/* Branch prediction routines for the GNU compiler.
- Copyright (C) 2000 Free Software Foundation, Inc.
+ Copyright (C) 2000, 2001, 2002, 2003 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
- the Free Software Foundation; either version 2, or (at your option)
- any later version.
+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. */
+You should have received a copy of the GNU General Public License
+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:
[2] "Static Branch Frequency and Program Profile Analysis"
Wu and Larus; MICRO-27.
[3] "Corpus-based Static Branch Prediction"
- Calder, Grunwald, Lindsay, Martin, Mozer, and Zorn; PLDI '95.
-*/
+ Calder, Grunwald, Lindsay, Martin, Mozer, and Zorn; PLDI '95. */
#include "config.h"
#include "system.h"
+#include "coretypes.h"
+#include "tm.h"
#include "tree.h"
#include "rtl.h"
#include "tm_p.h"
+#include "hard-reg-set.h"
#include "basic-block.h"
#include "insn-config.h"
#include "regs.h"
-#include "hard-reg-set.h"
#include "flags.h"
#include "output.h"
#include "function.h"
#include "except.h"
#include "toplev.h"
#include "recog.h"
-#include "insn-flags.h"
#include "expr.h"
+#include "predict.h"
+#include "coverage.h"
+#include "sreal.h"
+#include "params.h"
+#include "target.h"
+#include "loop.h"
+#include "cfgloop.h"
+
+/* real constants: 0, 1, 1-1/REG_BR_PROB_BASE, REG_BR_PROB_BASE,
+ 1/REG_BR_PROB_BASE, 0.5, BB_FREQ_MAX. */
+static sreal real_zero, real_one, real_almost_one, real_br_prob_base,
+ real_inv_br_prob_base, real_one_half, real_bb_freq_max;
+
+/* Random guesstimation given names. */
+#define PROB_VERY_UNLIKELY (REG_BR_PROB_BASE / 10 - 1)
+#define PROB_EVEN (REG_BR_PROB_BASE / 2)
+#define PROB_VERY_LIKELY (REG_BR_PROB_BASE - PROB_VERY_UNLIKELY)
+#define PROB_ALWAYS (REG_BR_PROB_BASE)
+
+static bool predicted_by_p (basic_block, enum br_predictor);
+static void combine_predictions_for_insn (rtx, basic_block);
+static void dump_prediction (enum br_predictor, int, basic_block, int);
+static void estimate_loops_at_level (struct loop *loop);
+static void propagate_freq (struct loop *);
+static void estimate_bb_frequencies (struct loops *);
+static void counts_to_freqs (void);
+static void process_note_predictions (basic_block, int *, dominance_info,
+ dominance_info);
+static void process_note_prediction (basic_block, int *, dominance_info,
+ dominance_info, int, int);
+static bool last_basic_block_p (basic_block);
+static void compute_function_frequency (void);
+static void choose_function_section (void);
+static bool can_predict_insn_p (rtx);
+
+/* Information we hold about each branch predictor.
+ Filled using information from predict.def. */
+
+struct predictor_info
+{
+ const char *const name; /* Name used in the debugging dumps. */
+ const int hitrate; /* Expected hitrate used by
+ predict_insn_def call. */
+ const int flags;
+};
+
+/* 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 predictors. */
+ {NULL, 0, 0}
+};
+#undef DEF_PREDICTOR
+
+/* Return true in case BB can be CPU intensive and should be optimized
+ for maximal performance. */
+
+bool
+maybe_hot_bb_p (basic_block bb)
+{
+ if (profile_info && flag_branch_probabilities
+ && (bb->count
+ < profile_info->sum_max / PARAM_VALUE (HOT_BB_COUNT_FRACTION)))
+ return false;
+ if (bb->frequency < BB_FREQ_MAX / PARAM_VALUE (HOT_BB_FREQUENCY_FRACTION))
+ return false;
+ return true;
+}
+
+/* Return true in case BB is cold and should be optimized for size. */
+
+bool
+probably_cold_bb_p (basic_block bb)
+{
+ if (profile_info && flag_branch_probabilities
+ && (bb->count
+ < profile_info->sum_max / PARAM_VALUE (HOT_BB_COUNT_FRACTION)))
+ return true;
+ if (bb->frequency < BB_FREQ_MAX / PARAM_VALUE (HOT_BB_FREQUENCY_FRACTION))
+ return true;
+ return false;
+}
+
+/* Return true in case BB is probably never executed. */
+bool
+probably_never_executed_bb_p (basic_block bb)
+{
+ if (profile_info && flag_branch_probabilities)
+ return ((bb->count + profile_info->runs / 2) / profile_info->runs) == 0;
+ return false;
+}
+
+/* Return true if the one of outgoing edges is already predicted by
+ PREDICTOR. */
+
+static bool
+predicted_by_p (basic_block bb, enum br_predictor predictor)
+{
+ rtx note;
+ if (!INSN_P (bb->end))
+ return false;
+ for (note = REG_NOTES (bb->end); note; note = XEXP (note, 1))
+ if (REG_NOTE_KIND (note) == REG_BR_PRED
+ && INTVAL (XEXP (XEXP (note, 0), 0)) == (int)predictor)
+ return true;
+ return false;
+}
+
+void
+predict_insn (rtx insn, enum br_predictor predictor, int probability)
+{
+ if (!any_condjump_p (insn))
+ abort ();
+ if (!flag_guess_branch_prob)
+ return;
+
+ REG_NOTES (insn)
+ = gen_rtx_EXPR_LIST (REG_BR_PRED,
+ gen_rtx_CONCAT (VOIDmode,
+ GEN_INT ((int) predictor),
+ GEN_INT ((int) probability)),
+ REG_NOTES (insn));
+}
+
+/* Predict insn by given predictor. */
+
+void
+predict_insn_def (rtx insn, enum br_predictor predictor,
+ enum prediction taken)
+{
+ int probability = predictor_info[(int) predictor].hitrate;
+
+ if (taken != TAKEN)
+ probability = REG_BR_PROB_BASE - probability;
+ predict_insn (insn, predictor, probability);
+}
+
+/* Predict edge E with given probability if possible. */
+
+void
+predict_edge (edge e, enum br_predictor predictor, int probability)
+{
+ rtx last_insn;
+ last_insn = e->src->end;
+
+ /* We can store the branch prediction information only about
+ conditional jumps. */
+ if (!any_condjump_p (last_insn))
+ return;
+
+ /* We always store probability of branching. */
+ if (e->flags & EDGE_FALLTHRU)
+ probability = REG_BR_PROB_BASE - probability;
+
+ predict_insn (last_insn, predictor, probability);
+}
+
+/* Return true when we can store prediction on insn INSN.
