1 /* Natural loop analysis code for GNU compiler.
2 Copyright (C) 2002-2023 Free Software Foundation, Inc.
4 This file is part of GCC.
6 GCC is free software; you can redistribute it and/or modify it under
7 the terms of the GNU General Public License as published by the Free
8 Software Foundation; either version 3, or (at your option) any later
11 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
12 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"
35 #include "function-abi.h"
37 struct target_cfgloop default_target_cfgloop
;
39 struct target_cfgloop
*this_target_cfgloop
= &default_target_cfgloop
;
42 /* Checks whether BB is executed exactly once in each LOOP iteration. */
45 just_once_each_iteration_p (const class loop
*loop
, const_basic_block bb
)
47 /* It must be executed at least once each iteration. */
48 if (!dominated_by_p (CDI_DOMINATORS
, loop
->latch
, bb
))
52 if (bb
->loop_father
!= loop
)
55 /* But this was not enough. We might have some irreducible loop here. */
56 if (bb
->flags
& BB_IRREDUCIBLE_LOOP
)
62 /* Marks blocks and edges that are part of non-recognized loops; i.e. we
63 throw away all latch edges and mark blocks inside any remaining cycle.
64 Everything is a bit complicated due to fact we do not want to do this
65 for parts of cycles that only "pass" through some loop -- i.e. for
66 each cycle, we want to mark blocks that belong directly to innermost
67 loop containing the whole cycle.
69 LOOPS is the loop tree. */
71 #define LOOP_REPR(LOOP) ((LOOP)->num + last_basic_block_for_fn (cfun))
72 #define BB_REPR(BB) ((BB)->index + 1)
75 mark_irreducible_loops (void)
78 struct graph_edge
*ge
;
84 int num
= number_of_loops (cfun
);
86 bool irred_loop_found
= false;
89 gcc_assert (current_loops
!= NULL
);
91 /* Reset the flags. */
92 FOR_BB_BETWEEN (act
, ENTRY_BLOCK_PTR_FOR_FN (cfun
),
93 EXIT_BLOCK_PTR_FOR_FN (cfun
), next_bb
)
95 act
->flags
&= ~BB_IRREDUCIBLE_LOOP
;
96 FOR_EACH_EDGE (e
, ei
, act
->succs
)
97 e
->flags
&= ~EDGE_IRREDUCIBLE_LOOP
;
100 /* Create the edge lists. */
101 g
= new_graph (last_basic_block_for_fn (cfun
) + num
);
103 FOR_BB_BETWEEN (act
, ENTRY_BLOCK_PTR_FOR_FN (cfun
),
104 EXIT_BLOCK_PTR_FOR_FN (cfun
), next_bb
)
105 FOR_EACH_EDGE (e
, ei
, act
->succs
)
107 /* Ignore edges to exit. */
108 if (e
->dest
== EXIT_BLOCK_PTR_FOR_FN (cfun
))
112 dest
= BB_REPR (e
->dest
);
114 /* Ignore latch edges. */
115 if (e
->dest
->loop_father
->header
== e
->dest
116 && dominated_by_p (CDI_DOMINATORS
, act
, e
->dest
))
119 /* Edges inside a single loop should be left where they are. Edges
120 to subloop headers should lead to representative of the subloop,
121 but from the same place.
123 Edges exiting loops should lead from representative
124 of the son of nearest common ancestor of the loops in that
127 if (e
->dest
->loop_father
->header
== e
->dest
)
128 dest
= LOOP_REPR (e
->dest
->loop_father
);
130 if (!flow_bb_inside_loop_p (act
->loop_father
, e
->dest
))
132 depth
= 1 + loop_depth (find_common_loop (act
->loop_father
,
133 e
->dest
->loop_father
));
134 if (depth
== loop_depth (act
->loop_father
))
135 cloop
= act
->loop_father
;
137 cloop
= (*act
->loop_father
->superloops
)[depth
];
139 src
= LOOP_REPR (cloop
);
142 add_edge (g
, src
, dest
)->data
= e
;
145 /* Find the strongly connected components. */
146 graphds_scc (g
, NULL
);
148 /* Mark the irreducible loops. */
149 for (i
= 0; i
< g
->n_vertices
; i
++)
150 for (ge
= g
->vertices
[i
].succ
; ge
; ge
= ge
->succ_next
)
152 edge real
= (edge
) ge
->data
;
153 /* edge E in graph G is irreducible if it connects two vertices in the
156 /* All edges should lead from a component with higher number to the
157 one with lower one. */
158 gcc_assert (g
->vertices
[ge
->src
].component
>= g
->vertices
[ge
->dest
].component
);
160 if (g
->vertices
[ge
->src
].component
!= g
->vertices
[ge
->dest
].component
)
163 real
->flags
|= EDGE_IRREDUCIBLE_LOOP
;
164 irred_loop_found
= true;
165 if (flow_bb_inside_loop_p (real
->src
->loop_father
, real
->dest
))
166 real
->src
->flags
|= BB_IRREDUCIBLE_LOOP
;
171 loops_state_set (LOOPS_HAVE_MARKED_IRREDUCIBLE_REGIONS
);
172 return irred_loop_found
;
175 /* Counts number of insns inside LOOP. */
177 num_loop_insns (const class loop
*loop
)
179 basic_block
*bbs
, bb
;
180 unsigned i
, ninsns
= 0;
183 bbs
= get_loop_body (loop
);
184 for (i
= 0; i
< loop
->num_nodes
; i
++)
187 FOR_BB_INSNS (bb
, insn
)
188 if (NONDEBUG_INSN_P (insn
))
194 ninsns
= 1; /* To avoid division by zero. */
199 /* Counts number of insns executed on average per iteration LOOP. */
201 average_num_loop_insns (const class loop
