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+/* Web construction code for GNU compiler.
+ Contributed by Jan Hubicka.
+ Copyright (C) 2001, 2002 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 2, 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 COPYING. If not, write to the Free
+Software Foundation, 59 Temple Place - Suite 330, Boston, MA
+02111-1307, USA. */
+
+/* Simple optimization pass that splits independent uses of each pseudo,
+ increasing effectiveness of other optimizations. The optimization can
+ serve as an example of use for the dataflow module.
+
+ We don't split registers with REG_USERVAR set unless -fmessy-debugging
+ is specified, because debugging information about such split variables
+ is almost unusable.
+
+ TODO
+ - Add code to keep debugging up-to-date after splitting user variable
+ pseudos. This can be done by keeping track of all the pseudos used
+ for the variable and using life analysis information before reload
+ to determine which one is live and, in case more than one are live,
+ choose the one with the latest definition.
+
+ Other optimization passes can benefit from the infrastructure too.
+
+ - We may use profile information and ignore infrequent use for the
+ purpose of web unifying, inserting the compensation code later to
+ implement full induction variable expansion for loops (currently
+ we expand only if the induction variable is dead afterward, which
+ is often the case). */
+
+#include "config.h"
+#include "system.h"
+#include "coretypes.h"
+#include "tm.h"
+#include "toplev.h"
+
+#include "rtl.h"
+#include "hard-reg-set.h"
+#include "flags.h"
+#include "basic-block.h"
+#include "output.h"
+#include "df.h"
+#include "function.h"
+
+
+/* This entry is allocated for each reference in the insn stream. */
+struct web_entry
+{
+ /* Pointer to the parent in the union/find tree. */
+ struct web_entry *pred;
+ /* Newly assigned register to the entry. Set only for roots. */
+ rtx reg;
+};
+
+static struct web_entry *unionfind_root (struct web_entry *);
+static void unionfind_union (struct web_entry *, struct web_entry *);
+static void union_defs (struct df *, struct ref *, struct web_entry *,
+ struct web_entry *);
+static rtx entry_register (struct web_entry *, struct ref *, char *, char *);
+static void replace_ref (struct ref *, rtx);
+static int mark_addressof (rtx *, void *);
+
+/* Find the root of unionfind tree (the representative of set). */
+
+static struct web_entry *
+unionfind_root (struct web_entry *element)
+{
+ struct web_entry *element1 = element, *element2;
+
+ while (element->pred)
+ element = element->pred;
+ while (element1->pred)
+ {
+ element2 = element1->pred;
+ element1->pred = element;
+ element1 = element2;
+ }
+ return element;
+}
+
+/* Union sets. */
+
+static void
+unionfind_union (struct web_entry *first, struct web_entry *second)
+{
+ first = unionfind_root (first);
+ second = unionfind_root (second);
+ if (first == second)
+ return;
+ second->pred = first;
+}
+
+/* For each use, all possible defs reaching it must come in the same
+ register, union them. */
+
+static void
+union_defs (struct df *df, struct ref *use, struct web_entry *def_entry,
+ struct web_entry *use_entry)
+{
+ rtx insn = DF_REF_INSN (use);
+ struct df_link *link = DF_REF_CHAIN (use);
+ struct df_link *use_link = DF_INSN_USES (df, insn);
+ struct df_link *def_link = DF_INSN_DEFS (df, insn);
+ rtx set = single_set (insn);
+
+ /* Some instructions may use match_dup for their operands. In case the
+ operands are dead, we will assign them different pseudos, creating
+ invalid instructions, so union all uses of the same operand for each
+ insn. */
+
+ while (use_link)
+ {
+ if (use != use_link->ref
+ && DF_REF_REAL_REG (use) == DF_REF_REAL_REG (use_link->ref))
+ unionfind_union (use_entry + DF_REF_ID (use),
+ use_entry + DF_REF_ID (use_link->ref));
+ use_link = use_link->next;
+ }
+
+ /* Recognize trivial noop moves and attempt to keep them as noop.
