| /* Backward propagation of indirect loads through PHIs. |
| Copyright (C) 2007-2021 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 "backend.h" |
| #include "tree.h" |
| #include "gimple.h" |
| #include "tree-pass.h" |
| #include "ssa.h" |
| #include "gimple-pretty-print.h" |
| #include "fold-const.h" |
| #include "tree-eh.h" |
| #include "gimplify.h" |
| #include "gimple-iterator.h" |
| #include "stor-layout.h" |
| #include "tree-ssa-loop.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; |
| } |
| } |
| |
| 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, gphi *phi, gimple *use_stmt, |
| struct phiprop_d *phivn, size_t n) |
| { |
| tree res; |
| gphi *new_phi = NULL; |
| edge_iterator ei; |
| edge e; |
| |
| gcc_assert (is_gimple_assign (use_stmt) |
| && gimple_assign_rhs_code (use_stmt) == MEM_REF); |
| |
| /* Build a new PHI node to replace the definition of |
| the indirect reference lhs. */ |
| res = gimple_assign_lhs (use_stmt); |
| if (TREE_CODE (res) == SSA_NAME) |
| 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); |
| } |
| |
| /* Add PHI arguments for each edge inserting loads of the |
| addressable operands. */ |
| FOR_EACH_EDGE (e, ei, bb->preds) |
| { |
| tree old_arg, new_var; |
| gassign *tmp; |
| location_t 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)); |
| fprintf (dump_file, " reusing PHI result "); |
| print_generic_expr (dump_file, |
| phivn[SSA_NAME_VERSION (old_arg)].value); |
| fprintf (dump_file, "\n"); |
| } |
| /* Reuse a formerly created dereference. */ |
| new_var = phivn[SSA_NAME_VERSION (old_arg)].value; |
| } |
| else |
| { |
| tree rhs = gimple_assign_rhs1 (use_stmt); |
| gcc_assert (TREE_CODE (old_arg) == ADDR_EXPR); |
| if (TREE_CODE (res) == SSA_NAME) |
| new_var = make_ssa_name (TREE_TYPE (rhs)); |
| else |
| new_var = unshare_expr (res); |
| if (!is_gimple_min_invariant (old_arg)) |
| old_arg = PHI_ARG_DEF_FROM_EDGE (phi, e); |
| else |
| old_arg = unshare_expr (old_arg); |
| tmp = gimple_build_assign (new_var, |
| fold_build2 (MEM_REF, TREE_TYPE (rhs), |
| old_arg, |
| TREE_OPERAND (rhs, 1))); |
| 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)); |
| fprintf (dump_file, " inserting load "); |
| print_gimple_stmt (dump_file, tmp, 0); |
| } |
| } |
| |
| if (new_phi) |
| add_phi_arg (new_phi, new_var, e, locus); |
| } |
| |
| if (new_phi) |
| { |
| update_stmt (new_phi); |
| |
| if (dump_file && (dump_flags & TDF_DETAILS)) |
| print_gimple_stmt (dump_file, new_phi, 0); |
| } |
| |
| return res; |
| } |
| |
| /* Verify if *idx is available at *DATA. */ |
| |
| static bool |
| chk_uses (tree, tree *idx, void *data) |
| { |
| basic_block dom = (basic_block) data; |
| if (TREE_CODE (*idx) == SSA_NAME) |
| return (SSA_NAME_IS_DEFAULT_DEF (*idx) |
| || ! dominated_by_p (CDI_DOMINATORS, |
| gimple_bb (SSA_NAME_DEF_STMT (*idx)), dom)); |
| return true; |
| } |
| |
| /* 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, gphi *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; |
| bool changed; |
| tree type = NULL_TREE; |
| |
| if (!POINTER_TYPE_P (TREE_TYPE (ptr)) |
| || (!is_gimple_reg_type (TREE_TYPE (TREE_TYPE (ptr))) |
| && TYPE_MODE (TREE_TYPE (TREE_TYPE (ptr))) == BLKmode)) |
