/* Combining of if-expressions on trees. Copyright (C) 2007, 2008 Free Software Foundation, Inc. Contributed by Richard Guenther 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 . */ #include "config.h" #include "system.h" #include "coretypes.h" #include "tm.h" #include "tree.h" #include "basic-block.h" #include "timevar.h" #include "diagnostic.h" #include "tree-flow.h" #include "tree-pass.h" #include "tree-dump.h" /* This pass combines COND_EXPRs to simplify control flow. It currently recognizes bit tests and comparisons in chains that represent logical and or logical or of two COND_EXPRs. It does so by walking basic blocks in a approximate reverse post-dominator order and trying to match CFG patterns that represent logical and or logical or of two COND_EXPRs. Transformations are done if the COND_EXPR conditions match either 1. two single bit tests X & (1 << Yn) (for logical and) 2. two bit tests X & Yn (for logical or) 3. two comparisons X OPn Y (for logical or) To simplify this pass, removing basic blocks and dead code is left to CFG cleanup and DCE. */ /* Recognize a if-then-else CFG pattern starting to match with the COND_BB basic-block containing the COND_EXPR. The recognized then end else blocks are stored to *THEN_BB and *ELSE_BB. If *THEN_BB and/or *ELSE_BB are already set, they are required to match the then and else basic-blocks to make the pattern match. Returns true if the pattern matched, false otherwise. */ static bool recognize_if_then_else (basic_block cond_bb, basic_block *then_bb, basic_block *else_bb) { edge t, e; if (EDGE_COUNT (cond_bb->succs) != 2) return false; /* Find the then/else edges. */ t = EDGE_SUCC (cond_bb, 0); e = EDGE_SUCC (cond_bb, 1); if (!(t->flags & EDGE_TRUE_VALUE)) { edge tmp = t; t = e; e = tmp; } if (!(t->flags & EDGE_TRUE_VALUE) || !(e->flags & EDGE_FALSE_VALUE)) return false; /* Check if the edge destinations point to the required block. */ if (*then_bb && t->dest != *then_bb) return false; if (*else_bb && e->dest != *else_bb) return false; if (!*then_bb) *then_bb = t->dest; if (!*else_bb) *else_bb = e->dest; return true; } /* Verify if the basic block BB does not have side-effects. Return true in this case, else false. */ static bool bb_no_side_effects_p (basic_block bb) { gimple_stmt_iterator gsi; for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi)) { gimple stmt = gsi_stmt (gsi); if (gimple_has_volatile_ops (stmt) || !ZERO_SSA_OPERANDS (stmt, SSA_OP_ALL_VIRTUALS)) return false; } return true; } /* Verify if all PHI node arguments in DEST for edges from BB1 or BB2 to DEST are the same. This makes the CFG merge point free from side-effects. Return true in this case, else false. */ static bool same_phi_args_p (basic_block bb1, basic_block bb2, basic_block dest) { edge e1 = find_edge (bb1, dest); edge e2 = find_edge (bb2, dest); gimple_stmt_iterator gsi; gimple phi; for (gsi = gsi_start_phis (dest); !gsi_end_p (gsi); gsi_next (&gsi)) { phi = gsi_stmt (gsi); if (!operand_equal_p (PHI_ARG_DEF_FROM_EDGE (phi, e1), PHI_ARG_DEF_FROM_EDGE (phi, e2), 0)) return false; } return true; } /* Return the best representative SSA name for CANDIDATE which is used in a bit test. */ static tree get_name_for_bit_test (tree candidate) { /* Skip single-use names in favor of using the name from a non-widening conversion definition. */ if (TREE_CODE (candidate) == SSA_NAME && has_single_use (candidate)) { gimple def_stmt = SSA_NAME_DEF_STMT (candidate); if (is_gimple_assign (def_stmt) && CONVERT_EXPR_CODE_P (gimple_assign_rhs_code (def_stmt))) { if (TYPE_PRECISION (TREE_TYPE (candidate)) <= TYPE_PRECISION (TREE_TYPE (gimple_assign_rhs1 (def_stmt)))) return gimple_assign_rhs1 (def_stmt); } } return candidate; } /* Recognize a single bit test pattern in GIMPLE_COND and its defining statements. Store the name being tested in *NAME and the bit in *BIT. The GIMPLE_COND computes *NAME & (1 << *BIT). Returns true if the pattern matched, false otherwise. */ static bool recognize_single_bit_test (gimple cond, tree *name, tree *bit) { gimple stmt; /* Get at the definition of the result of the bit test. */ if (gimple_cond_code (cond) != NE_EXPR || TREE_CODE (gimple_cond_lhs (cond)) != SSA_NAME || !integer_zerop (gimple_cond_rhs (cond))) return false; stmt = SSA_NAME_DEF_STMT (gimple_cond_lhs (cond)); if (!is_gimple_assign (stmt)) return false; /* Look at which bit is tested. One form to recognize is D.1985_5 = state_3(D) >> control1_4(D); D.1986_6 = (int) D.1985_5; D.1987_7 = op0 & 1; if (D.1987_7 != 0) */ if (gimple_assign_rhs_code (stmt) == BIT_AND_EXPR && integer_onep (gimple_assign_rhs2 (stmt)) && TREE_CODE (gimple_assign_rhs1 (stmt)) == SSA_NAME) { tree orig_name = gimple_assign_rhs1 (stmt); /* Look through copies and conversions to eventually find the stmt that computes the shift. */ stmt = SSA_NAME_DEF_STMT (orig_name); while (is_gimple_assign (stmt) && ((CONVERT_EXPR_CODE_P (gimple_assign_rhs_code (stmt)) && (TYPE_PRECISION (TREE_TYPE (gimple_assign_lhs (stmt))) <= TYPE_PRECISION (TREE_TYPE (gimple_assign_rhs1 (stmt))))) || gimple_assign_ssa_name_copy_p (stmt))) stmt = SSA_NAME_DEF_STMT (gimple_assign_rhs1 (stmt)); /* If we found such, decompose it. */ if (is_gimple_assign (stmt) && gimple_assign_rhs_code (stmt) == RSHIFT_EXPR) { /* op0 & (1 << op1) */ *bit = gimple_assign_rhs2 (stmt); *name = gimple_assign_rhs1 (stmt); } else { /* t & 1 */ *bit = integer_zero_node; *name = get_name_for_bit_test (orig_name); } return true; } /* Another form is D.1987_7 = op0 & (1 << CST) if (D.1987_7 != 0) */ if (gimple_assign_rhs_code (stmt) == BIT_AND_EXPR && TREE_CODE (gimple_assign_rhs1 (stmt)) == SSA_NAME && integer_pow2p (gimple_assign_rhs2 (stmt))) { *name = gimple_assign_rhs1 (stmt); *bit = build_int_cst (integer_type_node, tree_log2 (gimple_assign_rhs2 (stmt))); return true; } /* Another form is D.1986_6 = 1 << control1_4(D) D.1987_7 = op0 & D.1986_6 if (D.1987_7 != 0) */ if (gimple_assign_rhs_code (stmt) == BIT_AND_EXPR && TREE_CODE (gimple_assign_rhs1 (stmt)) == SSA_NAME && TREE_CODE (gimple_assign_rhs2 (stmt)) == SSA_NAME) { gimple tmp; /* Both arguments of the BIT_AND_EXPR can be the single-bit specifying expression. */ tmp = SSA_NAME_DEF_STMT (gimple_assign_rhs1 (stmt)); if (is_gimple_assign (tmp) && gimple_assign_rhs_code (tmp) == LSHIFT_EXPR && integer_onep (gimple_assign_rhs1 (tmp))) { *name = gimple_assign_rhs2 (stmt); *bit = gimple_assign_rhs2 (tmp); return true; } tmp = SSA_NAME_DEF_STMT (gimple_assign_rhs2 (stmt)); if (is_gimple_assign (tmp) && gimple_assign_rhs_code (tmp) == LSHIFT_EXPR && integer_onep (gimple_assign_rhs1 (tmp))) { *name = gimple_assign_rhs1 (stmt); *bit = gimple_assign_rhs2 (tmp); return true; } } return false; } /* Recognize a bit test pattern in a GIMPLE_COND and its defining statements. Store the name being tested in *NAME and the bits in *BITS. The