2 Copyright (C) 2015-2022 Free Software Foundation, Inc.
4 This file is part of GCC.
6 GCC is free software; you can redistribute it and/or modify it
7 under the terms of the GNU General Public License as published by the
8 Free Software Foundation; either version 3, or (at your option) any
11 GCC is distributed in the hope that it will be useful, but WITHOUT
12 ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
16 You should have received a copy of the GNU General Public License
17 along with GCC; see the file COPYING3. If not see
18 <http://www.gnu.org/licenses/>. */
22 #include "coretypes.h"
26 #include "tree-pass.h"
28 #include "fold-const.h"
31 #include "tree-ssa-loop-niter.h"
32 #include "tree-ssa-loop.h"
33 #include "tree-ssa-loop-manip.h"
34 #include "tree-into-ssa.h"
35 #include "tree-inline.h"
36 #include "tree-cfgcleanup.h"
38 #include "tree-scalar-evolution.h"
39 #include "gimple-iterator.h"
40 #include "gimple-pretty-print.h"
42 #include "gimple-fold.h"
43 #include "gimplify-me.h"
45 /* This file implements two kinds of loop splitting.
47 One transformation of loops like:
49 for (i = 0; i < 100; i++)
59 for (i = 0; i < 50; i++)
70 /* Return true when BB inside LOOP is a potential iteration space
71 split point, i.e. ends with a condition like "IV < comp", which
72 is true on one side of the iteration space and false on the other,
73 and the split point can be computed. If so, also return the border
74 point in *BORDER and the comparison induction variable in IV. */
77 split_at_bb_p (class loop
*loop
, basic_block bb
, tree
*border
, affine_iv
*iv
)
83 /* BB must end in a simple conditional jump. */
84 last
= last_stmt (bb
);
85 if (!last
|| gimple_code (last
) != GIMPLE_COND
)
87 stmt
= as_a
<gcond
*> (last
);
89 enum tree_code code
= gimple_cond_code (stmt
);
91 /* Only handle relational comparisons, for equality and non-equality
92 we'd have to split the loop into two loops and a middle statement. */
104 if (loop_exits_from_bb_p (loop
, bb
))
107 tree op0
= gimple_cond_lhs (stmt
);
108 tree op1
= gimple_cond_rhs (stmt
);
109 class loop
*useloop
= loop_containing_stmt (stmt
);
111 if (!simple_iv (loop
, useloop
, op0
, iv
, false))
113 if (!simple_iv (loop
, useloop
, op1
, &iv2
, false))
116 /* Make it so that the first argument of the condition is
118 if (!integer_zerop (iv2
.step
))
120 std::swap (op0
, op1
);
121 std::swap (*iv
, iv2
);
122 code
= swap_tree_comparison (code
);
123 gimple_cond_set_condition (stmt
, code
, op0
, op1
);
126 else if (integer_zerop (iv
->step
))
128 if (!integer_zerop (iv2
.step
))
130 if (!iv
->no_overflow
)
133 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
135 fprintf (dump_file
, "Found potential split point: ");
136 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
137 fprintf (dump_file
, " { ");
138 print_generic_expr (dump_file
, iv
->base
, TDF_SLIM
);
139 fprintf (dump_file
, " + I*");
140 print_generic_expr (dump_file
, iv
->step
, TDF_SLIM
);
141 fprintf (dump_file
, " } %s ", get_tree_code_name (code
));
142 print_generic_expr (dump_file
, iv2
.base
, TDF_SLIM
);
143 fprintf (dump_file
, "\n");
150 /* Given a GUARD conditional stmt inside LOOP, which we want to make always
151 true or false depending on INITIAL_TRUE, and adjusted values NEXTVAL
152 (a post-increment IV) and NEWBOUND (the comparator) adjust the loop
153 exit test statement to loop back only if the GUARD statement will
154 also be true/false in the next iteration. */
157 patch_loop_exit (class loop
*loop
, gcond
*guard
, tree nextval
, tree newbound
,
160 edge exit
= single_exit (loop
);
161 gcond
*stmt
= as_a
<gcond
*> (last_stmt (exit
->src
));
162 gimple_cond_set_condition (stmt
, gimple_cond_code (guard
),
166 edge stay
= EDGE_SUCC (exit
->src
, EDGE_SUCC (exit
->src
, 0) == exit
);
168 exit
->flags
&= ~(EDGE_TRUE_VALUE
| EDGE_FALSE_VALUE
);
169 stay
->flags
&= ~(EDGE_TRUE_VALUE
| EDGE_FALSE_VALUE
);
173 exit
->flags
|= EDGE_FALSE_VALUE
;
174 stay
->flags
|= EDGE_TRUE_VALUE
;
178 exit
->flags
|= EDGE_TRUE_VALUE
;
179 stay
->flags
|= EDGE_FALSE_VALUE
;
183 /* Give an induction variable GUARD_IV, and its affine descriptor IV,
184 find the loop phi node in LOOP defining it directly, or create
185 such phi node. Return that phi node. */
188 find_or_create_guard_phi (class loop
*loop
, tree guard_iv
, affine_iv
* /*iv*/)
190 gimple
*def
= SSA_NAME_DEF_STMT (guard_iv
);
192 if ((phi
= dyn_cast
<gphi
*> (def
))
193 && gimple_bb (phi
) == loop
->header
)
196 /* XXX Create the PHI instead. */
200 /* Returns true if the exit values of all loop phi nodes can be
201 determined easily (i.e. that connect_loop_phis can determine them). */
204 easy_exit_values (class loop
*loop
)
206 edge exit
= single_exit (loop
);
207 edge latch
= loop_latch_edge (loop
);
210 /* Currently we regard the exit values as easy if they are the same
211 as the value over the backedge. Which is the case if the definition
212 of the backedge value dominates the exit edge. */
213 for (psi
= gsi_start_phis (loop
->header
); !gsi_end_p (psi
); gsi_next (&psi
))
215 gphi
*phi
= psi
.phi ();
216 tree next
= PHI_ARG_DEF_FROM_EDGE (phi
, latch
);
218 if (TREE_CODE (next
) == SSA_NAME
219 && (bb
= gimple_bb (SSA_NAME_DEF_STMT (next
)))
220 && !dominated_by_p (CDI_DOMINATORS
, exit
->src
, bb
))
227 /* This function updates the SSA form after connect_loops made a new
228 edge NEW_E leading from LOOP1 exit to LOOP2 (via in intermediate
229 conditional). I.e. the second loop can now be entered either
230 via the original entry or via NEW_E, so the entry values of LOOP2
231 phi nodes are either the original ones or those at the exit
232 of LOOP1. Insert new phi nodes in LOOP2 pre-header reflecting
233 this. The loops need to fulfill easy_exit_values(). */
236 connect_loop_phis (class loop
*loop1
, class loop
*loop2
, edge new_e
)
238 basic_block rest
= loop_preheader_edge (loop2
)->src
;
239 gcc_assert (new_e
->dest
== rest
);
240 edge skip_first
= EDGE_PRED (rest
, EDGE_PRED (rest
, 0) == new_e
);
242 edge firste
= loop_preheader_edge (loop1
);
243 edge seconde
= loop_preheader_edge (loop2
);
244 edge firstn
= loop_latch_edge (loop1
);
245 gphi_iterator psi_first
, psi_second
;
246 for (psi_first
= gsi_start_phis (loop1
->header
),
247 psi_second
= gsi_start_phis (loop2
->header
);
248 !gsi_end_p (psi_first
);
249 gsi_next (&psi_first
), gsi_next (&psi_second
))
251 tree init
, next
, new_init
;
253 gphi
*phi_first
= psi_first
.phi ();
254 gphi
*phi_second
= psi_second
.phi ();
256 init
= PHI_ARG_DEF_FROM_EDGE (phi_first
, firste
);
257 next
= PHI_ARG_DEF_FROM_EDGE (phi_first
, firstn
);
258 op
= PHI_ARG_DEF_PTR_FROM_EDGE (phi_second
, seconde
);
259 gcc_assert (operand_equal_for_phi_arg_p (init
, USE_FROM_PTR (op
)));
261 /* Prefer using original variable as a base for the new ssa name.