| 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 |
| && !(TREE_CODE (arg) == SSA_NAME |
| && SSA_NAME_VERSION (arg) < n |
| && phivn[SSA_NAME_VERSION (arg)].value != NULL_TREE |
| && (!type |
| || types_compatible_p |
| (type, TREE_TYPE (phivn[SSA_NAME_VERSION (arg)].value))) |
| && phivn_valid_p (phivn, arg, bb))) |
| return false; |
| if (!type |
| && TREE_CODE (arg) == SSA_NAME) |
| type = TREE_TYPE (phivn[SSA_NAME_VERSION (arg)].value); |
| } |
| |
| /* 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; |
| changed = false; |
| FOR_EACH_IMM_USE_STMT (use_stmt, ui, ptr) |
| { |
| gimple *def_stmt; |
| tree vuse; |
| |
| /* Only replace loads in blocks that post-dominate the PHI node. That |
| makes sure we don't end up speculating loads. */ |
| if (!dominated_by_p (CDI_POST_DOMINATORS, |
| bb, gimple_bb (use_stmt))) |
| continue; |
| |
| /* Check whether this is a load of *ptr. */ |
| if (!(is_gimple_assign (use_stmt) |
| && gimple_assign_rhs_code (use_stmt) == MEM_REF |
| && TREE_OPERAND (gimple_assign_rhs1 (use_stmt), 0) == ptr |
| && integer_zerop (TREE_OPERAND (gimple_assign_rhs1 (use_stmt), 1)) |
| && (!type |
| || types_compatible_p |
| (TREE_TYPE (gimple_assign_lhs (use_stmt)), type)) |
| /* We cannot replace a load that may throw or is volatile. |
| For volatiles the transform can change the number of |
| executions if the load is inside a loop but the address |
| computations outside (PR91812). We could relax this |
| if we guard against that appropriately. For loads that can |
| throw we could relax things if the moved loads all are |
| known to not throw. */ |
| && !stmt_can_throw_internal (cfun, use_stmt) |
| && !gimple_has_volatile_ops (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. When the |
| def is an edge-inserted one we know it dominates us. */ |
| vuse = gimple_vuse (use_stmt); |
| def_stmt = SSA_NAME_DEF_STMT (vuse); |
| if (!SSA_NAME_IS_DEFAULT_DEF (vuse) |
| && (gimple_bb (def_stmt) == bb |
| || (gimple_bb (def_stmt) |
| && !dominated_by_p (CDI_DOMINATORS, |
| bb, gimple_bb (def_stmt))))) |
| goto next; |
| |
| /* Found a proper dereference with an aggregate copy. Just |
| insert aggregate copies on the edges instead. */ |
| if (!is_gimple_reg_type (TREE_TYPE (gimple_assign_lhs (use_stmt)))) |
| { |
| if (!gimple_vdef (use_stmt)) |
| goto next; |
| |
| /* As we replicate the lhs on each incoming edge all |
| used SSA names have to be available there. */ |
| if (! for_each_index (gimple_assign_lhs_ptr (use_stmt), |
| chk_uses, |
| get_immediate_dominator (CDI_DOMINATORS, |
| gimple_bb (phi)))) |
| goto next; |
| |
| gimple *vuse_stmt; |
| imm_use_iterator vui; |
| use_operand_p vuse_p; |
| /* In order to move the aggregate copies earlier, make sure |
| there are no statements that could read from memory |
| aliasing the lhs in between the start of bb and use_stmt. |
| As we require use_stmt to have a VDEF above, loads after |
| use_stmt will use a different virtual SSA_NAME. */ |
| FOR_EACH_IMM_USE_FAST (vuse_p, vui, vuse) |
| { |
| vuse_stmt = USE_STMT (vuse_p); |
| if (vuse_stmt == use_stmt) |
| continue; |
| if (!dominated_by_p (CDI_DOMINATORS, |
| gimple_bb (vuse_stmt), bb)) |
