/* Control flow optimization code for GNU compiler. Copyright (C) 1987, 1988, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001 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. */ /* This file contains optimizer of the control flow. The main entrypoint is cleanup_cfg. Following optimizations are performed: - Unreachable blocks removal - Edge forwarding (edge to the forwarder block is forwarded to it's succesor. Simplification of the branch instruction is performed by underlying infrastructure so branch can be converted to simplejump or elliminated). - Cross jumping (tail merging) - Conditional jump-around-simplejump simplification - Basic block merging. */ #include "config.h" #include "system.h" #include "rtl.h" #include "hard-reg-set.h" #include "basic-block.h" #include "timevar.h" #include "output.h" #include "insn-config.h" #include "flags.h" #include "recog.h" #include "toplev.h" #include "obstack.h" static bool try_crossjump_to_edge PARAMS ((int, edge, edge)); static bool try_crossjump_bb PARAMS ((int, basic_block)); static bool outgoing_edges_match PARAMS ((basic_block, basic_block)); static int flow_find_cross_jump PARAMS ((int, basic_block, basic_block, rtx *, rtx *)); static bool delete_unreachable_blocks PARAMS ((void)); static bool tail_recursion_label_p PARAMS ((rtx)); static void merge_blocks_move_predecessor_nojumps PARAMS ((basic_block, basic_block)); static void merge_blocks_move_successor_nojumps PARAMS ((basic_block, basic_block)); static bool merge_blocks PARAMS ((edge,basic_block,basic_block, int)); static bool try_optimize_cfg PARAMS ((int)); static bool try_simplify_condjump PARAMS ((basic_block)); static bool try_forward_edges PARAMS ((int, basic_block)); /* Simplify a conditional jump around an unconditional jump. Return true if something changed. */ static bool try_simplify_condjump (cbranch_block) basic_block cbranch_block; { basic_block jump_block, jump_dest_block, cbranch_dest_block; edge cbranch_jump_edge, cbranch_fallthru_edge; rtx cbranch_insn; /* Verify that there are exactly two successors. */ if (!cbranch_block->succ || !cbranch_block->succ->succ_next || cbranch_block->succ->succ_next->succ_next) return false; /* Verify that we've got a normal conditional branch at the end of the block. */ cbranch_insn = cbranch_block->end; if (!any_condjump_p (cbranch_insn)) return false; cbranch_fallthru_edge = FALLTHRU_EDGE (cbranch_block); cbranch_jump_edge = BRANCH_EDGE (cbranch_block); /* The next block must not have multiple predecessors, must not be the last block in the function, and must contain just the unconditional jump. */ jump_block = cbranch_fallthru_edge->dest; if (jump_block->pred->pred_next || jump_block->index == n_basic_blocks - 1 || !forwarder_block_p (jump_block)) return false; jump_dest_block = jump_block->succ->dest; /* The conditional branch must target the block after the unconditional branch. */ cbranch_dest_block = cbranch_jump_edge->dest; if (!can_fallthru (jump_block, cbranch_dest_block)) return false; /* Invert the conditional branch. */ if (!invert_jump (cbranch_insn, block_label (jump_dest_block), 0)) return false; if (rtl_dump_file) fprintf (rtl_dump_file, "Simplifying condjump %i around jump %i\n", INSN_UID (cbranch_insn), INSN_UID (jump_block->end)); /* Success. Update the CFG to match. Note that after this point the edge variable names appear backwards; the redirection is done this way to preserve edge profile data. */ cbranch_jump_edge = redirect_edge_succ_nodup (cbranch_jump_edge, cbranch_dest_block); cbranch_fallthru_edge = redirect_edge_succ_nodup (cbranch_fallthru_edge, jump_dest_block); cbranch_jump_edge->flags |= EDGE_FALLTHRU; cbranch_fallthru_edge->flags &= ~EDGE_FALLTHRU; /* Delete the block with the unconditional jump, and clean up the mess. */ flow_delete_block (jump_block); tidy_fallthru_edge (cbranch_jump_edge, cbranch_block, cbranch_dest_block); return true; } /* Attempt to forward edges leaving basic block B. Return true if sucessful. */ static bool try_forward_edges (mode, b) basic_block b; int mode; { bool changed = false; edge