| /* Copy propagation and SSA_NAME replacement support routines. |
| Copyright (C) 2004-2022 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 "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 "gimple-iterator.h" |
| #include "tree-cfg.h" |
| #include "tree-ssa-propagate.h" |
| #include "cfgloop.h" |
| #include "tree-scalar-evolution.h" |
| #include "tree-ssa-loop-niter.h" |
| #include "gimple-fold.h" |
| |
| |
| /* This file implements the copy propagation pass and provides a |
| handful of interfaces for performing const/copy propagation and |
| simple expression replacement which keep variable annotations |
| up-to-date. |
| |
| We require that for any copy operation where the RHS and LHS have |
| a non-null memory tag the memory tag be the same. It is OK |
| for one or both of the memory tags to be NULL. |
| |
| We also require tracking if a variable is dereferenced in a load or |
| store operation. |
| |
| We enforce these requirements by having all copy propagation and |
| replacements of one SSA_NAME with a different SSA_NAME to use the |
| APIs defined in this file. */ |
| |
| /*--------------------------------------------------------------------------- |
| Copy propagation |
| ---------------------------------------------------------------------------*/ |
| /* Lattice for copy-propagation. The lattice is initialized to |
| UNDEFINED (value == NULL) for SSA names that can become a copy |
| of something or VARYING (value == self) if not (see get_copy_of_val |
| and stmt_may_generate_copy). Other values make the name a COPY |
| of that value. |
| |
| When visiting a statement or PHI node the lattice value for an |
| SSA name can transition from UNDEFINED to COPY to VARYING. */ |
| |
| struct prop_value_t { |
| /* Copy-of value. */ |
| tree value; |
| }; |
| |
| class copy_prop : public ssa_propagation_engine |
| { |
| public: |
| enum ssa_prop_result visit_stmt (gimple *, edge *, tree *) final override; |
| enum ssa_prop_result visit_phi (gphi *) final override; |
| }; |
| |
| static prop_value_t *copy_of; |
| static unsigned n_copy_of; |
| |
| |
| /* Return true if this statement may generate a useful copy. */ |
| |
| static bool |
| stmt_may_generate_copy (gimple *stmt) |
| { |
| if (gimple_code (stmt) == GIMPLE_PHI) |
| return !SSA_NAME_OCCURS_IN_ABNORMAL_PHI (gimple_phi_result (stmt)); |
| |
| if (gimple_code (stmt) != GIMPLE_ASSIGN) |
| return false; |
| |
| /* If the statement has volatile operands, it won't generate a |
| useful copy. */ |
| if (gimple_has_volatile_ops (stmt)) |
| return false; |
| |
| /* Statements with loads and/or stores will never generate a useful copy. */ |
| if (gimple_vuse (stmt)) |
| return false; |
| |
| /* If the assignment is from a constant it generates a useful copy. */ |
| if (gimple_assign_single_p (stmt) |
| && is_gimple_min_invariant (gimple_assign_rhs1 (stmt))) |
| return true; |
| |
| /* Otherwise, the only statements that generate useful copies are |
| assignments whose single SSA use doesn't flow through abnormal |
| edges. */ |
| tree rhs = single_ssa_tree_operand (stmt, SSA_OP_USE); |
| return (rhs && !SSA_NAME_OCCURS_IN_ABNORMAL_PHI (rhs)); |
| } |
| |
| |
| /* Return the copy-of value for VAR. */ |
| |
| static inline prop_value_t * |
| get_copy_of_val (tree var) |
| { |
| prop_value_t *val = ©_of[SSA_NAME_VERSION (var)]; |
| |
| if (val->value == NULL_TREE |
| && !stmt_may_generate_copy (SSA_NAME_DEF_STMT (var))) |
| { |
| /* If the variable will never generate a useful copy relation, |
| make it its own copy. */ |
| val->value = var; |
| } |
| |
| return val; |
| } |
| |
| /* Return the variable VAR is a copy of or VAR if VAR isn't the result |
| of a copy. */ |
| |
| static inline tree |
| valueize_val (tree var) |
| { |