*loop
)
203 basic_block
*bbs
, bb
;
209 bbs
= get_loop_body (loop
);
210 for (i
= 0; i
< loop
->num_nodes
; i
++)
215 FOR_BB_INSNS (bb
, insn
)
216 if (NONDEBUG_INSN_P (insn
))
219 ninsns
+= (sreal
)binsns
* bb
->count
.to_sreal_scale (loop
->header
->count
);
220 /* Avoid overflows. */
221 if (ninsns
> 1000000)
229 int64_t ret
= ninsns
.to_int ();
231 ret
= 1; /* To avoid division by zero. */
236 /* Return true if BB profile can be used to determine the expected number of
237 iterations (that is number of executions of latch edge(s) for each
238 entry of the loop. If this is the case initialize RET with the number
241 RELIABLE is set if profile indiates that the returned value should be
242 realistic estimate. (This is the case if we read profile and did not
243 messed it up yet and not the case of guessed profiles.)
245 This function uses only CFG profile. We track more reliable info in
246 loop_info structure and for loop optimization heuristics more relevant
247 is get_estimated_loop_iterations API. */
250 expected_loop_iterations_by_profile (const class loop
*loop
, sreal
*ret
,
253 profile_count header_count
= loop
->header
->count
;
257 /* TODO: For single exit loops we can use loop exit edge probability.
258 It also may be reliable while loop itself was adjusted. */
259 if (!header_count
.initialized_p ()
260 || !header_count
.nonzero_p ())
263 profile_count count_in
= profile_count::zero ();
267 /* For single-latch loops avoid querying dominators. */
271 FOR_EACH_EDGE (e
, ei
, loop
->header
->preds
)
272 if (e
->src
!= loop
->latch
)
273 count_in
+= e
->count ();
276 /* If latch is not found, loop is inconsistent. */
277 gcc_checking_assert (found
);
280 FOR_EACH_EDGE (e
, ei
, loop
->header
->preds
)
281 if (!dominated_by_p (CDI_DOMINATORS
, e
->src
, loop
->header
))
282 count_in
+= e
->count ();
285 /* Number of iterations is number of executions of latch edge. */
286 *ret
= (header_count
- count_in
).to_sreal_scale (count_in
, &known
);
291 /* Header should have at least count_in many executions.
292 Give up on clearly inconsistent profile. */
293 if (header_count
< count_in
&& header_count
.differs_from_p (count_in
))
295 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
296 fprintf (dump_file
, "Inconsistent bb profile of loop %i\n",
301 *reliable
= count_in
.reliable_p () && header_count
.reliable_p ();
306 /* Returns expected number of iterations of LOOP, according to
307 measured or guessed profile.
309 This functions attempts to return "sane" value even if profile
310 information is not good enough to derive osmething. */
313 expected_loop_iterations_unbounded (const class loop
*loop
,
314 bool *read_profile_p
)
316 gcov_type expected
= -1;
319 *read_profile_p
= false;
321 sreal sreal_expected
;
322 if (expected_loop_iterations_by_profile
323 (loop
, &sreal_expected
, read_profile_p
))
324 expected
= sreal_expected
.to_nearest_int ();
326 expected
= param_avg_loop_niter
;
328 HOST_WIDE_INT max
= get_max_loop_iterations_int (loop
);
329 if (max
!= -1 && max
< expected
)
335 /* Returns expected number of LOOP iterations. The returned value is bounded
336 by REG_BR_PROB_BASE. */
339 expected_loop_iterations (class loop
*loop
)
341 gcov_type expected
= expected_loop_iterations_unbounded (loop
);
342 return (expected
> REG_BR_PROB_BASE
? REG_BR_PROB_BASE
: expected
);
345 /* Returns the maximum level of nesting of subloops of LOOP. */
348 get_loop_level (const class loop
*loop
)
350 const class loop
*ploop
;
353 for (ploop
= loop
->inner
; ploop
; ploop
= ploop
->next
)
355 l
= get_loop_level (ploop
);
362 /* Initialize the constants for computing set costs. */
365 init_set_costs (void)
369 rtx reg1
= gen_raw_REG (SImode
, LAST_VIRTUAL_REGISTER
+ 1);
370 rtx reg2
= gen_raw_REG (SImode
, LAST_VIRTUAL_REGISTER
+ 2);
371 rtx addr
= gen_raw_REG (Pmode
, LAST_VIRTUAL_REGISTER
+ 3);
372 rtx mem
= validize_mem (gen_rtx_MEM (SImode
, addr
));
375 target_avail_regs
= 0;
376 target_clobbered_regs
= 0;
377 for (i
= 0; i
< FIRST_PSEUDO_REGISTER
; i
++)
378 if (TEST_HARD_REG_BIT (reg_class_contents
[GENERAL_REGS
], i
)
382 /* ??? This is only a rough heuristic. It doesn't cope well
383 with alternative ABIs, but that's an optimization rather than
384 correctness issue. */
385 if (default_function_abi
.clobbers_full_reg_p (i
))
386 target_clobbered_regs
++;
391 for (speed
= 0; speed
< 2; speed
++)
393 crtl
->maybe_hot_insn_p
= speed
;
394 /* Set up the costs for using extra registers:
396 1) If not many free registers remain, we should prefer having an
397 additional move to decreasing the number of available registers.
