/* Branch prediction routines for the GNU compiler.
Copyright (C) 2000, 2001 Free Software Foundation, Inc.
- This file is part of GNU CC.
+ This file is part of GCC.
- GNU CC is free software; you can redistribute it and/or modify
- it under the terms of the GNU General Public License as published by
+ GCC is free software; you can redistribute it and/or modify it
+ under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.
- GNU CC is distributed in the hope that it will be useful,
- but WITHOUT ANY WARRANTY; without even the implied warranty of
- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
- GNU General Public License for more details.
+ GCC is distributed in the hope that it will be useful, but WITHOUT
+ ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public
+ License for more details.
You should have received a copy of the GNU General Public License
- along with GNU CC; see the file COPYING. If not, write to
- the Free Software Foundation, 59 Temple Place - Suite 330,
- Boston, MA 02111-1307, USA. */
+ along with GCC; see the file COPYING. If not, write to the Free
+ Software Foundation, 59 Temple Place - Suite 330, Boston, MA
+ 02111-1307, USA. */
/* References:
static void combine_predictions_for_insn PARAMS ((rtx, basic_block));
static void dump_prediction PARAMS ((enum br_predictor, int,
- basic_block));
+ basic_block, int));
static void estimate_loops_at_level PARAMS ((struct loop *loop));
static void propagate_freq PARAMS ((basic_block));
static void estimate_bb_frequencies PARAMS ((struct loops *));
Filled using information from predict.def. */
struct predictor_info
{
- const char *name; /* Name used in the debugging dumps. */
- int hitrate; /* Expected hitrate used by
- predict_insn_def call. */
+ const char *const name; /* Name used in the debugging dumps. */
+ const int hitrate; /* Expected hitrate used by
+ predict_insn_def call. */
+ const int flags;
};
-#define DEF_PREDICTOR(ENUM, NAME, HITRATE) {NAME, HITRATE},
-struct predictor_info predictor_info[] = {
+/* Use given predictor without Dempster-Shaffer theory if it matches
+ using first_match heuristics. */
+#define PRED_FLAG_FIRST_MATCH 1
+
+/* Recompute hitrate in percent to our representation. */
+
+#define HITRATE(VAL) ((int)((VAL) * REG_BR_PROB_BASE + 50) / 100)
+
+#define DEF_PREDICTOR(ENUM, NAME, HITRATE, FLAGS) {NAME, HITRATE, FLAGS},
+static const struct predictor_info predictor_info[] = {
#include "predict.def"
- /* Upper bound on non-language-specific builtins. */
- {NULL, 0}
+ /* Upper bound on predictors. */
+ {NULL, 0, 0}
};
#undef DEF_PREDICTOR
/* Dump information about the branch prediction to the output file. */
static void
-dump_prediction (predictor, probability, bb)
+dump_prediction (predictor, probability, bb, used)
enum br_predictor predictor;
int probability;
basic_block bb;
+ int used;
{
edge e = bb->succ;
while (e->flags & EDGE_FALLTHRU)
e = e->succ_next;
- fprintf (rtl_dump_file, " %s heuristics: %.1f%%",
+ fprintf (rtl_dump_file, " %s heuristics%s: %.1f%%",
predictor_info[predictor].name,
+ used ? "" : " (ignored)",
probability * 100.0 / REG_BR_PROB_BASE);
if (bb->count)
{
rtx prob_note = find_reg_note (insn, REG_BR_PROB, 0);
rtx *pnote = ®_NOTES (insn);
+ rtx note = REG_NOTES (insn);
int best_probability = PROB_EVEN;
int best_predictor = END_PREDICTORS;
+ int combined_probability = REG_BR_PROB_BASE / 2;
+ int d;
+ bool first_match = false;
+ bool found = false;
if (rtl_dump_file)
fprintf (rtl_dump_file, "Predictions for insn %i bb %i\n", INSN_UID (insn),
bb->index);
/* We implement "first match" heuristics and use probability guessed
- by predictor with smallest index. In future we will use better
+ by predictor with smallest index. In the future we will use better
probability combination techniques. */
