/* Backward propagation of indirect loads through PHIs. 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 "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 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 D.2080_5 = &this_1(D)->a0; ... # b_18 = PHI ... # b_21 = PHI 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.2115_14 = b; D.2125_17 = MIN_EXPR ; D.2119_16 = this_1(D)->a0; D.2124_32 = MIN_EXPR ; D.2076_33 = MAX_EXPR ; 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 set of virtual operands used for that dereference. */ struct phiprop_d { tree value; tree vop_stmt; }; /* 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 vop_stmt = phivn[SSA_NAME_VERSION (name)].vop_stmt; ssa_op_iter ui; tree vuse; /* The def stmts of all virtual uses need to be post-dominated by bb. */ FOR_EACH_SSA_TREE_OPERAND (vuse, vop_stmt, ui, SSA_OP_VUSE) { tree use_stmt; imm_use_iterator ui2; bool ok = true; FOR_EACH_IMM_USE_STMT (use_stmt, ui2, vuse) { /* If BB does not dominate a VDEF, the value is invalid. */ if (((TREE_CODE (use_stmt) == GIMPLE_MODIFY_STMT && !ZERO_SSA_OPERANDS (use_stmt, SSA_OP_VDEF)) || TREE_CODE (use_stmt) == PHI_NODE) && !dominated_by_p (CDI_DOMINATORS, bb_for_stmt (use_stmt), bb)) { ok = false; BREAK_FROM_IMM_USE_STMT (ui2); } } if (!ok) return false; } return true; } /* 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, tree phi, tree use_stmt, struct phiprop_d *phivn, size_t n) { tree res, new_phi; edge_iterator ei; edge e; /* Build a new PHI node to replace the definition of the indirect reference lhs. */ res = GIMPLE_STMT_OPERAND (use_stmt, 0); SSA_NAME_DEF_STMT (res) = new_phi = create_phi_node (res, bb); /* Add PHI arguments for each edge inserting loads of the addressable operands. */ FOR_EACH_EDGE (e, ei, bb->preds) { tree old_arg, new_var, tmp; old_arg = PHI_ARG_DEF_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)) { tree def_stmt = SSA_NAME_DEF_STMT (old_arg); old_arg = GIMPLE_STMT_OPERAND (def_stmt, 1); } if (TREE_CODE (old_arg) == SSA_NAME) /* Reuse a formerly created dereference. */ new_var = phivn[SSA_NAME_VERSION (old_arg)].value; else { old_arg = TREE_OPERAND (old_arg, 0); new_var = create_tmp_var (TREE_TYPE (old_arg), NULL); tmp = build2 (GIMPLE_MODIFY_STMT, void_type_node, NULL_TREE, 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; add_referenced_var (new_var); new_var = make_ssa_name (new_var, tmp); GIMPLE_STMT_OPERAND (tmp, 0) = new_var; bsi_insert_on_edge (e, tmp); update_stmt (tmp); mark_symbols_for_renaming (tmp); } add_phi_arg (new_phi, new_var, e); } update_stmt (new_phi); 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> :; p_3 = p_2; z_2 = *p_3; and converts it to # z_2 = PHI :; 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, tree phi, struct phiprop_d *phivn, size_t n) { tree ptr = PHI_RESULT (phi); tree use_stmt, res = NULL_TREE; block_stmt_iterator bsi; imm_use_iterator ui; use_operand_p arg_p, use; ssa_op_iter i; bool phi_inserted; if (MTAG_P (SSA_NAME_VAR (ptr)) || !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)) { tree def_stmt = SSA_NAME_DEF_STMT (arg); if (TREE_CODE (def_stmt) != GIMPLE_MODIFY_STMT) return false; arg = GIMPLE_STMT_OPERAND (def_stmt, 1); } 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 && 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) && TREE_CODE (use_stmt) == GIMPLE_MODIFY_STMT && GIMPLE_STMT_OPERAND (use_stmt, 1) == ptr && TREE_CODE (GIMPLE_STMT_OPERAND (use_stmt, 0)) == SSA_NAME) ptr = GIMPLE_STMT_OPERAND (use_stmt, 0); /* 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) { ssa_op_iter ui2; tree vuse; /* Check whether this is a load of *ptr. */ if (!(TREE_CODE (use_stmt) == GIMPLE_MODIFY_STMT && TREE_CODE (GIMPLE_STMT_OPERAND (use_stmt, 0)) == SSA_NAME && TREE_CODE (GIMPLE_STMT_OPERAND (use_stmt, 1)) == INDIRECT_REF && TREE_OPERAND (GIMPLE_STMT_OPERAND (use_stmt, 1), 0) == ptr /* We cannot replace a load that may throw or is volatile. */ && !tree_can_throw_internal (use_stmt))) continue; /* Check if we can move the loads. The def stmts of all virtual uses need to be post-dominated by bb. */ FOR_EACH_SSA_TREE_OPERAND (vuse, use_stmt, ui2, SSA_OP_VUSE) { tree def_stmt = SSA_NAME_DEF_STMT (vuse); if (!SSA_NAME_IS_DEFAULT_DEF (vuse) && (bb_for_stmt (def_stmt) == bb || !dominated_by_p (CDI_DOMINATORS, bb, bb_for_stmt (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)].vop_stmt = use_stmt; /* 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. */ bsi = bsi_for_stmt (use_stmt); bsi_remove (&bsi, 0); phi_inserted = true; } else { /* Further replacements are easy, just make a copy out of the load. */ GIMPLE_STMT_OPERAND (use_stmt, 1) = res; update_stmt (use_stmt); } next:; /* Continue searching for a proper dereference. */ } return phi_inserted; } /* Helper walking the dominator tree starting from BB and processing phi nodes with global data PHIVN and N. */ static bool tree_ssa_phiprop_1 (basic_block bb, struct phiprop_d *phivn, size_t n) { bool did_something = false; basic_block son; tree phi; for (phi = phi_nodes (bb); phi; phi = PHI_CHAIN (phi)) did_something |= propagate_with_phi (bb, phi, phivn, n); for (son = first_dom_son (CDI_DOMINATORS, bb); son; son = next_dom_son (CDI_DOMINATORS, son)) did_something |= tree_ssa_phiprop_1 (son, phivn, n); return did_something; } /* Main entry for phiprop pass. */ static unsigned int tree_ssa_phiprop (void) { struct phiprop_d *phivn; calculate_dominance_info (CDI_DOMINATORS); phivn = XCNEWVEC (struct phiprop_d, num_ssa_names); if (tree_ssa_phiprop_1 (ENTRY_BLOCK_PTR, phivn, num_ssa_names)) bsi_commit_edge_inserts (); free (phivn); return 0; } static bool gate_phiprop (void) { return 1; } 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 */ } };