// Pass to fuse adjacent loads/stores into paired memory accesses.
// Copyright (C) 2023-2025 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
#define INCLUDE_LIST
#define INCLUDE_TYPE_TRAITS
#define INCLUDE_ARRAY
#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "backend.h"
#include "rtl.h"
#include "df.h"
#include "rtl-iter.h"
#include "rtl-ssa.h"
#include "cfgcleanup.h"
#include "tree-pass.h"
#include "ordered-hash-map.h"
#include "tree-dfa.h"
#include "fold-const.h"
#include "tree-hash-traits.h"
#include "print-tree.h"
#include "pair-fusion.h"
using namespace rtl_ssa;
// We pack these fields (load_p, fpsimd_p, and size) into an integer
// (LFS) which we use as part of the key into the main hash tables.
//
// The idea is that we group candidates together only if they agree on
// the fields below. Candidates that disagree on any of these
// properties shouldn't be merged together.
struct lfs_fields
{
bool load_p;
bool fpsimd_p;
unsigned size;
};
using insn_list_t = std::list<insn_info *>;
// Information about the accesses at a given offset from a particular
// base. Stored in an access_group, see below.
struct access_record
{
poly_int64 offset;
std::list<insn_info *> cand_insns;
std::list<access_record>::iterator place;
access_record (poly_int64 off) : offset (off) {}
};
// A group of accesses where adjacent accesses could be ldp/stp
// candidates. The splay tree supports efficient insertion,
// while the list supports efficient iteration.
struct access_group
{
splay_tree<access_record *> tree;
std::list<access_record> list;
template<typename Alloc>
inline void track (Alloc node_alloc, poly_int64 offset, insn_info *insn);
};
// Test if this base candidate is viable according to HAZARDS.
bool
base_cand::viable () const
{
return !hazards[0] || !hazards[1] || (*hazards[0] > *hazards[1]);
}
// Information about an alternate base. For a def_info D, it may
// instead be expressed as D = BASE + OFFSET.
struct alt_base
{
def_info *base;
poly_int64 offset;
};
// Virtual base class for load/store walkers used in alias analysis.
struct alias_walker
{
virtual bool conflict_p (int &budget) const = 0;
virtual insn_info *insn () const = 0;
virtual bool valid () const = 0;
virtual void advance () = 0;
};
pair_fusion::pair_fusion ()
{
calculate_dominance_info (CDI_DOMINATORS);
df_analyze ();
crtl->ssa = new rtl_ssa::function_info (cfun);
}
pair_fusion::~pair_fusion ()
{
if (crtl->ssa->perform_pending_updates ())
cleanup_cfg (0);
free_dominance_info (CDI_DOMINATORS);
delete crtl->ssa;
crtl->ssa = nullptr;
}
// This is the main function to start the pass.
void
pair_fusion::run ()
{
if (!track_loads_p () && !track_stores_p ())
return;
for (auto bb : crtl->ssa->bbs ())
process_block (bb);
}
// State used by the pass for a given basic block.
struct pair_fusion_bb_info
{
using def_hash = nofree_ptr_hash<def_info>;
using expr_key_t = pair_hash<tree_operand_hash, int_hash<int, -1, -2>>;
using def_key_t = pair_hash<def_hash, int_hash<int, -1, -2>>;
// Map of <tree base, LFS> -> access_group.
ordered_hash_map<expr_key_t, access_group> expr_map;
// Map of <RTL-SSA def_info *, LFS> -> access_group.
ordered_hash_map<def_key_t, access_group> def_map;
// Given the def_info for an RTL base register, express it as an offset from
// some canonical base instead.
//
// Canonicalizing bases in this way allows us to identify adjacent accesses
// even if they see different base register defs.
hash_map<def_hash, alt_base> canon_base_map;
static const size_t obstack_alignment = sizeof (void *);
pair_fusion_bb_info (bb_info *bb, pair_fusion *d)
: m_bb (bb), m_pass (d), m_emitted_tombstone (false)
{
obstack_specify_allocation (&m_obstack, OBSTACK_CHUNK_SIZE,
obstack_alignment, obstack_chunk_alloc,
obstack_chunk_free);
}
~pair_fusion_bb_info ()
{
obstack_free (&m_obstack, nullptr);
if (m_emitted_tombstone)
{
bitmap_release (&m_tombstone_bitmap);
bitmap_obstack_release (&m_bitmap_obstack);
}
}
inline void track_access (insn_info *, bool load, rtx mem);
inline void transform ();
inline void cleanup_tombstones ();
private:
obstack m_obstack;
bb_info *m_bb;
pair_fusion *m_pass;
// State for keeping track of tombstone insns emitted for this BB.
bitmap_obstack m_bitmap_obstack;
bitmap_head m_tombstone_bitmap;
bool m_emitted_tombstone;
inline splay_tree_node<access_record *> *node_alloc (access_record *);
template<typename Map>
inline void traverse_base_map (Map &map);
inline void transform_for_base (int load_size, access_group &group);
inline void merge_pairs (insn_list_t &, insn_list_t &,
bool load_p, unsigned access_size);
inline bool try_fuse_pair (bool load_p, unsigned access_size,
insn_info *i1, insn_info *i2);
inline bool fuse_pair (bool load_p, unsigned access_size,
int writeback,
insn_info *i1, insn_info *i2,
base_cand &base,
const insn_range_info &move_range);
inline void track_tombstone (int uid);
inline bool track_via_mem_expr (insn_info *, rtx mem, lfs_fields lfs);
};
splay_tree_node<access_record *> *
pair_fusion_bb_info::node_alloc (access_record *access)
{
using T = splay_tree_node<access_record *>;
void *addr = obstack_alloc (&m_obstack, sizeof (T));
return new (addr) T (access);
}
// Given a mem MEM, if the address has side effects, return a MEM that accesses
// the same address but without the side effects. Otherwise, return
// MEM unchanged.
static rtx
drop_writeback (rtx mem)
{
rtx addr = XEXP (mem, 0);
if (!side_effects_p (addr))
return mem;
switch (GET_CODE (addr))
{
case PRE_MODIFY:
addr = XEXP (addr, 1);
break;
case POST_MODIFY:
case POST_INC:
case POST_DEC:
addr = XEXP (addr, 0);
break;
case PRE_INC:
case PRE_DEC:
{
poly_int64 adjustment = GET_MODE_SIZE (GET_MODE (mem));
if (GET_CODE (addr) == PRE_DEC)
adjustment *= -1;
addr = plus_constant (GET_MODE (addr), XEXP (addr, 0), adjustment);
break;
}
default:
gcc_unreachable ();
}
return change_address (mem, GET_MODE (mem), addr);
}
// Convenience wrapper around strip_offset that can also look through
// RTX_AUTOINC addresses. The interface is like strip_offset except we take a
// MEM so that we know the mode of the access.
static rtx
pair_mem_strip_offset (rtx mem, poly_int64 *offset)
{
rtx addr = XEXP (mem, 0);
switch (GET_CODE (addr))
{
case PRE_MODIFY:
case POST_MODIFY:
addr = strip_offset (XEXP (addr, 1), offset);
gcc_checking_assert (REG_P (addr));
gcc_checking_assert (rtx_equal_p (XEXP (XEXP (mem, 0), 0), addr));
break;
case PRE_INC:
case POST_INC:
addr = XEXP (addr, 0);
*offset = GET_MODE_SIZE (GET_MODE (mem));
gcc_checking_assert (REG_P (addr));
break;
case PRE_DEC:
case POST_DEC:
addr = XEXP (addr, 0);
*offset = -GET_MODE_SIZE (GET_MODE (mem));
gcc_checking_assert (REG_P (addr));
break;
default:
addr = strip_offset (addr, offset);
}
return addr;
}
// Return true if X is a PRE_{INC,DEC,MODIFY} rtx.
static bool
any_pre_modify_p (rtx x)
{
const auto code = GET_CODE (x);
return code == PRE_INC || code == PRE_DEC || code == PRE_MODIFY;
}
// Return true if X is a POST_{INC,DEC,MODIFY} rtx.
static bool
any_post_modify_p (rtx x)
{
const auto code = GET_CODE (x);
return code == POST_INC || code == POST_DEC || code == POST_MODIFY;
}
// Given LFS (load_p, fpsimd_p, size) fields in FIELDS, encode these
// into an integer for use as a hash table key.
static int
encode_lfs (lfs_fields fields)
{
int size_log2 = exact_log2 (fields.size);
gcc_checking_assert (size_log2 >= 2 && size_log2 <= 4);
return ((int)fields.load_p << 3)
| ((int)fields.fpsimd_p << 2)
| (size_log2 - 2);
}
// Inverse of encode_lfs.
static lfs_fields
decode_lfs (int lfs)
{
bool load_p = (lfs & (1 << 3));
bool fpsimd_p = (lfs & (1 << 2));
unsigned size = 1U << ((lfs & 3) + 2);
return { load_p, fpsimd_p, size };
}
// Track the access INSN at offset OFFSET in this access group.
// ALLOC_NODE is used to allocate splay tree nodes.
template<typename Alloc>
void
access_group::track (Alloc alloc_node, poly_int64 offset, insn_info *insn)
{
auto insert_before = [&](std::list<access_record>::iterator after)
{
auto it = list.emplace (after, offset);
it->cand_insns.push_back (insn);
it->place = it;
return &*it;
};
if (!list.size ())
{
auto access = insert_before (list.end ());
tree.insert_max_node (alloc_node (access));
return;
}
auto compare = [&](splay_tree_node<access_record *> *node)
{
return compare_sizes_for_sort (offset, node->value ()->offset);
};
auto result = tree.lookup (compare);
splay_tree_node<access_record *> *node = tree.root ();
if (result == 0)
node->value ()->cand_insns.push_back (insn);
else
{
auto it = node->value ()->place;
auto after = (result > 0) ? std::next (it) : it;
auto access = insert_before (after);
tree.insert_child (node, result > 0, alloc_node (access));
}
}
// Given a candidate access INSN (with mem MEM), see if it has a suitable
// MEM_EXPR base (i.e. a tree decl) relative to which we can track the access.
// LFS is used as part of the key to the hash table, see track_access.
bool
pair_fusion_bb_info::track_via_mem_expr (insn_info *insn, rtx mem,
lfs_fields lfs)
{
if (!MEM_EXPR (mem) || !MEM_OFFSET_KNOWN_P (mem))
return false;
poly_int64 offset;
tree base_expr = get_addr_base_and_unit_offset (MEM_EXPR (mem),
&offset);
if (!base_expr || !DECL_P (base_expr))
return false;
offset += MEM_OFFSET (mem);
const machine_mode mem_mode = GET_MODE (mem);
const HOST_WIDE_INT mem_size = GET_MODE_SIZE (mem_mode).to_constant ();
// Punt on misaligned offsets. Paired memory access instructions require
// offsets to be a multiple of the access size, and we believe that
// misaligned offsets on MEM_EXPR bases are likely to lead to misaligned
// offsets w.r.t. RTL bases.
if (!multiple_p (offset, mem_size))
return false;
const auto key = std::make_pair (base_expr, encode_lfs (lfs));
access_group &group = expr_map.get_or_insert (key, NULL);
auto alloc = [&](access_record *access) { return node_alloc (access); };
group.track (alloc, offset, insn);
if (dump_file)
{
fprintf (dump_file, "[bb %u] tracking insn %d via ",
m_bb->index (), insn->uid ());
print_node_brief (dump_file, "mem expr", base_expr, 0);
fprintf (dump_file, " [L=%d FP=%d, %smode, off=",
lfs.load_p, lfs.fpsimd_p, mode_name[mem_mode]);
print_dec (offset, dump_file);
fprintf (dump_file, "]\n");
}
return true;
}
// Main function to begin pair discovery. Given a memory access INSN,
// determine whether it could be a candidate for fusing into a paired
// access, and if so, track it in the appropriate data structure for
// this basic block. LOAD_P is true if the access is a load, and MEM
// is the mem rtx that occurs in INSN.
void
pair_fusion_bb_info::track_access (insn_info *insn, bool load_p, rtx mem)
{
// We can't combine volatile MEMs, so punt on these.
if (MEM_VOLATILE_P (mem))
return;
// Ignore writeback accesses if the hook says to do so.
if (!m_pass->should_handle_writeback (writeback_type::EXISTING)
&& GET_RTX_CLASS (GET_CODE (XEXP (mem, 0))) == RTX_AUTOINC)
return;
const machine_mode mem_mode = GET_MODE (mem);
if (!m_pass->pair_operand_mode_ok_p (mem_mode))
return;
rtx reg_op = XEXP (PATTERN (insn->rtl ()), !load_p);
if (!m_pass->pair_reg_operand_ok_p (load_p, reg_op, mem_mode))
return;
// We want to segregate FP/SIMD accesses from GPR accesses.
const bool fpsimd_op_p = m_pass->fpsimd_op_p (reg_op, mem_mode, load_p);
// Note pair_operand_mode_ok_p already rejected VL modes.
const unsigned mem_size = GET_MODE_SIZE (mem_mode).to_constant ();
const lfs_fields lfs = { load_p, fpsimd_op_p, mem_size };
if (track_via_mem_expr (insn, mem, lfs))
return;
poly_int64 mem_off;
rtx addr = XEXP (mem, 0);
const bool autoinc_p = GET_RTX_CLASS (GET_CODE (addr)) == RTX_AUTOINC;
rtx base = pair_mem_strip_offset (mem, &mem_off);
if (!REG_P (base))
return;
// Need to calculate two (possibly different) offsets:
// - Offset at which the access occurs.
