gcc/init-regs.c

   1 /* Initialization of uninitialized regs.
   2    Copyright (C) 2007 Free Software Foundation,
   3    Inc.
   4
   5 This file is part of GCC.
   6
   7 GCC is free software; you can redistribute it and/or modify it under
   8 the terms of the GNU General Public License as published by the Free
   9 Software Foundation; either version 3, or (at your option) any later
  10 version.
  11
  12 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
  13 WARRANTY; without even the implied warranty of MERCHANTABILITY or
  14 FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  15 for more details.
  16
  17 You should have received a copy of the GNU General Public License
  18 along with GCC; see the file COPYING3.  If not see
  19 <http://www.gnu.org/licenses/>.  */
  20
  21 #include "config.h"
  22 #include "system.h"
  23 #include "coretypes.h"
  24 #include "tm.h"
  25 #include "tree.h"
  26 #include "rtl.h"
  27 #include "regs.h"
  28 #include "expr.h"
  29 #include "tree-pass.h"
  30 #include "basic-block.h"
  31 #include "flags.h"
  32 #include "df.h"
  33
  34 /* Check all of the uses of pseudo variables.  If any use that is MUST
  35    uninitialized, add a store of 0 immediately before it.  For
  36    subregs, this makes combine happy.  For full word regs, this makes
  37    other optimizations, like the register allocator and the reg-stack
  38    happy as well as papers over some problems on the arm and other
  39    processors where certain isa constraints cannot be handled by gcc.
  40    These are of the form where two operands to an insn my not be the
  41    same.  The ra will only make them the same if they do not
  42    interfere, and this can only happen if one is not initialized.
  43
  44    There is also the unfortunate consequence that this may mask some
  45    buggy programs where people forget to initialize stack variable.
  46    Any programmer with half a brain would look at the uninitialized
  47    variable warnings.  */
  48
  49 static void
  50 initialize_uninitialized_regs (void)
  51 {
  52   basic_block bb;
  53   bitmap already_genned = BITMAP_ALLOC (NULL);
  54
  55   if (optimize == 1)
  56     {
  57       df_live_add_problem ();
  58       df_live_set_all_dirty ();
  59     }
  60
  61   df_analyze ();
  62
  63   FOR_EACH_BB (bb)
  64     {
  65       rtx insn;
  66       bitmap lr = DF_LR_IN (bb);
  67       bitmap ur = DF_LIVE_IN (bb);
  68       bitmap_clear (already_genned);
  69
  70       FOR_BB_INSNS (bb, insn)
  71         {
  72           unsigned int uid = INSN_UID (insn);
  73           struct df_ref **use_rec;
  74           if (!INSN_P (insn))
  75             continue;
  76
  77           for (use_rec = DF_INSN_UID_USES (uid); *use_rec; use_rec++)
  78             {
  79               struct df_ref *use = *use_rec;
  80               unsigned int regno = DF_REF_REGNO (use);
  81
  82               /* Only do this for the pseudos.  */
  83               if (regno < FIRST_PSEUDO_REGISTER)
  84                 continue;
  85
  86               /* Do not generate multiple moves for the same regno.
  87                  This is common for sequences of subreg operations.
  88                  They would be deleted during combine but there is no
  89                  reason to churn the system.  */
  90               if (bitmap_bit_p (already_genned, regno))
  91                 continue;
  92
  93               /* A use is MUST uninitialized if it reaches the top of
  94                  the block from the inside of the block (the lr test)
  95                  and no def for it reaches the top of the block from
  96                  outside of the block (the ur test).  */
  97               if (bitmap_bit_p (lr, regno)
  98                   && (!bitmap_bit_p (ur, regno)))
  99                 {
 100                   rtx move_insn;
 101                   rtx reg = DF_REF_REAL_REG (use);
 102
 103                   bitmap_set_bit (already_genned, regno);
 104
 105                   start_sequence ();
 106                   emit_move_insn (reg, CONST0_RTX (GET_MODE (reg)));
 107                   move_insn = get_insns ();
 108                   end_sequence ();
 109                   emit_insn_before (move_insn, insn);
 110                   if (dump_file)
 111                     fprintf (dump_file,
 112                              "adding initialization in %s of reg %d at in block %d for insn %d.\n",
 113                              current_function_name (), regno, bb->index, uid);
 114                 }
 115             }
 116         }
 117     }
 118
 119   if (optimize == 1)
 120     {
 121       if (dump_file)
 122         df_dump (dump_file);
 123       df_remove_problem (df_live);
 124     }
 125
 126   BITMAP_FREE (already_genned);
 127 }
 128
 129 static bool
 130 gate_initialize_regs (void)
 131 {
 132   return optimize > 0;
 133 }
 134
 135 static unsigned int
 136 rest_of_handle_initialize_regs (void)
 137 {
 138   initialize_uninitialized_regs ();
 139   return 0;
 140 }
 141
 142 struct rtl_opt_pass pass_initialize_regs =
 143 {
 144  {
 145   RTL_PASS,
 146   "init-regs",                          /* name */
 147   gate_initialize_regs,                 /* gate */
 148   rest_of_handle_initialize_regs,       /* execute */
 149   NULL,                                 /* sub */
 150   NULL,                                 /* next */
 151   0,                                    /* static_pass_number */
 152   0,                                    /* tv_id */
 153   0,                                    /* properties_required */
 154   0,                                    /* properties_provided */
 155   0,                                    /* properties_destroyed */
 156   0,                                    /* todo_flags_start */
 157   TODO_dump_func |
 158   TODO_df_finish                        /* todo_flags_finish */
 159  }
 160 };