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);
394 if (TREE_CODE (call) == CALL_EXPR)
397 /* If the statement has virtual operands, fail. */
398 ann = stmt_ann (stmt);
399 if (NUM_V_MAY_DEFS (V_MAY_DEF_OPS (ann))
400 || NUM_V_MUST_DEFS (V_MUST_DEF_OPS (ann))
401 || NUM_VUSES (VUSE_OPS (ann)))
407 /* Recurse to the predecessors. */
408 for (e = bb->pred; e; e = e->pred_next)
409 find_tail_calls (e->src, ret);
414 /* We found the call, check whether it is suitable. */
415 tail_recursion = false;
416 func = get_callee_fndecl (call);
417 if (func == current_function_decl)
419 for (param = DECL_ARGUMENTS (func), args = TREE_OPERAND (call, 1);
421 param = TREE_CHAIN (param), args = TREE_CHAIN (args))
423 tree arg = TREE_VALUE (args);
425 /* Make sure there are no problems with copying. Note we must
426 have a copyable type and the two arguments must have reasonably
427 equivalent types. The latter requirement could be relaxed if
428 we emitted a suitable type conversion statement. */
429 && (!is_gimple_reg_type (TREE_TYPE (param))
430 || !lang_hooks.types_compatible_p (TREE_TYPE (param),
435 tail_recursion = true;
438 /* Now check the statements after the call. None of them has virtual
439 operands, so they may only depend on the call through its return
440 value. The return value should also be dependent on each of them,
441 since we are running after dce. */
451 while (bsi_end_p (absi))
453 ass_var = propagate_through_phis (ass_var, abb->succ);
454 abb = abb->succ->dest;
455 absi = bsi_start (abb);
458 stmt = bsi_stmt (absi);
460 if (TREE_CODE (stmt) == LABEL_EXPR)
463 if (TREE_CODE (stmt) == RETURN_EXPR)
466 if (TREE_CODE (stmt) != MODIFY_EXPR)
469 if (!process_assignment (stmt, stmt, bsi, &m, &a, &ass_var))
473 /* See if this is a tail call we can handle. */
474 ret_var = TREE_OPERAND (stmt, 0);
476 && TREE_CODE (ret_var) == MODIFY_EXPR)
478 tree ret_op = TREE_OPERAND (ret_var, 1);
481 && TREE_CODE (ret_op) != SSA_NAME)
484 if (!process_assignment (ret_var, stmt, bsi, &m, &a, &ass_var))
486 ret_var = TREE_OPERAND (ret_var, 0);
489 /* We may proceed if there either is no return value, or the return value
490 is identical to the call's return. */
492 && (ret_var != ass_var))
495 /* If this is not a tail recursive call, we cannot handle addends or
497 if (!tail_recursion && (m || a))
500 nw = xmalloc (sizeof (struct tailcall));
505 nw->tail_recursion = tail_recursion;
514 /* Adjust the accumulator values according to A and M after BSI, and update
515 the phi nodes on edge BACK. */
518 adjust_accumulator_values (block_stmt_iterator bsi, tree m, tree a, edge back)
520 tree stmt, var, phi, tmp;
521 tree ret_type = TREE_TYPE (DECL_RESULT (current_function_decl));
522 tree a_acc_arg = a_acc, m_acc_arg = m_acc;
528 if (integer_onep (a))
532 stmt = build (MODIFY_EXPR, ret_type, NULL_TREE,
533 build (MULT_EXPR, ret_type, m_acc, a));
535 tmp = create_tmp_var (ret_type, "acc_tmp");
536 add_referenced_tmp_var (tmp);
538 var = make_ssa_name (tmp, stmt);
539 TREE_OPERAND (stmt, 0) = var;
540 bsi_insert_after (&bsi, stmt, BSI_NEW_STMT);
546 stmt = build (MODIFY_EXPR, ret_type, NULL_TREE,