e, next; for (e = b->succ; e ; e = next) { basic_block target, first; int counter; next = e->succ_next; /* Skip complex edges because we don't know how to update them. Still handle fallthru edges, as we can suceed to forward fallthru edge to the same place as the branch edge of conditional branch and turn conditional branch to an unconditonal branch. */ if (e->flags & EDGE_COMPLEX) continue; target = first = e->dest; counter = 0; /* Look for the real destination of the jump. Avoid inifinite loop in the infinite empty loop by counting up to n_basic_blocks. */ while (forwarder_block_p (target) && target->succ->dest != EXIT_BLOCK_PTR && counter < n_basic_blocks) { /* Bypass trivial infinite loops. */ if (target == target->succ->dest) counter = n_basic_blocks; /* Avoid killing of loop pre-headers, as it is the place loop optimizer wants to hoist code to. For fallthru forwarders, the LOOP_BEG note must appear between the header of block and CODE_LABEL of the loop, for non forwarders it must appear before the JUMP_INSN. */ if (mode & CLEANUP_PRE_LOOP) { rtx insn = (target->succ->flags & EDGE_FALLTHRU ? target->head : prev_nonnote_insn (target->end)); if (GET_CODE (insn) != NOTE) insn = NEXT_INSN (insn); for (;insn && GET_CODE (insn) != CODE_LABEL && !INSN_P (insn); insn = NEXT_INSN (insn)) if (GET_CODE (insn) == NOTE && NOTE_LINE_NUMBER (insn) == NOTE_INSN_LOOP_BEG) break; if (GET_CODE (insn) == NOTE) break; } target = target->succ->dest, counter++; } if (counter >= n_basic_blocks) { if (rtl_dump_file) fprintf (rtl_dump_file, "Infinite loop in BB %i.\n", target->index); } else if (target == first) ; /* We didn't do anything. */ else { /* Save the values now, as the edge may get removed. */ gcov_type edge_count = e->count; int edge_probability = e->probability; if (redirect_edge_and_branch (e, target)) { /* We successfully forwarded the edge. Now update profile data: for each edge we traversed in the chain, remove the original edge's execution count. */ int edge_frequency = ((edge_probability * b->frequency + REG_BR_PROB_BASE / 2) / REG_BR_PROB_BASE); do { first->count -= edge_count; first->succ->count -= edge_count; first->frequency -= edge_frequency; first = first->succ->dest; } while (first != target); changed = true; } else { if (rtl_dump_file) fprintf (rtl_dump_file, "Forwarding edge %i->%i to %i failed.\n", b->index, e->dest->index, target->index); } } } return changed; } /* Return true if LABEL is used for tail recursion. */ static bool tail_recursion_label_p (label) rtx label; { rtx x; for (x = tail_recursion_label_list; x; x = XEXP (x, 1)) if (label == XEXP (x, 0)) return true; return false; } /* Blocks A and B are to be merged into a single block. A has no incoming fallthru edge, so it can be moved before B without adding or modifying any jumps (aside from the jump from A to B). */ static void merge_blocks_move_predecessor_nojumps (a, b) basic_block a, b; { rtx barrier; int index; barrier = next_nonnote_insn (a->end); if (GET_CODE (barrier) != BARRIER) abort (); delete_insn (barrier); /* Move block and loop notes out of the chain so that we do not disturb their order. ??? A better solution would be to squeeze out all the non-nested notes and adjust the block trees appropriately. Even better would be to have a tighter connection between block trees and rtl so that this is not necessary. */ squeeze_notes (&a->head, &a->end); /* Scramble the insn chain. */ if (a->end != PREV_INSN (b->head)) reorder_insns_nobb (a->head, a->end, PREV_INSN (b->head)); if (rtl_dump_file) { fprintf (rtl_dump_file, "Moved block %d before %d and merged.