+ while (note)
+ {
+ if (REG_NOTE_KIND (note) == REG_BR_PRED)
+ {
+ int predictor = INTVAL (XEXP (XEXP (note, 0), 0));
+ int probability = INTVAL (XEXP (XEXP (note, 0), 1));
+
+ found = true;
+ if (best_predictor > predictor)
+ best_probability = probability, best_predictor = predictor;
+
+ d = (combined_probability * probability
+ + (REG_BR_PROB_BASE - combined_probability)
+ * (REG_BR_PROB_BASE - probability));
+ /* An FP math to avoid overflows of 32bit integers. */
+ combined_probability = (((double)combined_probability) * probability
+ * REG_BR_PROB_BASE / d + 0.5);
+ }
+ note = XEXP (note, 1);
+ }
+
+ /* Decide heuristic to use. In case we didn't match anything, use
+ no_prediction heuristic, in case we did match, use either
+ first match or Dempster-Shaffer theory depending on the flags. */
+
+ if (predictor_info [best_predictor].flags & PRED_FLAG_FIRST_MATCH)
+ first_match = true;
+
+ if (!found)
+ dump_prediction (PRED_NO_PREDICTION, combined_probability, bb, true);
+ else
+ {
+ dump_prediction (PRED_DS_THEORY, combined_probability, bb,
+ !first_match);
+ dump_prediction (PRED_FIRST_MATCH, best_probability, bb, first_match);
+ }
+
+ if (first_match)
+ combined_probability = best_probability;
+ dump_prediction (PRED_COMBINED, combined_probability, bb, true);
+
while (*pnote)
{
if (REG_NOTE_KIND (*pnote) == REG_BR_PRED)
int predictor = INTVAL (XEXP (XEXP (*pnote, 0), 0));
int probability = INTVAL (XEXP (XEXP (*pnote, 0), 1));
- dump_prediction (predictor, probability, bb);
- if (best_predictor > predictor)
- best_probability = probability, best_predictor = predictor;
- *pnote = XEXP (*pnote, 1);
+ dump_prediction (predictor, probability, bb,
+ !first_match || best_predictor == predictor);
+ *pnote = XEXP (*pnote, 1);
}
else
pnote = &XEXP (*pnote, 1);
}
- dump_prediction (PRED_FIRST_MATCH, best_probability, bb);
if (!prob_note)
{
REG_NOTES (insn)
= gen_rtx_EXPR_LIST (REG_BR_PROB,
- GEN_INT (best_probability), REG_NOTES (insn));
+ GEN_INT (combined_probability), REG_NOTES (insn));
+ /* Save the prediction into CFG in case we are seeing non-degenerated
+ conditional jump. */
+ if (bb->succ->succ_next)
+ {
+ BRANCH_EDGE (bb)->probability = combined_probability;
+ FALLTHRU_EDGE (bb)->probability = REG_BR_PROB_BASE - combined_probability;
+ }
}
}
{
sbitmap *dominators, *post_dominators;
int i;
+ int found_noreturn = 0;
dominators = sbitmap_vector_alloc (n_basic_blocks, n_basic_blocks);
post_dominators = sbitmap_vector_alloc (n_basic_blocks, n_basic_blocks);
- calculate_dominance_info (NULL, dominators, 0);
- calculate_dominance_info (NULL, post_dominators, 1);
+ calculate_dominance_info (NULL, dominators, CDI_DOMINATORS);
+ calculate_dominance_info (NULL, post_dominators, CDI_POST_DOMINATORS);
/* Try to predict out blocks in a loop that are not part of a
natural loop. */
{
int header_found = 0;
edge e;
-
- /* Loop branch heruistics - predict as taken an edge back to
+
+ /* Loop branch heuristics - predict as taken an edge back to
a loop's head. */
for (e = BASIC_BLOCK(j)->succ; e; e = e->succ_next)
- if (e->dest == loops_info->array[i].header)
+ if (e->dest == loops_info->array[i].header
+ && e->src == loops_info->array[i].latch)
{
header_found = 1;
predict_edge_def (e, PRED_LOOP_BRANCH, TAKEN);
}
- /* Loop exit heruistics - predict as not taken an edge exiting
- the loop if the conditinal has no loop header successors */
+ /* Loop exit heuristics - predict as not taken an edge
+ exiting the loop if the conditinal has no loop header
+ successors. */
if (!header_found)
for (e = BASIC_BLOCK(j)->succ; e; e = e->succ_next)
if (e->dest->index <= 0
}
}
- /* Attempt to predict conditional jumps using a number of heuristics.
- For each conditional jump, we try each heuristic in a fixed order.