| continue; |
| if (ref_maybe_used_by_stmt_p (vuse_stmt, |
| gimple_assign_lhs (use_stmt))) |
| goto next; |
| } |
| |
| phiprop_insert_phi (bb, phi, use_stmt, phivn, n); |
| |
| /* Remove old stmt. The phi is taken care of by DCE. */ |
| gsi = gsi_for_stmt (use_stmt); |
| /* Unlinking the VDEF here is fine as we are sure that we process |
| stmts in execution order due to aggregate copies having VDEFs |
| and we emit loads on the edges in the very same order. |
| We get multiple copies (or intermediate register loads) handled |
| only by walking PHIs or immediate uses in a lucky order though, |
| so we could signal the caller to re-start iterating over PHIs |
| when we come here which would make it quadratic in the number |
| of PHIs. */ |
| unlink_stmt_vdef (use_stmt); |
| gsi_remove (&gsi, true); |
| |
| changed = true; |
| } |
| |
| /* Found a proper dereference. Insert a phi node if this |
| is the first load transformation. */ |
| else if (!phi_inserted) |
| { |
| res = phiprop_insert_phi (bb, phi, use_stmt, phivn, n); |
| type = TREE_TYPE (res); |
| |
| /* 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, true); |
| |
| phi_inserted = true; |
| changed = 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); |
| changed = true; |
| } |
| |
| next:; |
| /* Continue searching for a proper dereference. */ |
| } |
| |
| return changed; |
| } |
| |
| /* Main entry for phiprop pass. */ |
| |
| namespace { |
| |
| const pass_data pass_data_phiprop = |
| { |
| GIMPLE_PASS, /* type */ |
| "phiprop", /* name */ |
| OPTGROUP_NONE, /* optinfo_flags */ |
| TV_TREE_PHIPROP, /* tv_id */ |
| ( PROP_cfg | PROP_ssa ), /* properties_required */ |
| 0, /* properties_provided */ |
| 0, /* properties_destroyed */ |
| 0, /* todo_flags_start */ |
| TODO_update_ssa, /* todo_flags_finish */ |
| }; |
| |
| class pass_phiprop : public gimple_opt_pass |
| { |
| public: |
| pass_phiprop (gcc::context *ctxt) |
| : gimple_opt_pass (pass_data_phiprop, ctxt) |
| {} |
| |
| /* opt_pass methods: */ |
| virtual bool gate (function *) { return flag_tree_phiprop; } |
| virtual unsigned int execute (function *); |
| |
| }; // class pass_phiprop |
| |
| unsigned int |
| pass_phiprop::execute (function *fun) |
| { |
| vec<basic_block> bbs; |
| struct phiprop_d *phivn; |
| bool did_something = false; |
| basic_block bb; |
| gphi_iterator gsi; |
| unsigned i; |
| size_t n; |
| |
| calculate_dominance_info (CDI_DOMINATORS); |
| calculate_dominance_info (CDI_POST_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_FN (fun))); |
| FOR_EACH_VEC_ELT (bbs, i, bb) |
| { |
| /* Since we're going to move dereferences across predecessor |
| edges avoid blocks with abnormal predecessors. */ |
| if (bb_has_abnormal_pred (bb)) |
| continue; |
| for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi)) |
| did_something |= propagate_with_phi (bb, gsi.phi (), phivn, n); |
| } |
| |
| if (did_something) |
| gsi_commit_edge_inserts (); |
| |
| bbs.release (); |
| free (phivn); |
| |
| free_dominance_info (CDI_POST_DOMINATORS); |
| |
| return 0; |
| } |
| |
| } // anon namespace |
| |
| gimple_opt_pass * |
| make_pass_phiprop (gcc::context *ctxt) |
| { |
| return new pass_phiprop (ctxt); |
| } |