\n", a->index, b->index); } /* Swap the records for the two blocks around. Although we are deleting B, A is now where B was and we want to compact the BB array from where A used to be. */ BASIC_BLOCK (a->index) = b; BASIC_BLOCK (b->index) = a; index = a->index; a->index = b->index; b->index = index; /* Now blocks A and B are contiguous. Merge them. */ merge_blocks_nomove (a, b); } /* Blocks A and B are to be merged into a single block. B has no outgoing fallthru edge, so it can be moved after A without adding or modifying any jumps (aside from the jump from A to B). */ static void merge_blocks_move_successor_nojumps (a, b) basic_block a, b; { rtx barrier, real_b_end; real_b_end = b->end; barrier = NEXT_INSN (b->end); /* Recognize a jump table following block B. */ if (barrier && GET_CODE (barrier) == CODE_LABEL && NEXT_INSN (barrier) && GET_CODE (NEXT_INSN (barrier)) == JUMP_INSN && (GET_CODE (PATTERN (NEXT_INSN (barrier))) == ADDR_VEC || GET_CODE (PATTERN (NEXT_INSN (barrier))) == ADDR_DIFF_VEC)) { /* Temporarily add the table jump insn to b, so that it will also be moved to the correct location. */ b->end = NEXT_INSN (barrier); barrier = NEXT_INSN (b->end); } /* There had better have been a barrier there. Delete it. */ if (barrier && GET_CODE (barrier) == BARRIER) delete_insn (barrier); /* Move block and loop notes out of the chain so that we do not disturb their order. ??? A better solution would be to squeeze out all the non-nested notes and adjust the block trees appropriately. Even better would be to have a tighter connection between block trees and rtl so that this is not necessary. */ squeeze_notes (&b->head, &b->end); /* Scramble the insn chain. */ reorder_insns_nobb (b->head, b->end, a->end); /* Restore the real end of b. */ b->end = real_b_end; /* Now blocks A and B are contiguous. Merge them. */ merge_blocks_nomove (a, b); if (rtl_dump_file) { fprintf (rtl_dump_file, "Moved block %d after %d and merged.\n", b->index, a->index); } } /* Attempt to merge basic blocks that are potentially non-adjacent. Return true iff the attempt succeeded. */ static bool merge_blocks (e, b, c, mode) edge e; basic_block b, c; int mode; { /* If C has a tail recursion label, do not merge. There is no edge recorded from the call_placeholder back to this label, as that would make optimize_sibling_and_tail_recursive_calls more complex for no gain. */ if ((mode & CLEANUP_PRE_SIBCALL) && GET_CODE (c->head) == CODE_LABEL && tail_recursion_label_p (c->head)) return false; /* If B has a fallthru edge to C, no need to move anything. */ if (e->flags & EDGE_FALLTHRU) { merge_blocks_nomove (b, c); if (rtl_dump_file) { fprintf (rtl_dump_file, "Merged %d and %d without moving.\n", b->index, c->index); } return true; } /* Otherwise we will need to move code around. Do that only if expensive transformations are allowed. */ else if (mode & CLEANUP_EXPENSIVE) { edge tmp_edge, b_fallthru_edge; bool c_has_outgoing_fallthru; bool b_has_incoming_fallthru; /* Avoid overactive code motion, as the forwarder blocks should be eliminated by edge redirection instead. One exception might have been if B is a forwarder block and C has no fallthru edge, but that should be cleaned up by bb-reorder instead. */ if (forwarder_block_p (b) || forwarder_block_p (c)) return false; /* We must make sure to not munge nesting of lexical blocks, and loop notes. This is done by squeezing out all the notes and leaving them there to lie. Not ideal, but functional. */ for (tmp_edge = c->succ; tmp_edge; tmp_edge = tmp_edge->succ_next) if (tmp_edge->flags & EDGE_FALLTHRU) break; c_has_outgoing_fallthru = (tmp_edge != NULL); for (tmp_edge = b->pred; tmp_edge; tmp_edge = tmp_edge->pred_next) if (tmp_edge->flags & EDGE_FALLTHRU) break; b_has_incoming_fallthru = (tmp_edge != NULL); b_fallthru_edge = tmp_edge; /* Otherwise, we're going to try to move C after B. If C does not have an outgoing fallthru, then it can be moved immediately after B without introducing or modifying jumps. */ if (! c_has_outgoing_fallthru) { merge_blocks_move_successor_nojumps (b, c); return true; } /* If B does not have an incoming fallthru, then it can be moved immediately before C without introducing or modifying jumps. C cannot be the first block, so we do not have to worry about accessing a non-existent block. */ if (b_has_incoming_fallthru) { if (b_fallthru_edge->src == ENTRY_BLOCK_PTR) return false; force_nonfallthru (b_fallthru_edge); } merge_blocks_move_predecessor_nojumps (b, c); return true; } return false; } /* Look through the insns at the end of BB1 and BB2 and find