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[/] [openrisc/] [trunk/] [gnu-src/] [gcc-4.5.1/] [gcc/] [tree-ssa-phiprop.c] - Rev 540
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/* Backward propagation of indirect loads through PHIs. Copyright (C) 2007, 2008 Free Software Foundation, Inc. Contributed by Richard Guenther <rguenther@suse.de> 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 "ggc.h" #include "tree.h" #include "rtl.h" #include "tm_p.h" #include "basic-block.h" #include "timevar.h" #include "diagnostic.h" #include "tree-flow.h" #include "tree-pass.h" #include "tree-dump.h" #include "langhooks.h" #include "flags.h" /* This pass propagates indirect loads through the PHI node for its address to make the load source possibly non-addressable and to allow for PHI optimization to trigger. For example the pass changes # addr_1 = PHI <&a, &b> tmp_1 = *addr_1; to # tmp_1 = PHI <a, b> but also handles more complex scenarios like D.2077_2 = &this_1(D)->a1; ... # b_12 = PHI <&c(2), D.2077_2(3)> D.2114_13 = *b_12; ... # b_15 = PHI <b_12(4), &b(5)> D.2080_5 = &this_1(D)->a0; ... # b_18 = PHI <D.2080_5(6), &c(7)> ... # b_21 = PHI <b_15(8), b_18(9)> D.2076_8 = *b_21; where the addresses loaded are defined by PHIs itself. The above happens for std::max(std::min(a0, c), std::min(std::max(a1, c), b)) where this pass transforms it to a form later PHI optimization recognizes and transforms it to the simple D.2109_10 = this_1(D)->a1; D.2110_11 = c; D.2114_31 = MAX_EXPR <D.2109_10, D.2110_11>; D.2115_14 = b; D.2125_17 = MIN_EXPR <D.2115_14, D.2114_31>; D.2119_16 = this_1(D)->a0; D.2124_32 = MIN_EXPR <D.2110_11, D.2119_16>; D.2076_33 = MAX_EXPR <D.2125_17, D.2124_32>; The pass does a dominator walk processing loads using a basic-block local analysis and stores the result for use by transformations on dominated basic-blocks. */ /* Structure to keep track of the value of a dereferenced PHI result and the virtual operand used for that dereference. */ struct phiprop_d { tree value; tree vuse; }; /* Verify if the value recorded for NAME in PHIVN is still valid at the start of basic block BB. */ static bool phivn_valid_p (struct phiprop_d *phivn, tree name, basic_block bb) { tree vuse = phivn[SSA_NAME_VERSION (name)].vuse; gimple use_stmt; imm_use_iterator ui2; bool ok = true; /* The def stmts of the virtual uses need to be dominated by bb. */ gcc_assert (vuse != NULL_TREE); FOR_EACH_IMM_USE_STMT (use_stmt, ui2, vuse) { /* If BB does not dominate a VDEF, the value is invalid. */ if ((gimple_vdef (use_stmt) != NULL_TREE || gimple_code (use_stmt) == GIMPLE_PHI) && !dominated_by_p (CDI_DOMINATORS, gimple_bb (use_stmt), bb)) { ok = false; BREAK_FROM_IMM_USE_STMT (ui2); } } return ok; } /* Insert a new phi node for the dereference of PHI at basic_block BB with the virtual operands from USE_STMT. */ static tree phiprop_insert_phi (basic_block bb, gimple phi, gimple use_stmt, struct phiprop_d *phivn, size_t n) { tree res; gimple new_phi; edge_iterator ei; edge e; gcc_assert (is_gimple_assign (use_stmt) && gimple_assign_rhs_code (use_stmt) == INDIRECT_REF); /* Build a new PHI node to replace the definition of the indirect reference lhs. */ res = gimple_assign_lhs (use_stmt); SSA_NAME_DEF_STMT (res) = new_phi = create_phi_node (res, bb); if (dump_file && (dump_flags & TDF_DETAILS)) { fprintf (dump_file, "Inserting