// - Offset of the new base def.
poly_int64 access_off;
if (autoinc_p && any_post_modify_p (addr))
access_off = 0;
else
access_off = mem_off;
poly_int64 new_def_off = mem_off;
// Punt on accesses relative to eliminable regs. Since we don't know the
// elimination offset pre-RA, we should postpone forming pairs on such
// accesses until after RA.
//
// As it stands, addresses in range for an individual load/store but not
// for a paired access are currently reloaded inefficiently,
// ending up with a separate base register for each pair.
//
// In theory LRA should make use of
// targetm.legitimize_address_displacement to promote sharing of
// bases among multiple (nearby) address reloads, but the current
// LRA code returns early from process_address_1 for operands that
// satisfy "m", even if they don't satisfy the real (relaxed) address
// constraint; this early return means we never get to the code
// that calls targetm.legitimize_address_displacement.
//
// So for now, it's better to punt when we can't be sure that the
// offset is in range for paired access. On aarch64, out-of-range cases
// can then be handled after RA by the out-of-range LDP/STP peepholes.
// Eventually, it would be nice to handle known out-of-range opportunities
// in the pass itself (for stack accesses, this would be in the post-RA pass).
if (!reload_completed
&& (REGNO (base) == FRAME_POINTER_REGNUM
|| REGNO (base) == ARG_POINTER_REGNUM))
return;
// Now need to find def of base register.
use_info *base_use = find_access (insn->uses (), REGNO (base));
gcc_assert (base_use);
def_info *base_def = base_use->def ();
if (!base_def)
{
if (dump_file)
fprintf (dump_file,
"base register (regno %d) of insn %d is undefined",
REGNO (base), insn->uid ());
return;
}
alt_base *canon_base = canon_base_map.get (base_def);
if (canon_base)
{
// Express this as the combined offset from the canonical base.
base_def = canon_base->base;
new_def_off += canon_base->offset;
access_off += canon_base->offset;
}
if (autoinc_p)
{
auto def = find_access (insn->defs (), REGNO (base));
gcc_assert (def);
// Record that DEF = BASE_DEF + MEM_OFF.
if (dump_file)
{
pretty_printer pp;
pp_access (&pp, def, 0);
pp_string (&pp, " = ");
pp_access (&pp, base_def, 0);
fprintf (dump_file, "[bb %u] recording %s + ",
m_bb->index (), pp_formatted_text (&pp));
print_dec (new_def_off, dump_file);
fprintf (dump_file, "\n");
}
alt_base base_rec { base_def, new_def_off };
if (canon_base_map.put (def, base_rec))
gcc_unreachable (); // Base defs should be unique.
}
// Punt on misaligned offsets. Paired memory accesses require offsets
// to be a multiple of the access size.
if (!multiple_p (mem_off, mem_size))
return;
const auto key = std::make_pair (base_def, encode_lfs (lfs));
access_group &group = def_map.get_or_insert (key, NULL);
auto alloc = [&](access_record *access) { return node_alloc (access); };
group.track (alloc, access_off, insn);
if (dump_file)
{
pretty_printer pp;
pp_access (&pp, base_def, 0);
fprintf (dump_file, "[bb %u] tracking insn %d via %s",
m_bb->index (), insn->uid (), pp_formatted_text (&pp));
fprintf (dump_file,
" [L=%d, WB=%d, FP=%d, %smode, off=",
lfs.load_p, autoinc_p, lfs.fpsimd_p, mode_name[mem_mode]);
print_dec (access_off, dump_file);
fprintf (dump_file, "]\n");
}
}
// Return the latest dataflow hazard before INSN.
//
// If IGNORE is non-NULL, this points to a sub-rtx which we should ignore for
// dataflow purposes. This is needed when considering changing the RTL base of
// an access discovered through a MEM_EXPR base.
//
// If IGNORE_INSN is non-NULL, we should further ignore any hazards arising
// from that insn.
//
// IS_LOAD_STORE is true if INSN is one of the loads or stores in the
// candidate pair. We ignore any defs/uses of memory in such instructions
// as we deal with that separately, making use of alias disambiguation.
static insn_info *
latest_hazard_before (insn_info *insn, rtx *ignore,
insn_info *ignore_insn = nullptr,
bool is_load_store = true)
{
insn_info *result = nullptr;
// If the insn can throw then it is at the end of a BB and we can't
// move it, model this by recording a hazard in the previous insn
// which will prevent moving the insn up.
if (cfun->can_throw_non_call_exceptions
&& find_reg_note (insn->rtl (), REG_EH_REGION, NULL_RTX))
return insn->prev_nondebug_insn ();
if (!is_load_store
&& accesses_include_memory (insn->defs ()))
return insn->prev_nondebug_insn ();
// Return true if we registered the hazard.
auto hazard = [&](insn_info *h) -> bool
{
gcc_checking_assert (*h < *insn);
if (h == ignore_insn)
return false;
if (!result || *h > *result)
result = h;
return true;
};
rtx pat = PATTERN (insn->rtl ());
auto ignore_use = [&](use_info *u)
{
if (u->is_mem ())
return true;
return !refers_to_regno_p (u->regno (), u->regno () + 1, pat, ignore);
};
// Find defs of uses in INSN (RaW).
for (auto use : insn->uses ())
if (!ignore_use (use) && use->def ())
hazard (use->def ()->insn ());
// Find previous defs (WaW) or previous uses (WaR) of defs in INSN.
for (auto def : insn->defs ())
{
if (def->is_mem ())
continue;
if (def->prev_def ())
{
hazard (def->prev_def ()->insn ()); // WaW
auto set = dyn_cast<set_info *> (def->prev_def ());
if (set && set->has_nondebug_insn_uses ())
for (auto use : set->reverse_nondebug_insn_uses ())
if (use->insn () != insn && hazard (use->insn ())) // WaR
break;
}
if (!HARD_REGISTER_NUM_P (def->regno ()))
continue;
// Also need to check backwards for call clobbers (WaW).
for (auto call_group : def->ebb ()->call_clobbers ())
{
if (!call_group->clobbers (def->resource ()))
continue;
auto clobber_insn = prev_call_clobbers (*call_group, def->insn (),
ignore_nothing ());
if (clobber_insn)
hazard (clobber_insn);
}
}
return result;
}
// Return the first dataflow hazard after INSN.
//
// If IGNORE is non-NULL, this points to a sub-rtx which we should ignore for
// dataflow purposes. This is needed when considering changing the RTL base of
// an access discovered through a MEM_EXPR base.
//
// N.B. we ignore any defs/uses of memory here as we deal with that separately,
// making use of alias disambiguation.
static insn_info *
first_hazard_after (insn_info *insn, rtx *ignore)
{
insn_info *result = nullptr;
auto hazard = [insn, &result](insn_info *h)
{
gcc_checking_assert (*h > *insn);
if (!result || *h < *result)
result = h;
};
rtx pat = PATTERN (insn->rtl ());
auto ignore_use = [&](use_info *u)
{
if (u->is_mem ())
return true;
return !refers_to_regno_p (u->regno (), u->regno () + 1, pat, ignore);
};
for (auto def : insn->defs ())
{
if (def->is_mem ())
continue;
if (def->next_def ())
hazard (def->next_def ()->insn ()); // WaW
auto set = dyn_cast<set_info *> (def);
if (set && set->has_nondebug_insn_uses ())
hazard (set->first_nondebug_insn_use ()->insn ()); // RaW
if (!HARD_REGISTER_NUM_P (def->regno ()))
continue;
// Also check for call clobbers of this def (WaW).
for (auto call_group : def->ebb ()->call_clobbers ())
{
if (!call_group->clobbers (def->resource ()))
continue;
auto clobber_insn = next_call_clobbers (*call_group, def->insn (),
ignore_nothing ());
if (clobber_insn)
hazard (clobber_insn);
}
}
// Find any subsequent defs of uses in INSN (WaR).
for (auto use : insn->uses ())
{
if (ignore_use (use))
continue;
if (use->def ())
{
auto def = use->def ()->next_def ();
if (def && def->insn () == insn)
def = def->next_def ();
if (def)
hazard (def->insn ());
}
if (!HARD_REGISTER_NUM_P (use->regno ()))
continue;
// Also need to handle call clobbers of our uses (again WaR).
//
// See restrict_movement_for_uses for why we don't need to check
// backwards for call clobbers.
for (auto call_group : use->ebb ()->call_clobbers ())
{
if (!call_group->clobbers (use->resource ()))
continue;
auto clobber_insn = next_call_clobbers (*call_group, use->insn (),
ignore_nothing ());
if (clobber_insn)
hazard (clobber_insn);
}
}
return result;
}
// Return true iff R1 and R2 overlap.
static bool
ranges_overlap_p (const insn_range_info &r1, const insn_range_info &r2)
{
// If either range is empty, then their intersection is empty.
if (!r1 || !r2)
return false;
// When do they not overlap? When one range finishes before the other
// starts, i.e. (*r1.last < *r2.first || *r2.last < *r1.first).