the longest sequence that are equivalent. Store the first insns for that sequence in *F1 and *F2 and return the sequence length. To simplify callers of this function, if the blocks match exactly, store the head of the blocks in *F1 and *F2. */ static int flow_find_cross_jump (mode, bb1, bb2, f1, f2) int mode ATTRIBUTE_UNUSED; basic_block bb1, bb2; rtx *f1, *f2; { rtx i1, i2, p1, p2, last1, last2, afterlast1, afterlast2; int ninsns = 0; /* Skip simple jumps at the end of the blocks. Complex jumps still need to be compared for equivalence, which we'll do below. */ i1 = bb1->end; if (onlyjump_p (i1) || (returnjump_p (i1) && !side_effects_p (PATTERN (i1)))) i1 = PREV_INSN (i1); i2 = bb2->end; if (onlyjump_p (i2) || (returnjump_p (i2) && !side_effects_p (PATTERN (i2)))) i2 = PREV_INSN (i2); last1 = afterlast1 = last2 = afterlast2 = NULL_RTX; while (true) { /* Ignore notes. */ while ((GET_CODE (i1) == NOTE && i1 != bb1->head)) i1 = PREV_INSN (i1); while ((GET_CODE (i2) == NOTE && i2 != bb2->head)) i2 = PREV_INSN (i2); if (i1 == bb1->head || i2 == bb2->head) break; /* Verify that I1 and I2 are equivalent. */ if (GET_CODE (i1) != GET_CODE (i2)) break; p1 = PATTERN (i1); p2 = PATTERN (i2); /* If this is a CALL_INSN, compare register usage information. If we don't check this on stack register machines, the two CALL_INSNs might be merged leaving reg-stack.c with mismatching numbers of stack registers in the same basic block. If we don't check this on machines with delay slots, a delay slot may be filled that clobbers a parameter expected by the subroutine. ??? We take the simple route for now and assume that if they're equal, they were constructed identically. */ if (GET_CODE (i1) == CALL_INSN && ! rtx_equal_p (CALL_INSN_FUNCTION_USAGE (i1), CALL_INSN_FUNCTION_USAGE (i2))) break; #ifdef STACK_REGS /* If cross_jump_death_matters is not 0, the insn's mode indicates whether or not the insn contains any stack-like regs. */ if ((mode & CLEANUP_POST_REGSTACK) && stack_regs_mentioned (i1)) { /* If register stack conversion has already been done, then death notes must also be compared before it is certain that the two instruction streams match. */ rtx note; HARD_REG_SET i1_regset, i2_regset; CLEAR_HARD_REG_SET (i1_regset); CLEAR_HARD_REG_SET (i2_regset); for (note = REG_NOTES (i1); note; note = XEXP (note, 1)) if (REG_NOTE_KIND (note) == REG_DEAD && STACK_REG_P (XEXP (note, 0))) SET_HARD_REG_BIT (i1_regset, REGNO (XEXP (note, 0))); for (note = REG_NOTES (i2); note; note = XEXP (note, 1)) if (REG_NOTE_KIND (note) == REG_DEAD && STACK_REG_P (XEXP (note, 0))) SET_HARD_REG_BIT (i2_regset, REGNO (XEXP (note, 0))); GO_IF_HARD_REG_EQUAL (i1_regset, i2_regset, done); break; done: ; } #endif if (GET_CODE (p1) != GET_CODE (p2)) break; if (! rtx_renumbered_equal_p (p1, p2)) { /* The following code helps take care of G++ cleanups. */ rtx equiv1 = find_reg_equal_equiv_note (i1); rtx equiv2 = find_reg_equal_equiv_note (i2); if (equiv1 && equiv2 /* If the equivalences are not to a constant, they may reference pseudos that no longer exist, so we can't use them. */ && CONSTANT_P (XEXP (equiv1, 0)) && rtx_equal_p (XEXP (equiv1, 0), XEXP (equiv2, 0))) { rtx s1 = single_set (i1); rtx s2 = single_set (i2); if (s1 != 0 && s2 != 0 && rtx_renumbered_equal_p (SET_DEST (s1), SET_DEST (s2))) { validate_change (i1, &SET_SRC (s1), XEXP (equiv1, 0), 1); validate_change (i2, &SET_SRC (s2), XEXP (equiv2, 0), 1); if (! rtx_renumbered_equal_p (p1, p2)) cancel_changes (0); else if (apply_change_group ()) goto win; } } break; } win: /* Don't begin a cross-jump with a USE or CLOBBER insn. */ if (GET_CODE (p1) != USE && GET_CODE (p1) != CLOBBER) { /* If the merged insns have different REG_EQUAL notes, then remove them. */ rtx equiv1 = find_reg_equal_equiv_note (i1); rtx equiv2 = find_reg_equal_equiv_note (i2); if (equiv1 && !equiv2) remove_note (i1, equiv1); else if (!equiv1 && equiv2) remove_note (i2, equiv2); else if (equiv1 && equiv2 && !rtx_equal_p (XEXP (equiv1, 0), XEXP (equiv2, 0))) { remove_note (i1, equiv1); remove_note (i2, equiv2); } afterlast1 = last1, afterlast2 = last2; last1 = i1, last2 = i2; ninsns++; } i1 = PREV_INSN (i1); i2 = PREV_INSN (i2); } #ifdef HAVE_cc0 if (ninsns) { /* Don't allow the insn after a compare to be shared by cross-jumping unless the compare is also shared. */ if (reg_mentioned_p (cc0_rtx, last1) && ! sets_cc0_p (last1)) last1 = afterlast1, last2 = afterlast2, ninsns--; } #endif /* Include preceeding notes and labels in the cross-jump. One, this may bring us to the head of the blocks as requested above. Two, it keeps line number notes as matched as may be. */ if (ninsns) { while (last1 != bb1->head && GET_CODE (PREV_INSN (last1)) == NOTE) last1 = PREV_INSN (last1); if (last1 != bb1->head && GET_CODE (PREV_INSN (last1)) == CODE_LABEL) last1 = PREV_INSN (last1); while (last2 != bb2->head && GET_CODE (PREV_INSN (last2)) == NOTE) last2 = PREV_INSN (last2); if (last2 != bb2->head && GET_CODE (PREV_INSN (last2)) == CODE_LABEL) last2 = PREV_INSN (last2); *f1 = last1; *f2 = last2; } return ninsns; } /* Return true iff outgoing edges of BB1 and BB2 match, together with the branch instruction. This means that if we commonize the control flow before end of the basic block, the semantic remains unchanged. We may assume that there exists one edge with a common destination. */ static bool outgoing_edges_match (bb1, bb2) basic_block bb1; basic_block bb2; { /* If BB1 has only one successor, we must be looking at an unconditional jump. Which, by the assumption above, means that we only need to check that BB2 has one successor. */ if (bb1->succ && !bb1->succ->succ_next) return (bb2->succ && !bb2->succ->succ_next); /* Match conditional jumps - this may get tricky when fallthru and branch edges are crossed. */ if (bb1->succ && bb1->succ->succ_next && !bb1->succ->succ_next->succ_next && any_condjump_p (bb1->end)) { edge b1, f1, b2, f2; bool reverse, match; rtx set1, set2, cond1, cond2; enum rtx_code code1, code2; if (!bb2->succ || !bb2->succ->succ_next || bb1->succ->succ_next->succ_next || !any_condjump_p (bb2->end)) return false; b1 = BRANCH_EDGE (bb1); b2 = BRANCH_EDGE (bb2); f1 = FALLTHRU_EDGE (bb1); f2 = FALLTHRU_EDGE (bb2); /* Get around possible forwarders on fallthru edges. Other cases should be optimized out already. */ if (forwarder_block_p (f1->dest)) f1 = f1->dest->succ; if (forwarder_block_p (f2->dest)) f2 = f2->dest->succ; /* To simplify use of this function, return false if there are unneeded forwarder blocks. These will get eliminated later during cleanup_cfg. */ if (forwarder_block_p (f1->dest) || forwarder_block_p (f2->dest) || forwarder_block_p (b1->dest) || forwarder_block_p (b2->dest)) return false; if (f1->dest == f2->dest && b1->dest == b2->dest) reverse = false; else if (f1->dest == b2->dest && b1->dest == f2->dest) reverse = true; else return false; set1 = pc_set (bb1->end); set2 = pc_set (bb2->end); if ((XEXP (SET_SRC (set1), 1) == pc_rtx) != (XEXP (SET_SRC (set2), 1) == pc_rtx)) reverse = !reverse; cond1 = XEXP (SET_SRC (set1), 0); cond2 = XEXP (SET_SRC (set2), 0); code1 = GET_CODE (cond1); if (reverse) code2 = reversed_comparison_code (cond2, bb2->end); else code2 = GET_CODE (cond2); if (code2 == UNKNOWN) return false; /* Verify codes and operands match. */ match = ((code1 == code2 && rtx_renumbered_equal_p (XEXP (cond1, 0), XEXP (cond2, 0)) && rtx_renumbered_equal_p (XEXP (cond1, 1), XEXP (cond2, 1))) || (code1 == swap_condition (code2) && rtx_renumbered_equal_p (XEXP (cond1, 1), XEXP (cond2, 0)) && rtx_renumbered_equal_p (XEXP (cond1, 0), XEXP (cond2, 1)))); /* If we return true, we will join the blocks. Which means that we will only have one branch prediction bit to work with. Thus we require the existing branches to have probabilities that are roughly similar. */ /* ??? We should use bb->frequency to allow merging in infrequently executed blocks, but at the moment it is not available when cleanup_cfg is run. */ if (match && !optimize_size) { rtx note1, note2; int prob1, prob2; note1 = find_reg_note (bb1->end, REG_BR_PROB, 0); note2 = find_reg_note (bb2->end, REG_BR_PROB, 0); if (note1 && note2) { prob1 = INTVAL (XEXP (note1, 0)); prob2 = INTVAL (XEXP (note2, 0)); if (reverse) prob2 = REG_BR_PROB_BASE - prob2; /* Fail if the difference in probabilities is greater than 5%. */ if (abs (prob1 - prob2) > REG_BR_PROB_BASE / 20) return false; } else if (note1 || note2) return false; } if (rtl_dump_file && match) fprintf (rtl_dump_file, "Conditionals in bb %i and %i match.