| if (TREE_CODE (var) == SSA_NAME) |
| { |
| tree val = get_copy_of_val (var)->value; |
| if (val) |
| return val; |
| } |
| return var; |
| } |
| |
| /* Set VAL to be the copy of VAR. If that changed return true. */ |
| |
| static inline bool |
| set_copy_of_val (tree var, tree val) |
| { |
| unsigned int ver = SSA_NAME_VERSION (var); |
| tree old; |
| |
| /* Set FIRST to be the first link in COPY_OF[DEST]. If that |
| changed, return true. */ |
| old = copy_of[ver].value; |
| copy_of[ver].value = val; |
| |
| if (old != val |
| && (!old || !operand_equal_p (old, val, 0))) |
| return true; |
| |
| return false; |
| } |
| |
| |
| /* Dump the copy-of value for variable VAR to FILE. */ |
| |
| static void |
| dump_copy_of (FILE *file, tree var) |
| { |
| tree val; |
| |
| print_generic_expr (file, var, dump_flags); |
| if (TREE_CODE (var) != SSA_NAME) |
| return; |
| |
| val = copy_of[SSA_NAME_VERSION (var)].value; |
| fprintf (file, " copy-of chain: "); |
| print_generic_expr (file, var); |
| fprintf (file, " "); |
| if (!val) |
| fprintf (file, "[UNDEFINED]"); |
| else if (val == var) |
| fprintf (file, "[NOT A COPY]"); |
| else |
| { |
| fprintf (file, "-> "); |
| print_generic_expr (file, val); |
| fprintf (file, " "); |
| fprintf (file, "[COPY]"); |
| } |
| } |
| |
| |
| /* Evaluate the RHS of STMT. If it produces a valid copy, set the LHS |
| value and store the LHS into *RESULT_P. */ |
| |
| static enum ssa_prop_result |
| copy_prop_visit_assignment (gimple *stmt, tree *result_p) |
| { |
| tree lhs = gimple_assign_lhs (stmt); |
| tree rhs = gimple_fold_stmt_to_constant_1 (stmt, valueize_val); |
| if (rhs |
| && (TREE_CODE (rhs) == SSA_NAME |
| || is_gimple_min_invariant (rhs))) |
| { |
| /* Straight copy between two SSA names or a constant. Make sure that |
| we can propagate the RHS into uses of LHS. */ |
| if (!may_propagate_copy (lhs, rhs)) |
| rhs = lhs; |
| } |
| else |
| rhs = lhs; |
| |
| *result_p = lhs; |
| if (set_copy_of_val (*result_p, rhs)) |
| return SSA_PROP_INTERESTING; |
| return rhs != lhs ? SSA_PROP_NOT_INTERESTING : SSA_PROP_VARYING; |
| } |
| |
| |
| /* Visit the GIMPLE_COND STMT. Return SSA_PROP_INTERESTING |
| if it can determine which edge will be taken. Otherwise, return |
| SSA_PROP_VARYING. */ |
| |
| static enum ssa_prop_result |
| copy_prop_visit_cond_stmt (gimple *stmt, edge *taken_edge_p) |
| { |
| enum ssa_prop_result retval = SSA_PROP_VARYING; |
| location_t loc = gimple_location (stmt); |
| |
| tree op0 = valueize_val (gimple_cond_lhs (stmt)); |
| tree op1 = valueize_val (gimple_cond_rhs (stmt)); |
| |
| /* See if we can determine the predicate's value. */ |
| if (dump_file && (dump_flags & TDF_DETAILS)) |
| { |
| fprintf (dump_file, "Trying to determine truth value of "); |
| fprintf (dump_file, "predicate "); |
| print_gimple_stmt (dump_file, stmt, 0); |
| } |
| |
| /* Fold COND and see whether we get a useful result. */ |
| tree folded_cond = fold_binary_loc (loc, gimple_cond_code (stmt), |
| boolean_type_node, op0, op1); |
| if (folded_cond) |
| { |
| basic_block bb = gimple_bb (stmt); |
| *taken_edge_p = find_taken_edge (bb, folded_cond); |
| if (*taken_edge_p) |
| retval = SSA_PROP_INTERESTING; |
| } |
| |
| if (dump_file && (dump_flags & TDF_DETAILS) && *taken_edge_p) |
| fprintf (dump_file, "\nConditional will always take edge %d->%d\n", |
| (*taken_edge_p)->src->index, (*taken_edge_p)->dest->index); |
| |
| return retval; |
| } |
| |
| |
| /* Evaluate statement STMT. If the statement produces a new output |
| value, return SSA_PROP_INTERESTING and store the SSA_NAME holding |
| the new value in *RESULT_P. |
| |
| If STMT is a conditional branch and we can determine its truth |
| value, set *TAKEN_EDGE_P accordingly. |
| |
| If the new value produced by STMT is varying, return |
