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// Implementation of instruction-related RTL SSA functions -*- C++ -*-
// Copyright (C) 2020-2021 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/>.
#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, "<unknown location>");
}
// 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<insn_call_clobbers_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_info::order_node> (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<insn_call_clobbers_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<insn_info> (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<access_info **> (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<use_info> (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<use_info *> (access);
if (!use)
{
set_info *value = safe_dyn_cast<set_info *> (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<ebb_call_clobbers_info> (&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<insn_call_clobbers_note> (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<clobber_info> (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<def_info *> (bi.last_access[ref.regno + 1]);
if (def && def->insn () == insn)
{
if (!ref.is_clobber ())
{
gcc_checking_assert (!is_a<clobber_info *> (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<clobber_info> (insn, regno);
else
def = allocate<set_info> (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<insn_info> (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<use_info *> (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<rtx_call_insn *> (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<set_info *> (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, "<null>");
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); }