// Inverting this, we get the below.
return *r1.last >= *r2.first && *r2.last >= *r1.first;
}
// Get the range of insns that def feeds.
static insn_range_info get_def_range (def_info *def)
{
insn_info *last = def->next_def ()->insn ()->prev_nondebug_insn ();
return { def->insn (), last };
}
// Given a def (of memory), return the downwards range within which we
// can safely move this def.
static insn_range_info
def_downwards_move_range (def_info *def)
{
auto range = get_def_range (def);
auto set = dyn_cast<set_info *> (def);
if (!set || !set->has_any_uses ())
return range;
auto use = set->first_nondebug_insn_use ();
if (use)
range = move_earlier_than (range, use->insn ());
return range;
}
// Given a def (of memory), return the upwards range within which we can
// safely move this def.
static insn_range_info
def_upwards_move_range (def_info *def)
{
def_info *prev = def->prev_def ();
insn_range_info range { prev->insn (), def->insn () };
auto set = dyn_cast<set_info *> (prev);
if (!set || !set->has_any_uses ())
return range;
auto use = set->last_nondebug_insn_use ();
if (use)
range = move_later_than (range, use->insn ());
return range;
}
// Class that implements a state machine for building the changes needed to form
// a store pair instruction. This allows us to easily build the changes in
// program order, as required by rtl-ssa.
struct store_change_builder
{
enum class state
{
FIRST,
INSERT,
FIXUP_USE,
LAST,
DONE
};
enum class action
{
TOMBSTONE,
CHANGE,
INSERT,
FIXUP_USE
};
struct change
{
action type;
insn_info *insn;
};
bool done () const { return m_state == state::DONE; }
store_change_builder (insn_info *insns[2],
insn_info *repurpose,
insn_info *dest)
: m_state (state::FIRST), m_insns { insns[0], insns[1] },
m_repurpose (repurpose), m_dest (dest), m_use (nullptr) {}
change get_change () const
{
switch (m_state)
{
case state::FIRST:
return {
m_insns[0] == m_repurpose ? action::CHANGE : action::TOMBSTONE,
m_insns[0]
};
case state::LAST:
return {
m_insns[1] == m_repurpose ? action::CHANGE : action::TOMBSTONE,
m_insns[1]
};
case state::INSERT:
return { action::INSERT, m_dest };
case state::FIXUP_USE:
return { action::FIXUP_USE, m_use->insn () };
case state::DONE:
break;
}
gcc_unreachable ();
}
// Transition to the next state.
void advance ()
{
switch (m_state)
{
case state::FIRST:
if (m_repurpose)
m_state = state::LAST;
else
m_state = state::INSERT;
break;
case state::INSERT:
{
def_info *def = memory_access (m_insns[0]->defs ());
while (*def->next_def ()->insn () <= *m_dest)
def = def->next_def ();
// Now we know DEF feeds the insertion point for the new stp.
// Look for any uses of DEF that will consume the new stp.
gcc_assert (*def->insn () <= *m_dest
&& *def->next_def ()->insn () > *m_dest);
auto set = as_a<set_info *> (def);
for (auto use : set->nondebug_insn_uses ())
if (*use->insn () > *m_dest)
{
m_use = use;
break;
}
if (m_use)
m_state = state::FIXUP_USE;
else
m_state = state::LAST;
break;
}
case state::FIXUP_USE:
m_use = m_use->next_nondebug_insn_use ();
if (!m_use)
m_state = state::LAST;
break;
case state::LAST:
m_state = state::DONE;
break;
case state::DONE:
gcc_unreachable ();
}
}
private:
state m_state;
// Original candidate stores.
insn_info *m_insns[2];
// If non-null, this is a candidate insn to change into an stp. Otherwise we
// are deleting both original insns and inserting a new insn for the stp.
insn_info *m_repurpose;
// Destionation of the stp, it will be placed immediately after m_dest.
insn_info *m_dest;
// Current nondebug use that needs updating due to stp insertion.
use_info *m_use;
};
// Given candidate store insns FIRST and SECOND, see if we can re-purpose one
// of them (together with its def of memory) for the stp insn. If so, return
// that insn. Otherwise, return null.
static insn_info *
try_repurpose_store (insn_info *first,
insn_info *second,
const insn_range_info &move_range)
{
def_info * const defs[2] = {
memory_access (first->defs ()),
memory_access (second->defs ())
};
if (move_range.includes (first)
|| ranges_overlap_p (move_range, def_downwards_move_range (defs[0])))
return first;
if (move_range.includes (second)
|| ranges_overlap_p (move_range, def_upwards_move_range (defs[1])))
return second;
return nullptr;
}
// Generate the RTL pattern for a "tombstone"; used temporarily during this pass
// to replace stores that are marked for deletion where we can't immediately
// delete the store (since there are uses of mem hanging off the store).
//
// These are deleted at the end of the pass and uses re-parented appropriately
// at this point.
static rtx
gen_tombstone (void)
{
return gen_rtx_CLOBBER (VOIDmode,
gen_rtx_MEM (BLKmode, gen_rtx_SCRATCH (Pmode)));
}
// Go through the reg notes rooted at NOTE, dropping those that we should drop,
// and preserving those that we want to keep by prepending them to (and
// returning) RESULT. EH_REGION is used to make sure we have at most one
// REG_EH_REGION note in the resulting list. FR_EXPR is used to return any
// REG_FRAME_RELATED_EXPR note we find, as these can need special handling in
// combine_reg_notes.
static rtx
filter_notes (rtx note, rtx result, bool *eh_region, rtx *fr_expr)
{
for (; note; note = XEXP (note, 1))
{
switch (REG_NOTE_KIND (note))
{
case REG_DEAD:
// REG_DEAD notes aren't required to be maintained.
case REG_EQUAL:
case REG_EQUIV:
case REG_UNUSED:
case REG_NOALIAS:
// These can all be dropped. For REG_EQU{AL,IV} they cannot apply to
// non-single_set insns, and REG_UNUSED is re-computed by RTl-SSA, see
// rtl-ssa/changes.cc:update_notes.
//
// Similarly, REG_NOALIAS cannot apply to a parallel.
case REG_INC:
// When we form the pair insn, the reg update is implemented
// as just another SET in the parallel, so isn't really an
// auto-increment in the RTL sense, hence we drop the note.
break;
case REG_EH_REGION:
gcc_assert (!*eh_region);
*eh_region = true;
result = alloc_reg_note (REG_EH_REGION, XEXP (note, 0), result);
break;
case REG_CFA_DEF_CFA:
case REG_CFA_OFFSET:
case REG_CFA_RESTORE:
result = alloc_reg_note (REG_NOTE_KIND (note),
copy_rtx (XEXP (note, 0)),
result);
break;
case REG_FRAME_RELATED_EXPR:
gcc_assert (!*fr_expr);
*fr_expr = copy_rtx (XEXP (note, 0));
break;
default:
// Unexpected REG_NOTE kind.
gcc_unreachable ();
}
}
return result;
}
// Return the notes that should be attached to a combination of I1 and I2, where
// *I1 < *I2. LOAD_P is true for loads.
static rtx
combine_reg_notes (insn_info *i1, insn_info *i2, bool load_p)
{
// Temporary storage for REG_FRAME_RELATED_EXPR notes.
rtx fr_expr[2] = {};
bool found_eh_region = false;
rtx result = NULL_RTX;
result = filter_notes (REG_NOTES (i2->rtl ()), result,
&found_eh_region, fr_expr + 1);
result = filter_notes (REG_NOTES (i1->rtl ()), result,
&found_eh_region, fr_expr);
if (!load_p)
{
// Simple frame-related sp-relative saves don't need CFI notes, but when
// we combine them into an stp we will need a CFI note as dwarf2cfi can't
// interpret the unspec pair representation directly.
if (RTX_FRAME_RELATED_P (i1->rtl ()) && !fr_expr[0])
fr_expr[0] = copy_rtx (PATTERN (i1->rtl ()));
if (RTX_FRAME_RELATED_P (i2->rtl ()) && !fr_expr[1])
fr_expr[1] = copy_rtx (PATTERN (i2->rtl ()));
}
rtx fr_pat = NULL_RTX;
if (fr_expr[0] && fr_expr[1])
{
// Combining two frame-related insns, need to construct
// a REG_FRAME_RELATED_EXPR note which represents the combined
// operation.
RTX_FRAME_RELATED_P (fr_expr[1]) = 1;
fr_pat = gen_rtx_PARALLEL (VOIDmode,
gen_rtvec (2, fr_expr[0], fr_expr[1]));
}
else
fr_pat = fr_expr[0] ? fr_expr[0] : fr_expr[1];
if (fr_pat)
result = alloc_reg_note (REG_FRAME_RELATED_EXPR,
fr_pat, result);
return result;
}
// Given two memory accesses in PATS, at least one of which is of a
// writeback form, extract two non-writeback memory accesses addressed
// relative to the initial value of the base register, and output these
// in PATS. Return an rtx that represents the overall change to the
// base register.
static rtx
extract_writebacks (bool load_p, rtx pats[2], int changed)
{
rtx base_reg = NULL_RTX;
poly_int64 current_offset = 0;
poly_int64 offsets[2];
for (int i = 0; i < 2; i++)
{
rtx mem = XEXP (pats[i], load_p);
rtx reg = XEXP (pats[i], !load_p);
rtx addr = XEXP (mem, 0);
const bool autoinc_p = GET_RTX_CLASS (GET_CODE (addr)) == RTX_AUTOINC;
poly_int64 offset;
rtx this_base = pair_mem_strip_offset (mem, &offset);
gcc_assert (REG_P (this_base));
if (base_reg)
gcc_assert (rtx_equal_p (base_reg, this_base));
else
base_reg = this_base;
// If we changed base for the current insn, then we already
// derived the correct mem for this insn from the effective
// address of the other access.
if (i == changed)
{
gcc_checking_assert (!autoinc_p);
offsets[i] = offset;
continue;
}
if (autoinc_p && any_pre_modify_p (addr))
current_offset += offset;
poly_int64 this_off = current_offset;
if (!autoinc_p)
this_off += offset;
offsets[i] = this_off;
rtx new_mem = change_address (mem, GET_MODE (mem),
plus_constant (GET_MODE (base_reg),
base_reg, this_off));
pats[i] = load_p
? gen_rtx_SET (reg, new_mem)
: gen_rtx_SET (new_mem, reg);
if (autoinc_p && any_post_modify_p (addr))
current_offset += offset;
}
if (known_eq (current_offset, 0))
return NULL_RTX;
return gen_rtx_SET (base_reg, plus_constant (GET_MODE (base_reg),
base_reg, current_offset));
}
// INSNS contains either {nullptr, pair insn} (when promoting an existing
// non-writeback pair) or contains the candidate insns used to form the pair
// (when fusing a new pair).
//
// PAIR_RANGE specifies where we want to form the final pair.
// INITIAL_OFFSET gives the current base offset for the pair.
// Bit I of INITIAL_WRITEBACK is set if INSNS[I] initially had writeback.
// ACCESS_SIZE gives the access size for a single arm of the pair.
// BASE_DEF gives the initial def of the base register consumed by the pair.
//
// Given the above, this function looks for a trailing destructive update of the
// base register. If there is one, we choose the first such update after
// PAIR_DST that is still in the same BB as our pair. We return the new def in
// *ADD_DEF and the resulting writeback effect in *WRITEBACK_EFFECT.
insn_info *
pair_fusion::find_trailing_add (insn_info *insns[2],
const insn_range_info &pair_range,
int initial_writeback,
rtx *writeback_effect,
def_info **add_def,
def_info *base_def,
poly_int64 initial_offset,
unsigned access_size)
{
// Punt on frame-related insns, it is better to be conservative and
// not try to form writeback pairs here, and means we don't have to
// worry about the writeback case in forming REG_FRAME_RELATED_EXPR
// notes (see combine_reg_notes).
if ((insns[0] && RTX_FRAME_RELATED_P (insns[0]->rtl ()))
|| RTX_FRAME_RELATED_P (insns[1]->rtl ()))
return nullptr;
insn_info *pair_dst = pair_range.singleton ();
gcc_assert (pair_dst);
def_info *def = base_def->next_def ();
// In the case that either of the initial pair insns had writeback,
// then there will be intervening defs of the base register.
