307 lines
9.1 KiB
C
307 lines
9.1 KiB
C
/* Web construction code for GNU compiler.
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Contributed by Jan Hubicka.
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Copyright (C) 2001, 2002 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, 59 Temple Place - Suite 330, Boston, MA
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02111-1307, USA. */
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/* Simple optimization pass that splits independent uses of each pseudo,
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increasing effectiveness of other optimizations. The optimization can
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serve as an example of use for the dataflow module.
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We don't split registers with REG_USERVAR set unless -fmessy-debugging
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is specified, because debugging information about such split variables
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is almost unusable.
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TODO
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- Add code to keep debugging up-to-date after splitting user variable
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pseudos. This can be done by keeping track of all the pseudos used
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for the variable and using life analysis information before reload
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to determine which one is live and, in case more than one are live,
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choose the one with the latest definition.
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Other optimization passes can benefit from the infrastructure too.
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- We may use profile information and ignore infrequent use for the
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purpose of web unifying, inserting the compensation code later to
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implement full induction variable expansion for loops (currently
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we expand only if the induction variable is dead afterward, which
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is often the case). */
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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 "tm.h"
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#include "toplev.h"
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#include "rtl.h"
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#include "hard-reg-set.h"
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#include "flags.h"
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#include "basic-block.h"
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#include "output.h"
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#include "df.h"
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#include "function.h"
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/* This entry is allocated for each reference in the insn stream. */
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struct web_entry
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{
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/* Pointer to the parent in the union/find tree. */
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struct web_entry *pred;
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/* Newly assigned register to the entry. Set only for roots. */
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rtx reg;
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};
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static struct web_entry *unionfind_root (struct web_entry *);
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static void unionfind_union (struct web_entry *, struct web_entry *);
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static void union_defs (struct df *, struct ref *, struct web_entry *,
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struct web_entry *);
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static rtx entry_register (struct web_entry *, struct ref *, char *, char *);
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static void replace_ref (struct ref *, rtx);
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static int mark_addressof (rtx *, void *);
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/* Find the root of unionfind tree (the representative of set). */
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static struct web_entry *
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unionfind_root (struct web_entry *element)
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{
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struct web_entry *element1 = element, *element2;
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while (element->pred)
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element = element->pred;
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while (element1->pred)
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{
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element2 = element1->pred;
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element1->pred = element;
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element1 = element2;
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}
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return element;
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}
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/* Union sets. */
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static void
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unionfind_union (struct web_entry *first, struct web_entry *second)
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{
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first = unionfind_root (first);
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second = unionfind_root (second);
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if (first == second)
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return;
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second->pred = first;
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}
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/* For each use, all possible defs reaching it must come in the same
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register, union them. */
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static void
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union_defs (struct df *df, struct ref *use, struct web_entry *def_entry,
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struct web_entry *use_entry)
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{
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rtx insn = DF_REF_INSN (use);
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struct df_link *link = DF_REF_CHAIN (use);
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struct df_link *use_link = DF_INSN_USES (df, insn);
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struct df_link *def_link = DF_INSN_DEFS (df, insn);
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rtx set = single_set (insn);
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/* Some instructions may use match_dup for their operands. In case the
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operands are dead, we will assign them different pseudos, creating
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invalid instructions, so union all uses of the same operand for each
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insn. */
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while (use_link)
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{
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if (use != use_link->ref
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&& DF_REF_REAL_REG (use) == DF_REF_REAL_REG (use_link->ref))
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unionfind_union (use_entry + DF_REF_ID (use),
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use_entry + DF_REF_ID (use_link->ref));
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use_link = use_link->next;
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}
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/* Recognize trivial noop moves and attempt to keep them as noop.
