814 lines
21 KiB
C
814 lines
21 KiB
C
/* RTL dead code elimination.
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Copyright (C) 2005, 2006, 2007 Free Software Foundation, Inc.
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This file is part of GCC.
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GCC is free software; you can redistribute it and/or modify it under
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the terms of the GNU General Public License as published by the Free
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Software Foundation; either version 2, or (at your option) any later
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version.
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GCC is distributed in the hope that it will be useful, but WITHOUT ANY
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WARRANTY; without even the implied warranty of MERCHANTABILITY or
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FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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for more details.
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You should have received a copy of the GNU General Public License
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along with GCC; see the file COPYING. If not, write to the Free
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Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA
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02110-1301, USA. */
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#include "config.h"
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#include "system.h"
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#include "coretypes.h"
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#include "hashtab.h"
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#include "tm.h"
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#include "rtl.h"
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#include "tree.h"
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#include "regs.h"
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#include "hard-reg-set.h"
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#include "flags.h"
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#include "df.h"
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#include "cselib.h"
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#include "dce.h"
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#include "timevar.h"
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#include "tree-pass.h"
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#include "dbgcnt.h"
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DEF_VEC_I(int);
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DEF_VEC_ALLOC_I(int,heap);
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/* -------------------------------------------------------------------------
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Core mark/delete routines
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------------------------------------------------------------------------- */
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/* The data-flow information needed by this pass. */
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static bool df_in_progress = false;
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/* True if we deleted at least one instruction. */
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static bool something_changed;
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/* Instructions that have been marked but whose dependencies have not
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yet been processed. */
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static VEC(rtx,heap) *worklist;
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static bitmap_obstack dce_blocks_bitmap_obstack;
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static bitmap_obstack dce_tmp_bitmap_obstack;
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static sbitmap marked = NULL;
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/* A subroutine for which BODY is part of the instruction being tested;
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either the top-level pattern, or an element of a PARALLEL. The
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instruction is known not to be a bare USE or CLOBBER. */
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static bool
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deletable_insn_p_1 (rtx body)
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{
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switch (GET_CODE (body))
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{
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case PREFETCH:
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case TRAP_IF:
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/* The UNSPEC case was added here because the ia-64 claims that
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USEs do not work after reload and generates UNSPECS rather
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than USEs. Since dce is run after reload we need to avoid
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deleting these even if they are dead. If it turns out that
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USEs really do work after reload, the ia-64 should be
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changed, and the UNSPEC case can be removed. */
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case UNSPEC:
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return false;
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default:
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if (volatile_insn_p (body))
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return false;
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if (flag_non_call_exceptions && may_trap_p (body))
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return false;
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return true;
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}
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}
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/* Return true if INSN is a normal instruction that can be deleted by
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the DCE pass. */
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static bool
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deletable_insn_p (rtx insn, bool fast)
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{
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rtx body, x;
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int i;
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if (!NONJUMP_INSN_P (insn))
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return false;
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body = PATTERN (insn);
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switch (GET_CODE (body))
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{
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case USE:
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return false;
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case CLOBBER:
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if (fast)
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{
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/* A CLOBBER of a dead pseudo register serves no purpose.
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That is not necessarily true for hard registers until
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after reload. */
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x = XEXP (body, 0);
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return REG_P (x) && (!HARD_REGISTER_P (x) || reload_completed);
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}
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else
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/* Because of the way that use-def chains are built, it is not