// Skip over these.
for (int i = 0; i < 2; i++)
if (initial_writeback & (1 << i))
{
gcc_assert (def->insn () == insns[i]);
def = def->next_def ();
}
if (!def || def->bb () != pair_dst->bb ())
return nullptr;
// DEF should now be the first def of the base register after PAIR_DST.
insn_info *cand = def->insn ();
gcc_assert (*cand > *pair_dst);
const auto base_regno = base_def->regno ();
// If CAND doesn't also use our base register,
// it can't destructively update it.
if (!find_access (cand->uses (), base_regno))
return nullptr;
auto rti = cand->rtl ();
if (!INSN_P (rti))
return nullptr;
auto pat = PATTERN (rti);
if (GET_CODE (pat) != SET)
return nullptr;
auto dest = XEXP (pat, 0);
if (!REG_P (dest) || REGNO (dest) != base_regno)
return nullptr;
poly_int64 offset;
rtx rhs_base = strip_offset (XEXP (pat, 1), &offset);
if (!REG_P (rhs_base)
|| REGNO (rhs_base) != base_regno
|| !offset.is_constant ())
return nullptr;
// If the initial base offset is zero, we can handle any add offset
// (post-inc). Otherwise, we require the offsets to match (pre-inc).
if (!known_eq (initial_offset, 0) && !known_eq (offset, initial_offset))
return nullptr;
auto off_hwi = offset.to_constant ();
if (off_hwi % access_size != 0)
return nullptr;
off_hwi /= access_size;
if (!pair_mem_in_range_p (off_hwi))
return nullptr;
auto dump_prefix = [&]()
{
if (!insns[0])
fprintf (dump_file, "existing pair i%d: ", insns[1]->uid ());
else
fprintf (dump_file, " (%d,%d)",
insns[0]->uid (), insns[1]->uid ());
};
insn_info *hazard = latest_hazard_before (cand, nullptr, insns[1], false);
if (!hazard || *hazard <= *pair_dst)
{
if (dump_file)
{
dump_prefix ();
fprintf (dump_file,
"folding in trailing add (%d) to use writeback form\n",
cand->uid ());
}
*add_def = def;
*writeback_effect = copy_rtx (pat);
return cand;
}
if (dump_file)
{
dump_prefix ();
fprintf (dump_file,
"can't fold in trailing add (%d), hazard = %d\n",
cand->uid (), hazard->uid ());
}
return nullptr;
}
// We just emitted a tombstone with uid UID, track it in a bitmap for
// this BB so we can easily identify it later when cleaning up tombstones.
void
pair_fusion_bb_info::track_tombstone (int uid)
{
if (!m_emitted_tombstone)
{
// Lazily initialize the bitmap for tracking tombstone insns.
bitmap_obstack_initialize (&m_bitmap_obstack);
bitmap_initialize (&m_tombstone_bitmap, &m_bitmap_obstack);
m_emitted_tombstone = true;
}
if (!bitmap_set_bit (&m_tombstone_bitmap, uid))
gcc_unreachable (); // Bit should have changed.
}
// Reset the debug insn containing USE (the debug insn has been
// optimized away).
static void
reset_debug_use (use_info *use)
{
auto use_insn = use->insn ();
auto use_rtl = use_insn->rtl ();
insn_change change (use_insn);
change.new_uses = {};
INSN_VAR_LOCATION_LOC (use_rtl) = gen_rtx_UNKNOWN_VAR_LOC ();
crtl->ssa->change_insn (change);
}
// USE is a debug use that needs updating because DEF (a def of the same
// register) is being re-ordered over it. If BASE is non-null, then DEF
// is an update of the register BASE by a constant, given by WB_OFFSET,
// and we can preserve debug info by accounting for the change in side
// effects.
static void
fixup_debug_use (obstack_watermark &attempt,
use_info *use,
def_info *def,
rtx base,
poly_int64 wb_offset)
{
auto use_insn = use->insn ();
if (base)
{
auto use_rtl = use_insn->rtl ();
insn_change change (use_insn);
gcc_checking_assert (REG_P (base) && use->regno () == REGNO (base));
change.new_uses = check_remove_regno_access (attempt,
change.new_uses,
use->regno ());
// The effect of the writeback is to add WB_OFFSET to BASE. If
// we're re-ordering DEF below USE, then we update USE by adding
// WB_OFFSET to it. Otherwise, if we're re-ordering DEF above
// USE, we update USE by undoing the effect of the writeback
// (subtracting WB_OFFSET).
use_info *new_use;
if (*def->insn () > *use_insn)
{
// We now need USE_INSN to consume DEF. Create a new use of DEF.
//
// N.B. this means until we call change_insns for the main change
// group we will temporarily have a debug use consuming a def that
// comes after it, but RTL-SSA doesn't currently support updating
// debug insns as part of the main change group (together with
// nondebug changes), so we will have to live with this update
// leaving the IR being temporarily inconsistent. It seems to
// work out OK once the main change group is applied.
wb_offset *= -1;
new_use = crtl->ssa->create_use (attempt,
use_insn,
as_a<set_info *> (def));
}
else
new_use = find_access (def->insn ()->uses (), use->regno ());
change.new_uses = insert_access (attempt, new_use, change.new_uses);
if (dump_file)
{
const char *dir = (*def->insn () < *use_insn) ? "down" : "up";
pretty_printer pp;
pp_string (&pp, "[");
pp_access (&pp, use, 0);
pp_string (&pp, "]");
pp_string (&pp, " due to wb def ");
pp_string (&pp, "[");
pp_access (&pp, def, 0);
pp_string (&pp, "]");
fprintf (dump_file,
" i%d: fix up debug use %s re-ordered %s, "
"sub r%u -> r%u + ",
use_insn->uid (), pp_formatted_text (&pp),
dir, REGNO (base), REGNO (base));
print_dec (wb_offset, dump_file);
fprintf (dump_file, "\n");
}
insn_propagation prop (use_rtl, base,
plus_constant (GET_MODE (base), base, wb_offset));
if (prop.apply_to_pattern (&INSN_VAR_LOCATION_LOC (use_rtl)))
crtl->ssa->change_insn (change);
else
{
if (dump_file)
fprintf (dump_file, " i%d: RTL substitution failed (%s)"
", resetting debug insn", use_insn->uid (),
prop.failure_reason);
reset_debug_use (use);
}
}
else
{
if (dump_file)
{
pretty_printer pp;
pp_string (&pp, "[");
pp_access (&pp, use, 0);
pp_string (&pp, "] due to re-ordered load def [");
pp_access (&pp, def, 0);
pp_string (&pp, "]");
fprintf (dump_file, " i%d: resetting debug use %s\n",
use_insn->uid (), pp_formatted_text (&pp));
}
reset_debug_use (use);
}
}
// Update debug uses when folding in a trailing add insn to form a
// writeback pair.
//
// ATTEMPT is used to allocate RTL-SSA temporaries for the changes,
// the final pair is placed immediately after PAIR_DST, TRAILING_ADD
// is a trailing add insn which is being folded into the pair to make it
// use writeback addressing, and WRITEBACK_EFFECT is the pattern for
// TRAILING_ADD.
static void
fixup_debug_uses_trailing_add (obstack_watermark &attempt,
insn_info *pair_dst,
insn_info *trailing_add,
rtx writeback_effect)
{
rtx base = SET_DEST (writeback_effect);
poly_int64 wb_offset;
rtx base2 = strip_offset (SET_SRC (writeback_effect), &wb_offset);
gcc_checking_assert (rtx_equal_p (base, base2));
auto defs = trailing_add->defs ();
gcc_checking_assert (defs.size () == 1);
def_info *def = defs[0];
if (auto set = safe_dyn_cast<set_info *> (def->prev_def ()))
for (auto use : iterate_safely (set->debug_insn_uses ()))
if (*use->insn () > *pair_dst)
// DEF is getting re-ordered above USE, fix up USE accordingly.
fixup_debug_use (attempt, use, def, base, wb_offset);
}
// Called from fuse_pair, fixes up any debug uses that will be affected
// by the changes.
//
// ATTEMPT is the obstack watermark used to allocate RTL-SSA temporaries for
// the changes, INSNS gives the candidate insns: at this point the use/def
// information should still be as on entry to fuse_pair, but the patterns may
// have changed, hence we pass ORIG_RTL which contains the original patterns
// for the candidate insns.
//
// The final pair will be placed immediately after PAIR_DST, LOAD_P is true if
// it is a load pair, bit I of WRITEBACK is set if INSNS[I] originally had
// writeback, and WRITEBACK_EFFECT is an rtx describing the overall update to
// the base register in the final pair (if any). BASE_REGNO gives the register
// number of the base register used in the final pair.
static void
fixup_debug_uses (obstack_watermark &attempt,
insn_info *insns[2],
rtx orig_rtl[2],
insn_info *pair_dst,
insn_info *trailing_add,
bool load_p,
int writeback,
rtx writeback_effect,
unsigned base_regno)
{
// USE is a debug use that needs updating because DEF (a def of the
// resource) is being re-ordered over it. If WRITEBACK_PAT is non-NULL,
// then it gives the original RTL pattern for DEF's insn, and DEF is a
// writeback update of the base register.
//
// This simply unpacks WRITEBACK_PAT if needed and calls fixup_debug_use.
auto update_debug_use = [&](use_info *use, def_info *def,
rtx writeback_pat)
{
poly_int64 offset = 0;
rtx base = NULL_RTX;
if (writeback_pat)
{
rtx mem = XEXP (writeback_pat, load_p);
gcc_checking_assert (GET_RTX_CLASS (GET_CODE (XEXP (mem, 0)))
== RTX_AUTOINC);
base = pair_mem_strip_offset (mem, &offset);
gcc_checking_assert (REG_P (base) && REGNO (base) == base_regno);
}
fixup_debug_use (attempt, use, def, base, offset);
};
// Reset any debug uses of mem over which we re-ordered a store.
//
// It would be nice to try and preserve debug info here, but it seems that
// would require doing alias analysis to see if the store aliases with the
// debug use, which seems a little extravagant just to preserve debug info.
if (!load_p)
{
auto def = memory_access (insns[0]->defs ());
auto last_def = memory_access (insns[1]->defs ());
for (; def != last_def; def = def->next_def ())
{
auto set = as_a<set_info *> (def);
for (auto use : iterate_safely (set->debug_insn_uses ()))
{
if (dump_file)
fprintf (dump_file, " i%d: resetting debug use of mem\n",
use->insn ()->uid ());
reset_debug_use (use);
}
}
}
// Now let's take care of register uses, starting with debug uses
// attached to defs from our first insn.
for (auto def : insns[0]->defs ())
{
auto set = dyn_cast<set_info *> (def);
if (!set || set->is_mem () || !set->first_debug_insn_use ())
continue;
def_info *defs[2] = {
def,
find_access (insns[1]->defs (), def->regno ())
};
rtx writeback_pats[2] = {};
if (def->regno () == base_regno)
for (int i = 0; i < 2; i++)
if (writeback & (1 << i))
{
gcc_checking_assert (defs[i]);
writeback_pats[i] = orig_rtl[i];
}
// Now that we've characterized the defs involved, go through the
// debug uses and determine how to update them (if needed).
for (auto use : iterate_safely (set->debug_insn_uses ()))
{
if (*pair_dst < *use->insn () && defs[1])
// We're re-ordering defs[1] above a previous use of the
// same resource.
update_debug_use (use, defs[1], writeback_pats[1]);
else if (*pair_dst >= *use->insn ())
// We're re-ordering defs[0] below its use.
update_debug_use (use, defs[0], writeback_pats[0]);
}
}
// Now let's look at registers which are def'd by the second insn
// but not by the first insn, there may still be debug uses of a
// previous def which can be affected by moving the second insn up.
for (auto def : insns[1]->defs ())
{
// This should be M log N where N is the number of defs in
// insns[0] and M is the number of defs in insns[1].
if (def->is_mem () || find_access (insns[0]->defs (), def->regno ()))
continue;
auto prev_set = safe_dyn_cast<set_info *> (def->prev_def ());
if (!prev_set)
continue;
rtx writeback_pat = NULL_RTX;
if (def->regno () == base_regno && (writeback & 2))
writeback_pat = orig_rtl[1];
// We have a def in insns[1] which isn't def'd by the first insn.
