1 /* Tail call optimization on trees.
2 Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012
3 Free Software Foundation, Inc.
5 This file is part of GCC.
7 GCC is free software; you can redistribute it and/or modify
8 it under the terms of the GNU General Public License as published by
9 the Free Software Foundation; either version 3, or (at your option)
12 GCC is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 GNU General Public License for more details.
17 You should have received a copy of the GNU General Public License
18 along with GCC; see the file COPYING3. If not see
19 <http://www.gnu.org/licenses/>. */
23 #include "coretypes.h"
27 #include "basic-block.h"
29 #include "tree-flow.h"
30 #include "gimple-pretty-print.h"
32 #include "tree-pass.h"
34 #include "langhooks.h"
37 #include "common/common-target.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 iterator pointing to the call statement. */
104 gimple_stmt_iterator call_gsi
;
106 /* True if it is a call to the current function. */
109 /* The return value of the caller is mult * f + add, where f is the return
110 value of the call. */
113 /* Next tailcall in the chain. */
114 struct tailcall
*next
;
117 /* The variables holding the value of multiplicative and additive
119 static tree m_acc
, a_acc
;
121 static bool suitable_for_tail_opt_p (void);
122 static bool optimize_tail_call (struct tailcall
*, bool);
123 static void eliminate_tail_call (struct tailcall
*);
124 static void find_tail_calls (basic_block
, struct tailcall
**);
126 /* Returns false when the function is not suitable for tail call optimization
127 from some reason (e.g. if it takes variable number of arguments). */
130 suitable_for_tail_opt_p (void)
137 /* Returns false when the function is not suitable for tail call optimization
138 from some reason (e.g. if it takes variable number of arguments).
139 This test must pass in addition to suitable_for_tail_opt_p in order to make
140 tail call discovery happen. */
143 suitable_for_tail_call_opt_p (void)
147 /* alloca (until we have stack slot life analysis) inhibits
148 sibling call optimizations, but not tail recursion. */
149 if (cfun
->calls_alloca
)
152 /* If we are using sjlj exceptions, we may need to add a call to
153 _Unwind_SjLj_Unregister at exit of the function. Which means
154 that we cannot do any sibcall transformations. */
155 if (targetm_common
.except_unwind_info (&global_options
) == UI_SJLJ
156 && current_function_has_exception_handlers ())
159 /* Any function that calls setjmp might have longjmp called from
160 any called function. ??? We really should represent this
161 properly in the CFG so that this needn't be special cased. */
162 if (cfun
->calls_setjmp
)
165 /* ??? It is OK if the argument of a function is taken in some cases,
166 but not in all cases. See PR15387 and PR19616. Revisit for 4.1. */
167 for (param
= DECL_ARGUMENTS (current_function_decl
);
169 param
= DECL_CHAIN (param
))
170 if (TREE_ADDRESSABLE (param
))
176 /* Checks whether the expression EXPR in stmt AT is independent of the
177 statement pointed to by GSI (in a sense that we already know EXPR's value
178 at GSI). We use the fact that we are only called from the chain of
179 basic blocks that have only single successor. Returns the expression
180 containing the value of EXPR at GSI. */
183 independent_of_stmt_p (tree expr
, gimple at