PHI for result of load "); print_gimple_stmt (dump_file, use_stmt, 0, 0); } /* Add PHI arguments for each edge inserting loads of the addressable operands. */ FOR_EACH_EDGE (e, ei, bb->preds) { tree old_arg, new_var; gimple tmp; source_location locus; old_arg = PHI_ARG_DEF_FROM_EDGE (phi, e); locus = gimple_phi_arg_location_from_edge (phi, e); while (TREE_CODE (old_arg) == SSA_NAME && (SSA_NAME_VERSION (old_arg) >= n || phivn[SSA_NAME_VERSION (old_arg)].value == NULL_TREE)) { gimple def_stmt = SSA_NAME_DEF_STMT (old_arg); old_arg = gimple_assign_rhs1 (def_stmt); locus = gimple_location (def_stmt); } if (TREE_CODE (old_arg) == SSA_NAME) { if (dump_file && (dump_flags & TDF_DETAILS)) { fprintf (dump_file, " for edge defining "); print_generic_expr (dump_file, PHI_ARG_DEF_FROM_EDGE (phi, e), 0); fprintf (dump_file, " reusing PHI result "); print_generic_expr (dump_file, phivn[SSA_NAME_VERSION (old_arg)].value, 0); fprintf (dump_file, "\n"); } /* Reuse a formerly created dereference. */ new_var = phivn[SSA_NAME_VERSION (old_arg)].value; } else { gcc_assert (TREE_CODE (old_arg) == ADDR_EXPR); old_arg = TREE_OPERAND (old_arg, 0); new_var = create_tmp_var (TREE_TYPE (old_arg), NULL); tmp = gimple_build_assign (new_var, unshare_expr (old_arg)); if (TREE_CODE (TREE_TYPE (old_arg)) == COMPLEX_TYPE || TREE_CODE (TREE_TYPE (old_arg)) == VECTOR_TYPE) DECL_GIMPLE_REG_P (new_var) = 1; gcc_assert (is_gimple_reg (new_var)); add_referenced_var (new_var); new_var = make_ssa_name (new_var, tmp); gimple_assign_set_lhs (tmp, new_var); gimple_set_location (tmp, locus); gsi_insert_on_edge (e, tmp); update_stmt (tmp); if (dump_file && (dump_flags & TDF_DETAILS)) { fprintf (dump_file, " for edge defining "); print_generic_expr (dump_file, PHI_ARG_DEF_FROM_EDGE (phi, e), 0); fprintf (dump_file, " inserting load "); print_gimple_stmt (dump_file, tmp, 0, 0); } } add_phi_arg (new_phi, new_var, e, locus); } update_stmt (new_phi); if (dump_file && (dump_flags & TDF_DETAILS)) print_gimple_stmt (dump_file, new_phi, 0, 0); return res; } /* Propagate between the phi node arguments of PHI in BB and phi result users. For now this matches # p_2 = PHI <&x, &y> <Lx>:; p_3 = p_2; z_2 = *p_3; and converts it to # z_2 = PHI <x, y> <Lx>:; Returns true if a transformation was done and edge insertions need to be committed. Global data PHIVN and N is used to track past transformation results. We need to be especially careful here with aliasing issues as we are moving memory reads. */ static bool propagate_with_phi (basic_block bb, gimple phi, struct phiprop_d *phivn, size_t n) { tree ptr = PHI_RESULT (phi); gimple use_stmt; tree res = NULL_TREE; gimple_stmt_iterator gsi; imm_use_iterator ui; use_operand_p arg_p, use; ssa_op_iter i; bool phi_inserted; if (!POINTER_TYPE_P (TREE_TYPE (ptr)) || !is_gimple_reg_type (TREE_TYPE (TREE_TYPE (ptr)))) return false; /* Check if we can "cheaply" dereference all phi arguments. */ FOR_EACH_PHI_ARG (arg_p, phi, i, SSA_OP_USE) { tree arg = USE_FROM_PTR (arg_p); /* Walk the ssa chain until we reach a ssa name we already created a value for or we reach a definition of the form ssa_name_n = &var; */ while (TREE_CODE (arg) == SSA_NAME && !SSA_NAME_IS_DEFAULT_DEF (arg) && (SSA_NAME_VERSION (arg) >= n || phivn[SSA_NAME_VERSION (arg)].value == NULL_TREE)) { gimple def_stmt = SSA_NAME_DEF_STMT (arg); if (!gimple_assign_single_p (def_stmt)) return false; arg = gimple_assign_rhs1 (def_stmt); } if ((TREE_CODE (arg) != ADDR_EXPR /* Avoid to have to decay *&a to a[0] later. */ || !is_gimple_reg_type (TREE_TYPE (TREE_OPERAND (arg, 0)))) && !