262 This is necessary for virtual ops, and useful in order to avoid
263 losing debug info for real ops. */
264 if (TREE_CODE (next
) == SSA_NAME
265 && useless_type_conversion_p (TREE_TYPE (next
),
267 new_init
= copy_ssa_name (next
);
268 else if (TREE_CODE (init
) == SSA_NAME
269 && useless_type_conversion_p (TREE_TYPE (init
),
271 new_init
= copy_ssa_name (init
);
272 else if (useless_type_conversion_p (TREE_TYPE (next
),
274 new_init
= make_temp_ssa_name (TREE_TYPE (next
), NULL
,
277 new_init
= make_temp_ssa_name (TREE_TYPE (init
), NULL
,
280 gphi
* newphi
= create_phi_node (new_init
, rest
);
281 add_phi_arg (newphi
, init
, skip_first
, UNKNOWN_LOCATION
);
282 add_phi_arg (newphi
, next
, new_e
, UNKNOWN_LOCATION
);
283 SET_USE (op
, new_init
);
287 /* The two loops LOOP1 and LOOP2 were just created by loop versioning,
288 they are still equivalent and placed in two arms of a diamond, like so:
290 .------if (cond)------.
303 This function transforms the program such that LOOP1 is conditionally
304 falling through to LOOP2, or skipping it. This is done by splitting
305 the ex1->join edge at X in the diagram above, and inserting a condition
306 whose one arm goes to pre2, resulting in this situation:
308 .------if (cond)------.
310 pre1 .---------->pre2
314 | ex1---. | .---ex2 |
316 '---l1 skip---' | l2---'
322 The condition used is the exit condition of LOOP1, which effectively means
323 that when the first loop exits (for whatever reason) but the real original
324 exit expression is still false the second loop will be entered.
325 The function returns the new edge cond->pre2.
327 This doesn't update the SSA form, see connect_loop_phis for that. */
330 connect_loops (class loop
*loop1
, class loop
*loop2
)
332 edge exit
= single_exit (loop1
);
333 basic_block skip_bb
= split_edge (exit
);
335 gimple_stmt_iterator gsi
;
338 gimple
*stmt
= last_stmt (exit
->src
);
339 skip_stmt
= gimple_build_cond (gimple_cond_code (stmt
),
340 gimple_cond_lhs (stmt
),
341 gimple_cond_rhs (stmt
),
342 NULL_TREE
, NULL_TREE
);
343 gsi
= gsi_last_bb (skip_bb
);
344 gsi_insert_after (&gsi
, skip_stmt
, GSI_NEW_STMT
);
346 skip_e
= EDGE_SUCC (skip_bb
, 0);
347 skip_e
->flags
&= ~EDGE_FALLTHRU
;
348 new_e
= make_edge (skip_bb
, loop_preheader_edge (loop2
)->src
, 0);
349 if (exit
->flags
& EDGE_TRUE_VALUE
)
351 skip_e
->flags
|= EDGE_TRUE_VALUE
;
352 new_e
->flags
|= EDGE_FALSE_VALUE
;
356 skip_e
->flags
|= EDGE_FALSE_VALUE
;
357 new_e
->flags
|= EDGE_TRUE_VALUE
;
360 new_e
->probability
= profile_probability::likely ();
361 skip_e
->probability
= new_e
->probability
.invert ();
366 /* This returns the new bound for iterations given the original iteration
367 space in NITER, an arbitrary new bound BORDER, assumed to be some
368 comparison value with a different IV, the initial value GUARD_INIT of
369 that other IV, and the comparison code GUARD_CODE that compares
370 that other IV with BORDER. We return an SSA name, and place any
371 necessary statements for that computation into *STMTS.
373 For example for such a loop:
375 for (i = beg, j = guard_init; i < end; i++, j++)
376 if (j < border) // this is supposed to be true/false
379 we want to return a new bound (on j) that makes the loop iterate
380 as long as the condition j < border stays true. We also don't want
381 to iterate more often than the original loop, so we have to introduce
382 some cut-off as well (via min/max), effectively resulting in:
384 newend = min (end+guard_init-beg, border)
385 for (i = beg; j = guard_init; j < newend; i++, j++)
389 Depending on the direction of the IVs and if the exit tests
390 are strict or non-strict we need to use MIN or MAX,
391 and add or subtract 1. This routine computes newend above. */
394 compute_new_first_bound (gimple_seq
*stmts
, class tree_niter_desc
*niter
,
396 enum tree_code guard_code
, tree guard_init
)
398 /* The niter structure contains the after-increment IV, we need
399 the loop-enter base, so subtract STEP once. */
400 tree controlbase
= force_gimple_operand (niter
->control
.base
,
401 stmts
, true, NULL_TREE
);
402 tree controlstep
= niter
->control
.step
;
404 if (POINTER_TYPE_P (TREE_TYPE (controlbase
)))
406 controlstep
= gimple_build (stmts
, NEGATE_EXPR
,
407 TREE_TYPE (controlstep
), controlstep
);
408 enddiff
= gimple_build (stmts
, POINTER_PLUS_EXPR
,
409 TREE_TYPE (controlbase
),
410 controlbase
, controlstep
);
413 enddiff
= gimple_build (stmts
, MINUS_EXPR
,
414 TREE_TYPE (controlbase
),
415 controlbase
, controlstep
);
417 /* Compute end-beg. */
419 tree end
= force_gimple_operand (niter
->bound
, &stmts2
,
421 gimple_seq_add_seq_without_update (stmts
, stmts2
);
422 if (POINTER_TYPE_P (TREE_TYPE (enddiff
)))
424 tree tem
= gimple_convert (stmts
, sizetype
, enddiff
);
425 tem
= gimple_build (stmts
, NEGATE_EXPR
, sizetype
, tem
);
426 enddiff
= gimple_build (stmts
, POINTER_PLUS_EXPR
,
431 enddiff
= gimple_build (stmts
, MINUS_EXPR
, TREE_TYPE (enddiff
),
434 /* Compute guard_init + (end-beg). */
436 enddiff
= gimple_convert (stmts
, TREE_TYPE (guard_init
), enddiff
);
437 if (POINTER_TYPE_P (TREE_TYPE (guard_init
)))
439 enddiff
= gimple_convert (stmts
, sizetype
, enddiff
);
440 newbound
= gimple_build (stmts
, POINTER_PLUS_EXPR
,
441 TREE_TYPE (guard_init
),
442 guard_init
, enddiff
);
445 newbound
= gimple_build (stmts
, PLUS_EXPR
, TREE_TYPE (guard_init
),
446 guard_init
, enddiff
);
448 /* Depending on the direction of the IVs the new bound for the first
449 loop is the minimum or maximum of old bound and border.