| SSA_PROP_VARYING. */ |
| |
| enum ssa_prop_result |
| copy_prop::visit_stmt (gimple *stmt, edge *taken_edge_p, tree *result_p) |
| { |
| enum ssa_prop_result retval; |
| |
| if (dump_file && (dump_flags & TDF_DETAILS)) |
| { |
| fprintf (dump_file, "\nVisiting statement:\n"); |
| print_gimple_stmt (dump_file, stmt, 0, dump_flags); |
| fprintf (dump_file, "\n"); |
| } |
| |
| if (is_gimple_assign (stmt) |
| && TREE_CODE (gimple_assign_lhs (stmt)) == SSA_NAME) |
| { |
| /* If the statement is a copy assignment, evaluate its RHS to |
| see if the lattice value of its output has changed. */ |
| retval = copy_prop_visit_assignment (stmt, result_p); |
| } |
| else if (gimple_code (stmt) == GIMPLE_COND) |
| { |
| /* See if we can determine which edge goes out of a conditional |
| jump. */ |
| retval = copy_prop_visit_cond_stmt (stmt, taken_edge_p); |
| } |
| else |
| retval = SSA_PROP_VARYING; |
| |
| if (retval == SSA_PROP_VARYING) |
| { |
| tree def; |
| ssa_op_iter i; |
| |
| /* Any other kind of statement is not interesting for constant |
| propagation and, therefore, not worth simulating. */ |
| if (dump_file && (dump_flags & TDF_DETAILS)) |
| fprintf (dump_file, "No interesting values produced.\n"); |
| |
| /* The assignment is not a copy operation. Don't visit this |
| statement again and mark all the definitions in the statement |
| to be copies of nothing. */ |
| FOR_EACH_SSA_TREE_OPERAND (def, stmt, i, SSA_OP_ALL_DEFS) |
| set_copy_of_val (def, def); |
| } |
| |
| return retval; |
| } |
| |
| |
| /* Visit PHI node PHI. If all the arguments produce the same value, |
| set it to be the value of the LHS of PHI. */ |
| |
| enum ssa_prop_result |
| copy_prop::visit_phi (gphi *phi) |
| { |
| enum ssa_prop_result retval; |
| unsigned i; |
| prop_value_t phi_val = { NULL_TREE }; |
| |
| tree lhs = gimple_phi_result (phi); |
| |
| if (dump_file && (dump_flags & TDF_DETAILS)) |
| { |
| fprintf (dump_file, "\nVisiting PHI node: "); |
| print_gimple_stmt (dump_file, phi, 0, dump_flags); |
| } |
| |
| for (i = 0; i < gimple_phi_num_args (phi); i++) |
| { |
| prop_value_t *arg_val; |
| tree arg_value; |
| tree arg = gimple_phi_arg_def (phi, i); |
| edge e = gimple_phi_arg_edge (phi, i); |
| |
| /* We don't care about values flowing through non-executable |
| edges. */ |
| if (!(e->flags & EDGE_EXECUTABLE)) |
| continue; |
| |
| /* Names that flow through abnormal edges cannot be used to |
| derive copies. */ |
| if (TREE_CODE (arg) == SSA_NAME && SSA_NAME_OCCURS_IN_ABNORMAL_PHI (arg)) |
| { |
| phi_val.value = lhs; |
| break; |
| } |
| |
| if (dump_file && (dump_flags & TDF_DETAILS)) |
| { |
| fprintf (dump_file, "\tArgument #%d: ", i); |
| dump_copy_of (dump_file, arg); |
| fprintf (dump_file, "\n"); |
| } |
| |
| if (TREE_CODE (arg) == SSA_NAME) |
| { |
| arg_val = get_copy_of_val (arg); |
| |
| /* If we didn't visit the definition of arg yet treat it as |
| UNDEFINED. This also handles PHI arguments that are the |
| same as lhs. We'll come here again. */ |
| if (!arg_val->value) |
| continue; |
| |
| arg_value = arg_val->value; |
| } |
| else |
| arg_value = valueize_val (arg); |
| |
| /* In loop-closed SSA form do not copy-propagate SSA-names across |
| loop exit edges. */ |
| if (loops_state_satisfies_p (LOOP_CLOSED_SSA) |
| && TREE_CODE (arg_value) == SSA_NAME |
| && loop_exit_edge_p (e->src->loop_father, e)) |
| { |
| phi_val.value = lhs; |
| break; |
| } |
| |
| /* If the LHS didn't have a value yet, make it a copy of the |
| first argument we find. */ |
| if (phi_val.value == NULL_TREE) |
| { |
| phi_val.value = arg_value; |
| continue; |
| } |
| |
| /* If PHI_VAL and ARG don't have a common copy-of chain, then |
| this PHI node cannot be a copy operation. */ |
| if (phi_val.value != arg_value |
