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[/] [openrisc/] [trunk/] [gnu-src/] [gcc-4.2.2/] [gcc/] [tree-ssa-loop-unswitch.c] - Rev 567
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/* Loop unswitching. Copyright (C) 2004, 2005, 2007 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 3, 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 COPYING3. If not see <http://www.gnu.org/licenses/>. */ #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 bool 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. */ unsigned int tree_ssa_unswitch_loops (struct loops *loops) { int i, num; struct loop *loop; bool changed = false; /* 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; changed |= tree_unswitch_single_loop (loops, loop, 0); } if (changed) return TODO_cleanup_cfg; return 0; } /* 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, use; basic_block def_bb; ssa_op_iter iter; /* 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. */ FOR_EACH_SSA_TREE_OPERAND (use, stmt, iter, SSA_OP_USE) { def = SSA_NAME_DEF_STMT (use); 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 unnecessarily). */ 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 (!single_pred_p (e->src)) return cond; e = single_pred_edge (e->src); 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 bool 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; bool changed = false; /* 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 false; } /* Only unswitch innermost loops. */ if (loop->inner) { if (dump_file && (dump_flags & TDF_DETAILS)) fprintf (dump_file, ";; Not unswitching, not innermost loop\n"); return false; } /* The loop should not be too large, to limit code growth. */ if (tree_num_loop_insns (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 false; } 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 changed; } 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; changed = true; } else if (integer_zerop (cond)) { /* Remove true path. */ COND_EXPR_COND (stmt) = boolean_false_node; changed = true; } else break; update_stmt (stmt); i++; } if (dump_file && (dump_flags & TDF_DETAILS)) fprintf (dump_file, ";; Unswitching loop\n"); initialize_original_copy_tables (); /* Unswitch the loop on this condition. */ nloop = tree_unswitch_loop (loops, loop, bbs[i], cond); if (!nloop) { free_original_copy_tables (); free (bbs); return changed; } /* Update the SSA form after unswitching. */ update_ssa (TODO_update_ssa); free_original_copy_tables (); /* Invoke itself on modified loops. */ tree_unswitch_single_loop (loops, nloop, num + 1); tree_unswitch_single_loop (loops, loop, num + 1); free (bbs); return true; } /* 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. */ gcc_assert (flow_bb_inside_loop_p (loop, unswitch_on)); gcc_assert (EDGE_COUNT (unswitch_on->succs) == 2); gcc_assert (loop->inner == NULL); return loop_version (loops, loop, unshare_expr (cond), &condition_bb, false); }
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