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possible to tell if the clobber is dead because it can
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never be the target of a use-def chain. */
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return false;
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case PARALLEL:
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for (i = XVECLEN (body, 0) - 1; i >= 0; i--)
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if (!deletable_insn_p_1 (XVECEXP (body, 0, i)))
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return false;
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return true;
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default:
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return deletable_insn_p_1 (body);
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}
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}
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/* Return true if INSN has not been marked as needed. */
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static inline int
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marked_insn_p (rtx insn)
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{
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if (insn)
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return TEST_BIT (marked, INSN_UID (insn));
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else
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/* Artificial defs are always needed and they do not have an
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insn. */
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return true;
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}
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/* If INSN has not yet been marked as needed, mark it now, and add it to
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the worklist. */
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static void
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mark_insn (rtx insn, bool fast)
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{
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if (!marked_insn_p (insn))
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{
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if (!fast)
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VEC_safe_push (rtx, heap, worklist, insn);
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SET_BIT (marked, INSN_UID (insn));
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if (dump_file)
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fprintf (dump_file, " Adding insn %d to worklist\n", INSN_UID (insn));
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}
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}
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/* A note_stores callback used by mark_nonreg_stores. DATA is the
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instruction containing DEST. */
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static void
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mark_nonreg_stores_1 (rtx dest, rtx pattern, void *data)
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{
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if (GET_CODE (pattern) != CLOBBER && !REG_P (dest))
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mark_insn ((rtx) data, true);
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}
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/* A note_stores callback used by mark_nonreg_stores. DATA is the
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instruction containing DEST. */
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static void
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mark_nonreg_stores_2 (rtx dest, rtx pattern, void *data)
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{
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if (GET_CODE (pattern) != CLOBBER && !REG_P (dest))
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mark_insn ((rtx) data, false);
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}
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/* Mark INSN if BODY stores to a non-register destination. */
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static void
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mark_nonreg_stores (rtx body, rtx insn, bool fast)
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{
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if (fast)
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note_stores (body, mark_nonreg_stores_1, insn);
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else
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note_stores (body, mark_nonreg_stores_2, insn);
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}
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/* Initialize global variables for a new DCE pass. */
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static void
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init_dce (bool fast)
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{
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if (!df_in_progress)
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{
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if (!fast)
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df_chain_add_problem (DF_UD_CHAIN);
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df_analyze ();
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}
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if (dump_file)
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df_dump (dump_file);
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bitmap_obstack_initialize (&dce_blocks_bitmap_obstack);
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bitmap_obstack_initialize (&dce_tmp_bitmap_obstack);
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marked = sbitmap_alloc (get_max_uid () + 1);
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sbitmap_zero (marked);
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}
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/* Delete all REG_EQUAL notes of the registers INSN writes, to prevent
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bad dangling REG_EQUAL notes. */
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static void
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delete_corresponding_reg_eq_notes (rtx insn)
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{
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struct df_ref **def_rec;
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for (def_rec = DF_INSN_DEFS (insn); *def_rec; def_rec++)
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{
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struct df_ref *def = *def_rec;
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unsigned int regno = DF_REF_REGNO (def);
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/* This loop is a little tricky. We cannot just go down the
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chain because it is being modified by the actions in the
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loop. So we just get the head. We plan to drain the list
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anyway. */
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while (DF_REG_EQ_USE_CHAIN (regno))
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{
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struct df_ref *eq_use = DF_REG_EQ_USE_CHAIN (regno);
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rtx noted_insn = DF_REF_INSN (eq_use);
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rtx note = find_reg_note (noted_insn, REG_EQUAL, NULL_RTX);
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if (!note)
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note = find_reg_note (noted_insn, REG_EQUIV, NULL_RTX);
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/* This assert is generally triggered when someone deletes a
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REG_EQUAL or REG_EQUIV note by hacking the list manually