, gimple_stmt_iterator gsi
)
185 basic_block bb
, call_bb
, at_bb
;
189 if (is_gimple_min_invariant (expr
))
192 if (TREE_CODE (expr
) != SSA_NAME
)
195 /* Mark the blocks in the chain leading to the end. */
196 at_bb
= gimple_bb (at
);
197 call_bb
= gimple_bb (gsi_stmt (gsi
));
198 for (bb
= call_bb
; bb
!= at_bb
; bb
= single_succ (bb
))
204 at
= SSA_NAME_DEF_STMT (expr
);
207 /* The default definition or defined before the chain. */
213 for (; !gsi_end_p (gsi
); gsi_next (&gsi
))
214 if (gsi_stmt (gsi
) == at
)
217 if (!gsi_end_p (gsi
))
222 if (gimple_code (at
) != GIMPLE_PHI
)
228 FOR_EACH_EDGE (e
, ei
, bb
->preds
)
233 expr
= PHI_ARG_DEF_FROM_EDGE (at
, e
);
234 if (TREE_CODE (expr
) != SSA_NAME
)
236 /* The value is a constant. */
241 /* Unmark the blocks. */
242 for (bb
= call_bb
; bb
!= at_bb
; bb
= single_succ (bb
))
249 /* Simulates the effect of an assignment STMT on the return value of the tail
250 recursive CALL passed in ASS_VAR. M and A are the multiplicative and the
251 additive factor for the real return value. */
254 process_assignment (gimple stmt
, gimple_stmt_iterator call
, tree
*m
,
255 tree
*a
, tree
*ass_var
)
257 tree op0
, op1
= NULL_TREE
, non_ass_var
= NULL_TREE
;
258 tree dest
= gimple_assign_lhs (stmt
);
259 enum tree_code code
= gimple_assign_rhs_code (stmt
);
260 enum gimple_rhs_class rhs_class
= get_gimple_rhs_class (code
);
261 tree src_var
= gimple_assign_rhs1 (stmt
);
263 /* See if this is a simple copy operation of an SSA name to the function
264 result. In that case we may have a simple tail call. Ignore type
265 conversions that can never produce extra code between the function
266 call and the function return. */
267 if ((rhs_class
== GIMPLE_SINGLE_RHS
|| gimple_assign_cast_p (stmt
))
268 && (TREE_CODE (src_var
) == SSA_NAME
))
270 /* Reject a tailcall if the type conversion might need
272 if (gimple_assign_cast_p (stmt
)
273 && TYPE_MODE (TREE_TYPE (dest
)) != TYPE_MODE (TREE_TYPE (src_var
)))
276 if (src_var
!= *ass_var
)
285 case GIMPLE_BINARY_RHS
:
286 op1
= gimple_assign_rhs2 (stmt
);
290 case GIMPLE_UNARY_RHS
:
291 op0
= gimple_assign_rhs1 (stmt
);
298 /* Accumulator optimizations will reverse the order of operations.
299 We can only do that for floating-point types if we're assuming
300 that addition and multiplication are associative. */
301 if (!flag_associative_math
)
302 if (FLOAT_TYPE_P (TREE_TYPE (DECL_RESULT (current_function_decl
))))
305 if (rhs_class
== GIMPLE_UNARY_RHS
)
307 else if (op0
== *ass_var
308 && (non_ass_var
= independent_of_stmt_p (op1
, stmt
, call
)))
310 else if (op1
== *ass_var
311 && (non_ass_var
= independent_of_stmt_p (op0
, stmt
, call
)))
329 if (FLOAT_TYPE_P (TREE_TYPE (op0
)))
330 *m
= build_real (TREE_TYPE (op0
), dconstm1
);
332 *m
= build_int_cst (TREE_TYPE (op0
), -1);
339 *a
= fold_build1 (NEGATE_EXPR
, TREE_TYPE (non_ass_var
), non_ass_var
);
342 if (FLOAT_TYPE_P (TREE_TYPE (non_ass_var
)))
343 *m
= build_real (TREE_TYPE (non_ass_var
), dconstm1
);
345 *m
= build_int_cst (TREE_TYPE (non_ass_var
), -1);
347 *a
= fold_build1 (NEGATE_EXPR
, TREE_TYPE (non_ass_var
), non_ass_var
);
353 /* TODO -- Handle POINTER_PLUS_EXPR. */
360 /* Propagate VAR through phis on edge E. */
363 propagate_through_phis (tree var
, edge e
)
365 basic_block dest
= e
->dest
;
366 gimple_stmt_iterator gsi
;
368 for (gsi
= gsi_start_phis (dest
); !gsi_end_p (gsi