- If more than one heuristic applies to a particular branch, the first
- is used as the prediction for the branch. */
+ /* Attempt to predict conditional jumps using a number of heuristics. */
for (i = 0; i < n_basic_blocks; i++)
{
basic_block bb = BASIC_BLOCK (i);
/* If block has no sucessor, predict all possible paths to
it as improbable, as the block contains a call to a noreturn
function and thus can be executed only once. */
- if (bb->succ == NULL)
+ if (bb->succ == NULL && !found_noreturn)
{
int y;
+
+ /* ??? Postdominator claims each noreturn block to be postdominated
+ by each, so we need to run only once. This needs to be changed
+ once postdominace algorithm is updated to say something more sane.
+ */
+ found_noreturn = 1;
for (y = 0; y < n_basic_blocks; y++)
if (!TEST_BIT (post_dominators[y], i))
{
if (GET_CODE (insn) == CALL_INSN
/* Constant and pure calls are hardly used to signalize
something exceptional. */
- && ! CONST_CALL_P (insn))
+ && ! CONST_OR_PURE_CALL_P (insn))
{
predict_edge_def (e, PRED_CALL, NOT_TAKEN);
break;
&& (XEXP (cond, 1) == const0_rtx
|| (GET_CODE (XEXP (cond, 1)) == REG
&& REG_POINTER (XEXP (cond, 1)))))
-
+
predict_insn_def (last_insn, PRED_POINTER, NOT_TAKEN);
break;
case NE:
}
\f
/* __builtin_expect dropped tokens into the insn stream describing
- expected values of registers. Generate branch probabilities
+ expected values of registers. Generate branch probabilities
based off these values. */
void
(set r71 -1)
(set r80 (lt r70 r71))
(set pc (if_then_else (ne r80 0) ...))
- as canonicalize_condition will render this to us as
+ as canonicalize_condition will render this to us as
(lt r70, r71)
Could use cselib to try and reduce this further. */
- cond = XEXP (SET_SRC (PATTERN (insn)), 0);
+ cond = XEXP (SET_SRC (pc_set (insn)), 0);
cond = canonicalize_condition (insn, cond, 0, NULL, ev_reg);
if (! cond
|| XEXP (cond, 0) != ev_reg
|| GET_CODE (XEXP (cond, 1)) != CONST_INT)
continue;
- /* Substitute and simplify. Given that the expression we're
+ /* Substitute and simplify. Given that the expression we're
building involves two constants, we should wind up with either
true or false. */
cond = gen_rtx_fmt_ee (GET_CODE (cond), VOIDmode,
}
}
\f
-/* This is used to carry information about basic blocks. It is
+/* This is used to carry information about basic blocks. It is
attached to the AUX field of the standard CFG block. */
typedef struct block_info_def
/* To keep queue of basic blocks to process. */
basic_block next;
- /* True if block already converted. */
- int visited:1;
+ /* True if block needs to be visited in prop_freqency. */
+ int tovisit:1;
- /* Number of block proceeded before adding basic block to the queue. Used
- to recognize irregular regions. */
- int nvisited;
+ /* Number of predecesors we need to visit first. */
+ int npredecesors;
} *block_info;
/* Similar information for edges. */
basic_block last = bb;
edge e;
basic_block nextbb;
- int nvisited = 0;
+ int n;
+
+ /* For each basic block we need to visit count number of his predecesors
+ we need to visit first. */
+ for (n = 0; n < n_basic_blocks; n++)
+ {
+ basic_block bb = BASIC_BLOCK (n);
+ if (BLOCK_INFO (bb)->tovisit)
+ {
+ int count = 0;
+ for (e = bb->pred; e; e = e->pred_next)
+ if (BLOCK_INFO (e->src)->tovisit && !(e->flags & EDGE_DFS_BACK))
+ count++;
+ else if (BLOCK_INFO (e->src)->tovisit
+ && rtl_dump_file && !EDGE_INFO (e)->back_edge)
+ fprintf (rtl_dump_file,
+ "Irreducible region hit, ignoring edge to %i->%i\n",
+ e->src->index, bb->index);
+ BLOCK_INFO (bb)->npredecesors = count;
+ }
+ }
BLOCK_INFO (head)->frequency = 1;
for (; bb; bb = nextbb)
/* Compute frequency of basic block. */
if (bb != head)
{
+#ifdef ENABLE_CHECKING
for (e = bb->pred; e; e = e->pred_next)
- if (!BLOCK_INFO (e->src)->visited && !EDGE_INFO (e)->back_edge)
- break;
-
- /* We didn't proceeded all predecesors of edge e yet. These may
- be waiting in the queue or we may hit irreducible region.
