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gcc/gcc/dce.c
Richard Sandiford 23a5b65a92 Update copyright years in gcc/ 
From-SVN: r206289
2014-01-02 22:23:26 +00:00

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/* RTL dead code elimination.
Copyright (C) 2005-2014 Free Software Foundation, Inc.
This file is part of GCC.
GCC is free software; you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free
Software Foundation; either version 3, or (at your option) any later
version.
GCC is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
for more details.
You should have received a copy of the GNU General Public License
along with GCC; see the file COPYING3. If not see
<http://www.gnu.org/licenses/>. */
#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "hashtab.h"
#include "tm.h"
#include "rtl.h"
#include "tree.h"
#include "regs.h"
#include "hard-reg-set.h"
#include "flags.h"
#include "except.h"
#include "df.h"
#include "cselib.h"
#include "dce.h"
#include "valtrack.h"
#include "tree-pass.h"
#include "dbgcnt.h"
#include "tm_p.h"
#include "emit-rtl.h" /* FIXME: Can go away once crtl is moved to rtl.h. */
/* -------------------------------------------------------------------------
Core mark/delete routines
------------------------------------------------------------------------- */
/* True if we are invoked while the df engine is running; in this case,
we don't want to reenter it. */
static bool df_in_progress = false;
/* True if we are allowed to alter the CFG in this pass. */
static bool can_alter_cfg = false;
/* Instructions that have been marked but whose dependencies have not
yet been processed. */
static vec<rtx> worklist;
/* Bitmap of instructions marked as needed indexed by INSN_UID. */
static sbitmap marked;
/* Bitmap obstacks used for block processing by the fast algorithm. */
static bitmap_obstack dce_blocks_bitmap_obstack;
static bitmap_obstack dce_tmp_bitmap_obstack;
static bool find_call_stack_args (rtx, bool, bool, bitmap);
/* A subroutine for which BODY is part of the instruction being tested;
either the top-level pattern, or an element of a PARALLEL. The
instruction is known not to be a bare USE or CLOBBER. */
static bool
deletable_insn_p_1 (rtx body)
{
switch (GET_CODE (body))
{
case PREFETCH:
case TRAP_IF:
/* The UNSPEC case was added here because the ia-64 claims that
USEs do not work after reload and generates UNSPECS rather
than USEs. Since dce is run after reload we need to avoid
deleting these even if they are dead. If it turns out that
USEs really do work after reload, the ia-64 should be
changed, and the UNSPEC case can be removed. */
case UNSPEC:
return false;
default:
return !volatile_refs_p (body);
}
}
/* Return true if INSN is a normal instruction that can be deleted by
the DCE pass. */
static bool
deletable_insn_p (rtx insn, bool fast, bitmap arg_stores)
{
rtx body, x;
int i;
if (CALL_P (insn)
/* We cannot delete calls inside of the recursive dce because
this may cause basic blocks to be deleted and this messes up
the rest of the stack of optimization passes. */
&& (!df_in_progress)
/* We cannot delete pure or const sibling calls because it is
hard to see the result. */
&& (!SIBLING_CALL_P (insn))
/* We can delete dead const or pure calls as long as they do not
infinite loop. */
&& (RTL_CONST_OR_PURE_CALL_P (insn)
&& !RTL_LOOPING_CONST_OR_PURE_CALL_P (insn)))
return find_call_stack_args (insn, false, fast, arg_stores);
/* Don't delete jumps, notes and the like. */
if (!NONJUMP_INSN_P (insn))
return false;
/* Don't delete insns that may throw if we cannot do so. */
if (!(cfun->can_delete_dead_exceptions && can_alter_cfg)
&& !insn_nothrow_p (insn))
return false;
/* If INSN sets a global_reg, leave it untouched. */
for (df_ref *def_rec = DF_INSN_DEFS (insn); *def_rec; def_rec++)
if (HARD_REGISTER_NUM_P (DF_REF_REGNO (*def_rec))
&& global_regs[DF_REF_REGNO (*def_rec)])
return false;
body = PATTERN (insn);
switch (GET_CODE (body))
{
case USE:
case VAR_LOCATION:
return false;
case CLOBBER:
if (fast)
{
/* A CLOBBER of a dead pseudo register serves no purpose.
That is not necessarily true for hard registers until
after reload. */
x = XEXP (body, 0);
return REG_P (x) && (!HARD_REGISTER_P (x) || reload_completed);
}
else
/* Because of the way that use-def chains are built, it is not
possible to tell if the clobber is dead because it can
never be the target of a use-def chain. */
return false;
case PARALLEL:
for (i = XVECLEN (body, 0) - 1; i >= 0; i--)
if (!deletable_insn_p_1 (XVECEXP (body, 0, i)))
return false;
return true;
default:
return deletable_insn_p_1 (body);
}
}
/* Return true if INSN has been marked as needed. */
static inline int
marked_insn_p (rtx insn)
{
/* Artificial defs are always needed and they do not have an insn.
