// Implementation of instruction-related RTL SSA functions -*- C++ -*- // Copyright (C) 2020-2023 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 // . #define INCLUDE_ALGORITHM #define INCLUDE_FUNCTIONAL #include "config.h" #include "system.h" #include "coretypes.h" #include "backend.h" #include "rtl.h" #include "df.h" #include "rtl-ssa.h" #include "rtl-ssa/internals.h" #include "rtl-ssa/internals.inl" #include "predict.h" #include "print-rtl.h" #include "rtl-iter.h" using namespace rtl_ssa; // The gap to leave between program points when building up the list // of instructions for the first time. Using 2 allows an instruction // to be inserted between two others without resorting to splay tree // ordering. Using 0 is useful as a debugging aid to stress the // splay tree code. static const unsigned int POINT_INCREASE = 2; // Calculate and record the cost of the instruction, based on the // form it had before any in-progress changes were made. void insn_info::calculate_cost () const { basic_block cfg_bb = BLOCK_FOR_INSN (m_rtl); temporarily_undo_changes (0); m_cost_or_uid = insn_cost (m_rtl, optimize_bb_for_speed_p (cfg_bb)); redo_changes (0); } // Add NOTE to the instruction's notes. void insn_info::add_note (insn_note *note) { insn_note **ptr = &m_first_note; // Always put the order node first, since it's the one that's likely // to be used most often. if (*ptr && (*ptr)->kind () == insn_note_kind::ORDER_NODE) ptr = &(*ptr)->m_next_note; note->m_next_note = *ptr; *ptr = note; } // Implement compare_with for the case in which this insn and OTHER // have the same program point. int insn_info::slow_compare_with (const insn_info &other) const { return order_splay_tree::compare_nodes (get_known_order_node (), other.get_known_order_node ()); } // Print insn uid UID to PP, where UID has the same form as insn_info::uid. void insn_info::print_uid (pretty_printer *pp, int uid) { char tmp[3 * sizeof (uid) + 2]; if (uid < 0) // An artificial instruction. snprintf (tmp, sizeof (tmp), "a%d", -uid); else // A real RTL instruction. snprintf (tmp, sizeof (tmp), "i%d", uid); pp_string (pp, tmp); } // See comment above declaration. void insn_info::print_identifier (pretty_printer *pp) const { print_uid (pp, uid ()); } // See comment above declaration. void insn_info::print_location (pretty_printer *pp) const { if (bb_info *bb = this->bb ()) { ebb_info *ebb = bb->ebb (); if (ebb && is_phi ()) ebb->print_identifier (pp); else bb->print_identifier (pp); pp_string (pp, " at point "); pp_decimal_int (pp, m_point); } else pp_string (pp, ""); } // See comment above declaration. void insn_info::print_identifier_and_location (pretty_printer *pp) const { if (m_is_asm) pp_string (pp, "asm "); if (m_is_debug_insn) pp_string (pp, "debug "); pp_string (pp, "insn "); print_identifier (pp); pp_string (pp, " in "); print_location (pp); } // See comment above declaration. void insn_info::print_full (pretty_printer *pp) const { print_identifier_and_location (pp); pp_colon (pp); if (is_real ()) { pp_newline_and_indent (pp, 2); if (has_been_deleted ()) pp_string (pp, "deleted"); else { // Print the insn pattern to a temporary printer. pretty_printer sub_pp; print_insn_with_notes (&sub_pp, rtl ()); const char *text = pp_formatted_text (&sub_pp); // Calculate the length of the maximum line in the pattern. unsigned int max_len = 0; const char *start = text; while (const char *end = strchr (start, '\n')) { max_len = MAX (max_len, (unsigned int) (end - start)); start = end + 1; } // Print a separator before or after the pattern. auto print_top_bottom = [&]() { pp_character (pp, '+'); for (unsigned int i = 0; i < max_len + 2; ++i) pp_character (pp, '-'); }; print_top_bottom (); start = text; while (const char *end = strchr (start, '\n')) { pp_newline_and_indent (pp, 0); pp_character (pp, '|'); // Each line of the pattern already starts with a space. // so we don't need to add another one here. pp_append_text (pp, start, end); start = end + 1; } pp_newline_and_indent (pp, 0); print_top_bottom (); if (m_cost_or_uid != UNKNOWN_COST) { pp_newline_and_indent (pp, 0); pp_string (pp, "cost: "); pp_decimal_int (pp, m_cost_or_uid); } if (m_has_pre_post_modify) { pp_newline_and_indent (pp, 0); pp_string (pp, "has pre/post-modify operations"); } if (m_has_volatile_refs) { pp_newline_and_indent (pp, 0); pp_string (pp, "has volatile refs"); } } pp_indentation (pp) -= 2; } auto print_accesses = [&](const char *heading, access_array accesses, unsigned int flags) { if (!accesses.empty ()) { pp_newline_and_indent (pp, 2); pp_string (pp, heading); pp_newline_and_indent (pp, 2); pp_accesses (pp, accesses, flags); pp_indentation (pp) -= 4; } }; print_accesses ("uses:", uses (), PP_ACCESS_USER); auto *call_clobbers_note = find_note (); if (call_clobbers_note) { pp_newline_and_indent (pp, 2); pp_string (pp, "has call clobbers for ABI "); pp_decimal_int (pp, call_clobbers_note->abi_id ()); pp_indentation (pp) -= 2; } print_accesses ("defines:", defs (), PP_ACCESS_SETTER); if (num_uses () == 0 && !call_clobbers_note && num_defs () == 0) { pp_newline_and_indent (pp, 2); pp_string (pp, "has no uses or defs"); pp_indentation (pp) -= 2; } if (order_node *node = get_order_node ()) { while (node->m_parent) node = node->m_parent; pp_newline_and_indent (pp, 2); pp_string (pp, "insn order: "); pp_newline_and_indent (pp, 2); auto print_order = [](pretty_printer *pp, order_node *node) { print_uid (pp, node->uid ()); }; order_splay_tree::print (pp, node, print_order); pp_indentation (pp) -= 4; } } // Return an insn_info::order_node for INSN, creating one if necessary. insn_info::order_node * function_info::need_order_node (insn_info *insn) { insn_info::order_node *order = insn->get_order_node (); if (!order) { order = allocate (insn->uid ()); insn->add_note (order); } return order; } // Add instruction INSN immediately after AFTER in the reverse postorder list. // INSN is not currently in the list. void function_info::add_insn_after (insn_info *insn, insn_info *after) { gcc_checking_assert (!insn->has_insn_links ()); insn->copy_next_from (after); after->set_next_any_insn (insn); // The prev link is easy if AFTER and INSN are the same type. // Handle the other cases below. if (after->is_debug_insn () == insn->is_debug_insn ()) insn->set_prev_sametype_insn (after); if (insn_info *next = insn->next_any_insn ()) { if (insn->is_debug_insn () == next->is_debug_insn ()) { // INSN might now be the start of the subsequence of debug insns, // and so its prev pointer might point to the end of the subsequence // instead of AFTER. insn->copy_prev_from (next); next->set_prev_sametype_insn (insn); } else if (insn->is_debug_insn ()) // && !next->is_debug_insn () { // INSN ends a subsequence of debug instructions. Find the // first debug instruction in the subsequence, which might // be INSN itself. (If it isn't, then AFTER is also a debug // instruction and we updated INSN's prev link above.) insn_info *first = next->prev_nondebug_insn ()->next_any_insn (); first->set_last_debug_insn (insn); } else // !insn->is_debug_insn () && next->is_debug_insn () // At present we don't (need to) support inserting a nondebug // instruction between two existing debug instructions. gcc_assert (!after->is_debug_insn ()); // If AFTER and NEXT are separated by at least two points, we can // use a unique point number for INSN. Otherwise INSN will have // the same point number as AFTER. insn->set_point ((next->point () + after->point ()) / 2); } else { if (!insn->is_debug_insn ()) { insn->set_prev_sametype_insn (m_last_nondebug_insn); m_last_nondebug_insn = insn; } else // There is now at least one debug instruction after // m_last_nondebug_insn: either INSN itself, or the start of // a longer subsequence of debug insns that now ends with AFTER // followed by INSN. m_last_nondebug_insn->next_any_insn ()->set_last_debug_insn (insn); m_last_insn = insn; insn->set_point (after->point () + POINT_INCREASE); } // If INSN's program point is the same as AFTER's, we need to use the // splay tree to record their relative order. if (insn->point () == after->point ()) { insn_info::order_node *after_node = need_order_node (after); insn_info::order_node *insn_node = need_order_node (insn); insn_info::order_splay_tree::insert_child (after_node, 1, insn_node); } } // Remove INSN from the function's list of instructions. void function_info::remove_insn (insn_info *insn) { if (insn_info::order_node *order = insn->get_order_node ()) insn_info::order_splay_tree::remove_node (order); if (auto *note = insn->find_note ()) { ebb_call_clobbers_info *ecc = insn->ebb ()->first_call_clobbers (); while (ecc->abi ()->id () != note->abi_id ()) ecc = ecc->next (); int comparison = lookup_call_clobbers (*ecc, insn); gcc_assert (comparison == 0); ecc->remove_root (); } insn_info *prev = insn->prev_any_insn (); insn_info *next = insn->next_any_insn (); insn_info *prev_nondebug = insn->prev_nondebug_insn (); insn_info *next_nondebug = insn->next_nondebug_insn (); // We should never remove the entry or exit block's instructions. // At present we also don't remove entire blocks, so should never // remove debug instructions. gcc_checking_assert (prev_nondebug && next_nondebug && !insn->is_debug_insn ()); if (prev->is_debug_insn () && next->is_debug_insn ()) { // We need to stitch together two subsequences of debug insns. insn_info *last = next->last_debug_insn (); next->set_prev_sametype_insn (prev); prev_nondebug->next_any_insn ()->set_last_debug_insn (last); } prev->set_next_any_insn (next); next_nondebug->set_prev_sametype_insn (prev_nondebug); insn->clear_insn_links (); } // Create an artificial instruction for BB, associating it with RTL (which can // be null). Add the new instruction to the end of the function's list and // return the new instruction. insn_info * function_info::append_artificial_insn (bb_info *bb, rtx_insn *rtl) { insn_info *insn = allocate (bb, rtl, m_next_artificial_uid); m_next_artificial_uid -= 1; append_insn (insn); return insn; } // Finish building a new list of uses and definitions for instruction INSN. void function_info::finish_insn_accesses (insn_info *insn) { unsigned int num_defs = m_temp_defs.length (); unsigned int num_uses = m_temp_uses.length (); obstack_make_room (&m_obstack, num_defs + num_uses); if (num_defs) { sort_accesses (m_temp_defs); obstack_grow (&m_obstack, m_temp_defs.address (), num_defs * sizeof (access_info *)); m_temp_defs.truncate (0); } if (num_uses) { sort_accesses (m_temp_uses); obstack_grow (&m_obstack, m_temp_uses.address (), num_uses * sizeof (access_info *)); m_temp_uses.truncate (0); } void *addr = obstack_finish (&m_obstack); insn->set_accesses (static_cast (addr), num_defs, num_uses); } // Called while building SSA form using BI. Create and return a use of // register RESOURCE in INSN. Create a degenerate phi where necessary. use_info * function_info::create_reg_use (build_info &bi, insn_info *insn, resource_info resource) { set_info *value = bi.current_reg_value (resource.regno); if (value && value->ebb () != bi.current_ebb) { if (insn->is_debug_insn ()) value = look_through_degenerate_phi (value); else if (bitmap_bit_p (bi.potential_phi_regs, resource.regno)) { // VALUE is defined by a previous EBB and RESOURCE has multiple // definitions. Create a degenerate phi in the current EBB // so that all definitions and uses follow a linear RPO view; // see rtl.texi for details. access_info *inputs[] = { look_through_degenerate_phi (value) }; value = create_phi (bi.current_ebb, value->resource (), inputs, 1); bi.record_reg_def (value); } } auto *use = allocate (insn, resource, value); add_use (use); return use; } // Called while building SSA form using BI. Record that INSN contains // read reference REF. If this requires new entries to be added to // INSN->uses (), add those entries to the list we're building in // m_temp_uses. void function_info::record_use (build_info &bi, insn_info *insn, rtx_obj_reference ref) { unsigned int regno = ref.regno; machine_mode mode = ref.is_reg () ? ref.mode : BLKmode; access_info *access = bi.last_access[ref.regno + 1]; use_info *use = safe_dyn_cast (access); if (!use) { set_info *value = safe_dyn_cast (access); // In order to ensure that -g doesn't affect codegen, uses in debug // instructions do not affect liveness, either in DF or here. // This means that there might be no correct definition of the resource // available (e.g. if it would require a phi node that the nondebug // code doesn't need). Perhaps we could have "debug phi nodes" as // well as "debug instructions", but that would require a method // of building phi nodes that didn't depend on DF liveness information, // and so might be significantly more expensive. // // Therefore, the only value we try to attach to a use by a debug // instruction is VALUE itself (as