1 /* Natural loop analysis code for GNU compiler.
2 Copyright (C) 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010
3 Free Software Foundation, Inc.
5 This file is part of GCC.
7 GCC is free software; you can redistribute it and/or modify it under
8 the terms of the GNU General Public License as published by the Free
9 Software Foundation; either version 3, or (at your option) any later
12 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
13 WARRANTY; without even the implied warranty of MERCHANTABILITY or
14 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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"
26 #include "hard-reg-set.h"
28 #include "basic-block.h"
34 struct target_cfgloop default_target_cfgloop
;
36 struct target_cfgloop
*this_target_cfgloop
= &default_target_cfgloop
;
39 /* Checks whether BB is executed exactly once in each LOOP iteration. */
42 just_once_each_iteration_p (const struct loop
*loop
, const_basic_block bb
)
44 /* It must be executed at least once each iteration. */
45 if (!dominated_by_p (CDI_DOMINATORS
, loop
->latch
, bb
))
49 if (bb
->loop_father
!= loop
)
52 /* But this was not enough. We might have some irreducible loop here. */
53 if (bb
->flags
& BB_IRREDUCIBLE_LOOP
)
59 /* Marks blocks and edges that are part of non-recognized loops; i.e. we
60 throw away all latch edges and mark blocks inside any remaining cycle.
61 Everything is a bit complicated due to fact we do not want to do this
62 for parts of cycles that only "pass" through some loop -- i.e. for
63 each cycle, we want to mark blocks that belong directly to innermost
64 loop containing the whole cycle.
66 LOOPS is the loop tree. */
68 #define LOOP_REPR(LOOP) ((LOOP)->num + last_basic_block)
69 #define BB_REPR(BB) ((BB)->index + 1)
72 mark_irreducible_loops (void)
75 struct graph_edge
*ge
;
81 int num
= number_of_loops ();
83 bool irred_loop_found
= false;
86 gcc_assert (current_loops
!= NULL
);
88 /* Reset the flags. */
89 FOR_BB_BETWEEN (act
, ENTRY_BLOCK_PTR
, EXIT_BLOCK_PTR
, next_bb
)
91 act
->flags
&= ~BB_IRREDUCIBLE_LOOP
;
92 FOR_EACH_EDGE (e
, ei
, act
->succs
)
93 e
->flags
&= ~EDGE_IRREDUCIBLE_LOOP
;
96 /* Create the edge lists. */
97 g
= new_graph (last_basic_block
+ num
);
99 FOR_BB_BETWEEN (act
, ENTRY_BLOCK_PTR
, EXIT_BLOCK_PTR
, next_bb
)
100 FOR_EACH_EDGE (e
, ei
, act
->succs
)
102 /* Ignore edges to exit. */
103 if (e
->dest
== EXIT_BLOCK_PTR
)
107 dest
= BB_REPR (e
->dest
);
109 /* Ignore latch edges. */
110 if (e
->dest
->loop_father
->header
== e
->dest
111 && e
->dest
->loop_father
->latch
== act
)
114 /* Edges inside a single loop should be left where they are. Edges
115 to subloop headers should lead to representative of the subloop,
116 but from the same place.