450 Also, if the guard condition isn't strictly less or greater,
451 we need to adjust the bound. */
453 enum tree_code minmax
;
454 if (niter
->cmp
== LT_EXPR
)
456 /* GT and LE are the same, inverted. */
457 if (guard_code
== GT_EXPR
|| guard_code
== LE_EXPR
)
463 gcc_assert (niter
->cmp
== GT_EXPR
);
464 if (guard_code
== GE_EXPR
|| guard_code
== LT_EXPR
)
471 tree type2
= TREE_TYPE (newbound
);
472 if (POINTER_TYPE_P (type2
))
474 newbound
= gimple_build (stmts
,
475 POINTER_TYPE_P (TREE_TYPE (newbound
))
476 ? POINTER_PLUS_EXPR
: PLUS_EXPR
,
477 TREE_TYPE (newbound
),
479 build_int_cst (type2
, addbound
));
482 tree newend
= gimple_build (stmts
, minmax
, TREE_TYPE (border
),
487 /* Fix the two loop's bb count after split based on the split edge probability,
488 don't adjust the bbs dominated by true branches of that loop to avoid
491 fix_loop_bb_probability (class loop
*loop1
, class loop
*loop2
, edge true_edge
,
494 update_ssa (TODO_update_ssa
);
496 /* Proportion first loop's bb counts except those dominated by true
497 branch to avoid drop 1s down. */
498 basic_block
*bbs1
, *bbs2
;
499 bbs1
= get_loop_body (loop1
);
501 for (j
= 0; j
< loop1
->num_nodes
; j
++)
502 if (bbs1
[j
] == loop1
->latch
503 || !dominated_by_p (CDI_DOMINATORS
, bbs1
[j
], true_edge
->dest
))
505 = bbs1
[j
]->count
.apply_probability (true_edge
->probability
);
508 /* Proportion second loop's bb counts except those dominated by false
509 branch to avoid drop 1s down. */
510 basic_block bbi_copy
= get_bb_copy (false_edge
->dest
);
511 bbs2
= get_loop_body (loop2
);
512 for (j
= 0; j
< loop2
->num_nodes
; j
++)
513 if (bbs2
[j
] == loop2
->latch
514 || !dominated_by_p (CDI_DOMINATORS
, bbs2
[j
], bbi_copy
))
516 = bbs2
[j
]->count
.apply_probability (true_edge
->probability
.invert ());
520 /* Checks if LOOP contains an conditional block whose condition
521 depends on which side in the iteration space it is, and if so
522 splits the iteration space into two loops. Returns true if the
523 loop was split. NITER must contain the iteration descriptor for the
524 single exit of LOOP. */
527 split_loop (class loop
*loop1
)
529 class tree_niter_desc niter
;
532 bool changed
= false;
534 tree border
= NULL_TREE
;
537 if (!single_exit (loop1
)
538 /* ??? We could handle non-empty latches when we split the latch edge
539 (not the exit edge), and put the new exit condition in the new block.
540 OTOH this executes some code unconditionally that might have been
541 skipped by the original exit before. */
542 || !empty_block_p (loop1
->latch
)
543 || !easy_exit_values (loop1
)
544 || !number_of_iterations_exit (loop1
, single_exit (loop1
), &niter
,
546 || niter
.cmp
== ERROR_MARK
547 /* We can't yet handle loops controlled by a != predicate. */
548 || niter
.cmp
== NE_EXPR
)
551 bbs
= get_loop_body (loop1
);
553 if (!can_copy_bbs_p (bbs
, loop1
->num_nodes
))
559 /* Find a splitting opportunity. */
560 for (i
= 0; i
< loop1
->num_nodes
; i
++)
561 if ((guard_iv
= split_at_bb_p (loop1
, bbs
[i
], &border
, &iv
)))
563 /* Handling opposite steps is not implemented yet. Neither
564 is handling different step sizes. */
565 if ((tree_int_cst_sign_bit (iv
.step
)
566 != tree_int_cst_sign_bit (niter
.control
.step
))
567 || !tree_int_cst_equal (iv
.step
, niter
.control
.step
))
570 /* Find a loop PHI node that defines guard_iv directly,
571 or create one doing that. */
572 gphi
*phi
= find_or_create_guard_phi (loop1
, guard_iv
, &iv
);
575 gcond
*guard_stmt
= as_a
<gcond
*> (last_stmt (bbs
[i
]));
576 tree guard_init
= PHI_ARG_DEF_FROM_EDGE (phi
,
577 loop_preheader_edge (loop1
));
578 enum tree_code guard_code
= gimple_cond_code (guard_stmt
);
580 /* Loop splitting is implemented by versioning the loop, placing
581 the new loop after the old loop, make the first loop iterate
582 as long as the conditional stays true (or false) and let the
583 second (new) loop handle the rest of the iterations.
585 First we need to determine if the condition will start being true
586 or false in the first loop. */
592 initial_true
= !tree_int_cst_sign_bit (iv
.step
);
596 initial_true
= tree_int_cst_sign_bit (iv
.step
);
602 /* Build a condition that will skip the first loop when the
603 guard condition won't ever be true (or false). */
605 border
= force_gimple_operand (border
, &stmts2
, true, NULL_TREE
);
607 gsi_insert_seq_on_edge_immediate (loop_preheader_edge (loop1
),
609 tree cond
= build2 (guard_code
, boolean_type_node
, guard_init
, border
);
611 cond
= fold_build1 (TRUTH_NOT_EXPR
, boolean_type_node
, cond
);
613 edge true_edge
, false_edge
;
614 extract_true_false_edges_from_block (bbs
[i
], &true_edge
, &false_edge
);
616 /* Now version the loop, placing loop2 after loop1 connecting
617 them, and fix up SSA form for that. */
618 initialize_original_copy_tables ();
621 class loop
*loop2
= loop_version (loop1
, cond
, &cond_bb
,
622 true_edge
->probability
,
623 true_edge
->probability
.invert (),
624 profile_probability::always (),
625 profile_probability::always (),
629 edge new_e
= connect_loops (loop1
, loop2
);
630 connect_loop_phis (loop1
, loop2
, new_e
);
632 /* The iterations of the second loop is now already
633 exactly those that the first loop didn't do, but the
634 iteration space of the first loop is still the original one.