+ At the moment we represent predictions only on conditional
+ jumps, not at computed jump or other complicated cases. */
+static bool
+can_predict_insn_p (rtx insn)
+{
+ return (GET_CODE (insn) == JUMP_INSN
+ && any_condjump_p (insn)
+ && BLOCK_FOR_INSN (insn)->succ->succ_next);
+}
+
+/* Predict edge E by given predictor if possible. */
+
+void
+predict_edge_def (edge e, enum br_predictor predictor,
+ enum prediction taken)
+{
+ int probability = predictor_info[(int) predictor].hitrate;
+
+ if (taken != TAKEN)
+ probability = REG_BR_PROB_BASE - probability;
+
+ predict_edge (e, predictor, probability);
+}
+
+/* Invert all branch predictions or probability notes in the INSN. This needs
+ to be done each time we invert the condition used by the jump. */
+
+void
+invert_br_probabilities (rtx insn)
+{
+ rtx note;
+
+ for (note = REG_NOTES (insn); note; note = XEXP (note, 1))
+ if (REG_NOTE_KIND (note) == REG_BR_PROB)
+ XEXP (note, 0) = GEN_INT (REG_BR_PROB_BASE - INTVAL (XEXP (note, 0)));
+ else if (REG_NOTE_KIND (note) == REG_BR_PRED)
+ XEXP (XEXP (note, 0), 1)
+ = GEN_INT (REG_BR_PROB_BASE - INTVAL (XEXP (XEXP (note, 0), 1)));
+}
+
+/* Dump information about the branch prediction to the output file. */
+
+static void
+dump_prediction (enum br_predictor predictor, int probability,
+ basic_block bb, int used)
+{
+ edge e = bb->succ;
+
+ if (!rtl_dump_file)
+ return;
+
+ while (e && (e->flags & EDGE_FALLTHRU))
+ e = e->succ_next;
+
+ fprintf (rtl_dump_file, " %s heuristics%s: %.1f%%",
+ predictor_info[predictor].name,
+ used ? "" : " (ignored)", probability * 100.0 / REG_BR_PROB_BASE);
+
+ if (bb->count)
+ {
+ fprintf (rtl_dump_file, " exec ");
+ fprintf (rtl_dump_file, HOST_WIDEST_INT_PRINT_DEC, bb->count);
+ if (e)
+ {
+ fprintf (rtl_dump_file, " hit ");
+ fprintf (rtl_dump_file, HOST_WIDEST_INT_PRINT_DEC, e->count);
+ fprintf (rtl_dump_file, " (%.1f%%)", e->count * 100.0 / bb->count);
+ }
+ }
+
+ fprintf (rtl_dump_file, "\n");
+}
+/* Combine all REG_BR_PRED notes into single probability and attach REG_BR_PROB
+ note if not already present. Remove now useless REG_BR_PRED notes. */
+
+static void
+combine_predictions_for_insn (rtx insn, basic_block bb)
+{
+ rtx prob_note = find_reg_note (insn, REG_BR_PROB, 0);
+ rtx *pnote = ®_NOTES (insn);
+ rtx note;
+ 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 the future we will use better
+ probability combination techniques. */
+ for (note = REG_NOTES (insn); note; note = XEXP (note, 1))
+ 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));
+
+ /* Use FP math to avoid overflows of 32bit integers. */
+ if (d == 0)
+ /* If one probability is 0% and one 100%, avoid division by zero. */
+ combined_probability = REG_BR_PROB_BASE / 2;
+ else
+ combined_probability = (((double) combined_probability) * probability
+ * REG_BR_PROB_BASE / d + 0.5);
+ }
+
+ /* Decide which 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,
+ !first_match || best_predictor == predictor);
+ *pnote = XEXP (*pnote, 1);
+ }
+ else
+ pnote = &XEXP (*pnote, 1);
+ }
+
+ if (!prob_note)
+ {
+ REG_NOTES (insn)
+ = gen_rtx_EXPR_LIST (REG_BR_PROB,
+ 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;
+ }
+ }
+}
/* Statically estimate the probability that a branch will be taken.