// Look to the previous def and see if it has any debug uses.
for (auto use : iterate_safely (prev_set->debug_insn_uses ()))
if (*pair_dst < *use->insn ())
// We're ordering DEF above a previous use of the same register.
update_debug_use (use, def, writeback_pat);
}
if ((writeback & 2) && !writeback_effect)
{
// If the second insn initially had writeback but the final
// pair does not, then there may be trailing debug uses of the
// second writeback def which need re-parenting: do that.
auto def = find_access (insns[1]->defs (), base_regno);
gcc_assert (def);
auto set = as_a<set_info *> (def);
for (auto use : iterate_safely (set->debug_insn_uses ()))
{
insn_change change (use->insn ());
change.new_uses = check_remove_regno_access (attempt,
change.new_uses,
base_regno);
auto new_use = find_access (insns[0]->uses (), base_regno);
// N.B. insns must have already shared a common base due to writeback.
gcc_assert (new_use);
if (dump_file)
fprintf (dump_file,
" i%d: cancelling wb, re-parenting trailing debug use\n",
use->insn ()->uid ());
change.new_uses = insert_access (attempt, new_use, change.new_uses);
crtl->ssa->change_insn (change);
}
}
else if (trailing_add)
fixup_debug_uses_trailing_add (attempt, pair_dst, trailing_add,
writeback_effect);
}
// Try and actually fuse the pair given by insns I1 and I2.
//
// Here we've done enough analysis to know this is safe, we only
// reject the pair at this stage if either the tuning policy says to,
// or recog fails on the final pair insn.
//
// LOAD_P is true for loads, ACCESS_SIZE gives the access size of each
// candidate insn. Bit i of WRITEBACK is set if the ith insn (in program
// order) uses writeback.
//
// BASE gives the chosen base candidate for the pair and MOVE_RANGE is
// a singleton range which says where to place the pair.
bool
pair_fusion_bb_info::fuse_pair (bool load_p,
unsigned access_size,
int writeback,
insn_info *i1, insn_info *i2,
base_cand &base,
const insn_range_info &move_range)
{
auto attempt = crtl->ssa->new_change_attempt ();
auto make_change = [&attempt](insn_info *insn)
{
return crtl->ssa->change_alloc<insn_change> (attempt, insn);
};
auto make_delete = [&attempt](insn_info *insn)
{
return crtl->ssa->change_alloc<insn_change> (attempt,
insn,
insn_change::DELETE);
};
insn_info *first = (*i1 < *i2) ? i1 : i2;
insn_info *second = (first == i1) ? i2 : i1;
insn_info *pair_dst = move_range.singleton ();
gcc_assert (pair_dst);
insn_info *insns[2] = { first, second };
auto_vec<insn_change *> changes;
auto_vec<int, 3> tombstone_uids;
rtx pats[2] = {
PATTERN (first->rtl ()),
PATTERN (second->rtl ())
};
// Make copies of the patterns as we might need to refer to the original RTL
// later, for example when updating debug uses (which is after we've updated
// one or both of the patterns in the candidate insns).
rtx orig_rtl[2];
for (int i = 0; i < 2; i++)
orig_rtl[i] = copy_rtx (pats[i]);
use_array input_uses[2] = { first->uses (), second->uses () };
def_array input_defs[2] = { first->defs (), second->defs () };
int changed_insn = -1;
if (base.from_insn != -1)
{
// If we're not already using a shared base, we need
// to re-write one of the accesses to use the base from
// the other insn.
gcc_checking_assert (base.from_insn == 0 || base.from_insn == 1);
changed_insn = !base.from_insn;
rtx base_pat = pats[base.from_insn];
rtx change_pat = pats[changed_insn];
rtx base_mem = XEXP (base_pat, load_p);
rtx change_mem = XEXP (change_pat, load_p);
const bool lower_base_p = (insns[base.from_insn] == i1);
HOST_WIDE_INT adjust_amt = access_size;
if (!lower_base_p)
adjust_amt *= -1;
rtx change_reg = XEXP (change_pat, !load_p);
rtx effective_base = drop_writeback (base_mem);
rtx adjusted_addr = plus_constant (Pmode,
XEXP (effective_base, 0),
adjust_amt);
rtx new_mem = replace_equiv_address_nv (change_mem, adjusted_addr);
rtx new_set = load_p
? gen_rtx_SET (change_reg, new_mem)
: gen_rtx_SET (new_mem, change_reg);
pats[changed_insn] = new_set;
auto keep_use = [&](use_info *u)
{
return refers_to_regno_p (u->regno (), u->regno () + 1,
change_pat, &XEXP (change_pat, load_p));
};
// Drop any uses that only occur in the old address.
input_uses[changed_insn] = filter_accesses (attempt,
input_uses[changed_insn],
keep_use);
}
rtx writeback_effect = NULL_RTX;
if (writeback)
writeback_effect = extract_writebacks (load_p, pats, changed_insn);
const auto base_regno = base.def->regno ();
if (base.from_insn == -1 && (writeback & 1))
{
// If the first of the candidate insns had a writeback form, we'll need to
// drop the use of the updated base register from the second insn's uses.
//
// N.B. we needn't worry about the base register occurring as a store
// operand, as we checked that there was no non-address true dependence
// between the insns in try_fuse_pair.
gcc_checking_assert (find_access (input_uses[1], base_regno));
input_uses[1] = check_remove_regno_access (attempt,
input_uses[1],
base_regno);
}
// Go through and drop uses that only occur in register notes,
// as we won't be preserving those.
for (int i = 0; i < 2; i++)
{
auto rti = insns[i]->rtl ();
if (!REG_NOTES (rti))
continue;
input_uses[i] = remove_note_accesses (attempt, input_uses[i]);
}
// Get the uses that the pair instruction would have, and punt if
// the unpaired instructions use different definitions of the same
// register. That would normally be caught as a side-effect of
// hazard detection below, but this check also deals with cases
// in which one use is undefined and the other isn't.
auto new_uses = merge_access_arrays (attempt,
drop_memory_access (input_uses[0]),
drop_memory_access (input_uses[1]));
if (!new_uses.is_valid ())
{
if (dump_file)
fprintf (dump_file,
" rejecting pair: i%d and i%d use different definiitions of"
" the same register\n",
insns[0]->uid (), insns[1]->uid ());
return false;
}
// Edge case: if the first insn is a writeback load and the
// second insn is a non-writeback load which transfers into the base
// register, then we should drop the writeback altogether as the
// update of the base register from the second load should prevail.
//
// For example:
// ldr x2, [x1], #8
// ldr x1, [x1]
// -->
// ldp x2, x1, [x1]
if (writeback == 1
&& load_p
&& find_access (input_defs[1], base_regno))
{
if (dump_file)
fprintf (dump_file,
" load pair: i%d has wb but subsequent i%d has non-wb "
"update of base (r%d), dropping wb\n",
insns[0]->uid (), insns[1]->uid (), base_regno);
gcc_assert (writeback_effect);
writeback_effect = NULL_RTX;
}
// So far the patterns have been in instruction order,
// now we want them in offset order.
if (i1 != first)
std::swap (pats[0], pats[1]);
poly_int64 offsets[2];
for (int i = 0; i < 2; i++)
{
rtx mem = XEXP (pats[i], load_p);
gcc_checking_assert (MEM_P (mem));
rtx base = strip_offset (XEXP (mem, 0), offsets + i);
gcc_checking_assert (REG_P (base));
gcc_checking_assert (base_regno == REGNO (base));
}
// If either of the original insns had writeback, but the resulting pair insn
// does not (can happen e.g. in the load pair edge case above, or if the
// writeback effects cancel out), then drop the def (s) of the base register
// as appropriate.
//
// Also drop the first def in the case that both of the original insns had
// writeback. The second def could well have uses, but the first def should
// only be used by the second insn (and we dropped that use above).
for (int i = 0; i < 2; i++)
if ((!writeback_effect && (writeback & (1 << i)))
|| (i == 0 && writeback == 3))
input_defs[i] = check_remove_regno_access (attempt,
input_defs[i],
base_regno);
// If we don't currently have a writeback pair, and we don't have
// a load that clobbers the base register, look for a trailing destructive
// update of the base register and try and fold it in to make this into a
// writeback pair.
insn_info *trailing_add = nullptr;
if (m_pass->should_handle_writeback (writeback_type::ALL)
&& !writeback_effect
&& (!load_p || (!refers_to_regno_p (base_regno, base_regno + 1,
XEXP (pats[0], 0), nullptr)
&& !refers_to_regno_p (base_regno, base_regno + 1,
XEXP (pats[1], 0), nullptr))))
{
def_info *add_def;
trailing_add = m_pass->find_trailing_add (insns, move_range, writeback,
&writeback_effect,
&add_def, base.def, offsets[0],
access_size);
if (trailing_add)
{
// The def of the base register from the trailing add should prevail.
input_defs[0] = insert_access (attempt, add_def, input_defs[0]);
gcc_assert (input_defs[0].is_valid ());
}
}
// Now that we know what base mem we're going to use, check if it's OK
// with the pair mem policy.
rtx first_mem = XEXP (pats[0], load_p);
if (!m_pass->pair_mem_ok_with_policy (first_mem, load_p))
{
if (dump_file)
fprintf (dump_file,
"punting on pair (%d,%d), pair mem policy says no\n",
i1->uid (), i2->uid ());
return false;
}
rtx reg_notes = combine_reg_notes (first, second, load_p);
rtx pair_pat = m_pass->gen_pair (pats, writeback_effect, load_p);
insn_change *pair_change = nullptr;
auto set_pair_pat = [pair_pat,reg_notes](insn_change *change) {
rtx_insn *rti = change->insn ()->rtl ();
validate_unshare_change (rti, &PATTERN (rti), pair_pat, true);
validate_change (rti, ®_NOTES (rti), reg_notes, true);
};
// Turn CHANGE into a memory definition tombstone.
auto make_tombstone = [&](insn_change *change)
{
tombstone_uids.quick_push (change->insn ()->uid ());
rtx_insn *rti = change->insn ()->rtl ();
validate_change (rti, &PATTERN (rti), gen_tombstone (), true);
validate_change (rti, ®_NOTES (rti), NULL_RTX, true);
change->new_uses = use_array ();
};
if (load_p)
{
changes.safe_push (make_delete (first));
pair_change = make_change (second);
changes.safe_push (pair_change);
pair_change->move_range = move_range;
pair_change->new_defs = merge_access_arrays (attempt,
input_defs[0],
input_defs[1]);
gcc_assert (pair_change->new_defs.is_valid ());
pair_change->new_uses = new_uses;
set_pair_pat (pair_change);
}
else
{
using Action = store_change_builder::action;
insn_info *store_to_change = try_repurpose_store (first, second,
move_range);
store_change_builder builder (insns, store_to_change, pair_dst);
insn_change *change;
set_info *new_set = nullptr;
for (; !builder.done (); builder.advance ())
{
auto action = builder.get_change ();
change = (action.type == Action::INSERT)
? nullptr : make_change (action.insn);
switch (action.type)
{
case Action::CHANGE:
{
set_pair_pat (change);
change->new_uses = new_uses;
auto d1 = drop_memory_access (input_defs[0]);
auto d2 = drop_memory_access (input_defs[1]);
change->new_defs = merge_access_arrays (attempt, d1, d2);
gcc_assert (change->new_defs.is_valid ());
def_info *store_def = memory_access (change->insn ()->defs ());
change->new_defs = insert_access (attempt,
store_def,
change->new_defs);
gcc_assert (change->new_defs.is_valid ());
change->move_range = move_range;
pair_change = change;
break;
}
case Action::TOMBSTONE:
{
make_tombstone (change);
break;
}
case Action::INSERT:
{
if (dump_file)
fprintf (dump_file,
" stp: cannot re-purpose candidate stores\n");
auto new_insn = crtl->ssa->create_insn (attempt, INSN, pair_pat);
change = make_change (new_insn);
change->move_range = move_range;
change->new_uses = new_uses;
gcc_assert (change->new_uses.is_valid ());
auto d1 = drop_memory_access (input_defs[0]);
auto d2 = drop_memory_access (input_defs[1]);
change->new_defs = merge_access_arrays (attempt, d1, d2);
gcc_assert (change->new_defs.is_valid ());
new_set = crtl->ssa->create_set (attempt, new_insn, memory);
change->new_defs = insert_access (attempt, new_set,
change->new_defs);
gcc_assert (change->new_defs.is_valid ());
pair_change = change;
break;
}
case Action::FIXUP_USE:
{
// This use now needs to consume memory from our stp.