We should never see them here. */
gcc_assert (insn);
return bitmap_bit_p (marked, INSN_UID (insn));
}
/* If INSN has not yet been marked as needed, mark it now, and add it to
the worklist. */
static void
mark_insn (rtx insn, bool fast)
{
if (!marked_insn_p (insn))
{
if (!fast)
worklist.safe_push (insn);
bitmap_set_bit (marked, INSN_UID (insn));
if (dump_file)
fprintf (dump_file, " Adding insn %d to worklist\n", INSN_UID (insn));
if (CALL_P (insn)
&& !df_in_progress
&& !SIBLING_CALL_P (insn)
&& (RTL_CONST_OR_PURE_CALL_P (insn)
&& !RTL_LOOPING_CONST_OR_PURE_CALL_P (insn)))
find_call_stack_args (insn, true, fast, NULL);
}
}
/* A note_stores callback used by mark_nonreg_stores. DATA is the
instruction containing DEST. */
static void
mark_nonreg_stores_1 (rtx dest, const_rtx pattern, void *data)
{
if (GET_CODE (pattern) != CLOBBER && !REG_P (dest))
mark_insn ((rtx) data, true);
}
/* A note_stores callback used by mark_nonreg_stores. DATA is the
instruction containing DEST. */
static void
mark_nonreg_stores_2 (rtx dest, const_rtx pattern, void *data)
{
if (GET_CODE (pattern) != CLOBBER && !REG_P (dest))
mark_insn ((rtx) data, false);
}
/* Mark INSN if BODY stores to a non-register destination. */
static void
mark_nonreg_stores (rtx body, rtx insn, bool fast)
{
if (fast)
note_stores (body, mark_nonreg_stores_1, insn);
else
note_stores (body, mark_nonreg_stores_2, insn);
}
/* Return true if store to MEM, starting OFF bytes from stack pointer,
is a call argument store, and clear corresponding bits from SP_BYTES
bitmap if it is. */
static bool
check_argument_store (rtx mem, HOST_WIDE_INT off, HOST_WIDE_INT min_sp_off,
HOST_WIDE_INT max_sp_off, bitmap sp_bytes)
{
HOST_WIDE_INT byte;
for (byte = off; byte < off + GET_MODE_SIZE (GET_MODE (mem)); byte++)
{
if (byte < min_sp_off
|| byte >= max_sp_off
|| !bitmap_clear_bit (sp_bytes, byte - min_sp_off))
return false;
}
return true;
}
/* Try to find all stack stores of CALL_INSN arguments if
ACCUMULATE_OUTGOING_ARGS. If all stack stores have been found
and it is therefore safe to eliminate the call, return true,
otherwise return false. This function should be first called
with DO_MARK false, and only when the CALL_INSN is actually
going to be marked called again with DO_MARK true. */
static bool
find_call_stack_args (rtx call_insn, bool do_mark, bool fast,
bitmap arg_stores)
{
rtx p, insn, prev_insn;
bool ret;
HOST_WIDE_INT min_sp_off, max_sp_off;
bitmap sp_bytes;
gcc_assert (CALL_P (call_insn));
if (!ACCUMULATE_OUTGOING_ARGS)
return true;
if (!do_mark)
{
gcc_assert (arg_stores);
bitmap_clear (arg_stores);
}
min_sp_off = INTTYPE_MAXIMUM (HOST_WIDE_INT);
max_sp_off = 0;
/* First determine the minimum and maximum offset from sp for
stored arguments. */
for (p = CALL_INSN_FUNCTION_USAGE (call_insn); p; p = XEXP (p, 1))
if (GET_CODE (XEXP (p, 0)) == USE
&& MEM_P (XEXP (XEXP (p, 0), 0)))
{
rtx mem = XEXP (XEXP (p, 0), 0), addr;
HOST_WIDE_INT off = 0, size;
if (!MEM_SIZE_KNOWN_P (mem))
return false;
size = MEM_SIZE (mem);
addr = XEXP (mem, 0);
if (GET_CODE (addr) == PLUS