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While most of noop moves should be removed, we still keep some
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of them at libcall boundaries and such. */
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if (set
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&& SET_SRC (set) == DF_REF_REG (use)
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&& SET_SRC (set) == SET_DEST (set))
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{
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while (def_link)
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{
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if (DF_REF_REAL_REG (use) == DF_REF_REAL_REG (def_link->ref))
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unionfind_union (use_entry + DF_REF_ID (use),
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def_entry + DF_REF_ID (def_link->ref));
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def_link = def_link->next;
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}
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}
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while (link)
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{
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unionfind_union (use_entry + DF_REF_ID (use),
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def_entry + DF_REF_ID (link->ref));
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link = link->next;
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}
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/* A READ_WRITE use requires the corresponding def to be in the same
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register. Find it and union. */
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if (use->flags & DF_REF_READ_WRITE)
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{
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struct df_link *link = DF_INSN_DEFS (df, DF_REF_INSN (use));
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while (DF_REF_REAL_REG (link->ref) != DF_REF_REAL_REG (use))
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link = link->next;
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unionfind_union (use_entry + DF_REF_ID (use),
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def_entry + DF_REF_ID (link->ref));
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}
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}
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/* Find the corresponding register for the given entry. */
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static rtx
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entry_register (struct web_entry *entry, struct ref *ref, char *used,
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char *use_addressof)
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{
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struct web_entry *root;
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rtx reg, newreg;
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/* Find the corresponding web and see if it has been visited. */
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root = unionfind_root (entry);
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if (root->reg)
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return root->reg;
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/* We are seeing this web for the first time, do the assignment. */
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reg = DF_REF_REAL_REG (ref);
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/* In case the original register is already assigned, generate new one. */
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if (!used[REGNO (reg)])
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newreg = reg, used[REGNO (reg)] = 1;
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else if (REG_USERVAR_P (reg) && 0/*&& !flag_messy_debugging*/)
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{
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newreg = reg;
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if (rtl_dump_file)
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fprintf (rtl_dump_file,
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"New web forced to keep reg=%i (user variable)\n",
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REGNO (reg));
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}
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else if (use_addressof [REGNO (reg)])
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{
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newreg = reg;
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if (rtl_dump_file)
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fprintf (rtl_dump_file,
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"New web forced to keep reg=%i (address taken)\n",
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REGNO (reg));
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}
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else
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{
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newreg = gen_reg_rtx (GET_MODE (reg));
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REG_USERVAR_P (newreg) = REG_USERVAR_P (reg);
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REG_POINTER (newreg) = REG_POINTER (reg);
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REG_LOOP_TEST_P (newreg) = REG_LOOP_TEST_P (reg);
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RTX_UNCHANGING_P (newreg) = RTX_UNCHANGING_P (reg);
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REG_ATTRS (newreg) = REG_ATTRS (reg);
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if (rtl_dump_file)
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fprintf (rtl_dump_file, "Web oldreg=%i newreg=%i\n", REGNO (reg),
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REGNO (newreg));
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}
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root->reg = newreg;
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return newreg;
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}
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/* Replace the reference by REG. */
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static void
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replace_ref (struct ref *ref, rtx reg)
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{
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rtx oldreg = DF_REF_REAL_REG (ref);
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rtx *loc = DF_REF_REAL_LOC (ref);
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if (oldreg == reg)
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return;
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if (rtl_dump_file)
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fprintf (rtl_dump_file, "Updating insn %i (%i->%i)\n",
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INSN_UID (DF_REF_INSN (ref)), REGNO (oldreg), REGNO (reg));
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*loc = reg;
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}
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/* Mark each pseudo whose address is taken. */
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static int
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mark_addressof (rtx *rtl, void *data)
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{
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if (!*rtl)
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return 0;
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if (GET_CODE (*rtl) == ADDRESSOF
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&& REG_P (XEXP (*rtl, 0)))
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((char *)data)[REGNO (XEXP (*rtl, 0))] = 1;
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return 0;
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}
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/* Main entry point. */
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void
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web_main (void)
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{
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struct df *df;
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struct web_entry *def_entry;
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struct web_entry *use_entry;
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unsigned int i;
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int max = max_reg_num ();
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char *used;
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char *use_addressof;
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rtx insn;
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df = df_init ();
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df_analyse (df, 0, DF_UD_CHAIN | DF_EQUIV_NOTES);
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def_entry =
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(struct web_entry *) xcalloc (df->n_defs, sizeof (struct web_entry));
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use_entry =
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(struct web_entry *) xcalloc (df->n_uses, sizeof (struct web_entry));
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used = (char *) xcalloc (max, sizeof (char));
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use_addressof = (char *) xcalloc (max, sizeof (char));
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if (rtl_dump_file)
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df_dump (df, DF_UD_CHAIN | DF_DU_CHAIN, rtl_dump_file);
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/* Produce the web. */
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for (i = 0; i < df->n_uses; i++)
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union_defs (df, df->uses[i], def_entry, use_entry);
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/* We can not safely rename registers whose address is taken. */
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for (insn = get_insns (); insn; insn = NEXT_INSN (insn))
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if (INSN_P (insn))
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for_each_rtx (&PATTERN (insn), mark_addressof, use_addressof);
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/* Update the instruction stream, allocating new registers for split pseudos
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in progress. */
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for (i = 0; i < df->n_uses; i++)
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replace_ref (df->uses[i], entry_register (use_entry + i, df->uses[i],
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used, use_addressof));
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for (i = 0; i < df->n_defs; i++)
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replace_ref (df->defs[i], entry_register (def_entry + i, df->defs[i],
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used, use_addressof));
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/* Dataflow information is corrupt here, but it can be easily updated
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by creating new entries for new registers and updates or calling
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df_insns_modify. */
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free (def_entry);
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free (use_entry);
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free (used);
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free (use_addressof);
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df_finish (df);
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}
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