gcc/init-regs.c

   1 /* Initialization of uninitialized regs.
   2    Copyright (C) 2007-2013 Free Software Foundation, Inc.
   3
   4 This file is part of GCC.
   5
   6 GCC is free software; you can redistribute it and/or modify it under
   7 the terms of the GNU General Public License as published by the Free
   8 Software Foundation; either version 3, or (at your option) any later
   9 version.
  10
  11 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
  12 WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13 FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14 for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GCC; see the file COPYING3.  If not see
  18 <http://www.gnu.org/licenses/>.  */
  19
  20 #include "config.h"
  21 #include "system.h"
  22 #include "coretypes.h"
  23 #include "tm.h"
  24 #include "tree.h"
  25 #include "rtl.h"
  26 #include "regs.h"
  27 #include "expr.h"
  28 #include "tree-pass.h"
  29 #include "basic-block.h"
  30 #include "flags.h"
  31 #include "df.h"
  32
  33 /* Check all of the uses of pseudo variables.  If any use that is MUST
  34    uninitialized, add a store of 0 immediately before it.  For
  35    subregs, this makes combine happy.  For full word regs, this makes
  36    other optimizations, like the register allocator and the reg-stack
  37    happy as well as papers over some problems on the arm and other
  38    processors where certain isa constraints cannot be handled by gcc.
  39    These are of the form where two operands to an insn my not be the
  40    same.  The ra will only make them the same if they do not
  41    interfere, and this can only happen if one is not initialized.
  42
  43    There is also the unfortunate consequence that this may mask some
  44    buggy programs where people forget to initialize stack variable.
  45    Any programmer with half a brain would look at the uninitialized
  46    variable warnings.  */
  47
  48 static void
  49 initialize_uninitialized_regs (void)
  50 {
  51   basic_block bb;
  52   bitmap already_genned = BITMAP_ALLOC (NULL);
  53
  54   if (optimize == 1)
  55     {
  56       df_live_add_problem ();
  57       df_live_set_all_dirty ();
  58     }
  59
  60   df_analyze ();
  61
  62   FOR_EACH_BB (bb)
  63     {
  64       rtx insn;
  65       bitmap lr = DF_LR_IN (bb);
  66       bitmap ur = DF_LIVE_IN (bb);
  67       bitmap_clear (already_genned);
  68
  69       FOR_BB_INSNS (bb, insn)
  70         {
  71           unsigned int uid = INSN_UID (insn);
  72           df_ref *use_rec;
  73           if (!NONDEBUG_INSN_P (insn))
  74             continue;
  75
  76           for (use_rec = DF_INSN_UID_USES (uid); *use_rec; use_rec++)
  77             {
  78               df_ref use = *use_rec;
  79               unsigned int regno = DF_REF_REGNO (use);
  80
  81               /* Only do this for the pseudos.  */
  82               if (regno < FIRST_PSEUDO_REGISTER)
  83                 continue;
  84
  85               /* Do not generate multiple moves for the same regno.
  86                  This is common for sequences of subreg operations.
  87                  They would be deleted during combine but there is no
  88                  reason to churn the system.  */
  89               if (bitmap_bit_p (already_genned, regno))
  90                 continue;
  91
  92               /* A use is MUST uninitialized if it reaches the top of
  93                  the block from the inside of the block (the lr test)
  94                  and no def for it reaches the top of the block from
  95                  outside of the block (the ur test).  */
  96               if (bitmap_bit_p (lr, regno)
  97                   && (!bitmap_bit_p (ur, regno)))
  98                 {
  99                   rtx move_insn;
 100                   rtx reg = DF_REF_REAL_REG (use);
 101
 102                   bitmap_set_bit (already_genned, regno);
 103
 104                   start_sequence ();
 105                   emit_move_insn (reg, CONST0_RTX (GET_MODE (reg)));
 106                   move_insn = get_insns ();
 107                   end_sequence ();
 108                   emit_insn_before (move_insn, insn);
 109                   if (dump_file)
 110                     fprintf (dump_file,
 111                              "adding initialization in %s of reg %d at in block %d for insn %d.\n",
 112                              current_function_name (), regno, bb->index, uid);
 113                 }
 114             }
 115         }
 116     }
 117
 118   if (optimize == 1)
 119     {
 120       if (dump_file)
 121         df_dump (dump_file);
 122       df_remove_problem (df_live);
 123     }
 124
 125   BITMAP_FREE (already_genned);
 126 }
 127
 128 static bool
 129 gate_initialize_regs (void)
 130 {
 131   return optimize > 0;
 132 }
 133
 134 static unsigned int
 135 rest_of_handle_initialize_regs (void)
 136 {
 137   initialize_uninitialized_regs ();
 138   return 0;
 139 }
 140
 141 struct rtl_opt_pass pass_initialize_regs =
 142 {
 143  {
 144   RTL_PASS,
 145   "init-regs",                          /* name */
 146   OPTGROUP_NONE,                        /* optinfo_flags */
 147   gate_initialize_regs,                 /* gate */
 148   rest_of_handle_initialize_regs,       /* execute */
 149   NULL,                                 /* sub */
 150   NULL,                                 /* next */
 151   0,                                    /* static_pass_number */
 152   TV_NONE,                              /* tv_id */
 153   0,                                    /* properties_required */
 154   0,                                    /* properties_provided */
 155   0,                                    /* properties_destroyed */
 156   0,                                    /* todo_flags_start */
 157   TODO_df_finish                        /* todo_flags_finish */
 158  }
 159 };