547 build (PLUS_EXPR, ret_type, a_acc, var));
548 var = make_ssa_name (SSA_NAME_VAR (a_acc), stmt);
549 TREE_OPERAND (stmt, 0) = var;
550 bsi_insert_after (&bsi, stmt, BSI_NEW_STMT);
556 stmt = build (MODIFY_EXPR, ret_type, NULL_TREE,
557 build (MULT_EXPR, ret_type, m_acc, m));
558 var = make_ssa_name (SSA_NAME_VAR (m_acc), stmt);
559 TREE_OPERAND (stmt, 0) = var;
560 bsi_insert_after (&bsi, stmt, BSI_NEW_STMT);
566 for (phi = phi_nodes (back->dest); phi; phi = PHI_CHAIN (phi))
567 if (PHI_RESULT (phi) == a_acc)
570 add_phi_arg (&phi, a_acc_arg, back);
575 for (phi = phi_nodes (back->dest); phi; phi = PHI_CHAIN (phi))
576 if (PHI_RESULT (phi) == m_acc)
579 add_phi_arg (&phi, m_acc_arg, back);
583 /* Adjust value of the return at the end of BB according to M and A
587 adjust_return_value (basic_block bb, tree m, tree a)
589 tree ret_stmt = last_stmt (bb), ret_var, var, stmt, tmp;
590 tree ret_type = TREE_TYPE (DECL_RESULT (current_function_decl));
591 block_stmt_iterator bsi = bsi_last (bb);
593 if (TREE_CODE (ret_stmt) != RETURN_EXPR)
596 ret_var = TREE_OPERAND (ret_stmt, 0);
600 if (TREE_CODE (ret_var) == MODIFY_EXPR)
602 ret_var->common.ann = (tree_ann_t) stmt_ann (ret_stmt);
603 bsi_replace (&bsi, ret_var, true);
604 SSA_NAME_DEF_STMT (TREE_OPERAND (ret_var, 0)) = ret_var;
605 ret_var = TREE_OPERAND (ret_var, 0);
606 ret_stmt = build1 (RETURN_EXPR, TREE_TYPE (ret_stmt), ret_var);
607 bsi_insert_after (&bsi, ret_stmt, BSI_NEW_STMT);
612 stmt = build (MODIFY_EXPR, ret_type, NULL_TREE,
613 build (MULT_EXPR, ret_type, m_acc, ret_var));
615 tmp = create_tmp_var (ret_type, "acc_tmp");
616 add_referenced_tmp_var (tmp);
618 var = make_ssa_name (tmp, stmt);
619 TREE_OPERAND (stmt, 0) = var;
620 bsi_insert_before (&bsi, stmt, BSI_NEW_STMT);
627 stmt = build (MODIFY_EXPR, ret_type, NULL_TREE,
628 build (PLUS_EXPR, ret_type, a_acc, var));
630 tmp = create_tmp_var (ret_type, "acc_tmp");
631 add_referenced_tmp_var (tmp);
633 var = make_ssa_name (tmp, stmt);
634 TREE_OPERAND (stmt, 0) = var;
635 bsi_insert_before (&bsi, stmt, BSI_NEW_STMT);
638 TREE_OPERAND (ret_stmt, 0) = var;
639 modify_stmt (ret_stmt);
642 /* Eliminates tail call described by T. TMP_VARS is a list of
643 temporary variables used to copy the function arguments. */
646 eliminate_tail_call (struct tailcall *t)
648 tree param, stmt, args, rslt, call;
649 basic_block bb, first;
653 v_may_def_optype v_may_defs;
655 block_stmt_iterator bsi;
657 stmt = bsi_stmt (t->call_bsi);
658 get_stmt_operands (stmt);
659 ann = stmt_ann (stmt);
662 if (dump_file && (dump_flags & TDF_DETAILS))
664 fprintf (dump_file, "Eliminated tail recursion in bb %d : ",
666 print_generic_stmt (dump_file, stmt, TDF_SLIM);
667 fprintf (dump_file, "\n");
670 if (TREE_CODE (stmt) == MODIFY_EXPR)
671 stmt = TREE_OPERAND (stmt, 1);
673 first = ENTRY_BLOCK_PTR->succ->dest;
675 /* Remove the code after call_bsi that will become unreachable. The
676 possibly unreachable code in other blocks is removed later in
680 while (!bsi_end_p (bsi))
682 /* Do not remove the return statement, so that redirect_edge_and_branch
683 sees how the block ends. */
684 if (TREE_CODE (bsi_stmt (bsi)) == RETURN_EXPR)