COND_EXPR computes *NAME & *BITS. Returns true if the pattern matched, false otherwise. */ static bool recognize_bits_test (gimple cond, tree *name, tree *bits) { gimple stmt; /* Get at the definition of the result of the bit test. */ if (gimple_cond_code (cond) != NE_EXPR || TREE_CODE (gimple_cond_lhs (cond)) != SSA_NAME || !integer_zerop (gimple_cond_rhs (cond))) return false; stmt = SSA_NAME_DEF_STMT (gimple_cond_lhs (cond)); if (!is_gimple_assign (stmt) || gimple_assign_rhs_code (stmt) != BIT_AND_EXPR) return false; *name = get_name_for_bit_test (gimple_assign_rhs1 (stmt)); *bits = gimple_assign_rhs2 (stmt); return true; } /* If-convert on a and pattern with a common else block. The inner if is specified by its INNER_COND_BB, the outer by OUTER_COND_BB. Returns true if the edges to the common else basic-block were merged. */ static bool ifcombine_ifandif (basic_block inner_cond_bb, basic_block outer_cond_bb) { gimple_stmt_iterator gsi; gimple inner_cond, outer_cond; tree name1, name2, bit1, bit2; inner_cond = last_stmt (inner_cond_bb); if (!inner_cond || gimple_code (inner_cond) != GIMPLE_COND) return false; outer_cond = last_stmt (outer_cond_bb); if (!outer_cond || gimple_code (outer_cond) != GIMPLE_COND) return false; /* See if we test a single bit of the same name in both tests. In that case remove the outer test, merging both else edges, and change the inner one to test for name & (bit1 | bit2) == (bit1 | bit2). */ if (recognize_single_bit_test (inner_cond, &name1, &bit1) && recognize_single_bit_test (outer_cond, &name2, &bit2) && name1 == name2) { tree t, t2; /* Do it. */ gsi = gsi_for_stmt (inner_cond); t = fold_build2 (LSHIFT_EXPR, TREE_TYPE (name1), build_int_cst (TREE_TYPE (name1), 1), bit1); t2 = fold_build2 (LSHIFT_EXPR, TREE_TYPE (name1), build_int_cst (TREE_TYPE (name1), 1), bit2); t = fold_build2 (BIT_IOR_EXPR, TREE_TYPE (name1), t, t2); t = force_gimple_operand_gsi (&gsi, t, true, NULL_TREE, true, GSI_SAME_STMT); t2 = fold_build2 (BIT_AND_EXPR, TREE_TYPE (name1), name1, t); t2 = force_gimple_operand_gsi (&gsi, t2, true, NULL_TREE, true, GSI_SAME_STMT); t = fold_build2 (EQ_EXPR, boolean_type_node, t2, t); gimple_cond_set_condition_from_tree (inner_cond, t); update_stmt (inner_cond); /* Leave CFG optimization to cfg_cleanup. */ gimple_cond_set_condition_from_tree (outer_cond, boolean_true_node); update_stmt (outer_cond); if (dump_file) { fprintf (dump_file, "optimizing double bit test to "); print_generic_expr (dump_file, name1, 0); fprintf (dump_file, " & T == T\nwith temporary T = (1 << "); print_generic_expr (dump_file, bit1, 0); fprintf (dump_file, ") | (1 << "); print_generic_expr (dump_file, bit2, 0); fprintf (dump_file, ")\n"); } return true; } return false; } /* If-convert on a or pattern with a common then block. The inner if is specified by its INNER_COND_BB, the outer by OUTER_COND_BB. Returns true, if the edges leading to the common then basic-block were merged. */ static bool ifcombine_iforif (basic_block inner_cond_bb, basic_block outer_cond_bb) { gimple inner_cond, outer_cond; tree name1, name2, bits1, bits2; inner_cond = last_stmt (inner_cond_bb); if (!inner_cond || gimple_code (inner_cond) != GIMPLE_COND) return false; outer_cond = last_stmt (outer_cond_bb); if (!outer_cond || gimple_code (outer_cond) != GIMPLE_COND) return false; /* See if we have two bit tests of the same name in both tests. In that case remove the