); gsi_next (&gsi
))
370 gimple phi
= gsi_stmt (gsi
);
371 if (PHI_ARG_DEF_FROM_EDGE (phi
, e
) == var
)
372 return PHI_RESULT (phi
);
377 /* Finds tailcalls falling into basic block BB. The list of found tailcalls is
378 added to the start of RET. */
381 find_tail_calls (basic_block bb
, struct tailcall
**ret
)
383 tree ass_var
= NULL_TREE
, ret_var
, func
, param
;
384 gimple stmt
, call
= NULL
;
385 gimple_stmt_iterator gsi
, agsi
;
394 if (!single_succ_p (bb
))
397 for (gsi
= gsi_last_bb (bb
); !gsi_end_p (gsi
); gsi_prev (&gsi
))
399 stmt
= gsi_stmt (gsi
);
401 /* Ignore labels, returns, clobbers and debug stmts. */
402 if (gimple_code (stmt
) == GIMPLE_LABEL
403 || gimple_code (stmt
) == GIMPLE_RETURN
404 || gimple_clobber_p (stmt
)
405 || is_gimple_debug (stmt
))
408 /* Check for a call. */
409 if (is_gimple_call (stmt
))
412 ass_var
= gimple_call_lhs (stmt
);
416 /* If the statement references memory or volatile operands, fail. */
417 if (gimple_references_memory_p (stmt
)
418 || gimple_has_volatile_ops (stmt
))
425 /* Recurse to the predecessors. */
426 FOR_EACH_EDGE (e
, ei
, bb
->preds
)
427 find_tail_calls (e
->src
, ret
);
432 /* If the LHS of our call is not just a simple register, we can't
433 transform this into a tail or sibling call. This situation happens,
434 in (e.g.) "*p = foo()" where foo returns a struct. In this case
435 we won't have a temporary here, but we need to carry out the side
436 effect anyway, so tailcall is impossible.
438 ??? In some situations (when the struct is returned in memory via
439 invisible argument) we could deal with this, e.g. by passing 'p'
440 itself as that argument to foo, but it's too early to do this here,
441 and expand_call() will not handle it anyway. If it ever can, then
442 we need to revisit this here, to allow that situation. */
443 if (ass_var
&& !is_gimple_reg (ass_var
))
446 /* We found the call, check whether it is suitable. */
447 tail_recursion
= false;
448 func
= gimple_call_fndecl (call
);
449 if (func
== current_function_decl
)
453 for (param
= DECL_ARGUMENTS (func
), idx
= 0;
454 param
&& idx
< gimple_call_num_args (call
);
455 param
= DECL_CHAIN (param
), idx
++)
457 arg
= gimple_call_arg (call
, idx
);
460 /* Make sure there are no problems with copying. The parameter
461 have a copyable type and the two arguments must have reasonably
462 equivalent types. The latter requirement could be relaxed if
463 we emitted a suitable type conversion statement. */
464 if (!is_gimple_reg_type (TREE_TYPE (param
))
465 || !useless_type_conversion_p (TREE_TYPE (param
),
469 /* The parameter should be a real operand, so that phi node
470 created for it at the start of the function has the meaning
471 of copying the value. This test implies is_gimple_reg_type
472 from the previous condition, however this one could be
473 relaxed by being more careful with copying the new value
474 of the parameter (emitting appropriate GIMPLE_ASSIGN and
475 updating the virtual operands). */
476 if (!is_gimple_reg (param
))
480 if (idx
== gimple_call_num_args (call
) && !param
)
481 tail_recursion
= true;
484 /* Make sure the tail invocation of this function does not refer
485 to local variables. */
486 FOR_EACH_LOCAL_DECL (cfun
, idx
, var
)
488 if (TREE_CODE (var
) != PARM_DECL
489 && auto_var_in_fn_p (var
, cfun
->decl
)
490 && (ref_maybe_used_by_stmt_p (call
, var
)