| && !operand_equal_p (phi_val.value, arg_value, 0)) |
| { |
| phi_val.value = lhs; |
| break; |
| } |
| } |
| |
| if (phi_val.value |
| && may_propagate_copy (lhs, phi_val.value) |
| && set_copy_of_val (lhs, phi_val.value)) |
| retval = (phi_val.value != lhs) ? SSA_PROP_INTERESTING : SSA_PROP_VARYING; |
| else |
| retval = SSA_PROP_NOT_INTERESTING; |
| |
| if (dump_file && (dump_flags & TDF_DETAILS)) |
| { |
| fprintf (dump_file, "PHI node "); |
| dump_copy_of (dump_file, lhs); |
| fprintf (dump_file, "\nTelling the propagator to "); |
| if (retval == SSA_PROP_INTERESTING) |
| fprintf (dump_file, "add SSA edges out of this PHI and continue."); |
| else if (retval == SSA_PROP_VARYING) |
| fprintf (dump_file, "add SSA edges out of this PHI and never visit again."); |
| else |
| fprintf (dump_file, "do nothing with SSA edges and keep iterating."); |
| fprintf (dump_file, "\n\n"); |
| } |
| |
| return retval; |
| } |
| |
| |
| /* Initialize structures used for copy propagation. */ |
| |
| static void |
| init_copy_prop (void) |
| { |
| basic_block bb; |
| |
| n_copy_of = num_ssa_names; |
| copy_of = XCNEWVEC (prop_value_t, n_copy_of); |
| |
| FOR_EACH_BB_FN (bb, cfun) |
| { |
| for (gimple_stmt_iterator si = gsi_start_bb (bb); !gsi_end_p (si); |
| gsi_next (&si)) |
| { |
| gimple *stmt = gsi_stmt (si); |
| ssa_op_iter iter; |
| tree def; |
| |
| /* The only statements that we care about are those that may |
| generate useful copies. We also need to mark conditional |
| jumps so that their outgoing edges are added to the work |
| lists of the propagator. */ |
| if (stmt_ends_bb_p (stmt)) |
| prop_set_simulate_again (stmt, true); |
| else if (stmt_may_generate_copy (stmt)) |
| prop_set_simulate_again (stmt, true); |
| else |
| prop_set_simulate_again (stmt, false); |
| |
| /* Mark all the outputs of this statement as not being |
| the copy of anything. */ |
| FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_ALL_DEFS) |
| if (!prop_simulate_again_p (stmt)) |
| set_copy_of_val (def, def); |
| } |
| |
| for (gphi_iterator si = gsi_start_phis (bb); !gsi_end_p (si); |
| gsi_next (&si)) |
| { |
| gphi *phi = si.phi (); |
| tree def; |
| |
| def = gimple_phi_result (phi); |
| if (virtual_operand_p (def)) |
| prop_set_simulate_again (phi, false); |
| else |
| prop_set_simulate_again (phi, true); |
| |
| if (!prop_simulate_again_p (phi)) |
| set_copy_of_val (def, def); |
| } |
| } |
| } |
| |
| class copy_folder : public substitute_and_fold_engine |
| { |
| public: |
| tree value_of_expr (tree name, gimple *) final override; |
| }; |
| |
| /* Callback for substitute_and_fold to get at the final copy-of values. */ |
| |
| tree |
| copy_folder::value_of_expr (tree name, gimple *) |
| { |
| tree val; |
| if (SSA_NAME_VERSION (name) >= n_copy_of) |
| return NULL_TREE; |
| val = copy_of[SSA_NAME_VERSION (name)].value; |
| if (val && val != name) |
| return val; |
| return NULL_TREE; |
| } |
| |
| /* Deallocate memory used in copy propagation and do final |
| substitution. */ |
| |
| static bool |
| fini_copy_prop (void) |
| { |
| unsigned i; |
| tree var; |
| |
| /* Set the final copy-of value for each variable by traversing the |
| copy-of chains. */ |
| FOR_EACH_SSA_NAME (i, var, cfun) |
| { |
| if (!copy_of[i].value |
| || copy_of[i].value == var) |
| continue; |
| |
| /* In theory the points-to solution of all members of the |
| copy chain is their intersection. For now we do not bother |
| to compute this but only make sure we do not lose points-to |
| information completely by setting the points-to solution |
| of the representative to the first solution we find if |
| it doesn't have one already. */ |
| if (copy_of[i].value != var |
| && TREE_CODE (copy_of[i].value) == SSA_NAME) |
| { |
| basic_block copy_of_bb |