(TREE_CODE (arg) == SSA_NAME && SSA_NAME_VERSION (arg) < n && phivn[SSA_NAME_VERSION (arg)].value != NULL_TREE && phivn_valid_p (phivn, arg, bb))) return false; } /* Find a dereferencing use. First follow (single use) ssa copy chains for ptr. */ while (single_imm_use (ptr, &use, &use_stmt) && gimple_assign_ssa_name_copy_p (use_stmt)) ptr = gimple_assign_lhs (use_stmt); /* Replace the first dereference of *ptr if there is one and if we can move the loads to the place of the ptr phi node. */ phi_inserted = false; FOR_EACH_IMM_USE_STMT (use_stmt, ui, ptr) { gimple def_stmt; tree vuse; /* Check whether this is a load of *ptr. */ if (!(is_gimple_assign (use_stmt) && TREE_CODE (gimple_assign_lhs (use_stmt)) == SSA_NAME && gimple_assign_rhs_code (use_stmt) == INDIRECT_REF && TREE_OPERAND (gimple_assign_rhs1 (use_stmt), 0) == ptr /* We cannot replace a load that may throw or is volatile. */ && !stmt_can_throw_internal (use_stmt))) continue; /* Check if we can move the loads. The def stmt of the virtual use needs to be in a different basic block dominating bb. */ vuse = gimple_vuse (use_stmt); def_stmt = SSA_NAME_DEF_STMT (vuse); if (!SSA_NAME_IS_DEFAULT_DEF (vuse) && (gimple_bb (def_stmt) == bb || !dominated_by_p (CDI_DOMINATORS, bb, gimple_bb (def_stmt)))) goto next; /* Found a proper dereference. Insert a phi node if this is the first load transformation. */ if (!phi_inserted) { res = phiprop_insert_phi (bb, phi, use_stmt, phivn, n); /* Remember the value we created for *ptr. */ phivn[SSA_NAME_VERSION (ptr)].value = res; phivn[SSA_NAME_VERSION (ptr)].vuse = vuse; /* Remove old stmt. The phi is taken care of by DCE, if we want to delete it here we also have to delete all intermediate copies. */ gsi = gsi_for_stmt (use_stmt); gsi_remove (&gsi, false); phi_inserted = true; } else { /* Further replacements are easy, just make a copy out of the load. */ gimple_assign_set_rhs1 (use_stmt, res); update_stmt (use_stmt); } next:; /* Continue searching for a proper dereference. */ } return phi_inserted; } /* Main entry for phiprop pass. */ static unsigned int tree_ssa_phiprop (void) { VEC(basic_block, heap) *bbs; struct phiprop_d *phivn; bool did_something = false; basic_block bb; gimple_stmt_iterator gsi; unsigned i; size_t n; calculate_dominance_info (CDI_DOMINATORS); n = num_ssa_names; phivn = XCNEWVEC (struct phiprop_d, n); /* Walk the dominator tree in preorder. */ bbs = get_all_dominated_blocks (CDI_DOMINATORS, single_succ (ENTRY_BLOCK_PTR)); for (i = 0; VEC_iterate (basic_block, bbs, i, bb); ++i) for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi)) did_something |= propagate_with_phi (bb, gsi_stmt (gsi), phivn, n); if (did_something) gsi_commit_edge_inserts (); VEC_free (basic_block, heap, bbs); free (phivn); return 0; } static bool gate_phiprop (void) { return flag_tree_phiprop; } struct gimple_opt_pass pass_phiprop = { { GIMPLE_PASS, "phiprop", /* name */ gate_phiprop, /* gate */ tree_ssa_phiprop, /* execute */ NULL, /* sub */ NULL, /* next */ 0, /* static_pass_number */ TV_TREE_PHIPROP, /* 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 */ } };
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