&& REG_P (XEXP (addr, 0))
&& CONST_INT_P (XEXP (addr, 1)))
{
off = INTVAL (XEXP (addr, 1));
addr = XEXP (addr, 0);
}
if (addr != stack_pointer_rtx)
{
if (!REG_P (addr))
return false;
/* If not fast, use chains to see if addr wasn't set to
sp + offset. */
if (!fast)
{
df_ref *use_rec;
struct df_link *defs;
rtx set;
for (use_rec = DF_INSN_USES (call_insn); *use_rec; use_rec++)
if (rtx_equal_p (addr, DF_REF_REG (*use_rec)))
break;
if (*use_rec == NULL)
return false;
for (defs = DF_REF_CHAIN (*use_rec); defs; defs = defs->next)
if (! DF_REF_IS_ARTIFICIAL (defs->ref))
break;
if (defs == NULL)
return false;
set = single_set (DF_REF_INSN (defs->ref));
if (!set)
return false;
if (GET_CODE (SET_SRC (set)) != PLUS
|| XEXP (SET_SRC (set), 0) != stack_pointer_rtx
|| !CONST_INT_P (XEXP (SET_SRC (set), 1)))
return false;
off += INTVAL (XEXP (SET_SRC (set), 1));
}
else
return false;
}
min_sp_off = MIN (min_sp_off, off);
max_sp_off = MAX (max_sp_off, off + size);
}
if (min_sp_off >= max_sp_off)
return true;
sp_bytes = BITMAP_ALLOC (NULL);
/* Set bits in SP_BYTES bitmap for bytes relative to sp + min_sp_off
which contain arguments. Checking has been done in the previous
loop. */
for (p = CALL_INSN_FUNCTION_USAGE (call_insn); p; p = XEXP (p, 1))
if (GET_CODE (XEXP (p, 0)) == USE
&& MEM_P (XEXP (XEXP (p, 0), 0)))
{
rtx mem = XEXP (XEXP (p, 0), 0), addr;
HOST_WIDE_INT off = 0, byte;
addr = XEXP (mem, 0);
if (GET_CODE (addr) == PLUS
&& REG_P (XEXP (addr, 0))
&& CONST_INT_P (XEXP (addr, 1)))
{
off = INTVAL (XEXP (addr, 1));
addr = XEXP (addr, 0);
}
if (addr != stack_pointer_rtx)
{
df_ref *use_rec;
struct df_link *defs;
rtx set;
for (use_rec = DF_INSN_USES (call_insn); *use_rec; use_rec++)
if (rtx_equal_p (addr, DF_REF_REG (*use_rec)))
break;
for (defs = DF_REF_CHAIN (*use_rec); defs; defs = defs->next)
if (! DF_REF_IS_ARTIFICIAL (defs->ref))
break;
set = single_set (DF_REF_INSN (defs->ref));
off += INTVAL (XEXP (SET_SRC (set), 1));
}
for (byte = off; byte < off + MEM_SIZE (mem); byte++)
{
if (!bitmap_set_bit (sp_bytes, byte - min_sp_off))
gcc_unreachable ();
}
}
/* Walk backwards, looking for argument stores. The search stops
when seeing another call, sp adjustment or memory store other than
argument store. */
ret = false;
for (insn = PREV_INSN (call_insn); insn; insn = prev_insn)
{
rtx set, mem, addr;
HOST_WIDE_INT off;
if (insn == BB_HEAD (BLOCK_FOR_INSN (call_insn)))
prev_insn = NULL_RTX;
else
prev_insn = PREV_INSN (insn);
if (CALL_P (insn))
break;
if (!NONDEBUG_INSN_P (insn))
continue;
set = single_set (insn);
if (!set || SET_DEST (set) == stack_pointer_rtx)
break;
if (!MEM_P (SET_DEST (set)))
continue;
mem = SET_DEST (set);
addr = XEXP (mem, 0);
off = 0;
if (GET_CODE (addr) == PLUS
&& REG_P (XEXP (addr, 0))
&& CONST_INT_P (XEXP (addr, 1)))
{
off = INTVAL (XEXP (addr, 1));
addr = XEXP (addr, 0);
}
if (addr != stack_pointer_rtx)
{
if (!REG_P (addr))
break;
if (!fast)
{
df_ref *use_rec;
struct df_link *defs;
rtx set;
for (use_rec = DF_INSN_USES (insn); *use_rec; use_rec++)
if (rtx_equal_p (addr, DF_REF_REG (*use_rec)))
break;