we would for nondebug instructions). // We then need to make a conservative check for whether VALUE is // actually correct. auto value_is_valid = [&]() { // Memmory always has a valid definition. if (ref.is_mem ()) return true; // If VALUE would lead to an uninitialized use anyway, there's // nothing to check. if (!value) return false; // If the previous definition occurs in the same EBB then it // is certainly correct. if (value->ebb () == bi.current_ebb) return true; // Check if VALUE is the function's only definition of REGNO. // (We already know that it dominates the use.) if (!bitmap_bit_p (bi.potential_phi_regs, regno)) return true; // If the register is live on entry to the EBB but not used // within it, VALUE is the correct live-in value. if (!bi.ebb_live_in_for_debug) calculate_ebb_live_in_for_debug (bi); if (bitmap_bit_p (bi.ebb_live_in_for_debug, regno)) return true; // Punt for other cases. return false; }; if (insn->is_debug_insn () && !value_is_valid ()) value = nullptr; use = create_reg_use (bi, insn, { mode, regno }); m_temp_uses.safe_push (use); bi.last_access[ref.regno + 1] = use; use->record_reference (ref, true); } else { // Record the mode of the largest use. The choice is arbitrary if // the instruction (unusually) references the same register in two // different but equal-sized modes. gcc_checking_assert (use->insn () == insn); if (HARD_REGISTER_NUM_P (regno) && partial_subreg_p (use->mode (), mode)) use->set_mode (mode); use->record_reference (ref, false); } } // Called while building SSA form for INSN using BI. Record the effect // of call clobbers in RTL. We have already added the explicit sets and // clobbers for RTL, which have priority over any call clobbers. void function_info::record_call_clobbers (build_info &bi, insn_info *insn, rtx_call_insn *rtl) { // See whether we should record this call in the EBB's list of // call clobbers. Three things affect this choice: // // (1) The list is the only way we have of recording partial clobbers. // All calls that only partially clobber registers must therefore // be in the list. // // (2) Adding calls to the list is much more memory-efficient than // creating a long list of clobber_infos. // // (3) Adding calls to the list limits the ability to move definitions // of registers that are normally fully or partially clobbered // by the associated predefined ABI. So adding calls to the list // can hamper optimization if (thanks to -fipa-ra) the number of // clobbers is much smaller than the usual set. // // The trade-off that we currently take is to use the list if there // are some registers that the call only partially clobbers or if // the set of clobbers is the standard set. function_abi abi = insn_callee_abi (rtl); if (abi.base_abi ().full_reg_clobbers () == abi.full_reg_clobbers () || abi.full_and_partial_reg_clobbers () != abi.full_reg_clobbers ()) { // Find an entry for this predefined ABI, creating one if necessary. ebb_call_clobbers_info *ecc = bi.current_ebb->first_call_clobbers (); while (ecc && ecc->abi () != &abi.base_abi ()) ecc = ecc->next (); if (!ecc) { ecc = allocate (&abi.base_abi ()); ecc->m_next = bi.current_ebb->first_call_clobbers (); bi.current_ebb->set_first_call_clobbers (ecc); } auto abi_id = abi.base_abi ().id (); auto *insn_clobbers = allocate (abi_id, insn); insn->add_note (insn_clobbers); ecc->insert_max_node (insn_clobbers); } else for (unsigned int regno = 0; regno < FIRST_PSEUDO_REGISTER; ++regno) if (TEST_HARD_REG_BIT (abi.full_reg_clobbers (), regno)) { def_info *def = m_defs[regno + 1]; if (!def || def->last_def ()->insn () != insn) { def = allocate (insn, regno); def->m_is_call_clobber = true; append_def (def); m_temp_defs.safe_push (def); bi.record_reg_def (def); } } } // Called while building SSA form using BI. Record that INSN contains // write reference REF. Add associated def_infos to the list of accesses // that we're building in m_temp_defs. Record the register's new live // value in BI. void function_info::record_def (build_info &bi, insn_info *insn, rtx_obj_reference ref) { // Punt if we see multiple definitions of the same resource. // This can happen for several reasons: // // - An instruction might store two values to memory at once, giving two // distinct memory references. // // - An