491 || call_may_clobber_ref_p (call
, var
)))
495 /* Now check the statements after the call. None of them has virtual
496 operands, so they may only depend on the call through its return
497 value. The return value should also be dependent on each of them,
498 since we are running after dce. */
506 tree tmp_a
= NULL_TREE
;
507 tree tmp_m
= NULL_TREE
;
510 while (gsi_end_p (agsi
))
512 ass_var
= propagate_through_phis (ass_var
, single_succ_edge (abb
));
513 abb
= single_succ (abb
);
514 agsi
= gsi_start_bb (abb
);
517 stmt
= gsi_stmt (agsi
);
519 if (gimple_code (stmt
) == GIMPLE_LABEL
)
522 if (gimple_code (stmt
) == GIMPLE_RETURN
)
525 if (gimple_clobber_p (stmt
))
528 if (is_gimple_debug (stmt
))
531 if (gimple_code (stmt
) != GIMPLE_ASSIGN
)
534 /* This is a gimple assign. */
535 if (! process_assignment (stmt
, gsi
, &tmp_m
, &tmp_a
, &ass_var
))
540 tree type
= TREE_TYPE (tmp_a
);
542 a
= fold_build2 (PLUS_EXPR
, type
, fold_convert (type
, a
), tmp_a
);
548 tree type
= TREE_TYPE (tmp_m
);
550 m
= fold_build2 (MULT_EXPR
, type
, fold_convert (type
, m
), tmp_m
);
555 a
= fold_build2 (MULT_EXPR
, type
, fold_convert (type
, a
), tmp_m
);
559 /* See if this is a tail call we can handle. */
560 ret_var
= gimple_return_retval (stmt
);
562 /* We may proceed if there either is no return value, or the return value
563 is identical to the call's return. */
565 && (ret_var
!= ass_var
))
568 /* If this is not a tail recursive call, we cannot handle addends or
570 if (!tail_recursion
&& (m
|| a
))
573 nw
= XNEW (struct tailcall
);
577 nw
->tail_recursion
= tail_recursion
;
586 /* Helper to insert PHI_ARGH to the phi of VAR in the destination of edge E. */
589 add_successor_phi_arg (edge e
, tree var
, tree phi_arg
)
591 gimple_stmt_iterator gsi
;
593 for (gsi
= gsi_start_phis (e
->dest
); !gsi_end_p (gsi
); gsi_next (&gsi
))
594 if (PHI_RESULT (gsi_stmt (gsi
)) == var
)
597 gcc_assert (!gsi_end_p (gsi
));
598 add_phi_arg (gsi_stmt (gsi
), phi_arg
, e
, UNKNOWN_LOCATION
);
601 /* Creates a GIMPLE statement which computes the operation specified by
602 CODE, OP0 and OP1 to a new variable with name LABEL and inserts the
603 statement in the position specified by GSI and UPDATE. Returns the
604 tree node of the statement's result. */
607 adjust_return_value_with_ops (enum tree_code code
, const char *label
,
608 tree acc
, tree op1
, gimple_stmt_iterator gsi
)
611 tree ret_type
= TREE_TYPE (DECL_RESULT (current_function_decl
));
612 tree tmp
= create_tmp_reg (ret_type
, label
);
616 if (types_compatible_p (TREE_TYPE (acc
), TREE_TYPE (op1
)))
617 stmt
= gimple_build_assign_with_ops (code
, tmp
, acc
, op1
);
620 tree rhs
= fold_convert (TREE_TYPE (acc
),
623 fold_convert (TREE_TYPE (op1
), acc
),
625 rhs
= force_gimple_operand_gsi (&gsi
, rhs
,
626 false, NULL
, true, GSI_CONTINUE_LINKING
);
627 stmt
= gimple_build_assign (NULL_TREE
, rhs
);
630 result
= make_ssa_name (tmp
, stmt
);
631 gimple_assign_set_lhs (stmt
, result
);
633 gsi_insert_before (&gsi
, stmt
, GSI_NEW_STMT
);
637 /* Creates a new GIMPLE statement that adjusts the value of accumulator ACC by
638 the computation specified by CODE and OP1 and insert the statement
639 at the position specified by GSI as a new statement. Returns new SSA name
640 of updated accumulator. */
643 update_accumulator_with_ops (enum tree_code code
, tree acc
, tree op1
,
644 gimple_stmt_iterator gsi
)