399 2) If no registers are available, we need to spill, which may require
400 storing the old value to memory and loading it back
401 (TARGET_SPILL_COST). */
404 emit_move_insn (reg1
, reg2
);
407 target_reg_cost
[speed
] = seq_cost (seq
, speed
);
410 emit_move_insn (mem
, reg1
);
411 emit_move_insn (reg2
, mem
);
414 target_spill_cost
[speed
] = seq_cost (seq
, speed
);
416 default_rtl_profile ();
419 /* Estimates cost of increased register pressure caused by making N_NEW new
420 registers live around the loop. N_OLD is the number of registers live
421 around the loop. If CALL_P is true, also take into account that
422 call-used registers may be clobbered in the loop body, reducing the
423 number of available registers before we spill. */
426 estimate_reg_pressure_cost (unsigned n_new
, unsigned n_old
, bool speed
,
430 unsigned regs_needed
= n_new
+ n_old
;
431 unsigned available_regs
= target_avail_regs
;
433 /* If there is a call in the loop body, the call-clobbered registers
434 are not available for loop invariants. */
436 available_regs
= available_regs
- target_clobbered_regs
;
438 /* If we have enough registers, we should use them and not restrict
439 the transformations unnecessarily. */
440 if (regs_needed
+ target_res_regs
<= available_regs
)
443 if (regs_needed
<= available_regs
)
444 /* If we are close to running out of registers, try to preserve
446 cost
= target_reg_cost
[speed
] * n_new
;
448 /* If we run out of registers, it is very expensive to add another
450 cost
= target_spill_cost
[speed
] * n_new
;
452 if (optimize
&& (flag_ira_region
== IRA_REGION_ALL
453 || flag_ira_region
== IRA_REGION_MIXED
)
454 && number_of_loops (cfun
) <= (unsigned) param_ira_max_loops_num
)
455 /* IRA regional allocation deals with high register pressure
456 better. So decrease the cost (to do more accurate the cost
457 calculation for IRA, we need to know how many registers lives
458 through the loop transparently). */
464 /* Sets EDGE_LOOP_EXIT flag for all loop exits. */
467 mark_loop_exit_edges (void)
472 if (number_of_loops (cfun
) <= 1)
475 FOR_EACH_BB_FN (bb
, cfun
)
479 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
481 if (loop_outer (bb
->loop_father
)
482 && loop_exit_edge_p (bb
->loop_father
, e
))
483 e
->flags
|= EDGE_LOOP_EXIT
;
485 e
->flags
&= ~EDGE_LOOP_EXIT
;
490 /* Return exit edge if loop has only one exit that is likely
491 to be executed on runtime (i.e. it is not EH or leading
495 single_likely_exit (class loop
*loop
, const vec
<edge
> &exits
)
497 edge found
= single_exit (loop
);
503 FOR_EACH_VEC_ELT (exits
, i
, ex
)
505 if (probably_never_executed_edge_p (cfun
, ex
)
506 /* We want to rule out paths to noreturns but not low probabilities
507 resulting from adjustments or combining.
508 FIXME: once we have better quality tracking, make this more
510 || ex
->probability
<= profile_probability::very_unlikely ())
521 /* Gets basic blocks of a LOOP. Header is the 0-th block, rest is in dfs
522 order against direction of edges from latch. Specially, if
523 header != latch, latch is the 1-st block. */
525 auto_vec
<basic_block
>
526 get_loop_hot_path (const class loop
*loop
)
528 basic_block bb
= loop
->header
;
529 auto_vec
<basic_block
> path
;
530 bitmap visited
= BITMAP_ALLOC (NULL
);
539 bitmap_set_bit (visited
, bb
->index
);
540 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
541 if ((!best
|| e
->probability
> best
->probability
)
542 && !loop_exit_edge_p (loop
, e
)
543 && !bitmap_bit_p (visited
, e
->dest
->index
))
545 if (!best
|| best
->dest
== loop
->header
)
549 BITMAP_FREE (visited
);