??? In the next revision there will be a number of other predictors added
from the above references. Further, each heuristic will be factored out
into its own function for clarity (and to facilitate the combination of
- predictions). */
+ predictions). */
void
-estimate_probability (loops_info)
- struct loops *loops_info;
+estimate_probability (struct loops *loops_info)
{
- int i;
+ dominance_info dominators, post_dominators;
+ basic_block bb;
+ unsigned i;
+
+ connect_infinite_loops_to_exit ();
+ dominators = calculate_dominance_info (CDI_DOMINATORS);
+ post_dominators = calculate_dominance_info (CDI_POST_DOMINATORS);
- /* Try to predict out blocks in a loop that are not part of a natural loop */
- for (i = 0; i < loops_info->num; i++)
+ /* Try to predict out blocks in a loop that are not part of a
+ natural loop. */
+ for (i = 1; i < loops_info->num; i++)
{
- int j;
+ basic_block bb, *bbs;
+ unsigned j;
+ int exits;
+ struct loop *loop = loops_info->parray[i];
+ struct loop_desc desc;
+ unsigned HOST_WIDE_INT niter;
- for (j = loops_info->array[i].header->index;
- j <= loops_info->array[i].latch->index;
- ++j)
+ flow_loop_scan (loops_info, loop, LOOP_EXIT_EDGES);
+ exits = loop->num_exits;
+
+ if (simple_loop_p (loops_info, loop, &desc)
+ && desc.const_iter)
{
+ int prob;
+ niter = desc.niter + 1;
+ if (niter == 0) /* We might overflow here. */
+ niter = desc.niter;
+
+ prob = (REG_BR_PROB_BASE
+ - (REG_BR_PROB_BASE + niter /2) / niter);
+ /* Branch prediction algorithm gives 0 frequency for everything
+ after the end of loop for loop having 0 probability to finish. */
+ if (prob == REG_BR_PROB_BASE)
+ prob = REG_BR_PROB_BASE - 1;
+ predict_edge (desc.in_edge, PRED_LOOP_ITERATIONS,
+ prob);
+ }
+
+ bbs = get_loop_body (loop);
+ for (j = 0; j < loop->num_nodes; j++)
+ {
+ int header_found = 0;
edge e;
-
- if (! TEST_BIT (loops_info->array[i].nodes, j))
- for (e = BASIC_BLOCK(j)->pred; e; e = e->pred_next)
- if (TEST_BIT (loops_info->array[i].nodes, e->src->index))
- {
- rtx last_insn = BLOCK_END (e->src->index);
- rtx cond, earliest;
-
- if (GET_CODE (last_insn) != JUMP_INSN
- || ! condjump_p (last_insn) || simplejump_p (last_insn))
- continue;
- cond = get_condition (last_insn, &earliest);
- if (!cond)
- continue;
- if (! find_reg_note (last_insn, REG_BR_PROB, 0))
- REG_NOTES (last_insn)
- = gen_rtx_EXPR_LIST (REG_BR_PROB, GEN_INT (REG_BR_PROB_BASE),
- REG_NOTES (last_insn));
- }
+
+ bb = bbs[j];
+
+ /* Bypass loop heuristics on continue statement. These
+ statements construct loops via "non-loop" constructs
+ in the source language and are better to be handled
+ separately. */
+ if (!can_predict_insn_p (bb->end)
+ || predicted_by_p (bb, PRED_CONTINUE))
+ continue;
+
+ /* Loop branch heuristics - predict an edge back to a
+ loop's head as taken. */
+ for (e = bb->succ; e; e = e->succ_next)
+ if (e->dest == loop->header
+ && e->src == loop->latch)
+ {
+ header_found = 1;
+ predict_edge_def (e, PRED_LOOP_BRANCH, TAKEN);
+ }
+
+ /* Loop exit heuristics - predict an edge exiting the loop if the
+ conditional has no loop header successors as not taken. */
+ if (!header_found)
+ for (e = bb->succ; e; e = e->succ_next)
+ if (e->dest->index < 0
+ || !flow_bb_inside_loop_p (loop, e->dest))
+ predict_edge
+ (e, PRED_LOOP_EXIT,
+ (REG_BR_PROB_BASE
+ - predictor_info [(int) PRED_LOOP_EXIT].hitrate)
+ / exits);
}
}
- /* Try to predict condjumps using same algorithm as mostly_true_jump */
- for (i = 0; i < n_basic_blocks - 1; i++)
+ /* Attempt to predict conditional jumps using a number of heuristics. */
+ FOR_EACH_BB (bb)
{
- rtx last_insn = BLOCK_END (i);
+ rtx last_insn = bb->end;
rtx cond, earliest;
- int prob = 0;
+ edge e;
- if (GET_CODE (last_insn) != JUMP_INSN
- || ! condjump_p (last_insn) || simplejump_p (last_insn))
+ if (! can_predict_insn_p (last_insn))
continue;
+
+ for (e = bb->succ; e; e = e->succ_next)
+ {
+ /* Predict early returns to be probable, as we've already taken
+ care for error returns and other are often used for fast paths