635 Compute the new bound for the guarding IV and patch the
636 loop exit to use it instead of original IV and bound. */
637 gimple_seq stmts
= NULL
;
638 tree newend
= compute_new_first_bound (&stmts
, &niter
, border
,
639 guard_code
, guard_init
);
641 gsi_insert_seq_on_edge_immediate (loop_preheader_edge (loop1
),
643 tree guard_next
= PHI_ARG_DEF_FROM_EDGE (phi
, loop_latch_edge (loop1
));
644 patch_loop_exit (loop1
, guard_stmt
, guard_next
, newend
, initial_true
);
646 fix_loop_bb_probability (loop1
, loop2
, true_edge
, false_edge
);
648 /* Fix first loop's exit probability after scaling. */
649 edge exit_to_latch1
= single_pred_edge (loop1
->latch
);
650 exit_to_latch1
->probability
*= true_edge
->probability
;
651 single_exit (loop1
)->probability
652 = exit_to_latch1
->probability
.invert ();
654 /* Finally patch out the two copies of the condition to be always
655 true/false (or opposite). */
656 gcond
*force_true
= as_a
<gcond
*> (last_stmt (bbs
[i
]));
657 gcond
*force_false
= as_a
<gcond
*> (last_stmt (get_bb_copy (bbs
[i
])));
659 std::swap (force_true
, force_false
);
660 gimple_cond_make_true (force_true
);
661 gimple_cond_make_false (force_false
);
662 update_stmt (force_true
);
663 update_stmt (force_false
);
665 free_original_copy_tables ();
668 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
669 fprintf (dump_file
, ";; Loop split.\n");
671 if (dump_enabled_p ())
672 dump_printf_loc (MSG_OPTIMIZED_LOCATIONS
, guard_stmt
, "loop split\n");
674 /* Only deal with the first opportunity. */
682 /* Another transformation of loops like:
684 for (i = INIT (); CHECK (i); i = NEXT ())
686 if (expr (a_1, a_2, ..., a_n)) // expr is pure
687 a_j = ...; // change at least one a_j
689 S; // not change any a_j
694 for (i = INIT (); CHECK (i); i = NEXT ())
696 if (expr (a_1, a_2, ..., a_n))
706 for (; CHECK (i); i = NEXT ())
713 /* Data structure to hold temporary information during loop split upon
714 semi-invariant conditional statement. */
717 /* Array of all basic blocks in a loop, returned by get_loop_body(). */
720 /* All memory store/clobber statements in a loop. */
721 auto_vec
<gimple
*> memory_stores
;
723 /* Whether above memory stores vector has been filled. */
726 /* Control dependencies of basic blocks in a loop. */
727 auto_vec
<hash_set
<basic_block
> *> control_deps
;
729 split_info () : bbs (NULL
), need_init (true) { }
736 for (unsigned i
= 0; i
< control_deps
.length (); i
++)
737 delete control_deps
[i
];
741 /* Find all statements with memory-write effect in LOOP, including memory
742 store and non-pure function call, and keep those in a vector. This work
743 is only done one time, for the vector should be constant during analysis
744 stage of semi-invariant condition. */
747 find_vdef_in_loop (struct loop
*loop
)
749 split_info
*info
= (split_info
*) loop
->aux
;
750 gphi
*vphi
= get_virtual_phi (loop
->header
);
752 /* Indicate memory store vector has been filled. */
753 info
->need_init
= false;
755 /* If loop contains memory operation, there must be a virtual PHI node in
756 loop header basic block. */
760 /* All virtual SSA names inside the loop are connected to be a cyclic
761 graph via virtual PHI nodes. The virtual PHI node in loop header just
762 links the first and the last virtual SSA names, by using the last as
763 PHI operand to define the first. */
764 const edge latch
= loop_latch_edge (loop
);
765 const tree first
= gimple_phi_result (vphi
);
766 const tree last
= PHI_ARG_DEF_FROM_EDGE (vphi
, latch
);
768 /* The virtual SSA cyclic graph might consist of only one SSA name, who
769 is defined by itself.
771 .MEM_1 = PHI <.MEM_2(loop entry edge), .MEM_1(latch edge)>
773 This means the loop contains only memory loads, so we can skip it. */
777 auto_vec
<gimple
*> other_stores
;
778 auto_vec
<tree
> worklist
;
781 bitmap_set_bit (visited
, SSA_NAME_VERSION (first
));
782 bitmap_set_bit (visited
, SSA_NAME_VERSION (last
));
783 worklist
.safe_push (last
);
787 tree vuse
= worklist
.pop ();
788 gimple
*stmt
= SSA_NAME_DEF_STMT (vuse
);
790 /* We mark the first and last SSA names as visited at the beginning,
791 and reversely start the process from the last SSA name towards the
792 first, which ensures that this do-while will not touch SSA names
793 defined outside the loop. */
794 gcc_assert (gimple_bb (stmt
)
795 && flow_bb_inside_loop_p (loop
, gimple_bb (stmt
)));
797 if (gimple_code (stmt
) == GIMPLE_PHI
)
799 gphi
*phi
= as_a
<gphi
*> (stmt
);
801 for (unsigned i
= 0; i
< gimple_phi_num_args (phi
); ++i
)
803 tree arg
= gimple_phi_arg_def (stmt
, i
);
805 if (bitmap_set_bit (visited
, SSA_NAME_VERSION (arg
)))
806 worklist
.safe_push (arg
);
811 tree prev
= gimple_vuse (stmt
);
813 /* Non-pure call statement is conservatively assumed to impact all
814 memory locations. So place call statements ahead of other memory
815 stores in the vector with an idea of using them as shortcut
816 terminators to memory alias analysis. */
817 if (gimple_code (stmt
) == GIMPLE_CALL
)
818 info
->memory_stores
.safe_push (stmt
);
820 other_stores
.safe_push (stmt
);
822 if (bitmap_set_bit (visited
, SSA_NAME_VERSION (prev
)))
823 worklist
.safe_push (prev
);
825 } while (!worklist
.is_empty ());
827 info
->memory_stores
.safe_splice (other_stores
);
830 /* Two basic blocks have equivalent control dependency if one dominates to
831 the other, and it is post-dominated by the latter. Given a basic block
832 BB in LOOP, find farest equivalent dominating basic block. For BB, there
833 is a constraint that BB does not post-dominate loop header of LOOP, this
834 means BB is control-dependent on at least one basic block in LOOP. */
837 get_control_equiv_head_block (struct loop
*loop
, basic_block bb
)
841 basic_block dom_bb
= get_immediate_dominator (CDI_DOMINATORS
, bb
);
843 gcc_checking_assert (dom_bb
&& flow_bb_inside_loop_p (loop
, dom_bb
));
845 if (!dominated_by_p (CDI_POST_DOMINATORS
, dom_bb
, bb
))
853 /* Given a BB in LOOP, find out all basic blocks in LOOP that BB is control-
856 static hash_set
<basic_block
> *
857 find_control_dep_blocks (struct loop
*loop
, basic_block bb
)
859 /* BB has same control dependency as loop header, then it is not control-
860 dependent on any basic block in LOOP. */
861 if (dominated_by_p (CDI_POST_DOMINATORS
, loop
->header
, bb
))
864 basic_block equiv_head
= get_control_equiv_head_block (loop
, bb
);
868 /* There is a basic block containing control dependency equivalent
869 to BB. No need to recompute that, and also set this information
870 to other equivalent basic blocks. */
871 for (; bb
!= equiv_head
;
872 bb
= get_immediate_dominator (CDI_DOMINATORS
, bb
))
873 bb
->aux
= equiv_head
->aux
;
874 return (hash_set
<basic_block
> *) equiv_head
->aux
;
877 /* A basic block X is control-dependent on another Y iff there exists
878 a path from X to Y, in which every basic block other than X and Y
879 is post-dominated by Y, but X is not post-dominated by Y.