if (*use_rec == NULL)
break;
for (defs = DF_REF_CHAIN (*use_rec); defs; defs = defs->next)
if (! DF_REF_IS_ARTIFICIAL (defs->ref))
break;
if (defs == NULL)
break;
set = single_set (DF_REF_INSN (defs->ref));
if (!set)
break;
if (GET_CODE (SET_SRC (set)) != PLUS
|| XEXP (SET_SRC (set), 0) != stack_pointer_rtx
|| !CONST_INT_P (XEXP (SET_SRC (set), 1)))
break;
off += INTVAL (XEXP (SET_SRC (set), 1));
}
else
break;
}
if (GET_MODE_SIZE (GET_MODE (mem)) == 0
|| !check_argument_store (mem, off, min_sp_off,
max_sp_off, sp_bytes))
break;
if (!deletable_insn_p (insn, fast, NULL))
break;
if (do_mark)
mark_insn (insn, fast);
else
bitmap_set_bit (arg_stores, INSN_UID (insn));
if (bitmap_empty_p (sp_bytes))
{
ret = true;
break;
}
}
BITMAP_FREE (sp_bytes);
if (!ret && arg_stores)
bitmap_clear (arg_stores);
return ret;
}
/* Remove all REG_EQUAL and REG_EQUIV notes referring to the registers INSN
writes to. */
static void
remove_reg_equal_equiv_notes_for_defs (rtx insn)
{
df_ref *def_rec;
for (def_rec = DF_INSN_DEFS (insn); *def_rec; def_rec++)
remove_reg_equal_equiv_notes_for_regno (DF_REF_REGNO (*def_rec));
}
/* Scan all BBs for debug insns and reset those that reference values
defined in unmarked insns. */
static void
reset_unmarked_insns_debug_uses (void)
{
basic_block bb;
rtx insn, next;
FOR_EACH_BB_REVERSE_FN (bb, cfun)
FOR_BB_INSNS_REVERSE_SAFE (bb, insn, next)
if (DEBUG_INSN_P (insn))
{
df_ref *use_rec;
for (use_rec = DF_INSN_USES (insn); *use_rec; use_rec++)
{
df_ref use = *use_rec;
struct df_link *defs;
for (defs = DF_REF_CHAIN (use); defs; defs = defs->next)
{
rtx ref_insn;
if (DF_REF_IS_ARTIFICIAL (defs->ref))
continue;
ref_insn = DF_REF_INSN (defs->ref);
if (!marked_insn_p (ref_insn))
break;
}
if (!defs)
continue;
/* ??? FIXME could we propagate the values assigned to
each of the DEFs? */
INSN_VAR_LOCATION_LOC (insn) = gen_rtx_UNKNOWN_VAR_LOC ();
df_insn_rescan_debug_internal (insn);
break;
}
}
}
/* Delete every instruction that hasn't been marked. */
static void
delete_unmarked_insns (void)
{
basic_block bb;
rtx insn, next;
bool must_clean = false;
FOR_EACH_BB_REVERSE_FN (bb, cfun)
FOR_BB_INSNS_REVERSE_SAFE (bb, insn, next)
if (NONDEBUG_INSN_P (insn))
{
/* Always delete no-op moves. */
if (noop_move_p (insn))
;
/* Otherwise rely only on the DCE algorithm. */
else if (marked_insn_p (insn))
continue;
/* Beware that reaching a dbg counter limit here can result
in miscompiled file. This occurs when a group of insns
must be deleted together, typically because the kept insn
depends on the output from the deleted insn. Deleting
this insns in reverse order (both at the bb level and
when looking at the blocks) minimizes this, but does not
eliminate it, since it is possible for the using insn to
be top of a block and the producer to be at the bottom of
the block. However, in most cases this will only result
in an uninitialized use of an insn that is dead anyway.
However, there is one rare case that will cause a
miscompile: deletion of non-looping pure and constant
calls on a machine where ACCUMULATE_OUTGOING_ARGS is true.
