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 "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_FN (bb, cfun)
  63     {
  64       rtx_insn *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           df_ref use;
  72           if (!NONDEBUG_INSN_P (insn))
  73             continue;
  74
  75           FOR_EACH_INSN_USE (use, insn)
  76             {
  77               unsigned int regno = DF_REF_REGNO (use);
  78
  79               /* Only do this for the pseudos.  */
  80               if (regno < FIRST_PSEUDO_REGISTER)
  81                 continue;
  82
  83               /* Ignore pseudo PIC register.  */
  84               if (pic_offset_table_rtx
  85                   && regno == REGNO (pic_offset_table_rtx))
  86                 continue;
  87
  88               /* Do not generate multiple moves for the same regno.
  89                  This is common for sequences of subreg operations.
  90                  They would be deleted during combine but there is no
  91                  reason to churn the system.  */
  92               if (bitmap_bit_p (already_genned, regno))
  93                 continue;
  94
  95               /* A use is MUST uninitialized if it reaches the top of
  96                  the block from the inside of the block (the lr test)
  97                  and no def for it reaches the top of the block from
  98                  outside of the block (the ur test).  */
  99               if (bitmap_bit_p (lr, regno)
 100                   && (!bitmap_bit_p (ur, regno)))
 101                 {
 102                   rtx_insn *move_insn;
 103                   rtx reg = DF_REF_REAL_REG (use);
 104
 105                   bitmap_set_bit (already_genned, regno);
 106
 107                   start_sequence ();
 108                   emit_move_insn (reg, CONST0_RTX (GET_MODE (reg)));
 109                   move_insn = get_insns ();
 110                   end_sequence ();
 111                   emit_insn_before (move_insn, insn);
 112                   if (dump_file)
 113                     fprintf (dump_file,
 114                              "adding initialization in %s of reg %d at in block %d for insn %d.\n",
 115                              current_function_name (), regno, bb->index,
 116                              INSN_UID (insn));
 117                 }
 118             }
 119         }
 120     }
 121
 122   if (optimize == 1)
 123     {
 124       if (dump_file)
 125         df_dump (dump_file);
 126       df_remove_problem (df_live);
 127     }
 128
 129   BITMAP_FREE (already_genned);
 130 }
 131
 132 namespace {
 133
 134 const pass_data pass_data_initialize_regs =
 135 {
 136   RTL_PASS, /* type */
 137   "init-regs", /* name */
 138   OPTGROUP_NONE, /* optinfo_flags */
 139   TV_NONE, /* tv_id */
 140   0, /* properties_required */
 141   0, /* properties_provided */
 142   0, /* properties_destroyed */
 143   0, /* todo_flags_start */
 144   TODO_df_finish, /* todo_flags_finish */
 145 };
 146
 147 class pass_initialize_regs : public rtl_opt_pass
 148 {
 149 public:
 150   pass_initialize_regs (gcc::context *ctxt)
 151     : rtl_opt_pass (pass_data_initialize_regs, ctxt)
 152   {}
 153
 154   /* opt_pass methods: */
 155   virtual bool gate (function *) { return optimize > 0; }
 156   virtual unsigned int execute (function *)
 157     {
 158       initialize_uninitialized_regs ();
 159       return 0;
 160     }
 161
 162 }; // class pass_initialize_regs
 163
 164 } // anon namespace
 165
 166 rtl_opt_pass *
 167 make_pass_initialize_regs (gcc::context *ctxt)
 168 {
 169   return new pass_initialize_regs (ctxt);
 170 }