648 if (types_compatible_p (TREE_TYPE (acc
), TREE_TYPE (op1
)))
649 stmt
= gimple_build_assign_with_ops (code
, SSA_NAME_VAR (acc
), acc
, op1
);
652 tree rhs
= fold_convert (TREE_TYPE (acc
),
655 fold_convert (TREE_TYPE (op1
), acc
),
657 rhs
= force_gimple_operand_gsi (&gsi
, rhs
,
658 false, NULL
, false, GSI_CONTINUE_LINKING
);
659 stmt
= gimple_build_assign (NULL_TREE
, rhs
);
661 var
= make_ssa_name (SSA_NAME_VAR (acc
), stmt
);
662 gimple_assign_set_lhs (stmt
, var
);
664 gsi_insert_after (&gsi
, stmt
, GSI_NEW_STMT
);
668 /* Adjust the accumulator values according to A and M after GSI, and update
669 the phi nodes on edge BACK. */
672 adjust_accumulator_values (gimple_stmt_iterator gsi
, tree m
, tree a
, edge back
)
674 tree var
, a_acc_arg
, m_acc_arg
;
677 m
= force_gimple_operand_gsi (&gsi
, m
, true, NULL
, true, GSI_SAME_STMT
);
679 a
= force_gimple_operand_gsi (&gsi
, a
, true, NULL
, true, GSI_SAME_STMT
);
687 if (integer_onep (a
))
690 var
= adjust_return_value_with_ops (MULT_EXPR
, "acc_tmp", m_acc
,
696 a_acc_arg
= update_accumulator_with_ops (PLUS_EXPR
, a_acc
, var
, gsi
);
700 m_acc_arg
= update_accumulator_with_ops (MULT_EXPR
, m_acc
, m
, gsi
);
703 add_successor_phi_arg (back
, a_acc
, a_acc_arg
);
706 add_successor_phi_arg (back
, m_acc
, m_acc_arg
);
709 /* Adjust value of the return at the end of BB according to M and A
713 adjust_return_value (basic_block bb
, tree m
, tree a
)
716 gimple ret_stmt
= gimple_seq_last_stmt (bb_seq (bb
));
717 gimple_stmt_iterator gsi
= gsi_last_bb (bb
);
719 gcc_assert (gimple_code (ret_stmt
) == GIMPLE_RETURN
);
721 retval
= gimple_return_retval (ret_stmt
);
722 if (!retval
|| retval
== error_mark_node
)
726 retval
= adjust_return_value_with_ops (MULT_EXPR
, "mul_tmp", m_acc
, retval
,
729 retval
= adjust_return_value_with_ops (PLUS_EXPR
, "acc_tmp", a_acc
, retval
,
731 gimple_return_set_retval (ret_stmt
, retval
);
732 update_stmt (ret_stmt
);
735 /* Subtract COUNT and FREQUENCY from the basic block and it's
738 decrease_profile (basic_block bb
, gcov_type count
, int frequency
)
744 bb
->frequency
-= frequency
;
745 if (bb
->frequency
< 0)
747 if (!single_succ_p (bb
))
749 gcc_assert (!EDGE_COUNT (bb
->succs
));
752 e
= single_succ_edge (bb
);
758 /* Returns true if argument PARAM of the tail recursive call needs to be copied
759 when the call is eliminated. */
762 arg_needs_copy_p (tree param
)
766 if (!is_gimple_reg (param
))
769 /* Parameters that are only defined but never used need not be copied. */
770 def
= ssa_default_def (cfun
, param
);
777 /* Eliminates tail call described by T. TMP_VARS is a list of
778 temporary variables used to copy the function arguments. */
781 eliminate_tail_call (struct tailcall
*t
)
787 basic_block bb
, first
;
790 gimple_stmt_iterator gsi
;
793 stmt
= orig_stmt
= gsi_stmt (t
->call_gsi
);
794 bb
= gsi_bb (t
->call_gsi
);
796 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
798 fprintf (dump_file
, "Eliminated tail recursion in bb %d : ",
800 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
801 fprintf (dump_file
, "\n");
804 gcc_assert (is_gimple_call (stmt
));
806 first
= single_succ (ENTRY_BLOCK_PTR
);
808 /* Remove the code after call_gsi that will become unreachable. The
809 possibly unreachable code in other blocks is removed later in
813 while (!gsi_end_p (gsi
))
815 gimple t
= gsi_stmt (gsi
);