118 Edges exiting loops should lead from representative
119 of the son of nearest common ancestor of the loops in that
122 if (e
->dest
->loop_father
->header
== e
->dest
)
123 dest
= LOOP_REPR (e
->dest
->loop_father
);
125 if (!flow_bb_inside_loop_p (act
->loop_father
, e
->dest
))
127 depth
= 1 + loop_depth (find_common_loop (act
->loop_father
,
128 e
->dest
->loop_father
));
129 if (depth
== loop_depth (act
->loop_father
))
130 cloop
= act
->loop_father
;
132 cloop
= (*act
->loop_father
->superloops
)[depth
];
134 src
= LOOP_REPR (cloop
);
137 add_edge (g
, src
, dest
)->data
= e
;
140 /* Find the strongly connected components. */
141 graphds_scc (g
, NULL
);
143 /* Mark the irreducible loops. */
144 for (i
= 0; i
< g
->n_vertices
; i
++)
145 for (ge
= g
->vertices
[i
].succ
; ge
; ge
= ge
->succ_next
)
147 edge real
= (edge
) ge
->data
;
148 /* edge E in graph G is irreducible if it connects two vertices in the
151 /* All edges should lead from a component with higher number to the
152 one with lower one. */
153 gcc_assert (g
->vertices
[ge
->src
].component
>= g
->vertices
[ge
->dest
].component
);
155 if (g
->vertices
[ge
->src
].component
!= g
->vertices
[ge
->dest
].component
)
158 real
->flags
|= EDGE_IRREDUCIBLE_LOOP
;
159 irred_loop_found
= true;
160 if (flow_bb_inside_loop_p (real
->src
->loop_father
, real
->dest
))
161 real
->src
->flags
|= BB_IRREDUCIBLE_LOOP
;
166 loops_state_set (LOOPS_HAVE_MARKED_IRREDUCIBLE_REGIONS
);
167 return irred_loop_found
;
170 /* Counts number of insns inside LOOP. */
172 num_loop_insns (const struct loop
*loop
)
174 basic_block
*bbs
, bb
;
175 unsigned i
, ninsns
= 0;
178 bbs
= get_loop_body (loop
);
179 for (i
= 0; i
< loop
->num_nodes
; i
++)
182 FOR_BB_INSNS (bb
, insn
)
183 if (NONDEBUG_INSN_P (insn
))
189 ninsns
= 1; /* To avoid division by zero. */
194 /* Counts number of insns executed on average per iteration LOOP. */
196 average_num_loop_insns (const struct loop
*loop
)
198 basic_block
*bbs
, bb
;
199 unsigned i
, binsns
, ninsns
, ratio
;
203 bbs
= get_loop_body (loop
);
204 for (i
= 0; i
< loop
->num_nodes
; i
++)
209 FOR_BB_INSNS (bb
, insn
)
210 if (NONDEBUG_INSN_P (insn
))
213 ratio
= loop
->header
->frequency
== 0
215 : (bb
->frequency
* BB_FREQ_MAX
) / loop
->header
->frequency
;
216 ninsns
+= binsns
* ratio
;
220 ninsns
/= BB_FREQ_MAX
;
222 ninsns
= 1; /* To avoid division by zero. */
227 /* Returns expected number of iterations of LOOP, according to
228 measured or guessed profile. No bounding is done on the
232 expected_loop_iterations_unbounded (const struct loop
*loop
)
237 if (loop
->latch
->count
|| loop
->header
->count
)
239 gcov_type count_in
, count_latch
, expected
;
244 FOR_EACH_EDGE (e
, ei
, loop
->header
->preds
)
245 if (e
->src
== loop
->latch
)
246 count_latch
= e
->count
;
248 count_in
+= e
->count
;
251 expected
= count_latch
* 2;
253 expected
= (count_latch
+ count_in
- 1) / count_in
;
259 int freq_in
, freq_latch
;
264 FOR_EACH_EDGE (e
, ei
, loop
->header
->preds
)
265 if (e
->src
== loop
->latch
)
266 freq_latch
= EDGE_FREQUENCY (e
);
268 freq_in
+= EDGE_FREQUENCY (e
);
271 return freq_latch
* 2;
273 return (freq_latch
+ freq_in
- 1) / freq_in
;
277 /* Returns expected number of LOOP iterations. The returned value is bounded
278 by REG_BR_PROB_BASE. */
281 expected_loop_iterations (const struct loop
*loop
)
283 gcov_type expected
= expected_loop_iterations_unbounded (loop
);
284 return (expected
> REG_BR_PROB_BASE
? REG_BR_PROB_BASE
: expected
);
287 /* Returns the maximum level of nesting of subloops of LOOP. */
290 get_loop_level (const struct loop
*loop
)
292 const struct loop
*ploop
;
295 for (ploop
= loop
->inner
; ploop
; ploop
= ploop
->next
)
297 l
= get_loop_level (ploop
);
304 /* Returns estimate on cost of computing SEQ. */
307 seq_cost (const_rtx seq
, bool speed
)
312 for (; seq
; seq
= NEXT_INSN (seq
))
314 set
= single_set (seq
);
316 cost
+= set_rtx_cost (set
, speed
);
324 /* Initialize the constants for computing set costs. */
327 init_set_costs (void)
331 rtx reg1
= gen_raw_REG (SImode
, FIRST_PSEUDO_REGISTER
);
332 rtx reg2
= gen_raw_REG (SImode
, FIRST_PSEUDO_REGISTER
+ 1);
333 rtx addr
= gen_raw_REG (Pmode
, FIRST_PSEUDO_REGISTER
+ 2);
334 rtx mem
= validize_mem (gen_rtx_MEM (SImode
, addr
));
337 target_avail_regs
= 0;
338 target_clobbered_regs
= 0;
339 for (i
= 0; i
< FIRST_PSEUDO_REGISTER
; i
++)
340 if (TEST_HARD_REG_BIT (reg_class_contents
[GENERAL_REGS
], i
)
344 if (call_used_regs
[i
])
345 target_clobbered_regs
++;
350 for (speed
= 0; speed
< 2; speed
++)
352 crtl
->maybe_hot_insn_p
= speed
;
353 /* Set up the costs for using extra registers:
355 1) If not many free registers remain, we should prefer having an
356 additional move to decreasing the number of available registers.