+ While most of noop moves should be removed, we still keep some
+ of them at libcall boundaries and such. */
+
+ if (set
+ && SET_SRC (set) == DF_REF_REG (use)
+ && SET_SRC (set) == SET_DEST (set))
+ {
+ while (def_link)
+ {
+ if (DF_REF_REAL_REG (use) == DF_REF_REAL_REG (def_link->ref))
+ unionfind_union (use_entry + DF_REF_ID (use),
+ def_entry + DF_REF_ID (def_link->ref));
+ def_link = def_link->next;
+ }
+ }
+ while (link)
+ {
+ unionfind_union (use_entry + DF_REF_ID (use),
+ def_entry + DF_REF_ID (link->ref));
+ link = link->next;
+ }
+
+ /* A READ_WRITE use requires the corresponding def to be in the same
+ register. Find it and union. */
+ if (use->flags & DF_REF_READ_WRITE)
+ {
+ struct df_link *link = DF_INSN_DEFS (df, DF_REF_INSN (use));
+
+ while (DF_REF_REAL_REG (link->ref) != DF_REF_REAL_REG (use))
+ link = link->next;
+
+ unionfind_union (use_entry + DF_REF_ID (use),
+ def_entry + DF_REF_ID (link->ref));
+ }
+}
+
+/* Find the corresponding register for the given entry. */
+
+static rtx
+entry_register (struct web_entry *entry, struct ref *ref, char *used,
+ char *use_addressof)
+{
+ struct web_entry *root;
+ rtx reg, newreg;
+
+ /* Find the corresponding web and see if it has been visited. */
+ root = unionfind_root (entry);
+ if (root->reg)
+ return root->reg;
+
+ /* We are seeing this web for the first time, do the assignment. */
+ reg = DF_REF_REAL_REG (ref);
+
+ /* In case the original register is already assigned, generate new one. */
+ if (!used[REGNO (reg)])
+ newreg = reg, used[REGNO (reg)] = 1;
+ else if (REG_USERVAR_P (reg) && 0/*&& !flag_messy_debugging*/)
+ {
+ newreg = reg;
+ if (rtl_dump_file)
+ fprintf (rtl_dump_file,
+ "New web forced to keep reg=%i (user variable)\n",
+ REGNO (reg));
+ }
+ else if (use_addressof [REGNO (reg)])
+ {
+ newreg = reg;
+ if (rtl_dump_file)
+ fprintf (rtl_dump_file,
+ "New web forced to keep reg=%i (address taken)\n",
+ REGNO (reg));
+ }
+ else
+ {
+ newreg = gen_reg_rtx (GET_MODE (reg));
+ REG_USERVAR_P (newreg) = REG_USERVAR_P (reg);
+ REG_POINTER (newreg) = REG_POINTER (reg);
+ REG_LOOP_TEST_P (newreg) = REG_LOOP_TEST_P (reg);
+ RTX_UNCHANGING_P (newreg) = RTX_UNCHANGING_P (reg);
+ REG_ATTRS (newreg) = REG_ATTRS (reg);
+ if (rtl_dump_file)
+ fprintf (rtl_dump_file, "Web oldreg=%i newreg=%i\n", REGNO (reg),
+ REGNO (newreg));
+ }
+
+ root->reg = newreg;
+ return newreg;
+}
+
+/* Replace the reference by REG. */
+
+static void
+replace_ref (struct ref *ref, rtx reg)
+{
+ rtx oldreg = DF_REF_REAL_REG (ref);
+ rtx *loc = DF_REF_REAL_LOC (ref);
+
+ if (oldreg == reg)
+ return;
+ if (rtl_dump_file)
+ fprintf (rtl_dump_file, "Updating insn %i (%i->%i)\n",
+ INSN_UID (DF_REF_INSN (ref)), REGNO (oldreg), REGNO (reg));
+ *loc = reg;
+}
+
+/* Mark each pseudo whose address is taken. */
+
+static int
+mark_addressof (rtx *rtl, void *data)
+{
+ if (!*rtl)
+ return 0;
+ if (GET_CODE (*rtl) == ADDRESSOF
+ && REG_P (XEXP (*rtl, 0)))
+ ((char *)data)[REGNO (XEXP (*rtl, 0))] = 1;
+ return 0;
+}
+
+/* Main entry point. */
+
+void
+web_main (void)
+{
+ struct df *df;
+ struct web_entry *def_entry;
+ struct web_entry *use_entry;
+ unsigned int i;
+ int max = max_reg_num ();
+ char *used;
+ char *use_addressof;
+ rtx insn;
+
+ df = df_init ();
+ df_analyse (df, 0, DF_UD_CHAIN | DF_EQUIV_NOTES);
+
+ def_entry =
+ (struct web_entry *) xcalloc (df->n_defs, sizeof (struct web_entry));
+ use_entry =
+ (struct web_entry *) xcalloc (df->n_uses, sizeof (struct web_entry));
+ used = (char *) xcalloc (max, sizeof (char));
+ use_addressof = (char *) xcalloc (max, sizeof (char));
+
+ if (rtl_dump_file)
+ df_dump (df, DF_UD_CHAIN | DF_DU_CHAIN, rtl_dump_file);
+
+ /* Produce the web. */
+ for (i = 0; i < df->n_uses; i++)
+ union_defs (df, df->uses[i], def_entry, use_entry);
+
+ /* We can not safely rename registers whose address is taken. */
+ for (insn = get_insns (); insn; insn = NEXT_INSN (insn))
+ if (INSN_P (insn))
+ for_each_rtx (&PATTERN (insn), mark_addressof, use_addressof);
+
+ /* Update the instruction stream, allocating new registers for split pseudos
+ in progress. */
+ for (i = 0; i < df->n_uses; i++)
+ replace_ref (df->uses[i], entry_register (use_entry + i, df->uses[i],
+ used, use_addressof));
+ for (i = 0; i < df->n_defs; i++)
+ replace_ref (df->defs[i], entry_register (def_entry + i, df->defs[i],
+ used, use_addressof));
+
+ /* Dataflow information is corrupt here, but it can be easily updated
+ by creating new entries for new registers and updates or calling
+ df_insns_modify. */
+ free (def_entry);
+ free (use_entry);
+ free (used);
+ free (use_addressof);
+ df_finish (df);
+}
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