on call to f.
88 To preserve the semantics described before we want this to be rewritten
89 in such a way that we finally return
91 a_acc + (a + m * f(...)) * m_acc = (a_acc + a * m_acc) + (m * m_acc) * f(...).
93 I.e. we increase a_acc by a * m_acc, multiply m_acc by m and
94 eliminate the tail call to f. Special cases when the value is just
95 added or just multiplied are obtained by setting a = 0 or m = 1.
97 TODO -- it is possible to do similar tricks for other operations. */
99 /* A structure that describes the tailcall. */
103 /* The block in that the call occur. */
104 basic_block call_block;
106 /* The iterator pointing to the call statement. */
107 block_stmt_iterator call_bsi;
109 /* True if it is a call to the current function. */
112 /* The return value of the caller is mult * f + add, where f is the return
113 value of the call. */
116 /* Next tailcall in the chain. */
117 struct tailcall *next;
120 /* The variables holding the value of multiplicative and additive
122 static tree m_acc, a_acc;
124 static bool suitable_for_tail_opt_p (void);
125 static bool optimize_tail_call (struct tailcall *, bool);
126 static void eliminate_tail_call (struct tailcall *);
127 static void find_tail_calls (basic_block, struct tailcall **);
129 /* Returns false when the function is not suitable for tail call optimization
130 from some reason (e.g. if it takes variable number of arguments). */
133 suitable_for_tail_opt_p (void)
137 if (current_function_stdarg)
140 /* No local variable should be call-clobbered. We ignore any kind
141 of memory tag, as these are not real variables. */
142 for (i = 0; i < (int) VARRAY_ACTIVE_SIZE (referenced_vars); i++)
144 tree var = VARRAY_TREE (referenced_vars, i);
146 if (decl_function_context (var) == current_function_decl
147 && !TREE_STATIC (var)
148 && var_ann (var)->mem_tag_kind == NOT_A_TAG
149 && is_call_clobbered (var))
155 /* Returns false when the function is not suitable for tail call optimization
156 from some reason (e.g. if it takes variable number of arguments).
157 This test must pass in addition to suitable_for_tail_opt_p in order to make
158 tail call discovery happen. */
161 suitable_for_tail_call_opt_p (void)
163 /* alloca (until we have stack slot life analysis) inhibits
164 sibling call optimizations, but not tail recursion. */
165 if (current_function_calls_alloca)
168 /* If we are using sjlj exceptions, we may need to add a call to
169 _Unwind_SjLj_Unregister at exit of the function. Which means
170 that we cannot do any sibcall transformations. */
171 if (USING_SJLJ_EXCEPTIONS && current_function_has_exception_handlers ())
174 /* Any function that calls setjmp might have longjmp called from
175 any called function. ??? We really should represent this
176 properly in the CFG so that this needn't be special cased. */
177 if (current_function_calls_setjmp)
183 /* Checks whether the expression EXPR in stmt AT is independent of the
184 statement pointed by BSI (in a sense that we already know EXPR's value
185 at BSI). We use the fact that we are only called from the chain of
186 basic blocks that have only single successor. Returns the expression
187 containing the value of EXPR at BSI. */