+ trought function. */
+ if ((e->dest == EXIT_BLOCK_PTR
+ || (e->dest->succ && !e->dest->succ->succ_next
+ && e->dest->succ->dest == EXIT_BLOCK_PTR))
+ && !predicted_by_p (bb, PRED_NULL_RETURN)
+ && !predicted_by_p (bb, PRED_CONST_RETURN)
+ && !predicted_by_p (bb, PRED_NEGATIVE_RETURN)
+ && !last_basic_block_p (e->dest))
+ predict_edge_def (e, PRED_EARLY_RETURN, TAKEN);
+
+ /* Look for block we are guarding (ie we dominate it,
+ but it doesn't postdominate us). */
+ if (e->dest != EXIT_BLOCK_PTR && e->dest != bb
+ && dominated_by_p (dominators, e->dest, e->src)
+ && !dominated_by_p (post_dominators, e->src, e->dest))
+ {
+ rtx insn;
+
+ /* The call heuristic claims that a guarded function call
+ is improbable. This is because such calls are often used
+ to signal exceptional situations such as printing error
+ messages. */
+ for (insn = e->dest->head; insn != NEXT_INSN (e->dest->end);
+ insn = NEXT_INSN (insn))
+ if (GET_CODE (insn) == CALL_INSN
+ /* Constant and pure calls are hardly used to signalize
+ something exceptional. */
+ && ! CONST_OR_PURE_CALL_P (insn))
+ {
+ predict_edge_def (e, PRED_CALL, NOT_TAKEN);
+ break;
+ }
+ }
+ }
+
cond = get_condition (last_insn, &earliest);
if (! cond)
continue;
- /* EQ tests are usually false and NE tests are usually true. Also,
+
+ /* Try "pointer heuristic."
+ A comparison ptr == 0 is predicted as false.
+ Similarly, a comparison ptr1 == ptr2 is predicted as false. */
+ if (GET_RTX_CLASS (GET_CODE (cond)) == '<'
+ && ((REG_P (XEXP (cond, 0)) && REG_POINTER (XEXP (cond, 0)))
+ || (REG_P (XEXP (cond, 1)) && REG_POINTER (XEXP (cond, 1)))))
+ {
+ if (GET_CODE (cond) == EQ)
+ predict_insn_def (last_insn, PRED_POINTER, NOT_TAKEN);
+ else if (GET_CODE (cond) == NE)
+ predict_insn_def (last_insn, PRED_POINTER, TAKEN);
+ }
+ else
+
+ /* Try "opcode heuristic."
+ EQ tests are usually false and NE tests are usually true. Also,
most quantities are positive, so we can make the appropriate guesses
about signed comparisons against zero. */
- switch (GET_CODE (cond))
- {
- case CONST_INT:
- /* Unconditional branch. */
- prob = REG_BR_PROB_BASE / 2;
- case EQ:
- prob = REG_BR_PROB_BASE / 10;
- case NE:
- prob = REG_BR_PROB_BASE / 2;
- case LE:
- case LT:
- if (XEXP (cond, 1) == const0_rtx)
- prob = REG_BR_PROB_BASE / 10;
- break;
- case GE:
- case GT:
- if (XEXP (cond, 1) == const0_rtx
- || (GET_CODE (XEXP (cond, 1)) == CONST_INT
- && INTVAL (XEXP (cond, 1)) == -1))
- prob = REG_BR_PROB_BASE / 2;
+ switch (GET_CODE (cond))
+ {
+ case CONST_INT:
+ /* Unconditional branch. */
+ predict_insn_def (last_insn, PRED_UNCONDITIONAL,
+ cond == const0_rtx ? NOT_TAKEN : TAKEN);
+ break;
+
+ case EQ:
+ case UNEQ:
+ /* Floating point comparisons appears to behave in a very
+ unpredictable way because of special role of = tests in
+ FP code. */
+ if (FLOAT_MODE_P (GET_MODE (XEXP (cond, 0))))
+ ;
+ /* Comparisons with 0 are often used for booleans and there is
+ nothing useful to predict about them. */
+ else if (XEXP (cond, 1) == const0_rtx
+ || XEXP (cond, 0) == const0_rtx)
+ ;
+ else
+ predict_insn_def (last_insn, PRED_OPCODE_NONEQUAL, NOT_TAKEN);
+ break;
+
+ case NE:
+ case LTGT:
+ /* Floating point comparisons appears to behave in a very
+ unpredictable way because of special role of = tests in
+ FP code. */
+ if (FLOAT_MODE_P (GET_MODE (XEXP (cond, 0))))
+ ;
+ /* Comparisons with 0 are often used for booleans and there is
+ nothing useful to predict about them. */
+ else if (XEXP (cond, 1) == const0_rtx
+ || XEXP (cond, 0) == const0_rtx)
+ ;
+ else
+ predict_insn_def (last_insn, PRED_OPCODE_NONEQUAL, TAKEN);
+ break;
+
+ case ORDERED:
+ predict_insn_def (last_insn, PRED_FPOPCODE, TAKEN);
+ break;
+
+ case UNORDERED:
+ predict_insn_def (last_insn, PRED_FPOPCODE, NOT_TAKEN);
+ break;
+
+ case LE:
+ case LT:
+ if (XEXP (cond, 1) == const0_rtx || XEXP (cond, 1) == const1_rtx
+ || XEXP (cond, 1) == constm1_rtx)
+ predict_insn_def (last_insn, PRED_OPCODE_POSITIVE, NOT_TAKEN);
+ break;
+
+ case GE:
+ case GT:
+ if (XEXP (cond, 1) == const0_rtx || XEXP (cond, 1) == const1_rtx
