| /* Branch prediction routines for the GNU compiler. |
| Copyright (C) 2000, 2001, 2002 Free Software Foundation, Inc. |
| |
| This file is part of GCC. |
| |
| 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. |
| |
| 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 GCC; see the file COPYING. If not, write to the Free |
| Software Foundation, 59 Temple Place - Suite 330, Boston, MA |
| 02111-1307, USA. */ |
| |
| /* References: |
| |
| [1] "Branch Prediction for Free" |
| Ball and Larus; PLDI '93. |
| [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. */ |
| |
| |
| #include "config.h" |
| #include "system.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 "flags.h" |
| #include "output.h" |
| #include "function.h" |
| #include "except.h" |
| #include "toplev.h" |
| #include "recog.h" |
| #include "expr.h" |
| #include "predict.h" |
| |
| /* Random guesstimation given names. */ |
| #define PROB_NEVER (0) |
| #define PROB_VERY_UNLIKELY (REG_BR_PROB_BASE / 10 - 1) |
| #define PROB_UNLIKELY (REG_BR_PROB_BASE * 4 / 10 - 1) |
| #define PROB_EVEN (REG_BR_PROB_BASE / 2) |
| #define PROB_LIKELY (REG_BR_PROB_BASE - PROB_UNLIKELY) |
| #define PROB_VERY_LIKELY (REG_BR_PROB_BASE - PROB_VERY_UNLIKELY) |
| #define PROB_ALWAYS (REG_BR_PROB_BASE) |
| |
| static void combine_predictions_for_insn PARAMS ((rtx, basic_block)); |
| static void dump_prediction PARAMS ((enum br_predictor, int, |
| 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 *)); |
| static void counts_to_freqs PARAMS ((void)); |
| |
| /* 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 |
| |
| void |
| predict_insn (insn, predictor, probability) |
| rtx insn; |
| int probability; |
| enum br_predictor predictor; |
| { |
| if (!any_condjump_p (insn)) |
| abort (); |
| |
| 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 (insn, predictor, taken) |
| 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 (e, predictor, probability) |
| edge e; |
| int probability; |
| enum br_predictor predictor; |
| { |
| 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); |
| } |
| |
| /* Predict edge E by given predictor if possible. */ |
| |
| void |
| predict_edge_def (e, predictor, taken) |
| 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 (insn) |
| 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 (predictor, probability, bb, used) |
| enum br_predictor predictor; |
| int probability; |
| basic_block bb; |
| int used; |
| { |
| edge e = bb->succ; |
| |
| if (!rtl_dump_file) |
| return; |
| |
| while (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); |
| 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 (insn, bb) |
| 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). */ |
| |
| void |
| estimate_probability (loops_info) |
| struct loops *loops_info; |
| { |
| 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, 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. */ |
| for (i = 0; i < loops_info->num; i++) |
| { |
| int j; |
| int exits; |
| struct loop *loop = &loops_info->array[i]; |
| |
| flow_loop_scan (loops_info, loop, LOOP_EXIT_EDGES); |
| exits = loop->num_exits; |
| |
| for (j = loop->first->index; j <= loop->last->index; ++j) |
| if (TEST_BIT (loop->nodes, j)) |
| { |
| int header_found = 0; |
| edge e; |
| |
| /* Loop branch heuristics - predict an edge back to a |
| loop's head as taken. */ |
| for (e = BASIC_BLOCK(j)->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 |
| conditinal has no loop header successors as not taken. */ |
| if (!header_found) |
| for (e = BASIC_BLOCK(j)->succ; e; e = e->succ_next) |
| if (e->dest->index < 0 |
| || !TEST_BIT (loop->nodes, e->dest->index)) |
| predict_edge |
| (e, PRED_LOOP_EXIT, |
| (REG_BR_PROB_BASE |
| - predictor_info [(int) PRED_LOOP_EXIT].hitrate) |
| / exits); |
| } |
| } |
| |