if (dump_file)
fprintf (dump_file,
" stp: changing i%d to use mem from new stp "
"(after i%d)\n",
action.insn->uid (), pair_dst->uid ());
change->new_uses = drop_memory_access (change->new_uses);
gcc_assert (new_set);
auto new_use = crtl->ssa->create_use (attempt, action.insn,
new_set);
change->new_uses = insert_access (attempt, new_use,
change->new_uses);
break;
}
}
changes.safe_push (change);
}
}
if (trailing_add)
{
if (auto *mem_def = memory_access (trailing_add->defs()))
{
auto *change = make_change (trailing_add);
change->new_defs = insert_access (attempt, mem_def, def_array ());
make_tombstone (change);
changes.safe_push (change);
}
else
changes.safe_push (make_delete (trailing_add));
}
else if ((writeback & 2) && !writeback_effect)
{
// The second insn initially had writeback but now the pair does not,
// need to update any nondebug uses of the base register def in the
// second insn. We'll take care of debug uses later.
auto def = find_access (insns[1]->defs (), base_regno);
gcc_assert (def);
auto set = dyn_cast<set_info *> (def);
if (set && set->has_nondebug_uses ())
{
auto orig_use = find_access (insns[0]->uses (), base_regno);
for (auto use : set->nondebug_insn_uses ())
{
auto change = make_change (use->insn ());
change->new_uses = check_remove_regno_access (attempt,
change->new_uses,
base_regno);
change->new_uses = insert_access (attempt,
orig_use,
change->new_uses);
changes.safe_push (change);
}
}
}
auto ignore = ignore_changing_insns (changes);
for (unsigned i = 0; i < changes.length (); i++)
gcc_assert (changes[i]->move_range.singleton ()
&& rtl_ssa::restrict_movement (*changes[i], ignore));
// Check the pair pattern is recog'd.
if (!rtl_ssa::recog (attempt, *pair_change, ignore))
{
if (dump_file)
fprintf (dump_file, " failed to form pair, recog failed\n");
// Free any reg notes we allocated.
while (reg_notes)
{
rtx next = XEXP (reg_notes, 1);
free_EXPR_LIST_node (reg_notes);
reg_notes = next;
}
cancel_changes (0);
return false;
}
gcc_assert (crtl->ssa->verify_insn_changes (changes));
// Fix up any debug uses that will be affected by the changes.
if (MAY_HAVE_DEBUG_INSNS)
fixup_debug_uses (attempt, insns, orig_rtl, pair_dst, trailing_add,
load_p, writeback, writeback_effect, base_regno);
confirm_change_group ();
crtl->ssa->change_insns (changes);
for (auto uid : tombstone_uids)
track_tombstone (uid);
return true;
}
// Return true if STORE_INSN may modify mem rtx MEM. Make sure we keep
// within our BUDGET for alias analysis.
static bool
store_modifies_mem_p (rtx mem, insn_info *store_insn, int &budget)
{
if (!budget)
{
if (dump_file)
{
fprintf (dump_file,
"exceeded budget, assuming store %d aliases with mem ",
store_insn->uid ());
print_simple_rtl (dump_file, mem);
fprintf (dump_file, "\n");
}
return true;
}
budget--;
return memory_modified_in_insn_p (mem, store_insn->rtl ());
}
// Return true if LOAD may be modified by STORE. Make sure we keep
// within our BUDGET for alias analysis.
static bool
load_modified_by_store_p (insn_info *load,
insn_info *store,
int &budget)
{
gcc_checking_assert (budget >= 0);
if (!budget)
{
if (dump_file)
{
fprintf (dump_file,
"exceeded budget, assuming load %d aliases with store %d\n",
load->uid (), store->uid ());
}
return true;
}
// It isn't safe to re-order stores over calls.
if (CALL_P (load->rtl ()))
return true;
budget--;
// Iterate over all MEMs in the load, seeing if any alias with
// our store.
subrtx_var_iterator::array_type array;
rtx pat = PATTERN (load->rtl ());
FOR_EACH_SUBRTX_VAR (iter, array, pat, NONCONST)
if (MEM_P (*iter) && memory_modified_in_insn_p (*iter, store->rtl ()))
return true;
return false;
}
// Implement some common functionality used by both store_walker
// and load_walker.
template<bool reverse>
class def_walker : public alias_walker
{
protected:
using def_iter_t = typename std::conditional<reverse,
reverse_def_iterator, def_iterator>::type;
static use_info *start_use_chain (def_iter_t &def_iter)
{
set_info *set = nullptr;
for (; *def_iter; def_iter++)
{
set = dyn_cast<set_info *> (*def_iter);
if (!set)
continue;
use_info *use = reverse
? set->last_nondebug_insn_use ()
: set->first_nondebug_insn_use ();
if (use)
return use;
}
return nullptr;
}
def_iter_t def_iter;
insn_info *limit;
// Array of register uses from the candidate insn which occur in MEMs.
use_array cand_addr_uses;
def_walker (def_info *def, insn_info *limit, use_array addr_uses) :
def_iter (def), limit (limit), cand_addr_uses (addr_uses) {}
virtual bool iter_valid () const { return *def_iter; }
// Implemented in {load,store}_walker.
virtual bool alias_conflict_p (int &budget) const = 0;
// Return true if the current (walking) INSN () uses a register R inside a
// MEM, where R is also used inside a MEM by the (static) candidate insn, and
// those uses see different definitions of that register. In this case we
// can't rely on RTL alias analysis, and for now we conservatively assume that
// there is an alias conflict. See PR116783.
bool addr_reg_conflict_p () const
{
use_array curr_insn_uses = insn ()->uses ();
auto cand_use_iter = cand_addr_uses.begin ();
auto insn_use_iter = curr_insn_uses.begin ();
while (cand_use_iter != cand_addr_uses.end ()
&& insn_use_iter != curr_insn_uses.end ())
{
auto insn_use = *insn_use_iter;
auto cand_use = *cand_use_iter;
if (insn_use->regno () > cand_use->regno ())
cand_use_iter++;
else if (insn_use->regno () < cand_use->regno ())
insn_use_iter++;
else
{
// As it stands I believe the alias code (memory_modified_in_insn_p)
// doesn't look at insn notes such as REG_EQU{IV,AL}, so it should
// be safe to skip over uses that only occur in notes.
if (insn_use->includes_address_uses ()
&& !insn_use->only_occurs_in_notes ()
&& insn_use->def () != cand_use->def ())
{
if (dump_file)
{
fprintf (dump_file,
"assuming aliasing of cand i%d and i%d:\n"
"-> insns see different defs of common addr reg r%u\n"
"-> ",
cand_use->insn ()->uid (), insn_use->insn ()->uid (),
insn_use->regno ());
// Note that while the following sequence could be made more
// concise by eliding pp_string calls into the pp_printf
// calls, doing so triggers -Wformat-diag.
pretty_printer pp;
pp_string (&pp, "[");
pp_access (&pp, cand_use, 0);
pp_string (&pp, "] in ");
pp_printf (&pp, "i%d", cand_use->insn ()->uid ());
pp_string (&pp, " vs [");
pp_access (&pp, insn_use, 0);
pp_string (&pp, "] in ");
pp_printf (&pp, "i%d", insn_use->insn ()->uid ());
fprintf (dump_file, "%s\n", pp_formatted_text (&pp));
}
return true;
}
cand_use_iter++;
insn_use_iter++;
}
}
return false;
}
public:
insn_info *insn () const override { return (*def_iter)->insn (); }
void advance () override { def_iter++; }
bool valid () const override final
{
if (!iter_valid ())
return false;
if (reverse)
return *(insn ()) > *limit;
else
return *(insn ()) < *limit;
}
bool conflict_p (int &budget) const override final
{
if (addr_reg_conflict_p ())
return true;
return alias_conflict_p (budget);
}
};
// alias_walker that iterates over stores.
template<bool reverse, typename InsnPredicate>
class store_walker : public def_walker<reverse>
{
rtx cand_mem;
InsnPredicate tombstone_p;
public:
store_walker (def_info *mem_def, rtx mem,
use_array addr_uses,
insn_info *limit_insn,
InsnPredicate tombstone_fn) :
def_walker<reverse> (mem_def, limit_insn, addr_uses),
cand_mem (mem), tombstone_p (tombstone_fn) {}
bool alias_conflict_p (int &budget) const override final
{
if (tombstone_p (this->insn ()))
return false;
return store_modifies_mem_p (cand_mem, this->insn (), budget);
}
};
// alias_walker that iterates over loads.
template<bool reverse>
class load_walker : public def_walker<reverse>
{
using Base = def_walker<reverse>;
using use_iter_t = typename std::conditional<reverse,
reverse_use_iterator, nondebug_insn_use_iterator>::type;
use_iter_t use_iter;
insn_info *cand_store;
bool iter_valid () const override final { return *use_iter; }
public:
void advance () override final
{
use_iter++;
if (*use_iter)
return;
this->def_iter++;
use_iter = Base::start_use_chain (this->def_iter);
}
insn_info *insn () const override final
{
return (*use_iter)->insn ();
}
bool alias_conflict_p (int &budget) const override final
{
return load_modified_by_store_p (insn (), cand_store, budget);
}
load_walker (def_info *def, insn_info *store, use_array addr_uses,
insn_info *limit_insn)
: Base (def, limit_insn, addr_uses),
use_iter (Base::start_use_chain (this->def_iter)),
cand_store (store) {}
};
// Process our alias_walkers in a round-robin fashion, proceeding until
// nothing more can be learned from alias analysis.
//
// We try to maintain the invariant that if a walker becomes invalid, we
// set its pointer to null.
void
pair_fusion::do_alias_analysis (insn_info *alias_hazards[4],
alias_walker *walkers[4],
bool load_p)
{
const int n_walkers = 2 + (2 * !load_p);
int budget = pair_mem_alias_check_limit ();
auto next_walker = [walkers,n_walkers](int current) -> int {
for (int j = 1; j <= n_walkers; j++)
{
int idx = (current + j) % n_walkers;
if (walkers[idx])
return idx;
}
return -1;
};
int i = -1;
for (int j = 0; j < n_walkers; j++)
{
alias_hazards[j] = nullptr;
if (!walkers[j])
continue;
if (!walkers[j]->valid ())
walkers[j] = nullptr;
else if (i == -1)
i = j;
}
while (i >= 0)
{
int insn_i = i % 2;
int paired_i = (i & 2) + !insn_i;
int pair_fst = (i & 2);
int pair_snd = (i & 2) + 1;
if (walkers[i]->conflict_p (budget))
{
alias_hazards[i] = walkers[i]->insn ();
// We got an aliasing conflict for this {load,store} walker,
// so we don't need to walk any further.
walkers[i] = nullptr;
// If we have a pair of alias conflicts that prevent
// forming the pair, stop. There's no need to do further
// analysis.
if (alias_hazards[paired_i]
&& (*alias_hazards[pair_fst] <= *alias_hazards[pair_snd]))
return;
if (!load_p)
{
int other_pair_fst = (pair_fst ? 0 : 2);
int other_paired_i = other_pair_fst + !insn_i;
int x_pair_fst = (i == pair_fst) ? i : other_paired_i;
int x_pair_snd = (i == pair_fst) ? other_paired_i : i;
// Similarly, handle the case where we have a {load,store}
// or {store,load} alias hazard pair that prevents forming
// the pair.
if (alias_hazards[other_paired_i]
&& *alias_hazards[x_pair_fst] <= *alias_hazards[x_pair_snd])
return;
}
}
if (walkers[i])
{
walkers[i]->advance ();
if (!walkers[i]->valid ())
walkers[i] = nullptr;
}
i = next_walker (i);
}
}
// Given INSNS (in program order) which are known to be adjacent, look
// to see if either insn has a suitable RTL (register) base that we can
// use to form a pair. Push these to BASE_CANDS if we find any. CAND_MEMs
// gives the relevant mems from the candidate insns, ACCESS_SIZE gives the
// size of a single candidate access, and REVERSED says whether the accesses
// are inverted in offset order.