+ || XEXP (cond, 1) == constm1_rtx)
+ predict_insn_def (last_insn, PRED_OPCODE_POSITIVE, TAKEN);
+ break;
+
+ default:
+ break;
+ }
+ }
+
+ /* Attach the combined probability to each conditional jump. */
+ FOR_EACH_BB (bb)
+ if (GET_CODE (bb->end) == JUMP_INSN
+ && any_condjump_p (bb->end)
+ && bb->succ->succ_next != NULL)
+ combine_predictions_for_insn (bb->end, bb);
+
+ free_dominance_info (post_dominators);
+ free_dominance_info (dominators);
+
+ remove_fake_edges ();
+ estimate_bb_frequencies (loops_info);
+}
+\f
+/* __builtin_expect dropped tokens into the insn stream describing expected
+ values of registers. Generate branch probabilities based off these
+ values. */
+
+void
+expected_value_to_br_prob (void)
+{
+ rtx insn, cond, ev = NULL_RTX, ev_reg = NULL_RTX;
+
+ for (insn = get_insns (); insn ; insn = NEXT_INSN (insn))
+ {
+ switch (GET_CODE (insn))
+ {
+ case NOTE:
+ /* Look for expected value notes. */
+ if (NOTE_LINE_NUMBER (insn) == NOTE_INSN_EXPECTED_VALUE)
+ {
+ ev = NOTE_EXPECTED_VALUE (insn);
+ ev_reg = XEXP (ev, 0);
+ delete_insn (insn);
+ }
+ continue;
+
+ case CODE_LABEL:
+ /* Never propagate across labels. */
+ ev = NULL_RTX;
+ continue;
+
+ case JUMP_INSN:
+ /* Look for simple conditional branches. If we haven't got an
+ expected value yet, no point going further. */
+ if (GET_CODE (insn) != JUMP_INSN || ev == NULL_RTX
+ || ! any_condjump_p (insn))
+ continue;
break;
default:
- prob = 0;
+ /* Look for insns that clobber the EV register. */
+ if (ev && reg_set_p (ev_reg, insn))
+ ev = NULL_RTX;
+ continue;
}
- if (! find_reg_note (last_insn, REG_BR_PROB, 0))
- REG_NOTES (last_insn)
- = gen_rtx_EXPR_LIST (REG_BR_PROB, GEN_INT (prob),
- REG_NOTES (last_insn));
+
+ /* Collect the branch condition, hopefully relative to EV_REG. */
+ /* ??? At present we'll miss things like
+ (expected_value (eq r70 0))
+ (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
+ (lt r70, r71)
+ Could use cselib to try and reduce this further. */
+ 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
+ building involves two constants, we should wind up with either
+ true or false. */
+ cond = gen_rtx_fmt_ee (GET_CODE (cond), VOIDmode,
+ XEXP (ev, 1), XEXP (cond, 1));
+ cond = simplify_rtx (cond);
+
+ /* Turn the condition into a scaled branch probability. */
+ if (cond != const_true_rtx && cond != const0_rtx)
+ abort ();
+ predict_insn_def (insn, PRED_BUILTIN_EXPECT,
+ cond == const_true_rtx ? TAKEN : NOT_TAKEN);
}
}
+\f
+/* Check whether this is the last basic block of function. Commonly
+ there is one extra common cleanup block. */
+static bool
+last_basic_block_p (basic_block bb)
+{
+ if (bb == EXIT_BLOCK_PTR)
+ return false;
+ return (bb->next_bb == EXIT_BLOCK_PTR
+ || (bb->next_bb->next_bb == EXIT_BLOCK_PTR
+ && bb->succ && !bb->succ->succ_next
+ && bb->succ->dest->next_bb == EXIT_BLOCK_PTR));
+}
+
+/* Sets branch probabilities according to PREDiction and
+ FLAGS. HEADS[bb->index] should be index of basic block in that we
+ need to alter branch predictions (i.e. the first of our dominators
+ such that we do not post-dominate it) (but we fill this information
+ on demand, so -1 may be there in case this was not needed yet). */
+
+static void
+process_note_prediction (basic_block bb, int *heads,
+ dominance_info dominators,
+ dominance_info post_dominators, int pred,
+ int flags)
+{
+ edge e;
+ int y;
+ bool taken;
+
+ taken = flags & IS_TAKEN;
+
+ if (heads[bb->index] < 0)
+ {
+ /* This is first time we need this field in heads array; so
+ find first dominator that we do not post-dominate (we are
+ using already known members of heads array). */
+ basic_block ai = bb;
+ basic_block next_ai = get_immediate_dominator (dominators, bb);
+ int head;
+
+ while (heads[next_ai->index] < 0)
+ {
+ if (!dominated_by_p (post_dominators, next_ai, bb))
+ break;
+ heads[next_ai->index] = ai->index;
+ ai = next_ai;
+ next_ai = get_immediate_dominator (dominators, next_ai);
+ }
+ if (!dominated_by_p (post_dominators, next_ai, bb))