In this case it is possible to remove the call, but leave
the argument pushes to the stack. Because of the changes
to the stack pointer, this will almost always lead to a
miscompile. */
if (!dbg_cnt (dce))
continue;
if (dump_file)
fprintf (dump_file, "DCE: Deleting insn %d\n", INSN_UID (insn));
/* Before we delete the insn we have to remove the REG_EQUAL notes
for the destination regs in order to avoid dangling notes. */
remove_reg_equal_equiv_notes_for_defs (insn);
/* If a pure or const call is deleted, this may make the cfg
have unreachable blocks. We rememeber this and call
delete_unreachable_blocks at the end. */
if (CALL_P (insn))
must_clean = true;
/* Now delete the insn. */
delete_insn_and_edges (insn);
}
/* Deleted a pure or const call. */
if (must_clean)
delete_unreachable_blocks ();
}
/* Go through the instructions and mark those whose necessity is not
dependent on inter-instruction information. Make sure all other
instructions are not marked. */
static void
prescan_insns_for_dce (bool fast)
{
basic_block bb;
rtx insn, prev;
bitmap arg_stores = NULL;
if (dump_file)
fprintf (dump_file, "Finding needed instructions:\n");
if (!df_in_progress && ACCUMULATE_OUTGOING_ARGS)
arg_stores = BITMAP_ALLOC (NULL);
FOR_EACH_BB_FN (bb, cfun)
{
FOR_BB_INSNS_REVERSE_SAFE (bb, insn, prev)
if (NONDEBUG_INSN_P (insn))
{
/* Don't mark argument stores now. They will be marked
if needed when the associated CALL is marked. */
if (arg_stores && bitmap_bit_p (arg_stores, INSN_UID (insn)))
continue;
if (deletable_insn_p (insn, fast, arg_stores))
mark_nonreg_stores (PATTERN (insn), insn, fast);
else
mark_insn (insn, fast);
}
/* find_call_stack_args only looks at argument stores in the
same bb. */
if (arg_stores)
bitmap_clear (arg_stores);
}
if (arg_stores)
BITMAP_FREE (arg_stores);
if (dump_file)
fprintf (dump_file, "Finished finding needed instructions:\n");
}
/* UD-based DSE routines. */
/* Mark instructions that define artificially-used registers, such as
the frame pointer and the stack pointer. */
static void
mark_artificial_uses (void)
{
basic_block bb;
struct df_link *defs;
df_ref *use_rec;
FOR_ALL_BB_FN (bb, cfun)
{
for (use_rec = df_get_artificial_uses (bb->index);
*use_rec; use_rec++)
for (defs = DF_REF_CHAIN (*use_rec); defs; defs = defs->next)
if (! DF_REF_IS_ARTIFICIAL (defs->ref))
mark_insn (DF_REF_INSN (defs->ref), false);
}
}
/* Mark every instruction that defines a register value that INSN uses. */
static void
mark_reg_dependencies (rtx insn)
{
struct df_link *defs;
df_ref *use_rec;
if (DEBUG_INSN_P (insn))
return;
for (use_rec = DF_INSN_USES (insn); *use_rec; use_rec++)
{
df_ref use = *use_rec;
if (dump_file)
{
fprintf (dump_file, "Processing use of ");
print_simple_rtl (dump_file, DF_REF_REG (use));
fprintf (dump_file, " in insn %d:\n", INSN_UID (insn));
}
for (defs = DF_REF_CHAIN (use); defs; defs = defs->next)
if (! DF_REF_IS_ARTIFICIAL (defs->ref))
mark_insn (DF_REF_INSN (defs->ref), false);
}
}
/* Initialize global variables for a new DCE pass. */
static void
init_dce (bool fast)
{
if (!df_in_progress)
{
if (!fast)
{
df_set_flags (DF_RD_PRUNE_DEAD_DEFS);
df_chain_add_problem (DF_UD_CHAIN);
}
df_analyze ();
}
if (dump_file)
df_dump (dump_file);
if (fast)
{
bitmap_obstack_initialize (&dce_blocks_bitmap_obstack);
bitmap_obstack_initialize (&dce_tmp_bitmap_obstack);
can_alter_cfg = false;
}
else
can_alter_cfg = true;
marked = sbitmap_alloc (get_max_uid () + 1);
bitmap_clear (marked);
}
/* Free the data allocated by init_dce. */
static void
fini_dce (bool fast)
{
sbitmap_free (marked);
if (fast)
{
bitmap_obstack_release (&dce_blocks_bitmap_obstack);
bitmap_obstack_release (&dce_tmp_bitmap_obstack);
}
}
/* UD-chain based DCE. */
static unsigned int
rest_of_handle_ud_dce (void)
{
rtx insn;
init_dce (false);
prescan_insns_for_dce (false);
mark_artificial_uses ();
while (worklist.length () > 0)
{
insn = worklist.pop ();
mark_reg_dependencies (insn);
}
worklist.release ();
if (MAY_HAVE_DEBUG_INSNS)
reset_unmarked_insns_debug_uses ();