816 /* Do not remove the return statement, so that redirect_edge_and_branch
817 sees how the block ends. */
818 if (gimple_code (t
) == GIMPLE_RETURN
)
821 gsi_remove (&gsi
, true);
825 /* Number of executions of function has reduced by the tailcall. */
826 e
= single_succ_edge (gsi_bb (t
->call_gsi
));
827 decrease_profile (EXIT_BLOCK_PTR
, e
->count
, EDGE_FREQUENCY (e
));
828 decrease_profile (ENTRY_BLOCK_PTR
, e
->count
, EDGE_FREQUENCY (e
));
829 if (e
->dest
!= EXIT_BLOCK_PTR
)
830 decrease_profile (e
->dest
, e
->count
, EDGE_FREQUENCY (e
));
832 /* Replace the call by a jump to the start of function. */
833 e
= redirect_edge_and_branch (single_succ_edge (gsi_bb (t
->call_gsi
)),
836 PENDING_STMT (e
) = NULL
;
838 /* Add phi node entries for arguments. The ordering of the phi nodes should
839 be the same as the ordering of the arguments. */
840 for (param
= DECL_ARGUMENTS (current_function_decl
),
841 idx
= 0, gsi
= gsi_start_phis (first
);
843 param
= DECL_CHAIN (param
), idx
++)
845 if (!arg_needs_copy_p (param
))
848 arg
= gimple_call_arg (stmt
, idx
);
849 phi
= gsi_stmt (gsi
);
850 gcc_assert (param
== SSA_NAME_VAR (PHI_RESULT (phi
)));
852 add_phi_arg (phi
, arg
, e
, gimple_location (stmt
));
856 /* Update the values of accumulators. */
857 adjust_accumulator_values (t
->call_gsi
, t
->mult
, t
->add
, e
);
859 call
= gsi_stmt (t
->call_gsi
);
860 rslt
= gimple_call_lhs (call
);
861 if (rslt
!= NULL_TREE
)
863 /* Result of the call will no longer be defined. So adjust the
864 SSA_NAME_DEF_STMT accordingly. */
865 SSA_NAME_DEF_STMT (rslt
) = gimple_build_nop ();
868 gsi_remove (&t
->call_gsi
, true);
872 /* Optimizes the tailcall described by T. If OPT_TAILCALLS is true, also
873 mark the tailcalls for the sibcall optimization. */
876 optimize_tail_call (struct tailcall
*t
, bool opt_tailcalls
)
878 if (t
->tail_recursion
)
880 eliminate_tail_call (t
);
886 gimple stmt
= gsi_stmt (t
->call_gsi
);
888 gimple_call_set_tail (stmt
, true);
889 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
891 fprintf (dump_file
, "Found tail call ");
892 print_gimple_stmt (dump_file
, stmt
, 0, dump_flags
);
893 fprintf (dump_file
, " in bb %i\n", (gsi_bb (t
->call_gsi
))->index
);
900 /* Creates a tail-call accumulator of the same type as the return type of the
901 current function. LABEL is the name used to creating the temporary
902 variable for the accumulator. The accumulator will be inserted in the
903 phis of a basic block BB with single predecessor with an initial value
904 INIT converted to the current function return type. */
907 create_tailcall_accumulator (const char *label
, basic_block bb
, tree init
)
909 tree ret_type
= TREE_TYPE (DECL_RESULT (current_function_decl
));
910 tree tmp
= create_tmp_reg (ret_type
, label
);
913 phi
= create_phi_node (tmp
, bb
);
914 /* RET_TYPE can be a float when -ffast-maths is enabled. */
915 add_phi_arg (phi
, fold_convert (ret_type
, init
), single_pred_edge (bb
),
917 return PHI_RESULT (phi
);
920 /* Optimizes tail calls in the function, turning the tail recursion
924 tree_optimize_tail_calls_1 (bool opt_tailcalls
)
927 bool phis_constructed
= false;
928 struct tailcall
*tailcalls
= NULL
, *act
, *next
;
929 bool changed
= false;
930 basic_block first
= single_succ (ENTRY_BLOCK_PTR
);
935 if (!suitable_for_tail_opt_p ())
938 opt_tailcalls
= suitable_for_tail_call_opt_p ();