+ head = next_ai->index;
+ else
+ head = heads[next_ai->index];
+ while (next_ai != bb)
+ {
+ next_ai = ai;
+ if (heads[ai->index] == ENTRY_BLOCK)
+ ai = ENTRY_BLOCK_PTR;
+ else
+ ai = BASIC_BLOCK (heads[ai->index]);
+ heads[next_ai->index] = head;
+ }
+ }
+ y = heads[bb->index];
+
+ /* Now find the edge that leads to our branch and aply the prediction. */
+
+ if (y == last_basic_block || !can_predict_insn_p (BASIC_BLOCK (y)->end))
+ return;
+ for (e = BASIC_BLOCK (y)->succ; e; e = e->succ_next)
+ if (e->dest->index >= 0
+ && dominated_by_p (post_dominators, e->dest, bb))
+ predict_edge_def (e, pred, taken);
+}
+
+/* Gathers NOTE_INSN_PREDICTIONs in given basic block and turns them
+ into branch probabilities. For description of heads array, see
+ process_note_prediction. */
+
+static void
+process_note_predictions (basic_block bb, int *heads,
+ dominance_info dominators,
+ dominance_info post_dominators)
+{
+ rtx insn;
+ edge e;
+
+ /* Additionally, we check here for blocks with no successors. */
+ int contained_noreturn_call = 0;
+ int was_bb_head = 0;
+ int noreturn_block = 1;
+
+ for (insn = bb->end; insn;
+ was_bb_head |= (insn == bb->head), insn = PREV_INSN (insn))
+ {
+ if (GET_CODE (insn) != NOTE)
+ {
+ if (was_bb_head)
+ break;
+ else
+ {
+ /* Noreturn calls cause program to exit, therefore they are
+ always predicted as not taken. */
+ if (GET_CODE (insn) == CALL_INSN
+ && find_reg_note (insn, REG_NORETURN, NULL))
+ contained_noreturn_call = 1;
+ continue;
+ }
+ }
+ if (NOTE_LINE_NUMBER (insn) == NOTE_INSN_PREDICTION)
+ {
+ int alg = (int) NOTE_PREDICTION_ALG (insn);
+ /* Process single prediction note. */
+ process_note_prediction (bb,
+ heads,
+ dominators,
+ post_dominators,
+ alg, (int) NOTE_PREDICTION_FLAGS (insn));
+ delete_insn (insn);
+ }
+ }
+ for (e = bb->succ; e; e = e->succ_next)
+ if (!(e->flags & EDGE_FAKE))
+ noreturn_block = 0;
+ if (contained_noreturn_call)
+ {
+ /* This block ended from other reasons than because of return.
+ If it is because of noreturn call, this should certainly not
+ be taken. Otherwise it is probably some error recovery. */
+ process_note_prediction (bb,
+ heads,
+ dominators,
+ post_dominators, PRED_NORETURN, NOT_TAKEN);
+ }
+}
+
+/* Gathers NOTE_INSN_PREDICTIONs and turns them into
+ branch probabilities. */
+
+void
+note_prediction_to_br_prob (void)
+{
+ basic_block bb;
+ dominance_info post_dominators, dominators;
+ int *heads;
+
+ /* To enable handling of noreturn blocks. */
+ add_noreturn_fake_exit_edges ();
+ connect_infinite_loops_to_exit ();
+
+ post_dominators = calculate_dominance_info (CDI_POST_DOMINATORS);
+ dominators = calculate_dominance_info (CDI_DOMINATORS);
+
+ heads = xmalloc (sizeof (int) * last_basic_block);
+ memset (heads, -1, sizeof (int) * last_basic_block);
+ heads[ENTRY_BLOCK_PTR->next_bb->index] = last_basic_block;
+
+ /* Process all prediction notes. */
+
+ FOR_EACH_BB (bb)
+ process_note_predictions (bb, heads, dominators, post_dominators);
+
+ free_dominance_info (post_dominators);
+ free_dominance_info (dominators);
+ free (heads);
+
+ remove_fake_edges ();
+}
+\f
+/* 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
+{
+ /* Estimated frequency of execution of basic_block. */
+ sreal frequency;
+
+ /* To keep queue of basic blocks to process. */
+ basic_block next;
+
+ /* True if block needs to be visited in prop_freqency. */
+ int tovisit:1;
+
+ /* Number of predecessors we need to visit first. */
+ int npredecessors;
+} *block_info;
+
+/* Similar information for edges. */
+typedef struct edge_info_def
+{
+ /* In case edge is an loopback edge, the probability edge will be reached
+ in case header is. Estimated number of iterations of the loop can be
+ then computed as 1 / (1 - back_edge_prob). */
+ sreal back_edge_prob;
+ /* True if the edge is an loopback edge in the natural loop. */
+ int back_edge:1;
+} *edge_info;
+
+#define BLOCK_INFO(B) ((block_info) (B)->aux)
+#define EDGE_INFO(E) ((edge_info) (E)->aux)
+
+/* Helper function for estimate_bb_frequencies.