690 /* Replace the call by a jump to the start of function. */
691 e = redirect_edge_and_branch (t->call_block->succ, first);
694 PENDING_STMT (e) = NULL_TREE;
696 /* Add phi node entries for arguments. Not every PHI node corresponds to
697 a function argument (there may be PHI nodes for virtual definitions of the
698 eliminated calls), so we search for a PHI corresponding to each argument
699 rather than searching for which argument a PHI node corresponds to. */
701 for (param = DECL_ARGUMENTS (current_function_decl),
702 args = TREE_OPERAND (stmt, 1);
704 param = TREE_CHAIN (param),
705 args = TREE_CHAIN (args))
708 for (phi = phi_nodes (first); phi; phi = PHI_CHAIN (phi))
709 if (param == SSA_NAME_VAR (PHI_RESULT (phi)))
712 /* The phi node indeed does not have to be there, in case the operand is
713 invariant in the function. */
717 add_phi_arg (&phi, TREE_VALUE (args), e);
720 /* Add phi nodes for the call clobbered variables. */
721 v_may_defs = V_MAY_DEF_OPS (ann);
722 for (i = 0; i < NUM_V_MAY_DEFS (v_may_defs); i++)
724 param = SSA_NAME_VAR (V_MAY_DEF_RESULT (v_may_defs, i));
725 for (phi = phi_nodes (first); phi; phi = PHI_CHAIN (phi))
726 if (param == SSA_NAME_VAR (PHI_RESULT (phi)))
731 tree name = var_ann (param)->default_def;
732 tree new_name = make_ssa_name (param, SSA_NAME_DEF_STMT (name));
734 var_ann (param)->default_def = new_name;
735 phi = create_phi_node (name, first);
736 SSA_NAME_DEF_STMT (name) = phi;
737 add_phi_arg (&phi, new_name, ENTRY_BLOCK_PTR->succ);
739 /* For all calls the same set of variables should be clobbered. This
740 means that there always should be the appropriate phi node except
741 for the first time we eliminate the call. */
742 if (first->pred->pred_next->pred_next)
746 add_phi_arg (&phi, V_MAY_DEF_OP (v_may_defs, i), e);
749 /* Update the values of accumulators. */
750 adjust_accumulator_values (t->call_bsi, t->mult, t->add, e);
752 call = bsi_stmt (t->call_bsi);
753 if (TREE_CODE (call) == MODIFY_EXPR)
755 rslt = TREE_OPERAND (call, 0);
757 /* Result of the call will no longer be defined. So adjust the
758 SSA_NAME_DEF_STMT accordingly. */
759 SSA_NAME_DEF_STMT (rslt) = build_empty_stmt ();
762 bsi_remove (&t->call_bsi);
765 /* Optimizes the tailcall described by T. If OPT_TAILCALLS is true, also
766 mark the tailcalls for the sibcall optimization. */
769 optimize_tail_call (struct tailcall *t, bool opt_tailcalls)
771 if (t->tail_recursion)
773 eliminate_tail_call (t);
779 tree stmt = bsi_stmt (t->call_bsi);
781 stmt = get_call_expr_in (stmt);
782 CALL_EXPR_TAILCALL (stmt) = 1;
783 if (dump_file && (dump_flags & TDF_DETAILS))
785 fprintf (dump_file, "Found tail call ");
786 print_generic_expr (dump_file, stmt, dump_flags);
787 fprintf (dump_file, " in bb %i\n", t->call_block->index);
794 /* Optimizes tail calls in the function, turning the tail recursion
798 tree_optimize_tail_calls_1 (bool opt_tailcalls)
801 bool phis_constructed = false;
802 struct tailcall *tailcalls = NULL, *act, *next;
803 bool changed = false;
804 basic_block first = ENTRY_BLOCK_PTR->succ->dest;
805 tree stmt, param, ret_type, tmp, phi;
807 if (!suitable_for_tail_opt_p ())