940 FOR_EACH_EDGE (e
, ei
, EXIT_BLOCK_PTR
->preds
)
942 /* Only traverse the normal exits, i.e. those that end with return
944 stmt
= last_stmt (e
->src
);
947 && gimple_code (stmt
) == GIMPLE_RETURN
)
948 find_tail_calls (e
->src
, &tailcalls
);
951 /* Construct the phi nodes and accumulators if necessary. */
952 a_acc
= m_acc
= NULL_TREE
;
953 for (act
= tailcalls
; act
; act
= act
->next
)
955 if (!act
->tail_recursion
)
958 if (!phis_constructed
)
960 /* Ensure that there is only one predecessor of the block
961 or if there are existing degenerate PHI nodes. */
962 if (!single_pred_p (first
)
963 || !gimple_seq_empty_p (phi_nodes (first
)))
964 first
= split_edge (single_succ_edge (ENTRY_BLOCK_PTR
));
966 /* Copy the args if needed. */
967 for (param
= DECL_ARGUMENTS (current_function_decl
);
969 param
= DECL_CHAIN (param
))
970 if (arg_needs_copy_p (param
))
972 tree name
= ssa_default_def (cfun
, param
);
973 tree new_name
= make_ssa_name (param
, SSA_NAME_DEF_STMT (name
));
976 set_ssa_default_def (cfun
, param
, new_name
);
977 phi
= create_phi_node (name
, first
);
978 add_phi_arg (phi
, new_name
, single_pred_edge (first
),
979 EXPR_LOCATION (param
));
981 phis_constructed
= true;
984 if (act
->add
&& !a_acc
)
985 a_acc
= create_tailcall_accumulator ("add_acc", first
,
988 if (act
->mult
&& !m_acc
)
989 m_acc
= create_tailcall_accumulator ("mult_acc", first
,
995 /* When the tail call elimination using accumulators is performed,
996 statements adding the accumulated value are inserted at all exits.
997 This turns all other tail calls to non-tail ones. */
998 opt_tailcalls
= false;
1001 for (; tailcalls
; tailcalls
= next
)
1003 next
= tailcalls
->next
;
1004 changed
|= optimize_tail_call (tailcalls
, opt_tailcalls
);
1010 /* Modify the remaining return statements. */
1011 FOR_EACH_EDGE (e
, ei
, EXIT_BLOCK_PTR
->preds
)
1013 stmt
= last_stmt (e
->src
);
1016 && gimple_code (stmt
) == GIMPLE_RETURN
)
1017 adjust_return_value (e
->src
, m_acc
, a_acc
);
1022 free_dominance_info (CDI_DOMINATORS
);
1024 /* Add phi nodes for the virtual operands defined in the function to the
1025 header of the loop created by tail recursion elimination. Do so
1026 by triggering the SSA renamer. */
1027 if (phis_constructed
)
1028 mark_virtual_operands_for_renaming (cfun
);
1031 return TODO_cleanup_cfg
| TODO_update_ssa_only_virtuals
;
1036 execute_tail_recursion (void)
1038 return tree_optimize_tail_calls_1 (false);
1042 gate_tail_calls (void)
1044 return flag_optimize_sibling_calls
!= 0 && dbg_cnt (tail_call
);
1048 execute_tail_calls (void)
1050 return tree_optimize_tail_calls_1 (true);
1053 struct gimple_opt_pass pass_tail_recursion
=
1058 gate_tail_calls
, /* gate */
1059 execute_tail_recursion
, /* execute */
1062 0, /* static_pass_number */
1063 TV_NONE
, /* tv_id */
1064 PROP_cfg
| PROP_ssa
, /* properties_required */
1065 0, /* properties_provided */
1066 0, /* properties_destroyed */
1067 0, /* todo_flags_start */
1068 TODO_verify_ssa
/* todo_flags_finish */
1072 struct gimple_opt_pass pass_tail_calls
=
1077 gate_tail_calls
, /* gate */
1078 execute_tail_calls
, /* execute */
1081 0, /* static_pass_number */
1082 TV_NONE
, /* tv_id */
1083 PROP_cfg
| PROP_ssa
, /* properties_required */
1084 0, /* properties_provided */
1085 0, /* properties_destroyed */
1086 0, /* todo_flags_start */
1087 TODO_verify_ssa
/* todo_flags_finish */