gcc/init-regs.c

   1 /* Initialization of uninitialized regs.
   2    Copyright (C) 2007-2014 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 "predict.h"
  30 #include "vec.h"
  31 #include "hashtab.h"
  32 #include "hash-set.h"
  33 #include "machmode.h"
  34 #include "hard-reg-set.h"
  35 #include "input.h"
  36 #include "function.h"
  37 #include "dominance.h"
  38 #include "cfg.h"
  39 #include "basic-block.h"
  40 #include "flags.h"
  41 #include "df.h"
  42
  43 /* Check all of the uses of pseudo variables.  If any use that is MUST
  44    uninitialized, add a store of 0 immediately before it.  For
  45    subregs, this makes combine happy.  For full word regs, this makes
  46    other optimizations, like the register allocator and the reg-stack
  47    happy as well as papers over some problems on the arm and other
  48    processors where certain isa constraints cannot be handled by gcc.
  49    These are of the form where two operands to an insn my not be the
  50    same.  The ra will only make them the same if they do not
  51    interfere, and this can only happen if one is not initialized.
  52
  53    There is also the unfortunate consequence that this may mask some
  54    buggy programs where people forget to initialize stack variable.
  55    Any programmer with half a brain would look at the uninitialized
  56    variable warnings.  */
  57
  58 static void
  59 initialize_uninitialized_regs (void)
  60 {
  61   basic_block bb;
  62   bitmap already_genned = BITMAP_ALLOC (NULL);
  63
  64   if (optimize == 1)
  65     {
  66       df_live_add_problem ();
  67       df_live_set_all_dirty ();
  68     }
  69
  70   df_analyze ();
  71
  72   FOR_EACH_BB_FN (bb, cfun)
  73     {
  74       rtx_insn *insn;
  75       bitmap lr = DF_LR_IN (bb);
  76       bitmap ur = DF_LIVE_IN (bb);
  77       bitmap_clear (already_genned);
  78
  79       FOR_BB_INSNS (bb, insn)
  80         {
  81           df_ref use;
  82           if (!NONDEBUG_INSN_P (insn))
  83             continue;
  84
  85           FOR_EACH_INSN_USE (use, insn)
  86             {
  87               unsigned int regno = DF_REF_REGNO (use);
  88
  89               /* Only do this for the pseudos.  */
  90               if (regno < FIRST_PSEUDO_REGISTER)
  91                 continue;
  92
  93               /* Ignore pseudo PIC register.  */
  94               if (pic_offset_table_rtx
  95                   && regno == REGNO (pic_offset_table_rtx))
  96                 continue;
  97
  98               /* Do not generate multiple moves for the same regno.
  99                  This is common for sequences of subreg operations.
 100                  They would be deleted during combine but there is no
 101                  reason to churn the system.  */
 102               if (bitmap_bit_p (already_genned, regno))
 103                 continue;
 104
 105               /* A use is MUST uninitialized if it reaches the top of
 106                  the block from the inside of the block (the lr test)
 107                  and no def for it reaches the top of the block from
 108                  outside of the block (the ur test).  */
 109               if (bitmap_bit_p (lr, regno)
 110                   && (!bitmap_bit_p (ur, regno)))
 111                 {
 112                   rtx_insn *move_insn;
 113                   rtx reg = DF_REF_REAL_REG (use);
 114
 115                   bitmap_set_bit (already_genned, regno);
 116
 117                   start_sequence ();
 118                   emit_move_insn (reg, CONST0_RTX (GET_MODE (reg)));
 119                   move_insn = get_insns ();
 120                   end_sequence ();
 121                   emit_insn_before (move_insn, insn);
 122                   if (dump_file)
 123                     fprintf (dump_file,
 124                              "adding initialization in %s of reg %d at in block %d for insn %d.\n",
 125                              current_function_name (), regno, bb->index,
 126                              INSN_UID (insn));
 127                 }
 128             }
 129         }
 130     }
 131
 132   if (optimize == 1)
 133     {
 134       if (dump_file)
 135         df_dump (dump_file);
 136       df_remove_problem (df_live);
 137     }
 138
 139   BITMAP_FREE (already_genned);
 140 }
 141
 142 namespace {
 143
 144 const pass_data pass_data_initialize_regs =
 145 {
 146   RTL_PASS, /* type */
 147   "init-regs", /* name */
 148   OPTGROUP_NONE, /* optinfo_flags */
 149   TV_NONE, /* tv_id */
 150   0, /* properties_required */
 151   0, /* properties_provided */
 152   0, /* properties_destroyed */
 153   0, /* todo_flags_start */
 154   TODO_df_finish, /* todo_flags_finish */
 155 };
 156
 157 class pass_initialize_regs : public rtl_opt_pass
 158 {
 159 public:
 160   pass_initialize_regs (gcc::context *ctxt)
 161     : rtl_opt_pass (pass_data_initialize_regs, ctxt)
 162   {}
 163
 164   /* opt_pass methods: */
 165   virtual bool gate (function *) { return optimize > 0; }
 166   virtual unsigned int execute (function *)
 167     {
 168       initialize_uninitialized_regs ();
 169       return 0;
 170     }
 171
 172 }; // class pass_initialize_regs
 173
 174 } // anon namespace
 175
 176 rtl_opt_pass *
 177 make_pass_initialize_regs (gcc::context *ctxt)
 178 {
 179   return new pass_initialize_regs (ctxt);
 180 }