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