outer test and change the inner one to test for name & (bits1 | bits2) != 0. */ if (recognize_bits_test (inner_cond, &name1, &bits1) && recognize_bits_test (outer_cond, &name2, &bits2)) { gimple_stmt_iterator gsi; tree t; /* Find the common name which is bit-tested. */ if (name1 == name2) ; else if (bits1 == bits2) { t = name2; name2 = bits2; bits2 = t; t = name1; name1 = bits1; bits1 = t; } else if (name1 == bits2) { t = name2; name2 = bits2; bits2 = t; } else if (bits1 == name2) { t = name1; name1 = bits1; bits1 = t; } else return false; /* As we strip non-widening conversions in finding a common name that is tested make sure to end up with an integral type for building the bit operations. */ if (TYPE_PRECISION (TREE_TYPE (bits1)) >= TYPE_PRECISION (TREE_TYPE (bits2))) { bits1 = fold_convert (unsigned_type_for (TREE_TYPE (bits1)), bits1); name1 = fold_convert (TREE_TYPE (bits1), name1); bits2 = fold_convert (unsigned_type_for (TREE_TYPE (bits2)), bits2); bits2 = fold_convert (TREE_TYPE (bits1), bits2); } else { bits2 = fold_convert (unsigned_type_for (TREE_TYPE (bits2)), bits2); name1 = fold_convert (TREE_TYPE (bits2), name1); bits1 = fold_convert (unsigned_type_for (TREE_TYPE (bits1)), bits1); bits1 = fold_convert (TREE_TYPE (bits2), bits1); } /* Do it. */ gsi = gsi_for_stmt (inner_cond); t = fold_build2 (BIT_IOR_EXPR, TREE_TYPE (name1), bits1, bits2); t = force_gimple_operand_gsi (&gsi, t, true, NULL_TREE, true, GSI_SAME_STMT); t = fold_build2 (BIT_AND_EXPR, TREE_TYPE (name1), name1, t); t = force_gimple_operand_gsi (&gsi, t, true, NULL_TREE, true, GSI_SAME_STMT); t = fold_build2 (NE_EXPR, boolean_type_node, t, build_int_cst (TREE_TYPE (t), 0)); gimple_cond_set_condition_from_tree (inner_cond, t); update_stmt (inner_cond); /* Leave CFG optimization to cfg_cleanup. */ gimple_cond_set_condition_from_tree (outer_cond, boolean_false_node); update_stmt (outer_cond); if (dump_file) { fprintf (dump_file, "optimizing bits or bits test to "); print_generic_expr (dump_file, name1, 0); fprintf (dump_file, " & T != 0\nwith temporary T = "); print_generic_expr (dump_file, bits1, 0); fprintf (dump_file, " | "); print_generic_expr (dump_file, bits2, 0); fprintf (dump_file, "\n"); } return true; } /* See if we have two comparisons that we can merge into one. This happens for C++ operator overloading where for example GE_EXPR is implemented as GT_EXPR || EQ_EXPR. */ else if (TREE_CODE_CLASS (gimple_cond_code (inner_cond)) == tcc_comparison && TREE_CODE_CLASS (gimple_cond_code (outer_cond)) == tcc_comparison && operand_equal_p (gimple_cond_lhs (inner_cond), gimple_cond_lhs (outer_cond), 0) && operand_equal_p (gimple_cond_rhs (inner_cond), gimple_cond_rhs (outer_cond), 0)) { enum tree_code code1 = gimple_cond_code (inner_cond); enum tree_code code2 = gimple_cond_code (outer_cond); enum tree_code code; tree t; #define CHK(a,b) ((code1 == a ## _EXPR && code2 == b ## _EXPR) \ || (code2 == a ## _EXPR && code1 == b ## _EXPR)) /* Merge the two condition codes if possible. */ if (code1 == code2) code = code1; else if (CHK (EQ, LT)) code = LE_EXPR; else if (CHK (EQ, GT)) code = GE_EXPR; else if (CHK (LT, LE)) code = LE_EXPR; else if (CHK (GT, GE)) code = GE_EXPR; else if (INTEGRAL_TYPE_P (TREE_TYPE (gimple_cond_lhs (inner_cond))) || flag_unsafe_math_optimizations) { if (CHK (LT, GT)) code = NE_EXPR; else if (CHK (LT, NE)) code = NE_EXPR; else if (CHK (GT, NE)) code = NE_EXPR; else