| /* Attempt to predict conditional jumps using a number of heuristics. */ |
| for (i = 0; i < n_basic_blocks; i++) |
| { |
| basic_block bb = BASIC_BLOCK (i); |
| rtx last_insn = bb->end; |
| rtx cond, earliest; |
| edge e; |
| |
| /* If block has no successor, 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 && !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)) |
| for (e = BASIC_BLOCK (y)->succ; e; e = e->succ_next) |
| if (e->dest->index >= 0 |
| && TEST_BIT (post_dominators[e->dest->index], i)) |
| predict_edge_def (e, PRED_NORETURN, NOT_TAKEN); |
| } |
| |
| if (GET_CODE (last_insn) != JUMP_INSN || ! any_condjump_p (last_insn)) |
| continue; |
| |
| for (e = bb->succ; e; e = e->succ_next) |
| { |
| /* Predict edges to blocks that return immediately to be |
| improbable. These are usually used to signal error states. */ |
| if (e->dest == EXIT_BLOCK_PTR |
| || (e->dest->succ && !e->dest->succ->succ_next |
| && e->dest->succ->dest == EXIT_BLOCK_PTR)) |
| predict_edge_def (e, PRED_ERROR_RETURN, NOT_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 |
| && TEST_BIT (dominators[e->dest->index], e->src->index) |
| && !TEST_BIT (post_dominators[e->src->index], e->dest->index)) |
| { |
| 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; |
| |
| /* 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. */ |
| 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 |
| inpredictable 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 usefull 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 |
| inpredictable 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 usefull 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 (i = 0; i < n_basic_blocks; i++) |
| if (GET_CODE (BLOCK_END (i)) == JUMP_INSN |
| && any_condjump_p (BLOCK_END (i))) |
| combine_predictions_for_insn (BLOCK_END (i), BASIC_BLOCK (i)); |
| |
| sbitmap_vector_free (post_dominators); |
| sbitmap_vector_free (dominators); |
| |
| estimate_bb_frequencies (loops_info); |
| } |
| |
| /* __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 () |
| { |
| 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: |
| /* Look for insns that clobber the EV register. */ |
| if (ev && reg_set_p (ev_reg, insn)) |
| ev = NULL_RTX; |
| continue; |
| } |
| |
| /* 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); |
| } |
| } |
| |
| /* 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. */ |
| volatile double 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). |
| |
| Volatile is needed to avoid differences in the optimized and unoptimized |
| builds on machines where FP registers are wider than double. */ |
| volatile double 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 loops headed by HEAD. */ |
| |
| static void |
| propagate_freq (head) |
| basic_block head; |
| { |
| basic_block bb = head; |
| basic_block last = bb; |
| edge e; |
| basic_block nextbb; |
| int n; |
| |
| /* For each basic block we need to visit count number of his predecessors |
| 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)->npredecessors = count; |
| } |
| } |
| |
| BLOCK_INFO (head)->frequency = 1; |
| for (; bb; bb = nextbb) |
| { |
| double cyclic_probability = 0, frequency = 0; |
| |
| 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) |
| cyclic_probability += EDGE_INFO (e)->back_edge_prob; |
| else if (!(e->flags & EDGE_DFS_BACK)) |
| frequency += (e->probability |
| * BLOCK_INFO (e->src)->frequency / |
| REG_BR_PROB_BASE); |
| |
| if (cyclic_probability > 1.0 - 1.0 / REG_BR_PROB_BASE) |
| cyclic_probability = 1.0 - 1.0 / REG_BR_PROB_BASE; |
| |
| BLOCK_INFO (bb)->frequency = frequency / (1 - cyclic_probability); |
| } |
| |
| BLOCK_INFO (bb)->tovisit = 0; |
| |
| /* Compute back edge frequencies. */ |
| for (e = bb->succ; e; e = e->succ_next) |
| if (e->dest == head) |
| EDGE_INFO (e)->back_edge_prob |