881 According to this rule, traverse basic blocks in the loop backwards
882 starting from BB, if a basic block is post-dominated by BB, extend
883 current post-dominating path to this block, otherwise it is another
884 one that BB is control-dependent on. */
886 auto_vec
<basic_block
> pdom_worklist
;
887 hash_set
<basic_block
> pdom_visited
;
888 hash_set
<basic_block
> *dep_bbs
= new hash_set
<basic_block
>;
890 pdom_worklist
.safe_push (equiv_head
);
894 basic_block pdom_bb
= pdom_worklist
.pop ();
898 if (pdom_visited
.add (pdom_bb
))
901 FOR_EACH_EDGE (e
, ei
, pdom_bb
->preds
)
903 basic_block pred_bb
= e
->src
;
905 if (!dominated_by_p (CDI_POST_DOMINATORS
, pred_bb
, bb
))
907 dep_bbs
->add (pred_bb
);
911 pred_bb
= get_control_equiv_head_block (loop
, pred_bb
);
913 if (pdom_visited
.contains (pred_bb
))
918 pdom_worklist
.safe_push (pred_bb
);
922 /* If control dependency of basic block is available, fast extend
923 post-dominating path using the information instead of advancing
924 forward step-by-step. */
925 hash_set
<basic_block
> *pred_dep_bbs
926 = (hash_set
<basic_block
> *) pred_bb
->aux
;
928 for (hash_set
<basic_block
>::iterator iter
= pred_dep_bbs
->begin ();
929 iter
!= pred_dep_bbs
->end (); ++iter
)
931 basic_block pred_dep_bb
= *iter
;
933 /* Basic blocks can either be in control dependency of BB, or
934 must be post-dominated by BB, if so, extend the path from
935 these basic blocks. */
936 if (!dominated_by_p (CDI_POST_DOMINATORS
, pred_dep_bb
, bb
))
937 dep_bbs
->add (pred_dep_bb
);
938 else if (!pdom_visited
.contains (pred_dep_bb
))
939 pdom_worklist
.safe_push (pred_dep_bb
);
942 } while (!pdom_worklist
.is_empty ());
944 /* Record computed control dependencies in loop so that we can reach them
945 when reclaiming resources. */
946 ((split_info
*) loop
->aux
)->control_deps
.safe_push (dep_bbs
);
948 /* Associate control dependence with related equivalent basic blocks. */
949 for (equiv_head
->aux
= dep_bbs
; bb
!= equiv_head
;
950 bb
= get_immediate_dominator (CDI_DOMINATORS
, bb
))
956 /* Forward declaration */
959 stmt_semi_invariant_p_1 (struct loop
*loop
, gimple
*stmt
,
960 const_basic_block skip_head
,
961 hash_map
<gimple
*, bool> &stmt_stat
);
963 /* Given STMT, memory load or pure call statement, check whether it is impacted
964 by some memory store in LOOP, excluding trace starting from SKIP_HEAD (the
965 trace is composed of SKIP_HEAD and those basic block dominated by it, always
966 corresponds to one branch of a conditional statement). If SKIP_HEAD is
967 NULL, all basic blocks of LOOP are checked. */
970 vuse_semi_invariant_p (struct loop
*loop
, gimple
*stmt
,
971 const_basic_block skip_head
)
973 split_info
*info
= (split_info
*) loop
->aux
;
974 tree rhs
= NULL_TREE
;
979 /* Collect memory store/clobber statements if haven't done that. */
981 find_vdef_in_loop (loop
);
983 if (is_gimple_assign (stmt
))
984 rhs
= gimple_assign_rhs1 (stmt
);
986 ao_ref_init (&ref
, rhs
);
988 FOR_EACH_VEC_ELT (info
->memory_stores
, i
, store
)
990 /* Skip basic blocks dominated by SKIP_HEAD, if non-NULL. */
992 && dominated_by_p (CDI_DOMINATORS
, gimple_bb (store
), skip_head
))
995 if (!ref
.ref
|| stmt_may_clobber_ref_p_1 (store
, &ref
))
1002 /* Suppose one condition branch, led by SKIP_HEAD, is not executed since
1003 certain iteration of LOOP, check whether an SSA name (NAME) remains
1004 unchanged in next iteration. We call this characteristic semi-
1005 invariantness. SKIP_HEAD might be NULL, if so, nothing excluded, all basic
1006 blocks and control flows in the loop will be considered. Semi-invariant
1007 state of checked statement is cached in hash map STMT_STAT to avoid
1008 redundant computation in possible following re-check. */
1011 ssa_semi_invariant_p (struct loop
*loop
, tree name
,
1012 const_basic_block skip_head
,
1013 hash_map
<gimple
*, bool> &stmt_stat
)
1015 gimple
*def
= SSA_NAME_DEF_STMT (name
);
1016 const_basic_block def_bb
= gimple_bb (def
);
1018 /* An SSA name defined outside loop is definitely semi-invariant. */
1019 if (!def_bb
|| !flow_bb_inside_loop_p (loop
, def_bb
))
1022 if (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (name
))
1025 return stmt_semi_invariant_p_1 (loop
, def
, skip_head
, stmt_stat
);
1028 /* Check whether a loop iteration PHI node (LOOP_PHI) defines a value that is
1029 semi-invariant in LOOP. Basic blocks dominated by SKIP_HEAD (if non-NULL),
1030 are excluded from LOOP. */
1033 loop_iter_phi_semi_invariant_p (struct loop
*loop
, gphi
*loop_phi
,
1034 const_basic_block skip_head
)
1036 const_edge latch
= loop_latch_edge (loop
);
1037 tree name
= gimple_phi_result (loop_phi
);
1038 tree from
= PHI_ARG_DEF_FROM_EDGE (loop_phi
, latch
);
1040 gcc_checking_assert (from
);
1042 /* Loop iteration PHI node locates in loop header, and it has two source
1043 operands, one is an initial value coming from outside the loop, the other
1044 is a value through latch of the loop, which is derived in last iteration,
1045 we call the latter latch value. From the PHI node to definition of latch
1046 value, if excluding branch trace starting from SKIP_HEAD, except copy-
1047 assignment or likewise, there is no other kind of value redefinition, SSA
1048 name defined by the PHI node is semi-invariant.