return false; } /* We could check for combinations leading to trivial true/false. */ else return false; #undef CHK /* Do it. */ t = fold_build2 (code, boolean_type_node, gimple_cond_lhs (outer_cond), gimple_cond_rhs (outer_cond)); t = canonicalize_cond_expr_cond (t); if (!t) return false; gimple_cond_set_condition_from_tree (inner_cond, t); update_stmt (inner_cond); /* Leave CFG optimization to cfg_cleanup. */ gimple_cond_set_condition_from_tree (outer_cond, boolean_false_node); update_stmt (outer_cond); if (dump_file) { fprintf (dump_file, "optimizing two comparisons to "); print_generic_expr (dump_file, t, 0); fprintf (dump_file, "\n"); } return true; } return false; } /* Recognize a CFG pattern and dispatch to the appropriate if-conversion helper. We start with BB as the innermost worker basic-block. Returns true if a transformation was done. */ static bool tree_ssa_ifcombine_bb (basic_block inner_cond_bb) { basic_block then_bb = NULL, else_bb = NULL; if (!recognize_if_then_else (inner_cond_bb, &then_bb, &else_bb)) return false; /* Recognize && and || of two conditions with a common then/else block which entry edges we can merge. That is: if (a || b) ; and if (a && b) ; This requires a single predecessor of the inner cond_bb. */ if (single_pred_p (inner_cond_bb)) { basic_block outer_cond_bb = single_pred (inner_cond_bb); /* The && form is characterized by a common else_bb with the two edges leading to it mergable. The latter is guaranteed by matching PHI arguments in the else_bb and the inner cond_bb having no side-effects. */ if (recognize_if_then_else (outer_cond_bb, &inner_cond_bb, &else_bb) && same_phi_args_p (outer_cond_bb, inner_cond_bb, else_bb) && bb_no_side_effects_p (inner_cond_bb)) { /* We have if (q) goto inner_cond_bb; else goto else_bb; if (p) goto ...; else goto else_bb; ... ... */ return ifcombine_ifandif (inner_cond_bb, outer_cond_bb); } /* The || form is characterized by a common then_bb with the two edges leading to it mergable. The latter is guaranteed by matching PHI arguments in the then_bb and the inner cond_bb having no side-effects. */ if (recognize_if_then_else (outer_cond_bb, &then_bb, &inner_cond_bb) && same_phi_args_p (outer_cond_bb, inner_cond_bb, then_bb) && bb_no_side_effects_p (inner_cond_bb)) { /* We have if (q) goto then_bb; else goto inner_cond_bb; if (q) goto then_bb; else goto ...; ... */ return ifcombine_iforif (inner_cond_bb, outer_cond_bb); } } return false; } /* Main entry for the tree if-conversion pass. */ static unsigned int tree_ssa_ifcombine (void) { basic_block *bbs; bool cfg_changed = false; int i; bbs = blocks_in_phiopt_order (); for (i = 0; i < n_basic_blocks - NUM_FIXED_BLOCKS; ++i) { basic_block bb = bbs[i]; gimple stmt = last_stmt (bb); if (stmt && gimple_code (stmt) == GIMPLE_COND) cfg_changed |= tree_ssa_ifcombine_bb (bb); } free (bbs); return cfg_changed ? TODO_cleanup_cfg : 0; } static bool gate_ifcombine (void) { return 1; } struct gimple_opt_pass pass_tree_ifcombine = { { GIMPLE_PASS, "ifcombine", /* name */ gate_ifcombine, /* gate */ tree_ssa_ifcombine, /* execute */ NULL, /* sub */ NULL, /* next */ 0, /* static_pass_number */ TV_TREE_IFCOMBINE, /* tv_id */ PROP_cfg | PROP_ssa, /* properties_required */ 0, /* properties_provided */ 0, /* properties_destroyed */ 0, /* todo_flags_start */ TODO_dump_func | TODO_ggc_collect | TODO_update_ssa | TODO_verify_ssa /* todo_flags_finish */ } };