190 independent_of_stmt_p (tree expr, tree at, block_stmt_iterator bsi)
192 basic_block bb, call_bb, at_bb;
195 if (is_gimple_min_invariant (expr))
198 if (TREE_CODE (expr) != SSA_NAME)
201 /* Mark the blocks in the chain leading to the end. */
202 at_bb = bb_for_stmt (at);
203 call_bb = bb_for_stmt (bsi_stmt (bsi));
204 for (bb = call_bb; bb != at_bb; bb = bb->succ->dest)
210 at = SSA_NAME_DEF_STMT (expr);
211 bb = bb_for_stmt (at);
213 /* The default definition or defined before the chain. */
219 for (; !bsi_end_p (bsi); bsi_next (&bsi))
220 if (bsi_stmt (bsi) == at)
223 if (!bsi_end_p (bsi))
228 if (TREE_CODE (at) != PHI_NODE)
234 for (e = bb->pred; e; e = e->pred_next)
240 expr = PHI_ARG_DEF_FROM_EDGE (at, e);
241 if (TREE_CODE (expr) != SSA_NAME)
243 /* The value is a constant. */
248 /* Unmark the blocks. */
249 for (bb = call_bb; bb != at_bb; bb = bb->succ->dest)
256 /* Simulates the effect of an assignment of ASS in STMT on the return value
257 of the tail recursive CALL passed in ASS_VAR. M and A are the
258 multiplicative and the additive factor for the real return value. */
261 process_assignment (tree ass, tree stmt, block_stmt_iterator call, tree *m,
262 tree *a, tree *ass_var)
264 tree op0, op1, non_ass_var;
265 tree dest = TREE_OPERAND (ass, 0);
266 tree src = TREE_OPERAND (ass, 1);
267 enum tree_code code = TREE_CODE (src);
270 /* See if this is a simple copy operation of an SSA name to the function
271 result. In that case we may have a simple tail call. Ignore type
272 conversions that can never produce extra code between the function
273 call and the function return. */
274 STRIP_NOPS (src_var);
275 if (TREE_CODE (src_var) == SSA_NAME)
277 if (src_var != *ass_var)
284 if (TREE_CODE_CLASS (code) != '2')
287 /* We only handle the code like
294 TODO -- Extend it for cases where the linear transformation of the output
295 is expressed in a more complicated way. */
297 op0 = TREE_OPERAND (src, 0);
298 op1 = TREE_OPERAND (src, 1);
301 && (non_ass_var = independent_of_stmt_p (op1, stmt, call)))
303 else if (op1 == *ass_var
304 && (non_ass_var = independent_of_stmt_p (op0, stmt, call)))
312 /* There should be no previous addition. TODO -- it should be fairly
313 straightforward to lift this restriction -- just allow storing
314 more complicated expressions in *A, and gimplify it in
315 adjust_accumulator_values. */
323 /* Similar remark applies here. Handling multiplication after addition
324 is just slightly more complicated -- we need to multiply both *A and
332 /* TODO -- Handle other codes (NEGATE_EXPR, MINUS_EXPR). */
339 /* Propagate VAR through phis on edge E. */
342 propagate_through_phis (tree var, edge e)
344 basic_block dest = e->dest;
347 for (phi = phi_nodes (dest); phi; phi = PHI_CHAIN (phi))
348 if (PHI_ARG_DEF_FROM_EDGE (phi, e) == var)
349 return PHI_RESULT (phi);
354 /* Finds tailcalls falling into basic block BB. The list of found tailcalls is
355 added to the start of RET. */
358 find_tail_calls (basic_block bb, struct tailcall **ret)
360 tree ass_var, ret_var, stmt, func, param, args, call = NULL_TREE;
361 block_stmt_iterator bsi, absi;
369 if (bb->succ->succ_next)
372 for (bsi = bsi_last (bb); !bsi_end_p (bsi); bsi_prev (&bsi))
374 stmt = bsi_stmt (bsi);