\n", bb1->index, bb2->index); return match; } /* ??? We can handle computed jumps too. This may be important for inlined functions containing switch statements. Also jumps w/o fallthru edges can be handled by simply matching whole insn. */ return false; } /* E1 and E2 are edges with the same destination block. Search their predecessors for common code. If found, redirect control flow from (maybe the middle of) E1->SRC to (maybe the middle of) E2->SRC. */ static bool try_crossjump_to_edge (mode, e1, e2) int mode; edge e1, e2; { int nmatch; basic_block src1 = e1->src, src2 = e2->src; basic_block redirect_to; rtx newpos1, newpos2; edge s; rtx last; rtx label; rtx note; /* Search backward through forwarder blocks. We don't need to worry about multiple entry or chained forwarders, as they will be optimized away. We do this to look past the unconditional jump following a conditional jump that is required due to the current CFG shape. */ if (src1->pred && !src1->pred->pred_next && forwarder_block_p (src1)) { e1 = src1->pred; src1 = e1->src; } if (src2->pred && !src2->pred->pred_next && forwarder_block_p (src2)) { e2 = src2->pred; src2 = e2->src; } /* Nothing to do if we reach ENTRY, or a common source block. */ if (src1 == ENTRY_BLOCK_PTR || src2 == ENTRY_BLOCK_PTR) return false; if (src1 == src2) return false; /* Seeing more than 1 forwarder blocks would confuse us later... */ if (forwarder_block_p (e1->dest) && forwarder_block_p (e1->dest->succ->dest)) return false; if (forwarder_block_p (e2->dest) && forwarder_block_p (e2->dest->succ->dest)) return false; /* Likewise with dead code (possibly newly created by the other optimizations of cfg_cleanup). */ if (!src1->pred || !src2->pred) return false; /* Likewise with complex edges. ??? We should be able to handle most complex edges later with some care. */ if (e1->flags & EDGE_COMPLEX) return false; /* Look for the common insn sequence, part the first ... */ if (!outgoing_edges_match (src1, src2)) return false; /* ... and part the second. */ nmatch = flow_find_cross_jump (mode, src1, src2, &newpos1, &newpos2); if (!nmatch) return false; /* Avoid splitting if possible. */ if (newpos2 == src2->head) redirect_to = src2; else { if (rtl_dump_file) fprintf (rtl_dump_file, "Splitting bb %i before %i insns\n", src2->index, nmatch); redirect_to = split_block (src2, PREV_INSN (newpos2))->dest; } if (rtl_dump_file) fprintf (rtl_dump_file, "Cross jumping from bb %i to bb %i; %i common insns\n", src1->index, src2->index, nmatch); redirect_to->count += src1->count; redirect_to->frequency += src1->frequency; /* Recompute the frequencies and counts of outgoing edges. */ for (s = redirect_to->succ; s; s = s->succ_next) { edge s2; basic_block d = s->dest; if (forwarder_block_p (d)) d = d->succ->dest; for (s2 = src1->succ; ; s2 = s2->succ_next) { basic_block d2 = s2->dest; if (forwarder_block_p (d2)) d2 = d2->succ->dest; if (d == d2) break; } s->count += s2->count; /* Take care to update possible forwarder blocks. We verified that there is no more than one in the chain, so we can't run into infinite loop. */ if (forwarder_block_p (s->dest)) { s->dest->succ->count += s2->count; s->dest->count += s2->count; s->dest->frequency += EDGE_FREQUENCY (s); } if (forwarder_block_p (s2->dest)) { s2->dest->succ->count -= s2->count; s2->dest->count -= s2->count; s2->dest->frequency -= EDGE_FREQUENCY (s); } if (!redirect_to->frequency && !src1->frequency) s->probability = (s->probability + s2->probability) / 2; else s->probability = ((s->probability * redirect_to->frequency + s2->probability * src1->frequency) / (redirect_to->frequency + src1->frequency)); } note = find_reg_note (redirect_to->end, REG_BR_PROB, 0); if (note) XEXP (note, 0) = GEN_INT (BRANCH_EDGE (redirect_to)->probability); /* Edit SRC1 to go to REDIRECT_TO at NEWPOS1. */ /* Skip possible basic block header. */ if (GET_CODE (newpos1) == CODE_LABEL) newpos1 = NEXT_INSN (newpos1); if (GET_CODE (newpos1) == NOTE) newpos1 = NEXT_INSN (newpos1); last = src1->end; /* Emit the jump insn. */ label = block_label (redirect_to); emit_jump_insn_after (gen_jump (label), src1->end); JUMP_LABEL (src1->end) = label; LABEL_NUSES (label)++; /* Delete the now unreachable instructions. */ delete_insn_chain (newpos1, last); /* Make sure there is a barrier after the new jump. */ last = next_nonnote_insn (src1->end); if (!last || GET_CODE (last) != BARRIER) emit_barrier_after (src1->end); /* Update CFG. */ while (src1->succ) remove_edge (src1->succ); make_single_succ_edge (src1, redirect_to, 0); return true; } /* Search the predecessors of BB for common insn sequences. When found, share code between them by redirecting control flow. Return true if any changes made. */ static bool try_crossjump_bb (mode, bb) int mode; basic_block bb; { edge e, e2, nexte2, nexte, fallthru; bool changed; /* Nothing to do if there is not at least two incomming edges. */ if (!bb->pred || !bb->pred->pred_next) return false; /* It is always cheapest to redirect a block that ends in a branch to a block that falls through into BB, as that adds no branches to the program. We'll try that combination first. */ for (fallthru = bb->pred; fallthru; fallthru = fallthru->pred_next) if (fallthru->flags & EDGE_FALLTHRU) break; changed = false; for (e = bb->pred; e; e = nexte) { nexte = e->pred_next; /* Elide complex edges now, as neither try_crossjump_to_edge nor outgoing_edges_match can handle them. */ if (e->flags & EDGE_COMPLEX) continue; /* As noted above, first try with the fallthru predecessor. */ if (fallthru) { /* Don't combine the fallthru edge into anything else. If there is a match, we'll do it the other way around. */ if (e == fallthru) continue; if (try_crossjump_to_edge (mode, e, fallthru)) { changed = true; nexte = bb->pred; continue; } } /* Non-obvious work limiting check: Recognize that we're going to call try_crossjump_bb on every basic block. So if we have two blocks with lots of outgoing edges (a switch) and they share lots of common destinations, then we would do the cross-jump check once for each common destination. Now, if the blocks actually are cross-jump candidates, then all of their destinations will be shared. Which means that we only need check them for cross-jump candidacy once. We can eliminate redundant checks of crossjump(A,B) by arbitrarily choosing to do the check from the block for which the edge in question is the first successor of A. */ if (e->src->succ != e) continue; for (e2 = bb->pred; e2; e2 = nexte2) { nexte2 = e2->pred_next; if (e2 == e) continue; /* We've already checked the fallthru edge above. */ if (e2 == fallthru) continue; /* Again, neither try_crossjump_to_edge nor outgoing_edges_match can handle complex edges. */ if (e2->flags & EDGE_COMPLEX) continue; /* The "first successor" check above only prevents multiple checks of crossjump(A,B). In order to prevent redundant checks of crossjump(B,A), require that A be the block with the lowest index. */ if (e->src->index > e2->src->index) continue; if (try_crossjump_to_edge (mode, e, e2)) { changed = true; nexte = bb->pred; break; } } } return changed; } /* Do simple CFG optimizations - basic block merging, simplifying of jump instructions etc. Return nonzero if changes were made. */ static bool try_optimize_cfg (mode) int mode; { int i; bool changed_overall = false; bool changed; int iterations = 0; if (mode & CLEANUP_CROSSJUMP) add_noreturn_fake_exit_edges (); /* Attempt to merge blocks as made possible by edge removal. If a block has only one successor, and the successor has only one predecessor, they may be combined. */ do { changed = false; iterations++; if (rtl_dump_file) fprintf (rtl_dump_file, "\n\ntry_optimize_cfg iteration %i\n\n", iterations); for (i = 0; i < n_basic_blocks;) { basic_block c, b = BASIC_BLOCK (i); edge s; bool changed_here = false; /* Delete trivially dead basic blocks. */ while (b->pred == NULL) { c = BASIC_BLOCK (b->index - 1); if (rtl_dump_file) fprintf (rtl_dump_file, "Deleting block %i.