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Diffstat (limited to 'gcc/tree-ssa-loop-unswitch.c')
| -rw-r--r-- | gcc/tree-ssa-loop-unswitch.c | 283 |
1 files changed, 283 insertions, 0 deletions
diff --git a/gcc/tree-ssa-loop-unswitch.c b/gcc/tree-ssa-loop-unswitch.c new file mode 100644 index 00000000000..ab8c4e0bab7 --- /dev/null +++ b/gcc/tree-ssa-loop-unswitch.c @@ -0,0 +1,283 @@ +/* Loop unswitching. + Copyright (C) 2004 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. */ + +#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 "output.h" +#include "diagnostic.h" +#include "tree-flow.h" +#include "tree-dump.h" +#include "timevar.h" +#include "cfgloop.h" +#include "domwalk.h" +#include "params.h" +#include "tree-pass.h" + +/* This file implements the loop unswitching, i.e. transformation of loops like + + while (A) + { + if (inv) + B; + + X; + + if (!inv) + C; + } + + where inv is the loop invariant, into + + if (inv) + { + while (A) + { + B; + X; + } + } + else + { + while (A) + { + X; + C; + } + } + + Inv is considered invariant iff the values it compares are both invariant; + tree-ssa-loop-im.c ensures that all the suitable conditions are in this + shape. */ + +static struct loop *tree_unswitch_loop (struct loops *, struct loop *, basic_block, + tree); +static void tree_unswitch_single_loop (struct loops *, struct loop *, int); +static tree tree_may_unswitch_on (basic_block, struct loop *); + +/* Main entry point. Perform loop unswitching on all suitable LOOPS. */ + +void +tree_ssa_unswitch_loops (struct loops *loops) +{ + int i, num; + struct loop *loop; + + /* Go through inner loops (only original ones). */ + num = loops->num; + + for (i = 1; i < num; i++) + { + /* Removed loop? */ + loop = loops->parray[i]; + if (!loop) + continue; + + if (loop->inner) + continue; + + tree_unswitch_single_loop (loops, loop, 0); +#ifdef ENABLE_CHECKING + verify_dominators (CDI_DOMINATORS); + verify_loop_structure (loops); +#endif + } +} + +/* Checks whether we can unswitch LOOP on condition at end of BB -- one of its + basic blocks (for what it means see comments below). */ + +static tree +tree_may_unswitch_on (basic_block bb, struct loop *loop) +{ + tree stmt, def, cond; + basic_block def_bb; + use_optype uses; + unsigned i; + + /* BB must end in a simple conditional jump. */ + stmt = last_stmt (bb); + if (!stmt || TREE_CODE (stmt) != COND_EXPR) + return NULL_TREE; + + /* Condition must be invariant. */ + get_stmt_operands (stmt); + uses = STMT_USE_OPS (stmt); + for (i = 0; i < NUM_USES (uses); i++) + { + def = SSA_NAME_DEF_STMT (USE_OP (uses, i)); + def_bb = bb_for_stmt (def); + if (def_bb + && flow_bb_inside_loop_p (loop, def_bb)) + return NULL_TREE; + } + + cond = COND_EXPR_COND (stmt); + /* To keep the things simple, we do not directly remove the conditions, + but just replace tests with 0/1. Prevent the infinite loop where we + would unswitch again on such a condition. */ + if (integer_zerop (cond) || integer_nonzerop (cond)) + return NULL_TREE; + + return cond; +} + +/* Simplifies COND using checks in front of the entry of the LOOP. Just very + simplish (sufficient to prevent us from duplicating loop in unswitching + unneccesarily). */ + +static tree +simplify_using_entry_checks (struct loop *loop, tree cond) +{ + edge e = loop_preheader_edge (loop); + tree stmt; + + while (1) + { + stmt = last_stmt (e->src); + if (stmt + && TREE_CODE (stmt) == COND_EXPR + && operand_equal_p (COND_EXPR_COND (stmt), cond, 0)) + return (e->flags & EDGE_TRUE_VALUE + ? boolean_true_node + : boolean_false_node); + + if (e->src->pred->pred_next) + return cond; + + e = e->src->pred; + if (e->src == ENTRY_BLOCK_PTR) + return cond; + } +} + +/* Unswitch single LOOP. NUM is number of unswitchings done; we do not allow + it to grow too much, it is too easy to create example on that the code would + grow exponentially. */ + +static void +tree_unswitch_single_loop (struct loops *loops, struct loop *loop, int num) +{ + basic_block *bbs; + struct loop *nloop; + unsigned i; + tree cond = NULL_TREE, stmt; + + /* Do not unswitch too much. */ + if (num > PARAM_VALUE (PARAM_MAX_UNSWITCH_LEVEL)) + { + if (dump_file && (dump_flags & TDF_DETAILS)) + fprintf (dump_file, ";; Not unswitching anymore, hit max level\n"); + return; + } + + /* Only unswitch innermost loops. */ + if (loop->inner) + { + if (dump_file && (dump_flags & TDF_DETAILS)) + fprintf (dump_file, ";; Not unswitching, not innermost loop\n"); + return; + } + + /* The loop should not be too large, to limit code growth. */ + if (estimate_loop_size (loop) + > (unsigned) PARAM_VALUE (PARAM_MAX_UNSWITCH_INSNS)) + { + if (dump_file && (dump_flags & TDF_DETAILS)) + fprintf (dump_file, ";; Not unswitching, loop too big\n"); + return; + } + + i = 0; + bbs = get_loop_body (loop); + + while (1) + { + /* Find a bb to unswitch on. */ + for (; i < loop->num_nodes; i++) + if ((cond = tree_may_unswitch_on (bbs[i], loop))) + break; + + if (i == loop->num_nodes) + { + free (bbs); + return; + } + + cond = simplify_using_entry_checks (loop, cond); + stmt = last_stmt (bbs[i]); + if (integer_nonzerop (cond)) + { + /* Remove false path. */ + COND_EXPR_COND (stmt) = boolean_true_node; + } + else if (integer_zerop (cond)) + { + /* Remove true path. */ + COND_EXPR_COND (stmt) = boolean_false_node; + } + else + break; + + modify_stmt (stmt); + i++; + } + + if (dump_file && (dump_flags & TDF_DETAILS)) + fprintf (dump_file, ";; Unswitching loop\n"); + + /* Unswitch the loop on this condition. */ + nloop = tree_unswitch_loop (loops, loop, bbs[i], cond); + if (!nloop) + return; + + /* Invoke itself on modified loops. */ + tree_unswitch_single_loop (loops, nloop, num + 1); + tree_unswitch_single_loop (loops, loop, num + 1); +} + +/* Unswitch a LOOP w.r. to given basic block UNSWITCH_ON. We only support + unswitching of innermost loops. COND is the condition determining which + loop is entered -- the new loop is entered if COND is true. Returns NULL + if impossible, new loop otherwise. */ + +static struct loop * +tree_unswitch_loop (struct loops *loops, struct loop *loop, + basic_block unswitch_on, tree cond) +{ + basic_block condition_bb; + /* Some sanity checking. */ + if (!flow_bb_inside_loop_p (loop, unswitch_on)) + abort (); + if (!unswitch_on->succ || !unswitch_on->succ->succ_next || + unswitch_on->succ->succ_next->succ_next) + abort (); + if (loop->inner) + abort (); + + return tree_ssa_loop_version (loops, loop, unshare_expr (cond), + &condition_bb); +} |