377 if (TREE_CODE (stmt) == LABEL_EXPR)
380 get_stmt_operands (stmt);
382 /* Check for a call. */
383 if (TREE_CODE (stmt) == MODIFY_EXPR)
385 ass_var = TREE_OPERAND (stmt, 0);
386 call = TREE_OPERAND (stmt, 1);
387 if (TREE_CODE (call) == WITH_SIZE_EXPR)
388 call = TREE_OPERAND (call, 0);
396 if (TREE_CODE (call) == CALL_EXPR)
399 /* If the statement has virtual operands, fail. */
400 ann = stmt_ann (stmt);
401 if (NUM_V_MAY_DEFS (V_MAY_DEF_OPS (ann))
402 || NUM_V_MUST_DEFS (V_MUST_DEF_OPS (ann))
403 || NUM_VUSES (VUSE_OPS (ann)))
409 /* Recurse to the predecessors. */
410 for (e = bb->pred; e; e = e->pred_next)
411 find_tail_calls (e->src, ret);
416 /* We found the call, check whether it is suitable. */
417 tail_recursion = false;
418 func = get_callee_fndecl (call);
419 if (func == current_function_decl)
421 for (param = DECL_ARGUMENTS (func), args = TREE_OPERAND (call, 1);
423 param = TREE_CHAIN (param), args = TREE_CHAIN (args))
425 tree arg = TREE_VALUE (args);
427 /* Make sure there are no problems with copying. Note we must
428 have a copyable type and the two arguments must have reasonably
429 equivalent types. The latter requirement could be relaxed if
430 we emitted a suitable type conversion statement. */
431 && (!is_gimple_reg_type (TREE_TYPE (param))
432 || !lang_hooks.types_compatible_p (TREE_TYPE (param),
437 tail_recursion = true;
440 /* Now check the statements after the call. None of them has virtual
441 operands, so they may only depend on the call through its return
442 value. The return value should also be dependent on each of them,
443 since we are running after dce. */
453 while (bsi_end_p (absi))
455 ass_var = propagate_through_phis (ass_var, abb->succ);
456 abb = abb->succ->dest;
457 absi = bsi_start (abb);
460 stmt = bsi_stmt (absi);
462 if (TREE_CODE (stmt) == LABEL_EXPR)
465 if (TREE_CODE (stmt) == RETURN_EXPR)
468 if (TREE_CODE (stmt) != MODIFY_EXPR)
471 if (!process_assignment (stmt, stmt, bsi, &m, &a, &ass_var))
475 /* See if this is a tail call we can handle. */
476 ret_var = TREE_OPERAND (stmt, 0);
478 && TREE_CODE (ret_var) == MODIFY_EXPR)
480 tree ret_op = TREE_OPERAND (ret_var, 1);
483 && TREE_CODE (ret_op) != SSA_NAME)
486 if (!process_assignment (ret_var, stmt, bsi, &m, &a, &ass_var))
488 ret_var = TREE_OPERAND (ret_var, 0);
491 /* We may proceed if there either is no return value, or the return value
492 is identical to the call's return. */
494 && (ret_var != ass_var))
497 /* If this is not a tail recursive call, we cannot handle addends or
499 if (!tail_recursion && (m || a))
502 nw = xmalloc (sizeof (struct tailcall));
507 nw->tail_recursion = tail_recursion;
516 /* Adjust the accumulator values according to A and M after BSI, and update
517 the phi nodes on edge BACK. */
520 adjust_accumulator_values (block_stmt_iterator bsi, tree m, tree a, edge back)
522 tree stmt, var, phi, tmp;
523 tree ret_type = TREE_TYPE (DECL_RESULT (current_function_decl));
524 tree a_acc_arg = a_acc, m_acc_arg = m_acc;
530 if (integer_onep (a))
534 stmt = build (MODIFY_EXPR, ret_type, NULL_TREE,
535 build (MULT_EXPR, ret_type, m_acc, a));
537 tmp = create_tmp_var (ret_type, "acc_tmp");
538 add_referenced_tmp_var (tmp);