/* Before any insns are deleted, we must remove the chains since
they are not bidirectional. */
df_remove_problem (df_chain);
delete_unmarked_insns ();
fini_dce (false);
return 0;
}
static bool
gate_ud_dce (void)
{
return optimize > 1 && flag_dce
&& dbg_cnt (dce_ud);
}
namespace {
const pass_data pass_data_ud_rtl_dce =
{
RTL_PASS, /* type */
"ud_dce", /* name */
OPTGROUP_NONE, /* optinfo_flags */
true, /* has_gate */
true, /* has_execute */
TV_DCE, /* tv_id */
0, /* properties_required */
0, /* properties_provided */
0, /* properties_destroyed */
0, /* todo_flags_start */
( TODO_df_finish | TODO_verify_rtl_sharing ), /* todo_flags_finish */
};
class pass_ud_rtl_dce : public rtl_opt_pass
{
public:
pass_ud_rtl_dce (gcc::context *ctxt)
: rtl_opt_pass (pass_data_ud_rtl_dce, ctxt)
{}
/* opt_pass methods: */
bool gate () { return gate_ud_dce (); }
unsigned int execute () { return rest_of_handle_ud_dce (); }
}; // class pass_ud_rtl_dce
} // anon namespace
rtl_opt_pass *
make_pass_ud_rtl_dce (gcc::context *ctxt)
{
return new pass_ud_rtl_dce (ctxt);
}
/* -------------------------------------------------------------------------
Fast DCE functions
------------------------------------------------------------------------- */
/* Process basic block BB. Return true if the live_in set has
changed. REDO_OUT is true if the info at the bottom of the block
needs to be recalculated before starting. AU is the proper set of
artificial uses. Track global substitution of uses of dead pseudos
in debug insns using GLOBAL_DEBUG. */
static bool
word_dce_process_block (basic_block bb, bool redo_out,
struct dead_debug_global *global_debug)
{
bitmap local_live = BITMAP_ALLOC (&dce_tmp_bitmap_obstack);
rtx insn;
bool block_changed;
struct dead_debug_local debug;
if (redo_out)
{
/* Need to redo the live_out set of this block if when one of
the succs of this block has had a change in it live in
set. */
edge e;
edge_iterator ei;
df_confluence_function_n con_fun_n = df_word_lr->problem->con_fun_n;
bitmap_clear (DF_WORD_LR_OUT (bb));
FOR_EACH_EDGE (e, ei, bb->succs)
(*con_fun_n) (e);
}
if (dump_file)
{
fprintf (dump_file, "processing block %d live out = ", bb->index);
df_print_word_regset (dump_file, DF_WORD_LR_OUT (bb));
}
bitmap_copy (local_live, DF_WORD_LR_OUT (bb));
dead_debug_local_init (&debug, NULL, global_debug);
FOR_BB_INSNS_REVERSE (bb, insn)
if (DEBUG_INSN_P (insn))
{
df_ref *use_rec;
for (use_rec = DF_INSN_USES (insn); *use_rec; use_rec++)
if (DF_REF_REGNO (*use_rec) >= FIRST_PSEUDO_REGISTER
&& (GET_MODE_SIZE (GET_MODE (DF_REF_REAL_REG (*use_rec)))
== 2 * UNITS_PER_WORD)
&& !bitmap_bit_p (local_live, 2 * DF_REF_REGNO (*use_rec))
&& !bitmap_bit_p (local_live, 2 * DF_REF_REGNO (*use_rec) + 1))
dead_debug_add (&debug, *use_rec, DF_REF_REGNO (*use_rec));
}
else if (INSN_P (insn))
{
bool any_changed;
/* No matter if the instruction is needed or not, we remove
any regno in the defs from the live set. */
any_changed = df_word_lr_simulate_defs (insn, local_live);
if (any_changed)
mark_insn (insn, true);
/* On the other hand, we do not allow the dead uses to set
anything in local_live. */
if (marked_insn_p (insn))
df_word_lr_simulate_uses (insn, local_live);
/* Insert debug temps for dead REGs used in subsequent debug
insns. We may have to emit a debug temp even if the insn
was marked, in case the debug use was after the point of
death. */
if (debug.used && !bitmap_empty_p (debug.used))
{
df_ref *def_rec;
for (def_rec = DF_INSN_DEFS (insn); *def_rec; def_rec++)
dead_debug_insert_temp (&debug, DF_REF_REGNO (*def_rec), insn,
marked_insn_p (insn)
&& !control_flow_insn_p (insn)
? DEBUG_TEMP_AFTER_WITH_REG_FORCE
: DEBUG_TEMP_BEFORE_WITH_VALUE);
}
if (dump_file)
{
fprintf (dump_file, "finished processing insn %d live out = ",
INSN_UID (insn));
df_print_word_regset (dump_file, local_live);
}
}
block_changed = !bitmap_equal_p (local_live, DF_WORD_LR_IN (bb));
if (block_changed)
bitmap_copy (DF_WORD_LR_IN (bb), local_live);
dead_debug_local_finish (&debug, NULL);
BITMAP_FREE (local_live);
return block_changed;
}