+ Propagate the frequencies for LOOP. */
+
+static void
+propagate_freq (struct loop *loop)
+{
+ basic_block head = loop->header;
+ basic_block bb;
+ basic_block last;
+ edge e;
+ basic_block nextbb;
+
+ /* For each basic block we need to visit count number of his predecessors
+ we need to visit first. */
+ FOR_EACH_BB (bb)
+ {
+ 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)->npredecessors = count;
+ }
+ }
+
+ memcpy (&BLOCK_INFO (head)->frequency, &real_one, sizeof (real_one));
+ last = head;
+ for (bb = head; bb; bb = nextbb)
+ {
+ sreal cyclic_probability, frequency;
+
+ memcpy (&cyclic_probability, &real_zero, sizeof (real_zero));
+ memcpy (&frequency, &real_zero, sizeof (real_zero));
+
+ nextbb = BLOCK_INFO (bb)->next;
+ BLOCK_INFO (bb)->next = NULL;
+
+ /* 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)->tovisit && !(e->flags & EDGE_DFS_BACK))
+ abort ();
+#endif
+
+ for (e = bb->pred; e; e = e->pred_next)
+ if (EDGE_INFO (e)->back_edge)
+ {
+ sreal_add (&cyclic_probability, &cyclic_probability,
+ &EDGE_INFO (e)->back_edge_prob);
+ }
+ else if (!(e->flags & EDGE_DFS_BACK))
+ {
+ sreal tmp;
+
+ /* frequency += (e->probability
+ * BLOCK_INFO (e->src)->frequency /
+ REG_BR_PROB_BASE); */
+
+ sreal_init (&tmp, e->probability, 0);
+ sreal_mul (&tmp, &tmp, &BLOCK_INFO (e->src)->frequency);
+ sreal_mul (&tmp, &tmp, &real_inv_br_prob_base);
+ sreal_add (&frequency, &frequency, &tmp);
+ }
+
+ if (sreal_compare (&cyclic_probability, &real_zero) == 0)
+ {
+ memcpy (&BLOCK_INFO (bb)->frequency, &frequency,
+ sizeof (frequency));
+ }
+ else
+ {
+ if (sreal_compare (&cyclic_probability, &real_almost_one) > 0)
+ {
+ memcpy (&cyclic_probability, &real_almost_one,
+ sizeof (real_almost_one));
+ }
+
+ /* BLOCK_INFO (bb)->frequency = frequency
+ / (1 - cyclic_probability) */
+
+ sreal_sub (&cyclic_probability, &real_one, &cyclic_probability);
+ sreal_div (&BLOCK_INFO (bb)->frequency,
+ &frequency, &cyclic_probability);
+ }
+ }
+
+ BLOCK_INFO (bb)->tovisit = 0;
+
+ /* Compute back edge frequencies. */
+ for (e = bb->succ; e; e = e->succ_next)
+ if (e->dest == head)
+ {
+ sreal tmp;
+
+ /* EDGE_INFO (e)->back_edge_prob
+ = ((e->probability * BLOCK_INFO (bb)->frequency)
+ / REG_BR_PROB_BASE); */
+
+ sreal_init (&tmp, e->probability, 0);
+ sreal_mul (&tmp, &tmp, &BLOCK_INFO (bb)->frequency);
+ sreal_mul (&EDGE_INFO (e)->back_edge_prob,
+ &tmp, &real_inv_br_prob_base);
+ }
+
+ /* Propagate to successor blocks. */
+ for (e = bb->succ; e; e = e->succ_next)
+ if (!(e->flags & EDGE_DFS_BACK)
+ && BLOCK_INFO (e->dest)->npredecessors)
+ {
+ BLOCK_INFO (e->dest)->npredecessors--;
+ if (!BLOCK_INFO (e->dest)->npredecessors)
+ {
+ if (!nextbb)
+ nextbb = e->dest;
+ else
+ BLOCK_INFO (last)->next = e->dest;
+
+ last = e->dest;
+ }
+ }
+ }
+}
+
+/* Estimate probabilities of loopback edges in loops at same nest level. */
+
+static void
+estimate_loops_at_level (struct loop *first_loop)
+{
+ struct loop *loop;
+
+ for (loop = first_loop; loop; loop = loop->next)
+ {
+ edge e;
+ basic_block *bbs;
+ unsigned i;
+
+ estimate_loops_at_level (loop->inner);
+
+ if (loop->latch->succ) /* Do not do this for dummy function loop. */
+ {
+ /* Find current loop back edge and mark it. */
+ e = loop_latch_edge (loop);
+ EDGE_INFO (e)->back_edge = 1;
+ }
+
+ bbs = get_loop_body (loop);
+ for (i = 0; i < loop->num_nodes; i++)
+ BLOCK_INFO (bbs[i])->tovisit = 1;
+ free (bbs);
+ propagate_freq (loop);
+ }
+}
+
+/* Convert counts measured by profile driven feedback to frequencies. */
+
+static void
+counts_to_freqs (void)
+{
+ gcov_type count_max = 1;
+ basic_block bb;
+
+ FOR_EACH_BB (bb)
+ count_max = MAX (bb->count, count_max);
+
+ FOR_BB_BETWEEN (bb, ENTRY_BLOCK_PTR, NULL, next_bb)
+ bb->frequency = (bb->count * BB_FREQ_MAX + count_max / 2) / count_max;
+}
+
+/* Return true if function is likely to be expensive, so there is no point to
+ optimize performance of prologue, epilogue or do inlining at the expense
+ of code size growth. THRESHOLD is the limit of number of instructions
+ function can execute at average to be still considered not expensive. */
+
+bool
+expensive_function_p (int threshold)
+{
+ unsigned int sum = 0;
+ basic_block bb;
+ 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 either 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_EACH_BB (bb)
+ {
+ 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 (struct loops *loops)
+{
+ basic_block bb;
+ sreal freq_max;
+
+ if (flag_branch_probabilities)
+ counts_to_freqs ();
+ else
+ {
+ static int real_values_initialized = 0;
+
+ if (!real_values_initialized)
+ {
+ real_values_initialized = 1;
+ sreal_init (&real_zero, 0, 0);
+ sreal_init (&real_one, 1, 0);
+ sreal_init (&real_br_prob_base, REG_BR_PROB_BASE, 0);
+ sreal_init (&real_bb_freq_max, BB_FREQ_MAX, 0);
+ sreal_init (&real_one_half, 1, -1);
+ sreal_div (&real_inv_br_prob_base, &real_one, &real_br_prob_base);
+ sreal_sub (&real_almost_one, &real_one, &real_inv_br_prob_base);
+ }
+
+ mark_dfs_back_edges ();
+ /* Fill in the probability values in flowgraph based on the REG_BR_PROB
+ notes. */
+ FOR_EACH_BB (bb)
+ {
+ rtx last_insn = bb->end;
+
+ if (!can_predict_insn_p (last_insn))
+ {
+ /* We can predict only conditional jumps at the moment.