540 var = make_ssa_name (tmp, stmt);
541 TREE_OPERAND (stmt, 0) = var;
542 bsi_insert_after (&bsi, stmt, BSI_NEW_STMT);
548 stmt = build (MODIFY_EXPR, ret_type, NULL_TREE,
549 build (PLUS_EXPR, ret_type, a_acc, var));
550 var = make_ssa_name (SSA_NAME_VAR (a_acc), stmt);
551 TREE_OPERAND (stmt, 0) = var;
552 bsi_insert_after (&bsi, stmt, BSI_NEW_STMT);
558 stmt = build (MODIFY_EXPR, ret_type, NULL_TREE,
559 build (MULT_EXPR, ret_type, m_acc, m));
560 var = make_ssa_name (SSA_NAME_VAR (m_acc), stmt);
561 TREE_OPERAND (stmt, 0) = var;
562 bsi_insert_after (&bsi, stmt, BSI_NEW_STMT);
568 for (phi = phi_nodes (back->dest); phi; phi = PHI_CHAIN (phi))
569 if (PHI_RESULT (phi) == a_acc)
572 add_phi_arg (&phi, a_acc_arg, back);
577 for (phi = phi_nodes (back->dest); phi; phi = PHI_CHAIN (phi))
578 if (PHI_RESULT (phi) == m_acc)
581 add_phi_arg (&phi, m_acc_arg, back);
585 /* Adjust value of the return at the end of BB according to M and A
589 adjust_return_value (basic_block bb, tree m, tree a)
591 tree ret_stmt = last_stmt (bb), ret_var, var, stmt, tmp;
592 tree ret_type = TREE_TYPE (DECL_RESULT (current_function_decl));
593 block_stmt_iterator bsi = bsi_last (bb);
595 if (TREE_CODE (ret_stmt) != RETURN_EXPR)
598 ret_var = TREE_OPERAND (ret_stmt, 0);
602 if (TREE_CODE (ret_var) == MODIFY_EXPR)
604 ret_var->common.ann = (tree_ann_t) stmt_ann (ret_stmt);
605 bsi_replace (&bsi, ret_var, true);
606 SSA_NAME_DEF_STMT (TREE_OPERAND (ret_var, 0)) = ret_var;
607 ret_var = TREE_OPERAND (ret_var, 0);
608 ret_stmt = build1 (RETURN_EXPR, TREE_TYPE (ret_stmt), ret_var);
609 bsi_insert_after (&bsi, ret_stmt, BSI_NEW_STMT);
614 stmt = build (MODIFY_EXPR, ret_type, NULL_TREE,
615 build (MULT_EXPR, ret_type, m_acc, ret_var));
617 tmp = create_tmp_var (ret_type, "acc_tmp");
618 add_referenced_tmp_var (tmp);
620 var = make_ssa_name (tmp, stmt);
621 TREE_OPERAND (stmt, 0) = var;
622 bsi_insert_before (&bsi, stmt, BSI_NEW_STMT);
629 stmt = build (MODIFY_EXPR, ret_type, NULL_TREE,
630 build (PLUS_EXPR, ret_type, a_acc, var));
632 tmp = create_tmp_var (ret_type, "acc_tmp");
633 add_referenced_tmp_var (tmp);
635 var = make_ssa_name (tmp, stmt);
636 TREE_OPERAND (stmt, 0) = var;
637 bsi_insert_before (&bsi, stmt, BSI_NEW_STMT);
640 TREE_OPERAND (ret_stmt, 0) = var;
641 modify_stmt (ret_stmt);
644 /* Eliminates tail call described by T. TMP_VARS is a list of
645 temporary variables used to copy the function arguments. */
648 eliminate_tail_call (struct tailcall *t)
650 tree param, stmt, args, rslt, call;
651 basic_block bb, first;
655 v_may_def_optype v_may_defs;
657 block_stmt_iterator bsi;
659 stmt = bsi_stmt (t->call_bsi);
660 get_stmt_operands (stmt);
661 ann = stmt_ann (stmt);
664 if (dump_file && (dump_flags & TDF_DETAILS))
666 fprintf (dump_file, "Eliminated tail recursion in bb %d : ",
668 print_generic_stmt (dump_file, stmt, TDF_SLIM);
669 fprintf (dump_file, "\n");
672 if (TREE_CODE (stmt) == MODIFY_EXPR)
673 stmt = TREE_OPERAND (stmt, 1);
675 first = ENTRY_BLOCK_PTR->succ->dest;
677 /* Remove the code after call_bsi that will become unreachable. The
678 possibly unreachable code in other blocks is removed later in
682 while (!bsi_end_p (bsi))
684 /* Do not remove the return statement, so that redirect_edge_and_branch