instruction might assign to multiple pieces of a wide pseudo // register. For example, on 32-bit targets, an instruction might // assign to both the upper and lower halves of a 64-bit pseudo register. // // - It's possible for the same register to be clobbered by the // CALL_INSN_FUNCTION_USAGE and to be set by the main instruction // pattern as well. In that case, the clobber conceptually happens // before the set and can essentially be ignored. // // - Similarly, global registers are implicitly set by a call but can // be explicitly set or clobbered as well. In that situation, the sets // are listed first and should win over a clobber. unsigned int regno = ref.regno; machine_mode mode = ref.is_reg () ? ref.mode : BLKmode; def_info *def = safe_dyn_cast (bi.last_access[ref.regno + 1]); if (def && def->insn () == insn) { if (!ref.is_clobber ()) { gcc_checking_assert (!is_a (def)); def->record_reference (ref, false); } return; } // Memory is always well-defined, so only use clobber_infos for registers. if (ref.is_reg () && ref.is_clobber ()) def = allocate (insn, regno); else def = allocate (insn, resource_info { mode, regno }); def->record_reference (ref, true); append_def (def); m_temp_defs.safe_push (def); bi.record_reg_def (def); } // Called while building SSA form using BI. Add an insn_info for RTL // to the block that we're current building. void function_info::add_insn_to_block (build_info &bi, rtx_insn *rtl) { insn_info *insn = allocate (bi.current_bb, rtl, UNKNOWN_COST); append_insn (insn); vec_rtx_properties properties; properties.add_insn (rtl, true); insn->set_properties (properties); start_insn_accesses (); // Record the uses. for (rtx_obj_reference ref : properties.refs ()) if (ref.is_read ()) record_use (bi, insn, ref); // Restore the contents of bi.last_access, which we used as a cache // when assembling the uses. for (access_info *access : m_temp_uses) { unsigned int regno = access->regno (); gcc_checking_assert (bi.last_access[regno + 1] == access); bi.last_access[regno + 1] = as_a (access)->def (); } // Record the definitions. for (rtx_obj_reference ref : properties.refs ()) if (ref.is_write ()) record_def (bi, insn, ref); // Logically these happen before the explicit definitions, but if the // explicit definitions and call clobbers reference the same register, // the explicit definition should win. if (auto *call_rtl = dyn_cast (rtl)) record_call_clobbers (bi, insn, call_rtl); finish_insn_accesses (insn); } // Check whether INSN sets any registers that are never subsequently used. // If so, add REG_UNUSED notes for them. The caller has already removed // any previous REG_UNUSED notes. void function_info::add_reg_unused_notes (insn_info *insn) { rtx_insn *rtl = insn->rtl (); auto handle_potential_set = [&](rtx pattern) { if (GET_CODE (pattern) != SET) return; rtx dest = SET_DEST (pattern); if (!REG_P (dest)) return; def_array defs = insn->defs (); unsigned int index = find_access_index (defs, REGNO (dest)); for (unsigned int i = 0; i < REG_NREGS (dest); ++i) { def_info *def = defs[index + i]; gcc_checking_assert (def->regno () == REGNO (dest) + i); set_info *set = dyn_cast (def); if (set && set->has_nondebug_uses ()) return; } add_reg_note (rtl, REG_UNUSED, dest); }; rtx pattern = PATTERN (rtl); if (GET_CODE (pattern) == PARALLEL) for (int i = 0; i < XVECLEN (pattern, 0); ++i) handle_potential_set (XVECEXP (pattern, 0, i)); else handle_potential_set (pattern); } // Search TREE for call clobbers at INSN. Return: // // - less than zero if INSN occurs before the root of TREE // - 0 if INSN is the root of TREE // - greater than zero if INSN occurs after the root of TREE int rtl_ssa::lookup_call_clobbers (insn_call_clobbers_tree &tree, insn_info *insn) { auto compare = [&](insn_call_clobbers_note *clobbers) { return insn->compare_with (clobbers->insn ()); }; return tree.lookup (compare); } // Print a description of INSN to PP. void rtl_ssa::pp_insn (pretty_printer *pp, const insn_info *insn) { if (!insn) pp_string (pp, ""); else insn->print_full (pp); } // Print a description of INSN to FILE. void dump (FILE *file, const insn_info *insn) { dump_using (file, pp_insn, insn); } // Debug interface to the dump routine above. void debug (const insn_info *x) { dump (stderr, x); }