1054 x_1 = PHI <x_0, x_3> |
1057 .------- if (cond) -------. |
1063 '---- T ---->.<---- F ----' |
1066 x_3 = PHI <x_1, x_2> |
1068 '----------------------'
1070 Suppose in certain iteration, execution flow in above graph goes through
1071 true branch, which means that one source value to define x_3 in false
1072 branch (x_2) is skipped, x_3 only comes from x_1, and x_1 in next
1073 iterations is defined by x_3, we know that x_1 will never changed if COND
1074 always chooses true branch from then on. */
1076 while (from
!= name
)
1078 /* A new value comes from a CONSTANT. */
1079 if (TREE_CODE (from
) != SSA_NAME
)
1082 gimple
*stmt
= SSA_NAME_DEF_STMT (from
);
1083 const_basic_block bb
= gimple_bb (stmt
);
1085 /* A new value comes from outside the loop. */
1086 if (!bb
|| !flow_bb_inside_loop_p (loop
, bb
))
1091 if (gimple_code (stmt
) == GIMPLE_PHI
)
1093 gphi
*phi
= as_a
<gphi
*> (stmt
);
1095 for (unsigned i
= 0; i
< gimple_phi_num_args (phi
); ++i
)
1099 const_edge e
= gimple_phi_arg_edge (phi
, i
);
1101 /* Don't consider redefinitions in excluded basic blocks. */
1102 if (dominated_by_p (CDI_DOMINATORS
, e
->src
, skip_head
))
1106 tree arg
= gimple_phi_arg_def (phi
, i
);
1110 else if (!operand_equal_p (from
, arg
, 0))
1111 /* There are more than one source operands that provide
1112 different values to the SSA name, it is variant. */
1116 else if (gimple_code (stmt
) == GIMPLE_ASSIGN
)
1118 /* For simple value copy, check its rhs instead. */
1119 if (gimple_assign_ssa_name_copy_p (stmt
))
1120 from
= gimple_assign_rhs1 (stmt
);
1123 /* Any other kind of definition is deemed to introduce a new value
1131 /* Check whether conditional predicates that BB is control-dependent on, are
1132 semi-invariant in LOOP. Basic blocks dominated by SKIP_HEAD (if non-NULL),
1133 are excluded from LOOP. Semi-invariant state of checked statement is cached
1134 in hash map STMT_STAT. */
1137 control_dep_semi_invariant_p (struct loop
*loop
, basic_block bb
,
1138 const_basic_block skip_head
,
1139 hash_map
<gimple
*, bool> &stmt_stat
)
1141 hash_set
<basic_block
> *dep_bbs
= find_control_dep_blocks (loop
, bb
);
1146 for (hash_set
<basic_block
>::iterator iter
= dep_bbs
->begin ();
1147 iter
!= dep_bbs
->end (); ++iter
)
1149 gimple
*last
= last_stmt (*iter
);
1154 /* Only check condition predicates. */
1155 if (gimple_code (last
) != GIMPLE_COND
1156 && gimple_code (last
) != GIMPLE_SWITCH
)
1159 if (!stmt_semi_invariant_p_1 (loop
, last
, skip_head
, stmt_stat
))
1166 /* Check whether STMT is semi-invariant in LOOP, iff all its operands are
1167 semi-invariant, consequently, all its defined values are semi-invariant.
1168 Basic blocks dominated by SKIP_HEAD (if non-NULL), are excluded from LOOP.
1169 Semi-invariant state of checked statement is cached in hash map
1173 stmt_semi_invariant_p_1 (struct loop
*loop
, gimple
*stmt
,
1174 const_basic_block skip_head
,
1175 hash_map
<gimple
*, bool> &stmt_stat
)
1178 bool &invar
= stmt_stat
.get_or_insert (stmt
, &existed
);
1183 /* A statement might depend on itself, which is treated as variant. So set
1184 state of statement under check to be variant to ensure that. */
1187 if (gimple_code (stmt
) == GIMPLE_PHI
)
1189 gphi
*phi
= as_a
<gphi
*> (stmt
);
1191 if (gimple_bb (stmt
) == loop
->header
)
1193 /* If the entry value is subject to abnormal coalescing
1194 avoid the transform since we're going to duplicate the
1195 loop header and thus likely introduce overlapping life-ranges
1196 between the PHI def and the entry on the path when the
1197 first loop is skipped. */
1199 = PHI_ARG_DEF_FROM_EDGE (phi
, loop_preheader_edge (loop
));
1200 if (TREE_CODE (entry_def
) == SSA_NAME
1201 && SSA_NAME_OCCURS_IN_ABNORMAL_PHI (entry_def
))
1203 invar
= loop_iter_phi_semi_invariant_p (loop
, phi
, skip_head
);
1207 /* For a loop PHI node that does not locate in loop header, it is semi-
1208 invariant only if two conditions are met. The first is its source
1209 values are derived from CONSTANT (including loop-invariant value), or
1210 from SSA name defined by semi-invariant loop iteration PHI node. The
1211 second is its source incoming edges are control-dependent on semi-
1212 invariant conditional predicates. */
1213 for (unsigned i
= 0; i
< gimple_phi_num_args (phi
); ++i
)
1215 const_edge e
= gimple_phi_arg_edge (phi
, i
);
1216 tree arg
= gimple_phi_arg_def (phi
, i
);
1218 if (TREE_CODE (arg
) == SSA_NAME
)
1220 if (!ssa_semi_invariant_p (loop
, arg
, skip_head
, stmt_stat
))
1223 /* If source value is defined in location from where the source
1224 edge comes in, no need to check control dependency again
1225 since this has been done in above SSA name check stage. */
1226 if (e
->src
== gimple_bb (SSA_NAME_DEF_STMT (arg
)))
1230 if (!control_dep_semi_invariant_p (loop
, e
->src
, skip_head
,
1240 /* Volatile memory load or return of normal (non-const/non-pure) call
1241 should not be treated as constant in each iteration of loop. */
1242 if (gimple_has_side_effects (stmt
))
1245 /* Check if any memory store may kill memory load at this place. */
1246 if (gimple_vuse (stmt
) && !vuse_semi_invariant_p (loop
, stmt
, skip_head
))
1249 /* Although operand of a statement might be SSA name, CONSTANT or
1250 VARDECL, here we only need to check SSA name operands. This is
1251 because check on VARDECL operands, which involve memory loads,
1252 must have been done prior to invocation of this function in
1253 vuse_semi_invariant_p. */
1254 FOR_EACH_SSA_TREE_OPERAND (use
, stmt
, iter
, SSA_OP_USE
)
1255 if (!ssa_semi_invariant_p (loop
, use
, skip_head
, stmt_stat
))
1259 if (!control_dep_semi_invariant_p (loop
, gimple_bb (stmt
), skip_head
,
1263 /* Here we SHOULD NOT use invar = true, since hash map might be changed due
1264 to new insertion, and thus invar may point to invalid memory. */
1265 stmt_stat
.put (stmt
, true);
1269 /* A helper function to check whether STMT is semi-invariant in LOOP. Basic
1270 blocks dominated by SKIP_HEAD (if non-NULL), are excluded from LOOP. */