685 sees how the block ends. */
686 if (TREE_CODE (bsi_stmt (bsi)) == RETURN_EXPR)
692 /* Replace the call by a jump to the start of function. */
693 e = redirect_edge_and_branch (t->call_block->succ, first);
696 PENDING_STMT (e) = NULL_TREE;
698 /* Add phi node entries for arguments. Not every PHI node corresponds to
699 a function argument (there may be PHI nodes for virtual definitions of the
700 eliminated calls), so we search for a PHI corresponding to each argument
701 rather than searching for which argument a PHI node corresponds to. */
703 for (param = DECL_ARGUMENTS (current_function_decl),
704 args = TREE_OPERAND (stmt, 1);
706 param = TREE_CHAIN (param),
707 args = TREE_CHAIN (args))
710 for (phi = phi_nodes (first); phi; phi = PHI_CHAIN (phi))
711 if (param == SSA_NAME_VAR (PHI_RESULT (phi)))
714 /* The phi node indeed does not have to be there, in case the operand is
715 invariant in the function. */
719 add_phi_arg (&phi, TREE_VALUE (args), e);
722 /* Add phi nodes for the call clobbered variables. */
723 v_may_defs = V_MAY_DEF_OPS (ann);
724 for (i = 0; i < NUM_V_MAY_DEFS (v_may_defs); i++)
726 param = SSA_NAME_VAR (V_MAY_DEF_RESULT (v_may_defs, i));
727 for (phi = phi_nodes (first); phi; phi = PHI_CHAIN (phi))
728 if (param == SSA_NAME_VAR (PHI_RESULT (phi)))
733 tree name = var_ann (param)->default_def;
734 tree new_name = make_ssa_name (param, SSA_NAME_DEF_STMT (name));
736 var_ann (param)->default_def = new_name;
737 phi = create_phi_node (name, first);
738 SSA_NAME_DEF_STMT (name) = phi;
739 add_phi_arg (&phi, new_name, ENTRY_BLOCK_PTR->succ);
741 /* For all calls the same set of variables should be clobbered. This
742 means that there always should be the appropriate phi node except
743 for the first time we eliminate the call. */
744 if (first->pred->pred_next->pred_next)
748 add_phi_arg (&phi, V_MAY_DEF_OP (v_may_defs, i), e);
751 /* Update the values of accumulators. */
752 adjust_accumulator_values (t->call_bsi, t->mult, t->add, e);
754 call = bsi_stmt (t->call_bsi);
755 if (TREE_CODE (call) == MODIFY_EXPR)
757 rslt = TREE_OPERAND (call, 0);
759 /* Result of the call will no longer be defined. So adjust the
760 SSA_NAME_DEF_STMT accordingly. */
761 SSA_NAME_DEF_STMT (rslt) = build_empty_stmt ();
764 bsi_remove (&t->call_bsi);
767 /* Optimizes the tailcall described by T. If OPT_TAILCALLS is true, also
768 mark the tailcalls for the sibcall optimization. */
771 optimize_tail_call (struct tailcall *t, bool opt_tailcalls)
773 if (t->tail_recursion)
775 eliminate_tail_call (t);
781 tree stmt = bsi_stmt (t->call_bsi);
783 stmt = get_call_expr_in (stmt);
784 CALL_EXPR_TAILCALL (stmt) = 1;
785 if (dump_file && (dump_flags & TDF_DETAILS))
787 fprintf (dump_file, "Found tail call ");
788 print_generic_expr (dump_file, stmt, dump_flags);
789 fprintf (dump_file, " in bb %i\n", t->call_block->index);
796 /* Optimizes tail calls in the function, turning the tail recursion
800 tree_optimize_tail_calls_1 (bool opt_tailcalls)
803 bool phis_constructed = false;
804 struct tailcall *tailcalls = NULL, *act, *next;
805 bool changed = false;
806 basic_block first = ENTRY_BLOCK_PTR->succ->dest;
807 tree stmt, param, ret_type, tmp, phi;