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rather than calling remove_note. */
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gcc_assert (note);
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remove_note (noted_insn, note);
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}
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}
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}
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/* Delete every instruction that hasn't been marked. Clear the insn
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from DCE_DF if DF_DELETE is true. */
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static void
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delete_unmarked_insns (void)
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{
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basic_block bb;
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rtx insn, next;
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something_changed = false;
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FOR_EACH_BB (bb)
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FOR_BB_INSNS_SAFE (bb, insn, next)
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if (INSN_P (insn))
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{
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if (noop_move_p (insn))
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{
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/* Note that this code does not handle the case where
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the last insn of libcall is deleted. As it turns out
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this case is excluded in the call to noop_move_p. */
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rtx note = find_reg_note (insn, REG_LIBCALL, NULL_RTX);
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if (note && (XEXP (note, 0) != insn))
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{
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rtx new_libcall_insn = next_real_insn (insn);
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rtx retval_note = find_reg_note (XEXP (note, 0),
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REG_RETVAL, NULL_RTX);
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REG_NOTES (new_libcall_insn)
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= gen_rtx_INSN_LIST (REG_LIBCALL, XEXP (note, 0),
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REG_NOTES (new_libcall_insn));
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XEXP (retval_note, 0) = new_libcall_insn;
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}
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}
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else if (marked_insn_p (insn))
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continue;
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/* WARNING, this debugging can itself cause problems if the
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edge of the counter causes part of a libcall to be
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deleted but not all of it. */
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if (!dbg_cnt (dce))
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continue;
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if (dump_file)
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fprintf (dump_file, "DCE: Deleting insn %d\n", INSN_UID (insn));
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/* Before we delete the insn, we have to delete
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REG_EQUAL of the destination regs of the deleted insn
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to prevent dangling REG_EQUAL. */
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delete_corresponding_reg_eq_notes (insn);
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delete_insn_and_edges (insn);
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something_changed = true;
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}
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}
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/* Mark all insns using DELETE_PARM in the libcall that contains
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START_INSN. */
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static void
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mark_libcall (rtx start_insn, bool delete_parm)
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{
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rtx note = find_reg_note (start_insn, REG_LIBCALL_ID, NULL_RTX);
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int id = INTVAL (XEXP (note, 0));
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rtx insn;
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mark_insn (start_insn, delete_parm);
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insn = NEXT_INSN (start_insn);
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/* There are tales, long ago and far away, of the mystical nested
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libcall. No one alive has actually seen one, but other parts of
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the compiler support them so we will here. */
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for (insn = NEXT_INSN (start_insn); insn; insn = NEXT_INSN (insn))
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{
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if (INSN_P (insn))
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{
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/* Stay in the loop as long as we are in any libcall. */
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if ((note = find_reg_note (insn, REG_LIBCALL_ID, NULL_RTX)))
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{
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if (id == INTVAL (XEXP (note, 0)))
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{
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mark_insn (insn, delete_parm);
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if (dump_file)
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fprintf (dump_file, "matching forward libcall %d[%d]\n",
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INSN_UID (insn), id);
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}
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}
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else
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break;
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}
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}
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for (insn = PREV_INSN (start_insn); insn; insn = PREV_INSN (insn))
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{
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if (INSN_P (insn))
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{
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/* Stay in the loop as long as we are in any libcall. */
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if ((note = find_reg_note (insn, REG_LIBCALL_ID, NULL_RTX)))
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{
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if (id == INTVAL (XEXP (note, 0)))
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{
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mark_insn (insn, delete_parm);
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if (dump_file)
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fprintf (dump_file, "matching backward libcall %d[%d]\n",
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INSN_UID (insn), id);
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}
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}
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else
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break;
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}
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}
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}