//
// Returns an integer where bit (1 << i) is set if INSNS[i] uses writeback
// addressing.
int
pair_fusion::get_viable_bases (insn_info *insns[2],
vec<base_cand> &base_cands,
rtx cand_mems[2],
unsigned access_size,
bool reversed)
{
// We discovered this pair through a common base. Need to ensure that
// we have a common base register that is live at both locations.
def_info *base_defs[2] = {};
int writeback = 0;
for (int i = 0; i < 2; i++)
{
const bool is_lower = (i == reversed);
poly_int64 poly_off;
rtx base = pair_mem_strip_offset (cand_mems[i], &poly_off);
if (GET_RTX_CLASS (GET_CODE (XEXP (cand_mems[i], 0))) == RTX_AUTOINC)
writeback |= (1 << i);
if (!REG_P (base) || !poly_off.is_constant ())
continue;
// Punt on accesses relative to eliminable regs. See the comment in
// pair_fusion_bb_info::track_access for a detailed explanation of this.
if (!reload_completed
&& (REGNO (base) == FRAME_POINTER_REGNUM
|| REGNO (base) == ARG_POINTER_REGNUM))
continue;
HOST_WIDE_INT base_off = poly_off.to_constant ();
// It should be unlikely that we ever punt here, since MEM_EXPR offset
// alignment should be a good proxy for register offset alignment.
if (base_off % access_size != 0)
{
if (dump_file)
fprintf (dump_file,
"base not viable, offset misaligned (insn %d)\n",
insns[i]->uid ());
continue;
}
base_off /= access_size;
if (!is_lower)
base_off--;
if (!pair_mem_in_range_p (base_off))
continue;
use_info *use = find_access (insns[i]->uses (), REGNO (base));
gcc_assert (use);
base_defs[i] = use->def ();
}
if (!base_defs[0] && !base_defs[1])
{
if (dump_file)
fprintf (dump_file, "no viable base register for pair (%d,%d)\n",
insns[0]->uid (), insns[1]->uid ());
return writeback;
}
for (int i = 0; i < 2; i++)
if ((writeback & (1 << i)) && !base_defs[i])
{
if (dump_file)
fprintf (dump_file, "insn %d has writeback but base isn't viable\n",
insns[i]->uid ());
return writeback;
}
if (writeback == 3
&& base_defs[0]->regno () != base_defs[1]->regno ())
{
if (dump_file)
fprintf (dump_file,
"pair (%d,%d): double writeback with distinct regs (%d,%d): "
"punting\n",
insns[0]->uid (), insns[1]->uid (),
base_defs[0]->regno (), base_defs[1]->regno ());
return writeback;
}
if (base_defs[0] && base_defs[1]
&& base_defs[0]->regno () == base_defs[1]->regno ())
{
// Easy case: insns already share the same base reg.
base_cands.quick_push (base_defs[0]);
return writeback;
}
// Otherwise, we know that one of the bases must change.
//
// Note that if there is writeback we must use the writeback base
// (we know now there is exactly one).
for (int i = 0; i < 2; i++)
if (base_defs[i] && (!writeback || (writeback & (1 << i))))
base_cands.quick_push (base_cand { base_defs[i], i });
return writeback;
}
// Given two adjacent memory accesses of the same size, I1 and I2, try
// and see if we can merge them into a paired access.
//
// ACCESS_SIZE gives the (common) size of a single access, LOAD_P is true
// if the accesses are both loads, otherwise they are both stores.
bool
pair_fusion_bb_info::try_fuse_pair (bool load_p, unsigned access_size,
insn_info *i1, insn_info *i2)
{
if (dump_file)
fprintf (dump_file, "analyzing pair (load=%d): (%d,%d)\n",
load_p, i1->uid (), i2->uid ());
insn_info *insns[2];
bool reversed = false;
if (*i1 < *i2)
{
insns[0] = i1;
insns[1] = i2;
}
else
{
insns[0] = i2;
insns[1] = i1;
reversed = true;
}
rtx cand_mems[2];
rtx reg_ops[2];
rtx pats[2];
for (int i = 0; i < 2; i++)
{
pats[i] = PATTERN (insns[i]->rtl ());
cand_mems[i] = XEXP (pats[i], load_p);
reg_ops[i] = XEXP (pats[i], !load_p);
}
if (load_p && reg_overlap_mentioned_p (reg_ops[0], reg_ops[1]))
{
if (dump_file)
fprintf (dump_file,
"punting on load pair due to reg conflcits (%d,%d)\n",
insns[0]->uid (), insns[1]->uid ());
return false;
}
if (cfun->can_throw_non_call_exceptions
&& find_reg_note (insns[0]->rtl (), REG_EH_REGION, NULL_RTX)
&& find_reg_note (insns[1]->rtl (), REG_EH_REGION, NULL_RTX))
{
if (dump_file)
fprintf (dump_file,
"can't combine insns with EH side effects (%d,%d)\n",
insns[0]->uid (), insns[1]->uid ());
return false;
}
auto_vec<base_cand, 2> base_cands (2);
int writeback = m_pass->get_viable_bases (insns, base_cands, cand_mems,
access_size, reversed);
if (base_cands.is_empty ())
{
if (dump_file)
fprintf (dump_file, "no viable base for pair (%d,%d)\n",
insns[0]->uid (), insns[1]->uid ());
return false;
}
// Punt on frame-related insns with writeback. We probably won't see
// these in practice, but this is conservative and ensures we don't
// have to worry about these later on.
if (writeback && (RTX_FRAME_RELATED_P (i1->rtl ())
|| RTX_FRAME_RELATED_P (i2->rtl ())))
{
if (dump_file)
fprintf (dump_file,
"rejecting pair (%d,%d): frame-related insn with writeback\n",
i1->uid (), i2->uid ());
return false;
}
rtx *ignore = &XEXP (pats[1], load_p);
for (auto use : insns[1]->uses ())
if (!use->is_mem ()
&& refers_to_regno_p (use->regno (), use->regno () + 1, pats[1], ignore)
&& use->def () && use->def ()->insn () == insns[0])
{
// N.B. we allow a true dependence on the base address, as this
// happens in the case of auto-inc accesses. Consider a post-increment
// load followed by a regular indexed load, for example.
if (dump_file)
fprintf (dump_file,
"%d has non-address true dependence on %d, rejecting pair\n",
insns[1]->uid (), insns[0]->uid ());
return false;
}
unsigned i = 0;
while (i < base_cands.length ())
{
base_cand &cand = base_cands[i];
rtx *ignore[2] = {};
for (int j = 0; j < 2; j++)
if (cand.from_insn == !j)
ignore[j] = &XEXP (cand_mems[j], 0);
insn_info *h = first_hazard_after (insns[0], ignore[0]);
if (h && *h < *insns[1])
cand.hazards[0] = h;
h = latest_hazard_before (insns[1], ignore[1]);
if (h && *h > *insns[0])
cand.hazards[1] = h;
if (!cand.viable ())
{
if (dump_file)
fprintf (dump_file,
"pair (%d,%d): rejecting base %d due to dataflow "
"hazards (%d,%d)\n",
insns[0]->uid (),
insns[1]->uid (),
cand.def->regno (),
cand.hazards[0]->uid (),
cand.hazards[1]->uid ());
base_cands.ordered_remove (i);
}
else
i++;
}
if (base_cands.is_empty ())
{
if (dump_file)
fprintf (dump_file,
"can't form pair (%d,%d) due to dataflow hazards\n",
insns[0]->uid (), insns[1]->uid ());
return false;
}
insn_info *alias_hazards[4] = {};
// First def of memory after the first insn, and last def of memory
// before the second insn, respectively.
def_info *mem_defs[2] = {};
if (load_p)
{
if (!MEM_READONLY_P (cand_mems[0]))
{
mem_defs[0] = memory_access (insns[0]->uses ())->def ();
gcc_checking_assert (mem_defs[0]);
mem_defs[0] = mem_defs[0]->next_def ();
}
if (!MEM_READONLY_P (cand_mems[1]))
{
mem_defs[1] = memory_access (insns[1]->uses ())->def ();
gcc_checking_assert (mem_defs[1]);
}
}
else
{
mem_defs[0] = memory_access (insns[0]->defs ())->next_def ();
mem_defs[1] = memory_access (insns[1]->defs ())->prev_def ();
gcc_checking_assert (mem_defs[0]);
gcc_checking_assert (mem_defs[1]);
}
auto tombstone_p = [&](insn_info *insn) -> bool {
return m_emitted_tombstone
&& bitmap_bit_p (&m_tombstone_bitmap, insn->uid ());
};
auto_vec<access_info *, 2> addr_use_vec[2];
use_array addr_uses[2];
// Collect the lists of register uses that occur in the candidate MEMs.
for (int i = 0; i < 2; i++)
{
// N.B. it's safe for us to ignore uses that only occur in notes
// here (e.g. in a REG_EQUIV expression) since we only pass the
// MEM down to the alias machinery, so it can't see any insn-level
// notes.
for (auto use : insns[i]->uses ())
if (use->is_reg ()
&& use->includes_address_uses ()
&& !use->only_occurs_in_notes ())
addr_use_vec[i].safe_push (use);
addr_uses[i] = use_array (addr_use_vec[i]);
}
store_walker<false, decltype(tombstone_p)>
forward_store_walker (mem_defs[0], cand_mems[0], addr_uses[0], insns[1],
tombstone_p);
store_walker<true, decltype(tombstone_p)>
backward_store_walker (mem_defs[1], cand_mems[1], addr_uses[1], insns[0],
tombstone_p);
alias_walker *walkers[4] = {};
if (mem_defs[0])
walkers[0] = &forward_store_walker;
if (mem_defs[1])
walkers[1] = &backward_store_walker;
if (load_p && (mem_defs[0] || mem_defs[1]))
m_pass->do_alias_analysis (alias_hazards, walkers, load_p);
else
{
// We want to find any loads hanging off the first store.
mem_defs[0] = memory_access (insns[0]->defs ());
load_walker<false> forward_load_walker (mem_defs[0], insns[0],
addr_uses[0], insns[1]);
load_walker<true> backward_load_walker (mem_defs[1], insns[1],
addr_uses[1], insns[0]);
walkers[2] = &forward_load_walker;
walkers[3] = &backward_load_walker;
m_pass->do_alias_analysis (alias_hazards, walkers, load_p);
// Now consolidate hazards back down.
if (alias_hazards[2]
&& (!alias_hazards[0] || (*alias_hazards[2] < *alias_hazards[0])))
alias_hazards[0] = alias_hazards[2];
if (alias_hazards[3]
&& (!alias_hazards[1] || (*alias_hazards[3] > *alias_hazards[1])))
alias_hazards[1] = alias_hazards[3];
}
if (alias_hazards[0] && alias_hazards[1]
&& *alias_hazards[0] <= *alias_hazards[1])
{
if (dump_file)
fprintf (dump_file,
"cannot form pair (%d,%d) due to alias conflicts (%d,%d)\n",
i1->uid (), i2->uid (),
alias_hazards[0]->uid (), alias_hazards[1]->uid ());
return false;
}
// Now narrow the hazards on each base candidate using
// the alias hazards.
i = 0;
while (i < base_cands.length ())
{
base_cand &cand = base_cands[i];
if (alias_hazards[0] && (!cand.hazards[0]
|| *alias_hazards[0] < *cand.hazards[0]))
cand.hazards[0] = alias_hazards[0];
if (alias_hazards[1] && (!cand.hazards[1]
|| *alias_hazards[1] > *cand.hazards[1]))
cand.hazards[1] = alias_hazards[1];
if (cand.viable ())
i++;
else
{
if (dump_file)
fprintf (dump_file, "pair (%d,%d): rejecting base %d due to "
"alias/dataflow hazards (%d,%d)",
insns[0]->uid (), insns[1]->uid (),
cand.def->regno (),
cand.hazards[0]->uid (),
cand.hazards[1]->uid ());
base_cands.ordered_remove (i);
}
}
if (base_cands.is_empty ())
{
if (dump_file)
fprintf (dump_file,
"cannot form pair (%d,%d) due to alias/dataflow hazards",
insns[0]->uid (), insns[1]->uid ());
return false;
}
base_cand *base = &base_cands[0];
if (base_cands.length () > 1)
{
// If there are still multiple viable bases, it makes sense
// to choose one that allows us to reduce register pressure,
// for loads this means moving further down, for stores this
// means moving further up.
gcc_checking_assert (base_cands.length () == 2);
const int hazard_i = !load_p;
if (base->hazards[hazard_i])
{
if (!base_cands[1].hazards[hazard_i])
base = &base_cands[1];
else if (load_p
&& *base_cands[1].hazards[hazard_i]
> *(base->hazards[hazard_i]))
base = &base_cands[1];
else if (!load_p
&& *base_cands[1].hazards[hazard_i]
< *(base->hazards[hazard_i]))
base = &base_cands[1];
}
}
// Otherwise, hazards[0] > hazards[1].