358 2) If no registers are available, we need to spill, which may require
359 storing the old value to memory and loading it back
360 (TARGET_SPILL_COST). */
363 emit_move_insn (reg1
, reg2
);
366 target_reg_cost
[speed
] = seq_cost (seq
, speed
);
369 emit_move_insn (mem
, reg1
);
370 emit_move_insn (reg2
, mem
);
373 target_spill_cost
[speed
] = seq_cost (seq
, speed
);
375 default_rtl_profile ();
378 /* Estimates cost of increased register pressure caused by making N_NEW new
379 registers live around the loop. N_OLD is the number of registers live
380 around the loop. If CALL_P is true, also take into account that
381 call-used registers may be clobbered in the loop body, reducing the
382 number of available registers before we spill. */
385 estimate_reg_pressure_cost (unsigned n_new
, unsigned n_old
, bool speed
,
389 unsigned regs_needed
= n_new
+ n_old
;
390 unsigned available_regs
= target_avail_regs
;
392 /* If there is a call in the loop body, the call-clobbered registers
393 are not available for loop invariants. */
395 available_regs
= available_regs
- target_clobbered_regs
;
397 /* If we have enough registers, we should use them and not restrict
398 the transformations unnecessarily. */
399 if (regs_needed
+ target_res_regs
<= available_regs
)
402 if (regs_needed
<= available_regs
)
403 /* If we are close to running out of registers, try to preserve
405 cost
= target_reg_cost
[speed
] * n_new
;
407 /* If we run out of registers, it is very expensive to add another
409 cost
= target_spill_cost
[speed
] * n_new
;
411 if (optimize
&& (flag_ira_region
== IRA_REGION_ALL
412 || flag_ira_region
== IRA_REGION_MIXED
)
413 && number_of_loops () <= (unsigned) IRA_MAX_LOOPS_NUM
)
414 /* IRA regional allocation deals with high register pressure
415 better. So decrease the cost (to do more accurate the cost
416 calculation for IRA, we need to know how many registers lives
417 through the loop transparently). */
423 /* Sets EDGE_LOOP_EXIT flag for all loop exits. */
426 mark_loop_exit_edges (void)
431 if (number_of_loops () <= 1)
438 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
440 if (loop_outer (bb
->loop_father
)
441 && loop_exit_edge_p (bb
->loop_father
, e
))
442 e
->flags
|= EDGE_LOOP_EXIT
;
444 e
->flags
&= ~EDGE_LOOP_EXIT
;
449 /* Return exit edge if loop has only one exit that is likely
450 to be executed on runtime (i.e. it is not EH or leading
454 single_likely_exit (struct loop
*loop
)
456 edge found
= single_exit (loop
);
463 exits
= get_loop_exit_edges (loop
);
464 FOR_EACH_VEC_ELT (exits
, i
, ex
)
466 if (ex
->flags
& (EDGE_EH
| EDGE_ABNORMAL_CALL
))
468 /* The constant of 5 is set in a way so noreturn calls are
469 ruled out by this test. The static branch prediction algorithm
470 will not assign such a low probability to conditionals for usual
472 if (profile_status
!= PROFILE_ABSENT
473 && ex
->probability
< 5 && !ex
->count
)
488 /* Gets basic blocks of a LOOP. Header is the 0-th block, rest is in dfs
489 order against direction of edges from latch. Specially, if
490 header != latch, latch is the 1-st block. */
493 get_loop_hot_path (const struct loop
*loop
)
495 basic_block bb
= loop
->header
;
496 vec
<basic_block
> path
= vNULL
;
497 bitmap visited
= BITMAP_ALLOC (NULL
);
506 bitmap_set_bit (visited
, bb
->index
);
507 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
508 if ((!best
|| e
->probability
> best
->probability
)
509 && !loop_exit_edge_p (loop
, e
)
510 && !bitmap_bit_p (visited
, e
->dest
->index
))
512 if (!best
|| best
->dest
== loop
->header
)
516 BITMAP_FREE (visited
);