| = ((e->probability * BLOCK_INFO (bb)->frequency) |
| / REG_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 (first_loop) |
| struct loop *first_loop; |
| { |
| struct loop *l, *loop = first_loop; |
| |
| for (loop = first_loop; loop; loop = loop->next) |
| { |
| int n; |
| edge e; |
| |
| estimate_loops_at_level (loop->inner); |
| |
| /* 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 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) |
| if (l->header == loop->header) |
| break; |
| |
| if (l) |
| continue; |
| } |
| |
| /* Now merge all nodes of all loops with given header as not visited. */ |
| 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))->tovisit = 1 |
| ); |
| |
| propagate_freq (loop->header); |
| } |
| } |
| |
| /* Convert counts measured by profile driven feedback to frequencies. */ |
| |
| static void |
| counts_to_freqs () |
| { |
| HOST_WIDEST_INT count_max = 1; |
| int i; |
| |
| for (i = 0; i < n_basic_blocks; i++) |
| count_max = MAX (BASIC_BLOCK (i)->count, count_max); |
| |
| for (i = -2; i < n_basic_blocks; i++) |
| { |
| basic_block bb; |
| |
| if (i == -2) |
| bb = ENTRY_BLOCK_PTR; |
| else if (i == -1) |
| bb = EXIT_BLOCK_PTR; |
| else |
| bb = BASIC_BLOCK (i); |
| |
| 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 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 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 (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; |
| { |
| int i; |
| double freq_max = 0; |
| |
| mark_dfs_back_edges (); |
| if (flag_branch_probabilities) |
| { |
| counts_to_freqs (); |
| return; |
| } |
| |
| /* Fill in the probability values in flowgraph based on the REG_BR_PROB |
| notes. */ |
| for (i = 0; i < n_basic_blocks; i++) |
| { |
| rtx last_insn = BLOCK_END (i); |
| int probability; |
| edge fallthru, branch; |
| |
| if (GET_CODE (last_insn) != JUMP_INSN || !any_condjump_p (last_insn) |
| /* 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 equally probable. |
| ?? In the future we want to make abnormal edges improbable. */ |
| int nedges = 0; |
| edge e; |
| |
| for (e = BASIC_BLOCK (i)->succ; e; e = e->succ_next) |
| { |
| nedges++; |
| if (e->probability != 0) |
| break; |
| } |
| if (!e) |
| for (e = BASIC_BLOCK (i)->succ; e; e = e->succ_next) |
| e->probability = (REG_BR_PROB_BASE + nedges / 2) / nedges; |
| } |
| else |
| { |
| probability = INTVAL (XEXP (find_reg_note (last_insn, |
| REG_BR_PROB, 0), 0)); |
| fallthru = BASIC_BLOCK (i)->succ; |
| if (!fallthru->flags & EDGE_FALLTHRU) |
| fallthru = fallthru->succ_next; |
| branch = BASIC_BLOCK (i)->succ; |
| if (branch->flags & EDGE_FALLTHRU) |
| branch = branch->succ_next; |
| |
| branch->probability = probability; |
| fallthru->probability = REG_BR_PROB_BASE - probability; |
| } |
| } |
| |
| 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 (i = -2; i < n_basic_blocks; i++) |
| { |
| edge e; |
| basic_block bb; |
| |
| if (i == -2) |
| bb = ENTRY_BLOCK_PTR; |
| else if (i == -1) |
| bb = EXIT_BLOCK_PTR; |
| else |
| bb = BASIC_BLOCK (i); |
| |
| BLOCK_INFO (bb)->tovisit = 0; |
| for (e = bb->succ; e; e = e->succ_next) |
| 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_root); |
| |
| /* Now fake loop around whole function to finalize probabilities. */ |
| for (i = 0; i < n_basic_blocks; i++) |
| 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++) |
| if (BLOCK_INFO (BASIC_BLOCK (i))->frequency > freq_max) |
| freq_max = BLOCK_INFO (BASIC_BLOCK (i))->frequency; |
| |
| for (i = -2; i < n_basic_blocks; i++) |
| { |
| basic_block bb; |
| |
| if (i == -2) |
| bb = ENTRY_BLOCK_PTR; |
| else if (i == -1) |
| bb = EXIT_BLOCK_PTR; |
| else |
| bb = BASIC_BLOCK (i); |
| bb->frequency |
| = BLOCK_INFO (bb)->frequency * BB_FREQ_MAX / freq_max + 0.5; |
| } |
| |
| free_aux_for_blocks (); |
| free_aux_for_edges (); |
| } |