gcc/init-regs.c

   1 /* Initialization of uninitialized regs.
   2    Copyright (C) 2007-2015 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 "backend.h"
  24 #include "tree.h"
  25 #include "rtl.h"
  26 #include "df.h"
  27 #include "alias.h"
  28 #include "regs.h"
  29 #include "flags.h"
  30 #include "insn-config.h"
  31 #include "expmed.h"
  32 #include "dojump.h"
  33 #include "explow.h"
  34 #include "calls.h"
  35 #include "emit-rtl.h"
  36 #include "varasm.h"
  37 #include "stmt.h"
  38 #include "expr.h"
  39 #include "tree-pass.h"
  40
  41 /* Check all of the uses of pseudo variables.  If any use that is MUST
  42    uninitialized, add a store of 0 immediately before it.  For
  43    subregs, this makes combine happy.  For full word regs, this makes
  44    other optimizations, like the register allocator and the reg-stack
  45    happy as well as papers over some problems on the arm and other
  46    processors where certain isa constraints cannot be handled by gcc.
  47    These are of the form where two operands to an insn my not be the
  48    same.  The ra will only make them the same if they do not
  49    interfere, and this can only happen if one is not initialized.
  50
  51    There is also the unfortunate consequence that this may mask some
  52    buggy programs where people forget to initialize stack variable.
  53    Any programmer with half a brain would look at the uninitialized
  54    variable warnings.  */
  55
  56 static void
  57 initialize_uninitialized_regs (void)
  58 {
  59   basic_block bb;
  60   bitmap already_genned = BITMAP_ALLOC (NULL);
  61
  62   if (optimize == 1)
  63     {
  64       df_live_add_problem ();
  65       df_live_set_all_dirty ();
  66     }
  67
  68   df_analyze ();
  69
  70   FOR_EACH_BB_FN (bb, cfun)
  71     {
  72       rtx_insn *insn;
  73       bitmap lr = DF_LR_IN (bb);
  74       bitmap ur = DF_LIVE_IN (bb);
  75       bitmap_clear (already_genned);
  76
  77       FOR_BB_INSNS (bb, insn)
  78         {
  79           df_ref use;
  80           if (!NONDEBUG_INSN_P (insn))
  81             continue;
  82
  83           FOR_EACH_INSN_USE (use, insn)
  84             {
  85               unsigned int regno = DF_REF_REGNO (use);
  86
  87               /* Only do this for the pseudos.  */
  88               if (regno < FIRST_PSEUDO_REGISTER)
  89                 continue;
  90
  91               /* Ignore pseudo PIC register.  */
  92               if (pic_offset_table_rtx
  93                   && regno == REGNO (pic_offset_table_rtx))
  94                 continue;
  95
  96               /* Do not generate multiple moves for the same regno.
  97                  This is common for sequences of subreg operations.
  98                  They would be deleted during combine but there is no
  99                  reason to churn the system.  */
 100               if (bitmap_bit_p (already_genned, regno))
 101                 continue;
 102
 103               /* A use is MUST uninitialized if it reaches the top of
 104                  the block from the inside of the block (the lr test)
 105                  and no def for it reaches the top of the block from
 106                  outside of the block (the ur test).  */
 107               if (bitmap_bit_p (lr, regno)
 108                   && (!bitmap_bit_p (ur, regno)))
 109                 {
 110                   rtx_insn *move_insn;
 111                   rtx reg = DF_REF_REAL_REG (use);
 112
 113                   bitmap_set_bit (already_genned, regno);
 114
 115                   start_sequence ();
 116                   emit_move_insn (reg, CONST0_RTX (GET_MODE (reg)));
 117                   move_insn = get_insns ();
 118                   end_sequence ();
 119                   emit_insn_before (move_insn, insn);
 120                   if (dump_file)
 121                     fprintf (dump_file,
 122                              "adding initialization in %s of reg %d at in block %d for insn %d.\n",
 123                              current_function_name (), regno, bb->index,
 124                              INSN_UID (insn));
 125                 }
 126             }
 127         }
 128     }
 129
 130   if (optimize == 1)
 131     {
 132       if (dump_file)
 133         df_dump (dump_file);
 134       df_remove_problem (df_live);
 135     }
 136
 137   BITMAP_FREE (already_genned);
 138 }
 139
 140 namespace {
 141
 142 const pass_data pass_data_initialize_regs =
 143 {
 144   RTL_PASS, /* type */
 145   "init-regs", /* name */
 146   OPTGROUP_NONE, /* optinfo_flags */
 147   TV_NONE, /* tv_id */
 148   0, /* properties_required */
 149   0, /* properties_provided */
 150   0, /* properties_destroyed */
 151   0, /* todo_flags_start */
 152   TODO_df_finish, /* todo_flags_finish */
 153 };
 154
 155 class pass_initialize_regs : public rtl_opt_pass
 156 {
 157 public:
 158   pass_initialize_regs (gcc::context *ctxt)
 159     : rtl_opt_pass (pass_data_initialize_regs, ctxt)
 160   {}
 161
 162   /* opt_pass methods: */
 163   virtual bool gate (function *) { return optimize > 0; }
 164   virtual unsigned int execute (function *)
 165     {
 166       initialize_uninitialized_regs ();
 167       return 0;
 168     }
 169
 170 }; // class pass_initialize_regs
 171
 172 } // anon namespace
 173
 174 rtl_opt_pass *
 175 make_pass_initialize_regs (gcc::context *ctxt)
 176 {
 177   return new pass_initialize_regs (ctxt);
 178 }