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/* Go through the instructions and mark those whose necessity is not
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dependent on inter-instruction information. Make sure all other
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instructions are not marked. */
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static void
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prescan_insns_for_dce (bool fast)
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{
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basic_block bb;
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rtx insn;
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if (dump_file)
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fprintf (dump_file, "Finding needed instructions:\n");
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FOR_EACH_BB (bb)
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FOR_BB_INSNS (bb, insn)
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if (INSN_P (insn))
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{
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rtx note = find_reg_note (insn, REG_LIBCALL_ID, NULL_RTX);
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if (note)
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mark_libcall (insn, fast);
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else if (deletable_insn_p (insn, fast))
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mark_nonreg_stores (PATTERN (insn), insn, fast);
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else
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mark_insn (insn, fast);
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}
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if (dump_file)
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fprintf (dump_file, "Finished finding needed instructions:\n");
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}
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/* UD-based DSE routines. */
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/* Mark instructions that define artifically-used registers, such as
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the frame pointer and the stack pointer. */
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static void
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mark_artificial_uses (void)
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{
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basic_block bb;
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struct df_link *defs;
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struct df_ref **use_rec;
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FOR_ALL_BB (bb)
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{
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for (use_rec = df_get_artificial_uses (bb->index);
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*use_rec; use_rec++)
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for (defs = DF_REF_CHAIN (*use_rec); defs; defs = defs->next)
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mark_insn (DF_REF_INSN (defs->ref), false);
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}
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}
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/* Mark every instruction that defines a register value that INSN uses. */
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static void
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mark_reg_dependencies (rtx insn)
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{
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struct df_link *defs;
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struct df_ref **use_rec;
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/* If this is part of a libcall, mark the entire libcall. */
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if (find_reg_note (insn, REG_LIBCALL_ID, NULL_RTX))
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mark_libcall (insn, false);
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for (use_rec = DF_INSN_USES (insn); *use_rec; use_rec++)
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{
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struct df_ref *use = *use_rec;
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if (dump_file)
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{
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fprintf (dump_file, "Processing use of ");
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print_simple_rtl (dump_file, DF_REF_REG (use));
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fprintf (dump_file, " in insn %d:\n", INSN_UID (insn));
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}
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for (defs = DF_REF_CHAIN (use); defs; defs = defs->next)
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mark_insn (DF_REF_INSN (defs->ref), false);
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}
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}
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static void
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end_ud_dce (void)
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{
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sbitmap_free (marked);
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gcc_assert (VEC_empty (rtx, worklist));
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}
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/* UD-chain based DCE. */
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static unsigned int
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rest_of_handle_ud_dce (void)
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{
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rtx insn;
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df_in_progress = false;
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init_dce (false);
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prescan_insns_for_dce (false);
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mark_artificial_uses ();
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while (VEC_length (rtx, worklist) > 0)
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{
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insn = VEC_pop (rtx, worklist);
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mark_reg_dependencies (insn);
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}
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/* Before any insns are deleted, we must remove the chains since
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they are not bidirectional. */
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df_remove_problem (df_chain);
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delete_unmarked_insns ();
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end_ud_dce ();
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return 0;
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}
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static bool
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gate_ud_dce (void)
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{
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return optimize > 1 && flag_dce;
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}
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struct tree_opt_pass pass_ud_rtl_dce =
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{
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"dce", /* name */
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gate_ud_dce, /* gate */
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rest_of_handle_ud_dce, /* execute */
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NULL, /* sub */
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NULL, /* next */
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0, /* static_pass_number */
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TV_DCE, /* tv_id */
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0, /* properties_required */