\n", b->index); flow_delete_block (b); changed = true; b = c; } /* Remove code labels no longer used. Don't do this before CALL_PLACEHOLDER is removed, as some branches may be hidden within. */ if (b->pred->pred_next == NULL && (b->pred->flags & EDGE_FALLTHRU) && !(b->pred->flags & EDGE_COMPLEX) && GET_CODE (b->head) == CODE_LABEL && (!(mode & CLEANUP_PRE_SIBCALL) || !tail_recursion_label_p (b->head)) /* If previous block ends with condjump jumping to next BB, we can't delete the label. */ && (b->pred->src == ENTRY_BLOCK_PTR || !reg_mentioned_p (b->head, b->pred->src->end))) { rtx label = b->head; b->head = NEXT_INSN (b->head); delete_insn_chain (label, label); if (rtl_dump_file) fprintf (rtl_dump_file, "Deleted label in block %i.\n", b->index); } /* If we fall through an empty block, we can remove it. */ if (b->pred->pred_next == NULL && (b->pred->flags & EDGE_FALLTHRU) && GET_CODE (b->head) != CODE_LABEL && forwarder_block_p (b) /* Note that forwarder_block_p true ensures that there is a successor for this block. */ && (b->succ->flags & EDGE_FALLTHRU) && n_basic_blocks > 1) { if (rtl_dump_file) fprintf (rtl_dump_file, "Deleting fallthru block %i.\n", b->index); c = BASIC_BLOCK (b->index ? b->index - 1 : 1); redirect_edge_succ_nodup (b->pred, b->succ->dest); flow_delete_block (b); changed = true; b = c; } /* Merge blocks. Loop because chains of blocks might be combineable. */ while ((s = b->succ) != NULL && s->succ_next == NULL && !(s->flags & EDGE_COMPLEX) && (c = s->dest) != EXIT_BLOCK_PTR && c->pred->pred_next == NULL /* If the jump insn has side effects, we can't kill the edge. */ && (GET_CODE (b->end) != JUMP_INSN || onlyjump_p (b->end)) && merge_blocks (s, b, c, mode)) changed_here = true; /* Simplify branch over branch. */ if ((mode & CLEANUP_EXPENSIVE) && try_simplify_condjump (b)) changed_here = true; /* If B has a single outgoing edge, but uses a non-trivial jump instruction without side-effects, we can either delete the jump entirely, or replace it with a simple unconditional jump. Use redirect_edge_and_branch to do the dirty work. */ if (b->succ && ! b->succ->succ_next && b->succ->dest != EXIT_BLOCK_PTR && onlyjump_p (b->end) && redirect_edge_and_branch (b->succ, b->succ->dest)) changed_here = true; /* Simplify branch to branch. */ if (try_forward_edges (mode, b)) changed_here = true; /* Look for shared code between blocks. */ if ((mode & CLEANUP_CROSSJUMP) && try_crossjump_bb (mode, b)) changed_here = true; /* Don't get confused by the index shift caused by deleting blocks. */ if (!changed_here) i = b->index + 1; else changed = true; } if ((mode & CLEANUP_CROSSJUMP) && try_crossjump_bb (mode, EXIT_BLOCK_PTR)) changed = true; #ifdef ENABLE_CHECKING if (changed) verify_flow_info (); #endif changed_overall |= changed; } while (changed); if (mode & CLEANUP_CROSSJUMP) remove_fake_edges (); return changed_overall; } /* Delete all unreachable basic blocks. */ static bool delete_unreachable_blocks () { int i; bool changed = false; find_unreachable_blocks (); /* Delete all unreachable basic blocks. Count down so that we don't interfere with the block renumbering that happens in flow_delete_block. */ for (i = n_basic_blocks - 1; i >= 0; --i) { basic_block b = BASIC_BLOCK (i); if (!(b->flags & BB_REACHABLE)) flow_delete_block (b), changed = true; } if (changed) tidy_fallthru_edges (); return changed; } /* Tidy the CFG by deleting unreachable code and whatnot. */ bool cleanup_cfg (mode) int mode; { int i; bool changed = false; timevar_push (TV_CLEANUP_CFG); changed = delete_unreachable_blocks (); if (try_optimize_cfg (mode)) delete_unreachable_blocks (), changed = true; /* Kill the data we won't maintain. */ free_EXPR_LIST_list (&label_value_list); free_EXPR_LIST_list (&tail_recursion_label_list); timevar_pop (TV_CLEANUP_CFG); /* Clear bb->aux on all basic blocks. */ for (i = 0; i < n_basic_blocks; ++i) BASIC_BLOCK (i)->aux = NULL; return changed; }