| = gimple_bb (SSA_NAME_DEF_STMT (copy_of[i].value)); |
| basic_block var_bb = gimple_bb (SSA_NAME_DEF_STMT (var)); |
| if (POINTER_TYPE_P (TREE_TYPE (var)) |
| && SSA_NAME_PTR_INFO (var) |
| && !SSA_NAME_PTR_INFO (copy_of[i].value)) |
| { |
| duplicate_ssa_name_ptr_info (copy_of[i].value, |
| SSA_NAME_PTR_INFO (var)); |
| /* Points-to information is cfg insensitive, |
| but [E]VRP might record context sensitive alignment |
| info, non-nullness, etc. So reset context sensitive |
| info if the two SSA_NAMEs aren't defined in the same |
| basic block. */ |
| if (var_bb != copy_of_bb) |
| reset_flow_sensitive_info (copy_of[i].value); |
| } |
| else if (!POINTER_TYPE_P (TREE_TYPE (var)) |
| && SSA_NAME_RANGE_INFO (var) |
| && !SSA_NAME_RANGE_INFO (copy_of[i].value) |
| && var_bb == copy_of_bb) |
| duplicate_ssa_name_range_info (copy_of[i].value, var); |
| } |
| } |
| |
| class copy_folder copy_folder; |
| bool changed = copy_folder.substitute_and_fold (); |
| if (changed) |
| { |
| free_numbers_of_iterations_estimates (cfun); |
| if (scev_initialized_p ()) |
| scev_reset (); |
| } |
| |
| free (copy_of); |
| |
| return changed; |
| } |
| |
| |
| /* Main entry point to the copy propagator. |
| |
| PHIS_ONLY is true if we should only consider PHI nodes as generating |
| copy propagation opportunities. |
| |
| The algorithm propagates the value COPY-OF using ssa_propagate. For |
| every variable X_i, COPY-OF(X_i) indicates which variable is X_i created |
| from. The following example shows how the algorithm proceeds at a |
| high level: |
| |
| 1 a_24 = x_1 |
| 2 a_2 = PHI <a_24, x_1> |
| 3 a_5 = PHI <a_2> |
| 4 x_1 = PHI <x_298, a_5, a_2> |
| |
| The end result should be that a_2, a_5, a_24 and x_1 are a copy of |
| x_298. Propagation proceeds as follows. |
| |
| Visit #1: a_24 is copy-of x_1. Value changed. |
| Visit #2: a_2 is copy-of x_1. Value changed. |
| Visit #3: a_5 is copy-of x_1. Value changed. |
| Visit #4: x_1 is copy-of x_298. Value changed. |
| Visit #1: a_24 is copy-of x_298. Value changed. |
| Visit #2: a_2 is copy-of x_298. Value changed. |
| Visit #3: a_5 is copy-of x_298. Value changed. |
| Visit #4: x_1 is copy-of x_298. Stable state reached. |
| |
| When visiting PHI nodes, we only consider arguments that flow |
| through edges marked executable by the propagation engine. So, |
| when visiting statement #2 for the first time, we will only look at |
| the first argument (a_24) and optimistically assume that its value |
| is the copy of a_24 (x_1). */ |
| |
| static unsigned int |
| execute_copy_prop (void) |
| { |
| init_copy_prop (); |
| class copy_prop copy_prop; |
| copy_prop.ssa_propagate (); |
| if (fini_copy_prop ()) |
| return TODO_cleanup_cfg; |
| return 0; |
| } |
| |
| namespace { |
| |
| const pass_data pass_data_copy_prop = |
| { |
| GIMPLE_PASS, /* type */ |
| "copyprop", /* name */ |
| OPTGROUP_NONE, /* optinfo_flags */ |
| TV_TREE_COPY_PROP, /* tv_id */ |
| ( PROP_ssa | PROP_cfg ), /* properties_required */ |
| 0, /* properties_provided */ |
| 0, /* properties_destroyed */ |
| 0, /* todo_flags_start */ |
| 0, /* todo_flags_finish */ |
| }; |
| |
| class pass_copy_prop : public gimple_opt_pass |
| { |
| public: |
| pass_copy_prop (gcc::context *ctxt) |
| : gimple_opt_pass (pass_data_copy_prop, ctxt) |
| {} |
| |
| /* opt_pass methods: */ |
| opt_pass * clone () final override { return new pass_copy_prop (m_ctxt); } |
| bool gate (function *) final override { return flag_tree_copy_prop != 0; } |
| unsigned int execute (function *) final override |
| { |
| return execute_copy_prop (); |
| } |
| |
| }; // class pass_copy_prop |
| |
| } // anon namespace |
| |
| gimple_opt_pass * |
| make_pass_copy_prop (gcc::context *ctxt) |
| { |
| return new pass_copy_prop (ctxt); |
| } |