/* Process basic block BB. Return true if the live_in set has
changed. REDO_OUT is true if the info at the bottom of the block
needs to be recalculated before starting. AU is the proper set of
artificial uses. Track global substitution of uses of dead pseudos
in debug insns using GLOBAL_DEBUG. */
static bool
dce_process_block (basic_block bb, bool redo_out, bitmap au,
struct dead_debug_global *global_debug)
{
bitmap local_live = BITMAP_ALLOC (&dce_tmp_bitmap_obstack);
rtx insn;
bool block_changed;
df_ref *def_rec;
struct dead_debug_local debug;
if (redo_out)
{
/* Need to redo the live_out set of this block if when one of
the succs of this block has had a change in it live in
set. */
edge e;
edge_iterator ei;
df_confluence_function_n con_fun_n = df_lr->problem->con_fun_n;
bitmap_clear (DF_LR_OUT (bb));
FOR_EACH_EDGE (e, ei, bb->succs)
(*con_fun_n) (e);
}
if (dump_file)
{
fprintf (dump_file, "processing block %d lr out = ", bb->index);
df_print_regset (dump_file, DF_LR_OUT (bb));
}
bitmap_copy (local_live, DF_LR_OUT (bb));
df_simulate_initialize_backwards (bb, local_live);
dead_debug_local_init (&debug, NULL, global_debug);
FOR_BB_INSNS_REVERSE (bb, insn)
if (DEBUG_INSN_P (insn))
{
df_ref *use_rec;
for (use_rec = DF_INSN_USES (insn); *use_rec; use_rec++)
if (!bitmap_bit_p (local_live, DF_REF_REGNO (*use_rec))
&& !bitmap_bit_p (au, DF_REF_REGNO (*use_rec)))
dead_debug_add (&debug, *use_rec, DF_REF_REGNO (*use_rec));
}
else if (INSN_P (insn))
{
bool needed = marked_insn_p (insn);
/* The insn is needed if there is someone who uses the output. */
if (!needed)
for (def_rec = DF_INSN_DEFS (insn); *def_rec; def_rec++)
if (bitmap_bit_p (local_live, DF_REF_REGNO (*def_rec))
|| bitmap_bit_p (au, DF_REF_REGNO (*def_rec)))
{
needed = true;
mark_insn (insn, true);
break;
}
/* No matter if the instruction is needed or not, we remove
any regno in the defs from the live set. */
df_simulate_defs (insn, local_live);
/* On the other hand, we do not allow the dead uses to set
anything in local_live. */
if (needed)
df_simulate_uses (insn, local_live);
/* Insert debug temps for dead REGs used in subsequent debug
insns. We may have to emit a debug temp even if the insn
was marked, in case the debug use was after the point of
death. */
if (debug.used && !bitmap_empty_p (debug.used))
for (def_rec = DF_INSN_DEFS (insn); *def_rec; def_rec++)
dead_debug_insert_temp (&debug, DF_REF_REGNO (*def_rec), insn,
needed && !control_flow_insn_p (insn)
? DEBUG_TEMP_AFTER_WITH_REG_FORCE
: DEBUG_TEMP_BEFORE_WITH_VALUE);
}
dead_debug_local_finish (&debug, NULL);
df_simulate_finalize_backwards (bb, local_live);
block_changed = !bitmap_equal_p (local_live, DF_LR_IN (bb));
if (block_changed)
bitmap_copy (DF_LR_IN (bb), local_live);
BITMAP_FREE (local_live);
return block_changed;
}
/* Perform fast DCE once initialization is done. If WORD_LEVEL is
true, use the word level dce, otherwise do it at the pseudo
level. */
static void
fast_dce (bool word_level)
{
int *postorder = df_get_postorder (DF_BACKWARD);
int n_blocks = df_get_n_blocks (DF_BACKWARD);
/* The set of blocks that have been seen on this iteration. */
bitmap processed = BITMAP_ALLOC (&dce_blocks_bitmap_obstack);
/* The set of blocks that need to have the out vectors reset because
the in of one of their successors has changed. */
bitmap redo_out = BITMAP_ALLOC (&dce_blocks_bitmap_obstack);
bitmap all_blocks = BITMAP_ALLOC (&dce_blocks_bitmap_obstack);
bool global_changed = true;
/* These regs are considered always live so if they end up dying
because of some def, we need to bring the back again. Calling
df_simulate_fixup_sets has the disadvantage of calling
bb_has_eh_pred once per insn, so we cache the information
here. */
bitmap au = &df->regular_block_artificial_uses;
bitmap au_eh = &df->eh_block_artificial_uses;
int i;
struct dead_debug_global global_debug;
prescan_insns_for_dce (true);
for (i = 0; i < n_blocks; i++)
bitmap_set_bit (all_blocks, postorder[i]);
dead_debug_global_init (&global_debug, NULL);
while (global_changed)
{
global_changed = false;