810 opt_tailcalls = suitable_for_tail_call_opt_p ();
812 for (e = EXIT_BLOCK_PTR->pred; e; e = e->pred_next)
814 /* Only traverse the normal exits, i.e. those that end with return
816 stmt = last_stmt (e->src);
819 && TREE_CODE (stmt) == RETURN_EXPR)
820 find_tail_calls (e->src, &tailcalls);
823 /* Construct the phi nodes and accumulators if necessary. */
824 a_acc = m_acc = NULL_TREE;
825 for (act = tailcalls; act; act = act->next)
827 if (!act->tail_recursion)
830 if (!phis_constructed)
832 /* Ensure that there is only one predecessor of the block. */
833 if (first->pred->pred_next)
834 first = split_edge (ENTRY_BLOCK_PTR->succ);
836 /* Copy the args if needed. */
837 for (param = DECL_ARGUMENTS (current_function_decl);
839 param = TREE_CHAIN (param))
841 /* Also parameters that are only defined but never used need not
843 && (var_ann (param)->default_def
844 && TREE_CODE (var_ann (param)->default_def) == SSA_NAME))
846 tree name = var_ann (param)->default_def;
847 tree new_name = make_ssa_name (param, SSA_NAME_DEF_STMT (name));
850 var_ann (param)->default_def = new_name;
851 phi = create_phi_node (name, first);
852 SSA_NAME_DEF_STMT (name) = phi;
853 add_phi_arg (&phi, new_name, first->pred);
855 phis_constructed = true;
858 if (act->add && !a_acc)
860 ret_type = TREE_TYPE (DECL_RESULT (current_function_decl));
862 tmp = create_tmp_var (ret_type, "add_acc");
863 add_referenced_tmp_var (tmp);
865 phi = create_phi_node (tmp, first);
866 add_phi_arg (&phi, fold_convert (ret_type, integer_zero_node),
868 a_acc = PHI_RESULT (phi);
871 if (act->mult && !m_acc)
873 ret_type = TREE_TYPE (DECL_RESULT (current_function_decl));
875 tmp = create_tmp_var (ret_type, "mult_acc");
876 add_referenced_tmp_var (tmp);
878 phi = create_phi_node (tmp, first);
879 add_phi_arg (&phi, fold_convert (ret_type, integer_one_node),
881 m_acc = PHI_RESULT (phi);
885 for (; tailcalls; tailcalls = next)
887 next = tailcalls->next;
888 changed |= optimize_tail_call (tailcalls, opt_tailcalls);
894 /* Modify the remaining return statements. */
895 for (e = EXIT_BLOCK_PTR->pred; e; e = e->pred_next)
897 stmt = last_stmt (e->src);
900 && TREE_CODE (stmt) == RETURN_EXPR)
901 adjust_return_value (e->src, m_acc, a_acc);
907 free_dominance_info (CDI_DOMINATORS);
913 execute_tail_recursion (void)
915 tree_optimize_tail_calls_1 (false);
919 gate_tail_calls (void)
921 return flag_optimize_sibling_calls != 0;
925 execute_tail_calls (void)
927 tree_optimize_tail_calls_1 (true);
930 struct tree_opt_pass pass_tail_recursion =
934 execute_tail_recursion, /* execute */
937 0, /* static_pass_number */
939 PROP_cfg | PROP_ssa, /* properties_required */
940 0, /* properties_provided */
941 0, /* properties_destroyed */
942 0, /* todo_flags_start */
943 TODO_dump_func | TODO_verify_ssa /* todo_flags_finish */
946 struct tree_opt_pass pass_tail_calls =
949 gate_tail_calls, /* gate */
950 execute_tail_calls, /* execute */
953 0, /* static_pass_number */
955 PROP_cfg | PROP_ssa, /* properties_required */
956 0, /* properties_provided */
957 0, /* properties_destroyed */
958 0, /* todo_flags_start */
959 TODO_dump_func | TODO_verify_ssa /* todo_flags_finish */