+ Expect each edge to be equally probable.
+ ?? In the future we want to make abnormal edges improbable. */
+ int nedges = 0;
+ edge e;
+
+ for (e = bb->succ; e; e = e->succ_next)
+ {
+ nedges++;
+ if (e->probability != 0)
+ break;
+ }
+ if (!e)
+ for (e = bb->succ; e; e = e->succ_next)
+ e->probability = (REG_BR_PROB_BASE + nedges / 2) / nedges;
+ }
+ }
+
+ ENTRY_BLOCK_PTR->succ->probability = REG_BR_PROB_BASE;
+
+ /* Set up block info for each basic block. */
+ alloc_aux_for_blocks (sizeof (struct block_info_def));
+ alloc_aux_for_edges (sizeof (struct edge_info_def));
+ FOR_BB_BETWEEN (bb, ENTRY_BLOCK_PTR, NULL, next_bb)
+ {
+ edge e;
+
+ BLOCK_INFO (bb)->tovisit = 0;
+ for (e = bb->succ; e; e = e->succ_next)
+ {
+ sreal_init (&EDGE_INFO (e)->back_edge_prob, e->probability, 0);
+ sreal_mul (&EDGE_INFO (e)->back_edge_prob,
+ &EDGE_INFO (e)->back_edge_prob,
+ &real_inv_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_root);
+
+ memcpy (&freq_max, &real_zero, sizeof (real_zero));
+ FOR_EACH_BB (bb)
+ if (sreal_compare (&freq_max, &BLOCK_INFO (bb)->frequency) < 0)
+ memcpy (&freq_max, &BLOCK_INFO (bb)->frequency, sizeof (freq_max));
+
+ sreal_div (&freq_max, &real_bb_freq_max, &freq_max);
+ FOR_BB_BETWEEN (bb, ENTRY_BLOCK_PTR, NULL, next_bb)
+ {
+ sreal tmp;
+
+ sreal_mul (&tmp, &BLOCK_INFO (bb)->frequency, &freq_max);
+ sreal_add (&tmp, &tmp, &real_one_half);
+ bb->frequency = sreal_to_int (&tmp);
+ }
+
+ free_aux_for_blocks ();
+ free_aux_for_edges ();
+ }
+ compute_function_frequency ();
+ if (flag_reorder_functions)
+ choose_function_section ();
+}
+
+/* Decide whether function is hot, cold or unlikely executed. */
+static void
+compute_function_frequency (void)
+{
+ basic_block bb;
+
+ if (!profile_info || !flag_branch_probabilities)
+ return;
+ cfun->function_frequency = FUNCTION_FREQUENCY_UNLIKELY_EXECUTED;
+ FOR_EACH_BB (bb)
+ {
+ if (maybe_hot_bb_p (bb))
+ {
+ cfun->function_frequency = FUNCTION_FREQUENCY_HOT;
+ return;
+ }
+ if (!probably_never_executed_bb_p (bb))
+ cfun->function_frequency = FUNCTION_FREQUENCY_NORMAL;
+ }
+}
+
+/* Choose appropriate section for the function. */
+static void
+choose_function_section (void)
+{
+ if (DECL_SECTION_NAME (current_function_decl)
+ || !targetm.have_named_sections
+ /* Theoretically we can split the gnu.linkonce text section too,
+ but this requires more work as the frequency needs to match
+ for all generated objects so we need to merge the frequency
+ of all instances. For now just never set frequency for these. */
+ || DECL_ONE_ONLY (current_function_decl))
+ return;
+ if (cfun->function_frequency == FUNCTION_FREQUENCY_HOT)
+ DECL_SECTION_NAME (current_function_decl) =
+ build_string (strlen (HOT_TEXT_SECTION_NAME), HOT_TEXT_SECTION_NAME);
+ if (cfun->function_frequency == FUNCTION_FREQUENCY_UNLIKELY_EXECUTED)
+ DECL_SECTION_NAME (current_function_decl) =
+ build_string (strlen (UNLIKELY_EXECUTED_TEXT_SECTION_NAME),
+ UNLIKELY_EXECUTED_TEXT_SECTION_NAME);
+}
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