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0, /* properties_provided */
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0, /* properties_destroyed */
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0, /* todo_flags_start */
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TODO_dump_func |
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TODO_df_finish |
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TODO_ggc_collect, /* todo_flags_finish */
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'w' /* letter */
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};
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/* -------------------------------------------------------------------------
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Fast DCE functions
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------------------------------------------------------------------------- */
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/* Free the data allocated by init_dce. */
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static void
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fini_dce (void)
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{
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sbitmap_free (marked);
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bitmap_obstack_release (&dce_blocks_bitmap_obstack);
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bitmap_obstack_release (&dce_tmp_bitmap_obstack);
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df_in_progress = false;
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}
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/* Process basic block BB. Return true if the live_in set has
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changed. */
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static bool
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dce_process_block (basic_block bb, bool redo_out)
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{
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bitmap local_live = BITMAP_ALLOC (&dce_tmp_bitmap_obstack);
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rtx insn;
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bool block_changed;
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struct df_ref **def_rec, **use_rec;
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unsigned int bb_index = bb->index;
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if (redo_out)
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{
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/* Need to redo the live_out set of this block if when one of
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the succs of this block has had a change in it live in
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set. */
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edge e;
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edge_iterator ei;
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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 live out = ", bb->index);
|
|
df_print_regset (dump_file, DF_LR_OUT (bb));
|
|
}
|
|
|
|
bitmap_copy (local_live, DF_LR_OUT (bb));
|
|
|
|
/* Process the artificial defs and uses at the bottom of the block. */
|
|
for (def_rec = df_get_artificial_defs (bb_index); *def_rec; def_rec++)
|
|
{
|
|
struct df_ref *def = *def_rec;
|
|
if (((DF_REF_FLAGS (def) & DF_REF_AT_TOP) == 0)
|
|
&& (!(DF_REF_FLAGS (def) & (DF_REF_PARTIAL | DF_REF_CONDITIONAL))))
|
|
bitmap_clear_bit (local_live, DF_REF_REGNO (def));
|
|
}
|
|
|
|
for (use_rec = df_get_artificial_uses (bb_index); *use_rec; use_rec++)
|
|
{
|
|
struct df_ref *use = *use_rec;
|
|
if ((DF_REF_FLAGS (use) & DF_REF_AT_TOP) == 0)
|
|
bitmap_set_bit (local_live, DF_REF_REGNO (use));
|
|
}
|
|
|
|
FOR_BB_INSNS_REVERSE (bb, insn)
|
|
if (INSN_P (insn))
|
|
{
|
|
/* If this is a recursive call, the libcall will have already
|
|
been marked. */
|
|
if (!marked_insn_p (insn))
|
|
{
|
|
bool needed = false;
|
|
|
|
/* The insn is needed if there is someone who uses the output. */
|
|
for (def_rec = DF_INSN_DEFS (insn); *def_rec; def_rec++)
|
|
if (bitmap_bit_p (local_live, DF_REF_REGNO (*def_rec)))
|
|
{
|
|
needed = true;
|
|
break;
|
|
}
|
|
|
|
if (needed)
|
|
{
|
|
rtx note = find_reg_note (insn, REG_LIBCALL_ID, NULL_RTX);
|
|
|
|
/* If we need to mark an insn in the middle of a
|
|
libcall, we need to back up to mark the entire
|
|
libcall. Given that libcalls are rare, rescanning
|
|
the block should be a reasonable solution to trying
|
|
to figure out how to back up. */
|
|
if (note)
|
|
{
|
|
if (dump_file)
|
|
fprintf (dump_file, "needed libcall %d\n", INSN_UID (insn));
|
|
mark_libcall (insn, true);
|
|
BITMAP_FREE (local_live);
|
|
return dce_process_block (bb, false);
|
|
}
|
|
else
|
|
mark_insn (insn, true);
|
|
}
|
|
}
|
|
|
|
/* 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 (marked_insn_p (insn))
|
|
df_simulate_uses (insn, local_live);
|
|
}
|
|
|
|
for (def_rec = df_get_artificial_defs (bb_index); *def_rec; def_rec++)
|
|
{
|
|
struct df_ref *def = *def_rec;
|
|
if ((DF_REF_FLAGS (def) & DF_REF_AT_TOP)
|
|
&& (!(DF_REF_FLAGS (def) & (DF_REF_PARTIAL | DF_REF_CONDITIONAL))))
|
|
bitmap_clear_bit (local_live, DF_REF_REGNO (def));
|
|
}
|
|
#ifdef EH_USES
|
|
/* Process the uses that are live into an exception handler. */
|
|
for (use_rec = df_get_artificial_uses (bb_index); *use_rec; use_rec++)
|
|
{
|
|
/* Add use to set of uses in this BB. */
|
|
struct df_ref *use = *use_rec;
|
|
if (DF_REF_FLAGS (use) & DF_REF_AT_TOP)
|
|
bitmap_set_bit (local_live, DF_REF_REGNO (use));
|
|
}
|
|
#endif
|
|
|
|
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;
|
|
}
|
|
|
|
static void
|
|
fast_dce (void)
|
|
{
|
|
int *postorder = df_get_postorder (DF_BACKWARD);
|
|
int n_blocks = df_get_n_blocks (DF_BACKWARD);
|
|
int i;
|
|
/* 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;
|
|
|
|
int loop_count = 0;
|
|
|
|
prescan_insns_for_dce (true);
|
|
|
|
for (i = 0; i < n_blocks; i++)
|
|
bitmap_set_bit (all_blocks, postorder[i]);
|
|
|
|
while (global_changed)
|
|
{
|
|
global_changed = false;
|
|
for (i = 0; i < n_blocks; i++)
|
|
{
|
|
int index = postorder[i];
|
|
basic_block bb = BASIC_BLOCK (index);
|
|
bool local_changed;
|
|
|
|
if (index < NUM_FIXED_BLOCKS)
|
|
{
|
|
bitmap_set_bit (processed, index);
|
|
continue;
|
|
}
|
|
|
|
local_changed
|
|
= dce_process_block (bb, bitmap_bit_p (redo_out, index));
|
|
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 ();
|
|
sbitmap_zero (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. */
|
|
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);
|
|
}
|
|
loop_count++;
|
|
}
|
|
|
|
delete_unmarked_insns ();
|
|
|
|
BITMAP_FREE (processed);
|
|
BITMAP_FREE (redo_out);
|
|
BITMAP_FREE (all_blocks);
|
|
}
|
|
|
|
|
|
/* Callback for running pass_rtl_dce. */
|
|
|
|
static unsigned int
|
|
rest_of_handle_fast_dce (void)
|
|
{
|
|
init_dce (true);
|
|
fast_dce ();
|
|
fini_dce ();
|
|
df_in_progress = false;
|
|
return 0;
|
|
}
|
|
|
|
|
|
/* 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. */
|
|
enum df_changeable_flags old_flags
|
|
= df_clear_flags (DF_DEFER_INSN_RESCAN + DF_NO_INSN_RESCAN);
|
|
|
|
df_in_progress = true;
|
|
rest_of_handle_fast_dce ();
|
|
df_set_flags (old_flags);
|
|
}
|
|
}
|
|
|
|
static bool
|
|
gate_fast_dce (void)
|
|
{
|
|
return optimize > 0 && flag_dce;
|
|
}
|
|
|
|
|
|
/* Run a fast DCE pass and return true if any instructions were
|
|
deleted. */
|
|
|
|
bool
|
|
run_fast_dce (void)
|
|
{
|
|
return gate_fast_dce () && (rest_of_handle_fast_dce (), something_changed);
|
|
}
|
|
|
|
|
|
struct tree_opt_pass pass_fast_rtl_dce =
|
|
{
|
|
"dce", /* name */
|
|
gate_fast_dce, /* gate */
|
|
rest_of_handle_fast_dce, /* execute */
|
|
NULL, /* sub */
|
|
NULL, /* next */
|
|
0, /* static_pass_number */
|
|
TV_DCE, /* tv_id */
|
|
0, /* properties_required */
|
|
0, /* properties_provided */
|
|
0, /* properties_destroyed */
|
|
0, /* todo_flags_start */
|
|
TODO_dump_func |
|
|
TODO_df_finish |
|
|
TODO_ggc_collect, /* todo_flags_finish */
|
|
'w' /* letter */
|
|
};
|
|
|