1273 stmt_semi_invariant_p (struct loop
*loop
, gimple
*stmt
,
1274 const_basic_block skip_head
)
1276 hash_map
<gimple
*, bool> stmt_stat
;
1277 return stmt_semi_invariant_p_1 (loop
, stmt
, skip_head
, stmt_stat
);
1280 /* Determine when conditional statement never transfers execution to one of its
1281 branch, whether we can remove the branch's leading basic block (BRANCH_BB)
1282 and those basic blocks dominated by BRANCH_BB. */
1285 branch_removable_p (basic_block branch_bb
)
1290 if (single_pred_p (branch_bb
))
1293 FOR_EACH_EDGE (e
, ei
, branch_bb
->preds
)
1295 if (dominated_by_p (CDI_DOMINATORS
, e
->src
, branch_bb
))
1298 if (dominated_by_p (CDI_DOMINATORS
, branch_bb
, e
->src
))
1301 /* The branch can be reached from opposite branch, or from some
1302 statement not dominated by the conditional statement. */
1309 /* Find out which branch of a conditional statement (COND) is invariant in the
1310 execution context of LOOP. That is: once the branch is selected in certain
1311 iteration of the loop, any operand that contributes to computation of the
1312 conditional statement remains unchanged in all following iterations. */
1315 get_cond_invariant_branch (struct loop
*loop
, gcond
*cond
)
1317 basic_block cond_bb
= gimple_bb (cond
);
1318 basic_block targ_bb
[2];
1320 unsigned invar_checks
= 0;
1322 for (unsigned i
= 0; i
< 2; i
++)
1324 targ_bb
[i
] = EDGE_SUCC (cond_bb
, i
)->dest
;
1326 /* One branch directs to loop exit, no need to perform loop split upon
1327 this conditional statement. Firstly, it is trivial if the exit branch
1328 is semi-invariant, for the statement is just to break loop. Secondly,
1329 if the opposite branch is semi-invariant, it means that the statement
1330 is real loop-invariant, which is covered by loop unswitch. */
1331 if (!flow_bb_inside_loop_p (loop
, targ_bb
[i
]))
1335 for (unsigned i
= 0; i
< 2; i
++)
1339 if (!branch_removable_p (targ_bb
[i
]))
1342 /* Given a semi-invariant branch, if its opposite branch dominates
1343 loop latch, it and its following trace will only be executed in
1344 final iteration of loop, namely it is not part of repeated body
1345 of the loop. Similar to the above case that the branch is loop
1346 exit, no need to split loop. */
1347 if (dominated_by_p (CDI_DOMINATORS
, loop
->latch
, targ_bb
[i
]))
1350 invar
[!i
] = stmt_semi_invariant_p (loop
, cond
, targ_bb
[i
]);
1354 /* With both branches being invariant (handled by loop unswitch) or
1355 variant is not what we want. */
1356 if (invar
[0] ^ !invar
[1])
1359 /* Found a real loop-invariant condition, do nothing. */
1360 if (invar_checks
< 2 && stmt_semi_invariant_p (loop
, cond
, NULL
))
1363 return EDGE_SUCC (cond_bb
, invar
[0] ? 0 : 1);
1366 /* Calculate increased code size measured by estimated insn number if applying
1367 loop split upon certain branch (BRANCH_EDGE) of a conditional statement. */
1370 compute_added_num_insns (struct loop
*loop
, const_edge branch_edge
)
1372 basic_block cond_bb
= branch_edge
->src
;
1373 unsigned branch
= EDGE_SUCC (cond_bb
, 1) == branch_edge
;
1374 basic_block opposite_bb
= EDGE_SUCC (cond_bb
, !branch
)->dest
;
1375 basic_block
*bbs
= ((split_info
*) loop
->aux
)->bbs
;
1378 for (unsigned i
= 0; i
< loop
->num_nodes
; i
++)
1380 /* Do no count basic blocks only in opposite branch. */
1381 if (dominated_by_p (CDI_DOMINATORS
, bbs
[i
], opposite_bb
))
1384 num
+= estimate_num_insns_seq (bb_seq (bbs
[i
]), &eni_size_weights
);
1387 /* It is unnecessary to evaluate expression of the conditional statement
1388 in new loop that contains only invariant branch. This expression should
1389 be constant value (either true or false). Exclude code size of insns
1390 that contribute to computation of the expression. */
1392 auto_vec
<gimple
*> worklist
;
1393 hash_set
<gimple
*> removed
;
1394 gimple
*stmt
= last_stmt (cond_bb
);
1396 worklist
.safe_push (stmt
);
1398 num
-= estimate_num_insns (stmt
, &eni_size_weights
);
1402 ssa_op_iter opnd_iter
;
1403 use_operand_p opnd_p
;
1405 stmt
= worklist
.pop ();
1406 FOR_EACH_PHI_OR_STMT_USE (opnd_p
, stmt
, opnd_iter
, SSA_OP_USE
)
1408 tree opnd
= USE_FROM_PTR (opnd_p
);
1410 if (TREE_CODE (opnd
) != SSA_NAME
|| SSA_NAME_IS_DEFAULT_DEF (opnd
))
1413 gimple
*opnd_stmt
= SSA_NAME_DEF_STMT (opnd
);
1414 use_operand_p use_p
;
1415 imm_use_iterator use_iter
;
1417 if (removed
.contains (opnd_stmt
)
1418 || !flow_bb_inside_loop_p (loop
, gimple_bb (opnd_stmt
)))
1421 FOR_EACH_IMM_USE_FAST (use_p
, use_iter
, opnd
)
1423 gimple
*use_stmt
= USE_STMT (use_p
);
1425 if (!is_gimple_debug (use_stmt
) && !removed
.contains (use_stmt
))
1434 worklist
.safe_push (opnd_stmt
);
1435 removed
.add (opnd_stmt
);
1436 num
-= estimate_num_insns (opnd_stmt
, &eni_size_weights
);
1439 } while (!worklist
.is_empty ());
1441 gcc_assert (num
>= 0);
1445 /* Find out loop-invariant branch of a conditional statement (COND) if it has,
1446 and check whether it is eligible and profitable to perform loop split upon
1447 this branch in LOOP. */
1450 get_cond_branch_to_split_loop (struct loop
*loop
, gcond
*cond
)
1452 edge invar_branch
= get_cond_invariant_branch (loop
, cond
);
1456 /* When accurate profile information is available, and execution
1457 frequency of the branch is too low, just let it go. */
1458 profile_probability prob
= invar_branch
->probability
;
1459 if (prob
.reliable_p ())
1461 int thres
= param_min_loop_cond_split_prob
;
1463 if (prob
< profile_probability::always ().apply_scale (thres
, 100))
1467 /* Add a threshold for increased code size to disable loop split. */
1468 if (compute_added_num_insns (loop
, invar_branch
) > param_max_peeled_insns
)
1471 return invar_branch
;
1474 /* Given a loop (LOOP1) with a loop-invariant branch (INVAR_BRANCH) of some
1475 conditional statement, perform loop split transformation illustrated
1476 as the following graph.
1478 .-------T------ if (true) ------F------.
1479 | .---------------. |
1482 pre-header | pre-header
1483 | .------------. | | .------------.