-
- To avoid infinite looping on irrecudible regions, count number
- of block proceeded at the time basic block has been queued. In the
- case number didn't changed, we've hit irreducible region and we
- forget the backward edge. This can increase time complexity
- by the number of irreducible blocks, but in same way standard the
- loop does, so it should not result in noticeable slowodwn.
-
- Alternativly we may distinquish backward and cross edges in the
- DFS tree by preprocesing pass and ignore existence of non-loop
- backward edges. */
- if (e && BLOCK_INFO (bb)->nvisited != nvisited)
- {
- if (!nextbb)
- nextbb = e->dest;
- else
- BLOCK_INFO (last)->next = e->dest;
- BLOCK_INFO (last)->nvisited = nvisited;
- last = e->dest;
- continue;
- }
- else if (e && rtl_dump_file)
- fprintf (rtl_dump_file, "Irreducible region hit, ignoring edge to bb %i\n",
- bb->index);
+ if (BLOCK_INFO (e->src)->tovisit && !(e->flags & EDGE_DFS_BACK))
+ abort ();
+#endif
for (e = bb->pred; e; e = e->pred_next)
if (EDGE_INFO (e)->back_edge)
cyclic_probability += EDGE_INFO (e)->back_edge_prob;
- else if (BLOCK_INFO (e->src)->visited)
+ else if (!(e->flags & EDGE_DFS_BACK))
frequency += (e->probability
* BLOCK_INFO (e->src)->frequency /
REG_BR_PROB_BASE);
BLOCK_INFO (bb)->frequency = frequency / (1 - cyclic_probability);
}
- BLOCK_INFO (bb)->visited = 1;
+ BLOCK_INFO (bb)->tovisit = 0;
/* Compute back edge frequencies. */
for (e = bb->succ; e; e = e->succ_next)
* BLOCK_INFO (bb)->frequency
/ REG_BR_PROB_BASE);
- /* Propagate to succesor blocks. */
+ /* Propagate to successor blocks. */
for (e = bb->succ; e; e = e->succ_next)
- if (!EDGE_INFO (e)->back_edge
- && !BLOCK_INFO (e->dest)->visited
- && !BLOCK_INFO (e->dest)->next && e->dest != last)
+ if (!(e->flags & EDGE_DFS_BACK)
+ && BLOCK_INFO (e->dest)->npredecesors)
{
- if (!nextbb)
- nextbb = e->dest;
- else
- BLOCK_INFO (last)->next = e->dest;
- BLOCK_INFO (last)->nvisited = nvisited;
- last = e->dest;
- }
- nvisited ++;
+ BLOCK_INFO (e->dest)->npredecesors--;
+ if (!BLOCK_INFO (e->dest)->npredecesors)
+ {
+ if (!nextbb)
+ nextbb = e->dest;
+ else
+ BLOCK_INFO (last)->next = e->dest;
+ last = e->dest;
+ }
+ }
}
}
-/* Estimate probabilities of the loopback edges in loops at same nest level. */
+/* Estimate probabilities of loopback edges in loops at same nest level. */
static void
estimate_loops_at_level (first_loop)
struct loop *first_loop;
estimate_loops_at_level (loop->inner);
- /* find current loop back edge and mark it. */
+ /* Find current loop back edge and mark it. */
for (e = loop->latch->succ; e->dest != loop->header; e = e->succ_next);
EDGE_INFO (e)->back_edge = 1;
- /* In case loop header is shared, ensure that it is the last one sharing
- same header, so we avoid redundant work. */
+ /* In case the loop header is shared, ensure that it is the last
+ one sharing the same header, so we avoid redundant work. */
if (loop->shared)
{
for (l = loop->next; l; l = l->next)
for (l = loop->shared ? first_loop : loop; l != loop->next; l = l->next)
if (loop->header == l->header)
EXECUTE_IF_SET_IN_SBITMAP (l->nodes, 0, n,
- BLOCK_INFO (BASIC_BLOCK (n))->visited =
- 0);
+ BLOCK_INFO (BASIC_BLOCK (n))->tovisit = 1
+ );
propagate_freq (loop->header);
}
}
}
}
+/* Return true if function is likely to be expensive, so there is no point
+ to optimizer performance of prologue, epilogue or do inlining at the
+ expense of code size growth. THRESHOLD is the limit of number