// Pair can be formed anywhere in (hazards[1], hazards[0]).
insn_range_info range (insns[0], insns[1]);
if (base->hazards[1])
range.first = base->hazards[1];
if (base->hazards[0])
range.last = base->hazards[0]->prev_nondebug_insn ();
// If the second insn can throw, narrow the move range to exactly that insn.
// This prevents us trying to move the second insn from the end of the BB.
if (cfun->can_throw_non_call_exceptions
&& find_reg_note (insns[1]->rtl (), REG_EH_REGION, NULL_RTX))
{
gcc_assert (range.includes (insns[1]));
range = insn_range_info (insns[1]);
}
// Placement strategy: push loads down and pull stores up, this should
// help register pressure by reducing live ranges.
if (load_p)
range.first = range.last;
else
range.last = range.first;
if (dump_file)
{
auto print_hazard = [](insn_info *i)
{
if (i)
fprintf (dump_file, "%d", i->uid ());
else
fprintf (dump_file, "-");
};
auto print_pair = [print_hazard](insn_info **i)
{
print_hazard (i[0]);
fprintf (dump_file, ",");
print_hazard (i[1]);
};
fprintf (dump_file, "fusing pair [L=%d] (%d,%d), base=%d, hazards: (",
load_p, insns[0]->uid (), insns[1]->uid (),
base->def->regno ());
print_pair (base->hazards);
fprintf (dump_file, "), move_range: (%d,%d)\n",
range.first->uid (), range.last->uid ());
}
return fuse_pair (load_p, access_size, writeback,
i1, i2, *base, range);
}
static void
dump_insn_list (FILE *f, const insn_list_t &l)
{
fprintf (f, "(");
auto i = l.begin ();
auto end = l.end ();
if (i != end)
fprintf (f, "%d", (*i)->uid ());
i++;
for (; i != end; i++)
fprintf (f, ", %d", (*i)->uid ());
fprintf (f, ")");
}
DEBUG_FUNCTION void
debug (const insn_list_t &l)
{
dump_insn_list (stderr, l);
fprintf (stderr, "\n");
}
// LEFT_LIST and RIGHT_LIST are lists of candidate instructions where all insns
// in LEFT_LIST are known to be adjacent to those in RIGHT_LIST.
//
// This function traverses the resulting 2D matrix of possible pair candidates
// and attempts to merge them into pairs.
//
// The algorithm is straightforward: if we consider a combined list of
// candidates X obtained by merging LEFT_LIST and RIGHT_LIST in program order,
// then we advance through X until we reach a crossing point (where X[i] and
// X[i+1] come from different source lists).
//
// At this point we know X[i] and X[i+1] are adjacent accesses, and we try to
// fuse them into a pair. If this succeeds, we remove X[i] and X[i+1] from
// their original lists and continue as above.
//
// In the failure case, we advance through the source list containing X[i] and
// continue as above (proceeding to the next crossing point).
//
// The rationale for skipping over groups of consecutive candidates from the
// same source list is as follows:
//
// In the store case, the insns in the group can't be re-ordered over each
// other as they are guaranteed to store to the same location, so we're
// guaranteed not to lose opportunities by doing this.
//
// In the load case, subsequent loads from the same location are either
// redundant (in which case they should have been cleaned up by an earlier
// optimization pass) or there is an intervening aliasing hazard, in which case
// we can't re-order them anyway, so provided earlier passes have cleaned up
// redundant loads, we shouldn't miss opportunities by doing this.
void
pair_fusion_bb_info::merge_pairs (insn_list_t &left_list,
insn_list_t &right_list,
bool load_p,
unsigned access_size)
{
if (dump_file)
{
fprintf (dump_file, "merge_pairs [L=%d], cand vecs ", load_p);
dump_insn_list (dump_file, left_list);
fprintf (dump_file, " x ");
dump_insn_list (dump_file, right_list);
fprintf (dump_file, "\n");
}
auto iter_l = left_list.begin ();
auto iter_r = right_list.begin ();
while (iter_l != left_list.end () && iter_r != right_list.end ())
{
auto next_l = std::next (iter_l);
auto next_r = std::next (iter_r);
if (**iter_l < **iter_r
&& next_l != left_list.end ()
&& **next_l < **iter_r)
iter_l = next_l;
else if (**iter_r < **iter_l
&& next_r != right_list.end ()
&& **next_r < **iter_l)
iter_r = next_r;
else if (try_fuse_pair (load_p, access_size, *iter_l, *iter_r))
{
left_list.erase (iter_l);
iter_l = next_l;
right_list.erase (iter_r);
iter_r = next_r;
}
else if (**iter_l < **iter_r)
iter_l = next_l;
else
iter_r = next_r;
}
}
// Iterate over the accesses in GROUP, looking for adjacent sets
// of accesses. If we find two sets of adjacent accesses, call
// merge_pairs.
void
pair_fusion_bb_info::transform_for_base (int encoded_lfs,
access_group &group)
{
const auto lfs = decode_lfs (encoded_lfs);
const unsigned access_size = lfs.size;
bool skip_next = true;
access_record *prev_access = nullptr;
for (auto &access : group.list)
{
if (skip_next)
skip_next = false;
else if (known_eq (access.offset, prev_access->offset + access_size))
{
merge_pairs (prev_access->cand_insns,
access.cand_insns,
lfs.load_p,
access_size);
skip_next = access.cand_insns.empty ();
}
prev_access = &access;
}
}
// If we emitted tombstone insns for this BB, iterate through the BB
// and remove all the tombstone insns, being sure to reparent any uses
// of mem to previous defs when we do this.
void
pair_fusion_bb_info::cleanup_tombstones ()
{
// No need to do anything if we didn't emit a tombstone insn for this BB.
if (!m_emitted_tombstone)
return;
for (auto insn : iterate_safely (m_bb->nondebug_insns ()))
{
if (!insn->is_real ()
|| !bitmap_bit_p (&m_tombstone_bitmap, insn->uid ()))
continue;
auto set = as_a<set_info *> (memory_access (insn->defs ()));
if (set->has_any_uses ())
{
auto prev_set = as_a<set_info *> (set->prev_def ());
while (set->first_use ())
crtl->ssa->reparent_use (set->first_use (), prev_set);
}
// Now set has no uses, we can delete it.
insn_change change (insn, insn_change::DELETE);
crtl->ssa->change_insn (change);
}
}
template<typename Map>
void
pair_fusion_bb_info::traverse_base_map (Map &map)
{
for (auto kv : map)
{
const auto &key = kv.first;
auto &value = kv.second;
transform_for_base (key.second, value);
}
}
void
pair_fusion_bb_info::transform ()
{
traverse_base_map (expr_map);
traverse_base_map (def_map);
}
// Given an existing pair insn INSN, look for a trailing update of
// the base register which we can fold in to make this pair use
// a writeback addressing mode.
void
pair_fusion::try_promote_writeback (insn_info *insn, bool load_p)
{
rtx regs[2];
rtx mem = destructure_pair (regs, PATTERN (insn->rtl ()), load_p);
gcc_checking_assert (MEM_P (mem));
poly_int64 offset;
rtx base = strip_offset (XEXP (mem, 0), &offset);
gcc_assert (REG_P (base));
const auto access_size = GET_MODE_SIZE (GET_MODE (mem)).to_constant () / 2;
if (find_access (insn->defs (), REGNO (base)))
{
gcc_assert (load_p);
if (dump_file)
fprintf (dump_file,
"ldp %d clobbers base r%d, can't promote to writeback\n",
insn->uid (), REGNO (base));
return;
}
auto base_use = find_access (insn->uses (), REGNO (base));
gcc_assert (base_use);
if (!base_use->def ())
{
if (dump_file)
fprintf (dump_file,
"found pair (i%d, L=%d): but base r%d is upwards exposed\n",
insn->uid (), load_p, REGNO (base));
return;
}
auto base_def = base_use->def ();
rtx wb_effect = NULL_RTX;
def_info *add_def;
const insn_range_info pair_range (insn);
insn_info *insns[2] = { nullptr, insn };
insn_info *trailing_add
= find_trailing_add (insns, pair_range, 0, &wb_effect,
&add_def, base_def, offset,
access_size);
if (!trailing_add)
return;
auto attempt = crtl->ssa->new_change_attempt ();
insn_change pair_change (insn);
insn_change del_change (trailing_add, insn_change::DELETE);
insn_change *changes[] = { &pair_change, &del_change };
rtx pair_pat = gen_promote_writeback_pair (wb_effect, mem, regs, load_p);
validate_unshare_change (insn->rtl (), &PATTERN (insn->rtl ()), pair_pat,
true);
// The pair must gain the def of the base register from the add.
pair_change.new_defs = insert_access (attempt,
add_def,
pair_change.new_defs);
gcc_assert (pair_change.new_defs.is_valid ());
auto ignore = ignore_changing_insns (changes);
for (unsigned i = 0; i < ARRAY_SIZE (changes); i++)
gcc_assert (changes[i]->move_range.singleton ()
&& rtl_ssa::restrict_movement (*changes[i], ignore));
if (!rtl_ssa::recog (attempt, pair_change, ignore))
{
if (dump_file)
fprintf (dump_file, "i%d: recog failed on wb pair, bailing out\n",
insn->uid ());
cancel_changes (0);
return;
}
gcc_assert (crtl->ssa->verify_insn_changes (changes));
if (MAY_HAVE_DEBUG_INSNS)
fixup_debug_uses_trailing_add (attempt, insn, trailing_add, wb_effect);
confirm_change_group ();
crtl->ssa->change_insns (changes);
}
// Main function for the pass. Iterate over the insns in BB looking
// for load/store candidates. If running after RA, also try and promote
// non-writeback pairs to use writeback addressing. Then try to fuse
// candidates into pairs.
void pair_fusion::process_block (bb_info *bb)
{
const bool track_loads = track_loads_p ();
const bool track_stores = track_stores_p ();
pair_fusion_bb_info bb_state (bb, this);
for (auto insn : bb->nondebug_insns ())
{
rtx_insn *rti = insn->rtl ();
if (!rti || !INSN_P (rti))
continue;
rtx pat = PATTERN (rti);
bool load_p;
if (reload_completed
&& should_handle_writeback (writeback_type::ALL)
&& pair_mem_insn_p (rti, load_p))
try_promote_writeback (insn, load_p);
if (GET_CODE (pat) != SET)
continue;
if (track_stores && MEM_P (XEXP (pat, 0)))
bb_state.track_access (insn, false, XEXP (pat, 0));
else if (track_loads && MEM_P (XEXP (pat, 1)))
bb_state.track_access (insn, true, XEXP (pat, 1));
}
bb_state.transform ();
bb_state.cleanup_tombstones ();
}