809 if (!suitable_for_tail_opt_p ())
812 opt_tailcalls = suitable_for_tail_call_opt_p ();
814 for (e = EXIT_BLOCK_PTR->pred; e; e = e->pred_next)
816 /* Only traverse the normal exits, i.e. those that end with return
818 stmt = last_stmt (e->src);
821 && TREE_CODE (stmt) == RETURN_EXPR)
822 find_tail_calls (e->src, &tailcalls);
825 /* Construct the phi nodes and accumulators if necessary. */
826 a_acc = m_acc = NULL_TREE;
827 for (act = tailcalls; act; act = act->next)
829 if (!act->tail_recursion)
832 if (!phis_constructed)
834 /* Ensure that there is only one predecessor of the block. */
835 if (first->pred->pred_next)
836 first = split_edge (ENTRY_BLOCK_PTR->succ);
838 /* Copy the args if needed. */
839 for (param = DECL_ARGUMENTS (current_function_decl);
841 param = TREE_CHAIN (param))
843 /* Also parameters that are only defined but never used need not
845 && (var_ann (param)->default_def
846 && TREE_CODE (var_ann (param)->default_def) == SSA_NAME))
848 tree name = var_ann (param)->default_def;
849 tree new_name = make_ssa_name (param, SSA_NAME_DEF_STMT (name));
852 var_ann (param)->default_def = new_name;
853 phi = create_phi_node (name, first);
854 SSA_NAME_DEF_STMT (name) = phi;
855 add_phi_arg (&phi, new_name, first->pred);
857 phis_constructed = true;
860 if (act->add && !a_acc)
862 ret_type = TREE_TYPE (DECL_RESULT (current_function_decl));
864 tmp = create_tmp_var (ret_type, "add_acc");
865 add_referenced_tmp_var (tmp);
867 phi = create_phi_node (tmp, first);
868 add_phi_arg (&phi, fold_convert (ret_type, integer_zero_node),
870 a_acc = PHI_RESULT (phi);
873 if (act->mult && !m_acc)
875 ret_type = TREE_TYPE (DECL_RESULT (current_function_decl));
877 tmp = create_tmp_var (ret_type, "mult_acc");
878 add_referenced_tmp_var (tmp);
880 phi = create_phi_node (tmp, first);
881 add_phi_arg (&phi, fold_convert (ret_type, integer_one_node),
883 m_acc = PHI_RESULT (phi);
887 for (; tailcalls; tailcalls = next)
889 next = tailcalls->next;
890 changed |= optimize_tail_call (tailcalls, opt_tailcalls);
896 /* Modify the remaining return statements. */
897 for (e = EXIT_BLOCK_PTR->pred; e; e = e->pred_next)
899 stmt = last_stmt (e->src);
902 && TREE_CODE (stmt) == RETURN_EXPR)
903 adjust_return_value (e->src, m_acc, a_acc);
909 free_dominance_info (CDI_DOMINATORS);
915 execute_tail_recursion (void)
917 tree_optimize_tail_calls_1 (false);
921 gate_tail_calls (void)
923 return flag_optimize_sibling_calls != 0;
927 execute_tail_calls (void)
929 tree_optimize_tail_calls_1 (true);
932 struct tree_opt_pass pass_tail_recursion =
936 execute_tail_recursion, /* execute */
939 0, /* static_pass_number */
941 PROP_cfg | PROP_ssa, /* properties_required */
942 0, /* properties_provided */
943 0, /* properties_destroyed */
944 0, /* todo_flags_start */
945 TODO_dump_func | TODO_verify_ssa /* todo_flags_finish */
948 struct tree_opt_pass pass_tail_calls =
951 gate_tail_calls, /* gate */
952 execute_tail_calls, /* execute */
955 0, /* static_pass_number */
957 PROP_cfg | PROP_ssa, /* properties_required */
958 0, /* properties_provided */
959 0, /* properties_destroyed */
960 0, /* todo_flags_start */
961 TODO_dump_func | TODO_verify_ssa /* todo_flags_finish */