+ of isntructions function can execute at average to be still considered
+ not expensive. */
+bool
+expensive_function_p (threshold)
+ int threshold;
+{
+ unsigned int sum = 0;
+ int i;
+ unsigned int limit;
+
+ /* We can not compute accurately for large thresholds due to scaled
+ frequencies. */
+ if (threshold > BB_FREQ_MAX)
+ abort ();
+
+ /* Frequencies are out of range. This eighter means that function contains
+ internal loop executing more than BB_FREQ_MAX times or profile feedback
+ is available and function has not been executed at all. */
+ if (ENTRY_BLOCK_PTR->frequency == 0)
+ return true;
+
+ /* Maximally BB_FREQ_MAX^2 so overflow won't happen. */
+ limit = ENTRY_BLOCK_PTR->frequency * threshold;
+ for (i = 0; i < n_basic_blocks; i++)
+ {
+ basic_block bb = BASIC_BLOCK (i);
+ rtx insn;
+
+ for (insn = bb->head; insn != NEXT_INSN (bb->end);
+ insn = NEXT_INSN (insn))
+ {
+ if (active_insn_p (insn))
+ {
+ sum += bb->frequency;
+ if (sum > limit)
+ return true;
+ }
+ }
+ }
+ return false;
+}
+
/* Estimate basic blocks frequency by given branch probabilities. */
static void
estimate_bb_frequencies (loops)
struct loops *loops;
{
- block_info bi;
- edge_info ei;
- int edgenum = 0;
int i;
double freq_max = 0;
+ mark_dfs_back_edges ();
if (flag_branch_probabilities)
{
counts_to_freqs ();
edge fallthru, branch;
if (GET_CODE (last_insn) != JUMP_INSN || !any_condjump_p (last_insn)
- /* Avoid handling of conditionals jump jumping to fallthru edge. */
+ /* Avoid handling of conditional jumps jumping to fallthru edge. */
|| BASIC_BLOCK (i)->succ->succ_next == NULL)
{
/* We can predict only conditional jumps at the moment.
- Expect each edge to be equall probable.
- ?? In future we want to make abnormal edges improbable. */
+ Expect each edge to be equally probable.
+ ?? In the future we want to make abnormal edges improbable. */
int nedges = 0;
edge e;
ENTRY_BLOCK_PTR->succ->probability = REG_BR_PROB_BASE;
/* Set up block info for each basic block. */
- bi = (block_info) xcalloc ((n_basic_blocks + 2), sizeof (*bi));
- ei = (edge_info) xcalloc ((n_edges), sizeof (*ei));
+ alloc_aux_for_blocks (sizeof (struct block_info_def));
+ alloc_aux_for_edges (sizeof (struct edge_info_def));
for (i = -2; i < n_basic_blocks; i++)
{
edge e;
bb = EXIT_BLOCK_PTR;
else
bb = BASIC_BLOCK (i);
- bb->aux = bi + i + 2;
- BLOCK_INFO (bb)->visited = 1;
+ BLOCK_INFO (bb)->tovisit = 0;
for (e = bb->succ; e; e = e->succ_next)
- {
- e->aux = ei + edgenum, edgenum++;
- EDGE_INFO (e)->back_edge_prob = ((double) e->probability
- / REG_BR_PROB_BASE);
- }
+ EDGE_INFO (e)->back_edge_prob = ((double) e->probability
+ / REG_BR_PROB_BASE);
}
/* First compute probabilities locally for each loop from innermost
to outermost to examine probabilities for back edges. */
- estimate_loops_at_level (loops->tree);
+ estimate_loops_at_level (loops->tree_root);
/* Now fake loop around whole function to finalize probabilities. */
for (i = 0; i < n_basic_blocks; i++)
- BLOCK_INFO (BASIC_BLOCK (i))->visited = 0;
- BLOCK_INFO (ENTRY_BLOCK_PTR)->visited = 0;
- BLOCK_INFO (EXIT_BLOCK_PTR)->visited = 0;
+ BLOCK_INFO (BASIC_BLOCK (i))->tovisit = 1;
+ BLOCK_INFO (ENTRY_BLOCK_PTR)->tovisit = 1;
+ BLOCK_INFO (EXIT_BLOCK_PTR)->tovisit = 1;
propagate_freq (ENTRY_BLOCK_PTR);
for (i = 0; i < n_basic_blocks; i++)
+ 0.5);
}
- free (ei);
- free (bi);
+ free_aux_for_blocks ();
+ free_aux_for_edges ();
}
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