for (i = 0; i < n_blocks; i++)
{
int index = postorder[i];
basic_block bb = BASIC_BLOCK_FOR_FN (cfun, index);
bool local_changed;
if (index < NUM_FIXED_BLOCKS)
{
bitmap_set_bit (processed, index);
continue;
}
if (word_level)
local_changed
= word_dce_process_block (bb, bitmap_bit_p (redo_out, index),
&global_debug);
else
local_changed
= dce_process_block (bb, bitmap_bit_p (redo_out, index),
bb_has_eh_pred (bb) ? au_eh : au,
&global_debug);
bitmap_set_bit (processed, index);
if (local_changed)
{
edge e;
edge_iterator ei;
FOR_EACH_EDGE (e, ei, bb->preds)
if (bitmap_bit_p (processed, e->src->index))
/* Be tricky about when we need to iterate the
analysis. We only have redo the analysis if the
bitmaps change at the top of a block that is the
entry to a loop. */
global_changed = true;
else
bitmap_set_bit (redo_out, e->src->index);
}
}
if (global_changed)
{
/* Turn off the RUN_DCE flag to prevent recursive calls to
dce. */
int old_flag = df_clear_flags (DF_LR_RUN_DCE);
/* So something was deleted that requires a redo. Do it on
the cheap. */
delete_unmarked_insns ();
bitmap_clear (marked);
bitmap_clear (processed);
bitmap_clear (redo_out);
/* We do not need to rescan any instructions. We only need
to redo the dataflow equations for the blocks that had a
change at the top of the block. Then we need to redo the
iteration. */
if (word_level)
df_analyze_problem (df_word_lr, all_blocks, postorder, n_blocks);
else
df_analyze_problem (df_lr, all_blocks, postorder, n_blocks);
if (old_flag & DF_LR_RUN_DCE)
df_set_flags (DF_LR_RUN_DCE);
prescan_insns_for_dce (true);
}
}
dead_debug_global_finish (&global_debug, NULL);
delete_unmarked_insns ();
BITMAP_FREE (processed);
BITMAP_FREE (redo_out);
BITMAP_FREE (all_blocks);
}
/* Fast register level DCE. */
static unsigned int
rest_of_handle_fast_dce (void)
{
init_dce (true);
fast_dce (false);
fini_dce (true);
return 0;
}
/* Fast byte level DCE. */
void
run_word_dce (void)
{
int old_flags;
if (!flag_dce)
return;
timevar_push (TV_DCE);
old_flags = df_clear_flags (DF_DEFER_INSN_RESCAN + DF_NO_INSN_RESCAN);
df_word_lr_add_problem ();
init_dce (true);
fast_dce (true);
fini_dce (true);
df_set_flags (old_flags);
timevar_pop (TV_DCE);
}
/* This is an internal call that is used by the df live register
problem to run fast dce as a side effect of creating the live
information. The stack is organized so that the lr problem is run,
this pass is run, which updates the live info and the df scanning
info, and then returns to allow the rest of the problems to be run.
This can be called by elsewhere but it will not update the bit
vectors for any other problems than LR. */
void
run_fast_df_dce (void)
{
if (flag_dce)
{
/* If dce is able to delete something, it has to happen
immediately. Otherwise there will be problems handling the
eq_notes. */
int old_flags =
df_clear_flags (DF_DEFER_INSN_RESCAN + DF_NO_INSN_RESCAN);
df_in_progress = true;
rest_of_handle_fast_dce ();
df_in_progress = false;
df_set_flags (old_flags);
}
}
/* Run a fast DCE pass. */
void
run_fast_dce (void)
{
if (flag_dce)
rest_of_handle_fast_dce ();
}
static bool
gate_fast_dce (void)
{
return optimize > 0 && flag_dce
&& dbg_cnt (dce_fast);
}
namespace {
const pass_data pass_data_fast_rtl_dce =
{
RTL_PASS, /* type */
"rtl_dce", /* name */
OPTGROUP_NONE, /* optinfo_flags */
true, /* has_gate */
true, /* has_execute */
TV_DCE, /* tv_id */
0, /* properties_required */
0, /* properties_provided */
0, /* properties_destroyed */
0, /* todo_flags_start */
( TODO_df_finish | TODO_verify_rtl_sharing ), /* todo_flags_finish */
};
class pass_fast_rtl_dce : public rtl_opt_pass
{
public:
pass_fast_rtl_dce (gcc::context *ctxt)
: rtl_opt_pass (pass_data_fast_rtl_dce, ctxt)
{}
/* opt_pass methods: */
bool gate () { return gate_fast_dce (); }
unsigned int execute () { return rest_of_handle_fast_dce (); }
}; // class pass_fast_rtl_dce
} // anon namespace
rtl_opt_pass *
make_pass_fast_rtl_dce (gcc::context *ctxt)
{
return new pass_fast_rtl_dce (ctxt);
}
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