1488 .--- if (cond) ---. | | .--- if (true) ---. |
1490 invariant | | | invariant | |
1492 '---T--->.<---F---' | | '---T--->.<---F---' |
1497 .-------* * [ if (cond) ] .-------* * |
1501 | '------------' | '------------'
1502 '------------------------. .-----------'
1507 In the graph, loop1 represents the part derived from original one, and
1508 loop2 is duplicated using loop_version (), which corresponds to the part
1509 of original one being splitted out. In original latch edge of loop1, we
1510 insert a new conditional statement duplicated from the semi-invariant cond,
1511 and one of its branch goes back to loop1 header as a latch edge, and the
1512 other branch goes to loop2 pre-header as an entry edge. And also in loop2,
1513 we abandon the variant branch of the conditional statement by setting a
1514 constant bool condition, based on which branch is semi-invariant. */
1517 do_split_loop_on_cond (struct loop
*loop1
, edge invar_branch
)
1519 basic_block cond_bb
= invar_branch
->src
;
1520 bool true_invar
= !!(invar_branch
->flags
& EDGE_TRUE_VALUE
);
1521 gcond
*cond
= as_a
<gcond
*> (last_stmt (cond_bb
));
1523 gcc_assert (cond_bb
->loop_father
== loop1
);
1525 if (dump_enabled_p ())
1526 dump_printf_loc (MSG_OPTIMIZED_LOCATIONS
, cond
,
1527 "loop split on semi-invariant condition at %s branch\n",
1528 true_invar
? "true" : "false");
1530 initialize_original_copy_tables ();
1532 struct loop
*loop2
= loop_version (loop1
, boolean_true_node
, NULL
,
1533 invar_branch
->probability
.invert (),
1534 invar_branch
->probability
,
1535 profile_probability::always (),
1536 profile_probability::always (),
1540 free_original_copy_tables ();
1544 basic_block cond_bb_copy
= get_bb_copy (cond_bb
);
1545 gcond
*cond_copy
= as_a
<gcond
*> (last_stmt (cond_bb_copy
));
1547 /* Replace the condition in loop2 with a bool constant to let PassManager
1548 remove the variant branch after current pass completes. */
1550 gimple_cond_make_true (cond_copy
);
1552 gimple_cond_make_false (cond_copy
);
1554 update_stmt (cond_copy
);
1556 /* Insert a new conditional statement on latch edge of loop1, its condition
1557 is duplicated from the semi-invariant. This statement acts as a switch
1558 to transfer execution from loop1 to loop2, when loop1 enters into
1560 basic_block latch_bb
= split_edge (loop_latch_edge (loop1
));
1561 basic_block break_bb
= split_edge (single_pred_edge (latch_bb
));
1562 gimple
*break_cond
= gimple_build_cond (gimple_cond_code(cond
),
1563 gimple_cond_lhs (cond
),
1564 gimple_cond_rhs (cond
),
1565 NULL_TREE
, NULL_TREE
);
1567 gimple_stmt_iterator gsi
= gsi_last_bb (break_bb
);
1568 gsi_insert_after (&gsi
, break_cond
, GSI_NEW_STMT
);
1570 edge to_loop1
= single_succ_edge (break_bb
);
1571 edge to_loop2
= make_edge (break_bb
, loop_preheader_edge (loop2
)->src
, 0);
1573 to_loop1
->flags
&= ~EDGE_FALLTHRU
;
1574 to_loop1
->flags
|= true_invar
? EDGE_FALSE_VALUE
: EDGE_TRUE_VALUE
;
1575 to_loop2
->flags
|= true_invar
? EDGE_TRUE_VALUE
: EDGE_FALSE_VALUE
;
1577 /* Due to introduction of a control flow edge from loop1 latch to loop2
1578 pre-header, we should update PHIs in loop2 to reflect this connection
1579 between loop1 and loop2. */
1580 connect_loop_phis (loop1
, loop2
, to_loop2
);
1582 edge true_edge
, false_edge
, skip_edge1
, skip_edge2
;
1583 extract_true_false_edges_from_block (cond_bb
, &true_edge
, &false_edge
);
1585 skip_edge1
= true_invar
? false_edge
: true_edge
;
1586 skip_edge2
= true_invar
? true_edge
: false_edge
;
1587 fix_loop_bb_probability (loop1
, loop2
, skip_edge1
, skip_edge2
);
1589 /* Fix first loop's exit probability after scaling. */
1590 to_loop1
->probability
= invar_branch
->probability
.invert ();
1591 to_loop2
->probability
= invar_branch
->probability
;
1593 free_original_copy_tables ();
1598 /* Traverse all conditional statements in LOOP, to find out a good candidate
1599 upon which we can do loop split. */
1602 split_loop_on_cond (struct loop
*loop
)
1604 split_info
*info
= new split_info ();
1605 basic_block
*bbs
= info
->bbs
= get_loop_body (loop
);
1606 bool do_split
= false;
1608 /* Allocate an area to keep temporary info, and associate its address
1609 with loop aux field. */
1612 for (unsigned i
= 0; i
< loop
->num_nodes
; i
++)
1615 for (unsigned i
= 0; i
< loop
->num_nodes
; i
++)
1617 basic_block bb
= bbs
[i
];
1619 /* We only consider conditional statement, which be executed at most once
1620 in each iteration of the loop. So skip statements in inner loops. */
1621 if ((bb
->loop_father
!= loop
) || (bb
->flags
& BB_IRREDUCIBLE_LOOP
))
1624 /* Actually this check is not a must constraint. With it, we can ensure
1625 conditional statement will always be executed in each iteration. */
1626 if (!dominated_by_p (CDI_DOMINATORS
, loop
->latch
, bb
))
1629 gimple
*last
= last_stmt (bb
);
1631 if (!last
|| gimple_code (last
) != GIMPLE_COND
)
1634 gcond
*cond
= as_a
<gcond
*> (last
);
1635 edge branch_edge
= get_cond_branch_to_split_loop (loop
, cond
);
1639 do_split_loop_on_cond (loop
, branch_edge
);
1651 /* Main entry point. Perform loop splitting on all suitable loops. */
1654 tree_ssa_split_loops (void)
1656 bool changed
= false;
1658 gcc_assert (scev_initialized_p ());
1660 calculate_dominance_info (CDI_POST_DOMINATORS
);
1662 for (auto loop
: loops_list (cfun
, LI_INCLUDE_ROOT
))
1665 /* Go through all loops starting from innermost. */
1666 for (auto loop
: loops_list (cfun
, LI_FROM_INNERMOST
))
1670 /* If any of our inner loops was split, don't split us,
1671 and mark our containing loop as having had splits as well. */
1672 loop_outer (loop
)->aux
= loop
;
1676 if (optimize_loop_for_size_p (loop
))
1679 if (split_loop (loop
) || split_loop_on_cond (loop
))
1681 /* Mark our containing loop as having had some split inner loops. */
1682 loop_outer (loop
)->aux
= loop
;
1687 for (auto loop
: loops_list (cfun
, LI_INCLUDE_ROOT
))
1690 clear_aux_for_blocks ();
1692 free_dominance_info (CDI_POST_DOMINATORS
);
1696 rewrite_into_loop_closed_ssa (NULL
, TODO_update_ssa
);
1697 return TODO_cleanup_cfg
;
1702 /* Loop splitting pass. */
1706 const pass_data pass_data_loop_split
=
1708 GIMPLE_PASS
, /* type */
1709 "lsplit", /* name */
1710 OPTGROUP_LOOP
, /* optinfo_flags */
1711 TV_LOOP_SPLIT
, /* tv_id */
1712 PROP_cfg
, /* properties_required */
1713 0, /* properties_provided */
1714 0, /* properties_destroyed */
1715 0, /* todo_flags_start */
1716 0, /* todo_flags_finish */
1719 class pass_loop_split
: public gimple_opt_pass
1722 pass_loop_split (gcc::context
*ctxt
)
1723 : gimple_opt_pass (pass_data_loop_split
, ctxt
)
1726 /* opt_pass methods: */
1727 virtual bool gate (function
*) { return flag_split_loops
!= 0; }
1728 virtual unsigned int execute (function
*);
1730 }; // class pass_loop_split
1733 pass_loop_split::execute (function
*fun
)
1735 if (number_of_loops (fun
) <= 1)
1738 return tree_ssa_split_loops ();
1744 make_pass_loop_split (gcc::context
*ctxt
)
1746 return new pass_loop_split (ctxt
);