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 "tm.h"
  24 #include "input.h"
  25 #include "alias.h"
  26 #include "symtab.h"
  27 #include "tree.h"
  28 #include "rtl.h"
  29 #include "regs.h"
  30 #include "hard-reg-set.h"
  31 #include "function.h"
  32 #include "flags.h"
  33 #include "insn-config.h"
  34 #include "expmed.h"
  35 #include "dojump.h"
  36 #include "explow.h"
  37 #include "calls.h"
  38 #include "emit-rtl.h"
  39 #include "varasm.h"
  40 #include "stmt.h"
  41 #include "expr.h"
  42 #include "tree-pass.h"
  43 #include "predict.h"
  44 #include "dominance.h"
  45 #include "cfg.h"
  46 #include "basic-block.h"
  47 #include "df.h"
  48
  49 /* Check all of the uses of pseudo variables.  If any use that is MUST
  50    uninitialized, add a store of 0 immediately before it.  For
  51    subregs, this makes combine happy.  For full word regs, this makes
  52    other optimizations, like the register allocator and the reg-stack
  53    happy as well as papers over some problems on the arm and other
  54    processors where certain isa constraints cannot be handled by gcc.
  55    These are of the form where two operands to an insn my not be the
  56    same.  The ra will only make them the same if they do not
  57    interfere, and this can only happen if one is not initialized.
  58
  59    There is also the unfortunate consequence that this may mask some
  60    buggy programs where people forget to initialize stack variable.
  61    Any programmer with half a brain would look at the uninitialized
  62    variable warnings.  */
  63
  64 static void
  65 initialize_uninitialized_regs (void)
  66 {
  67   basic_block bb;
  68   bitmap already_genned = BITMAP_ALLOC (NULL);
  69
  70   if (optimize == 1)
  71     {
  72       df_live_add_problem ();
  73       df_live_set_all_dirty ();
  74     }
  75
  76   df_analyze ();
  77
  78   FOR_EACH_BB_FN (bb, cfun)
  79     {
  80       rtx_insn *insn;
  81       bitmap lr = DF_LR_IN (bb);
  82       bitmap ur = DF_LIVE_IN (bb);
  83       bitmap_clear (already_genned);
  84
  85       FOR_BB_INSNS (bb, insn)
  86         {
  87           df_ref use;
  88           if (!NONDEBUG_INSN_P (insn))
  89             continue;
  90
  91           FOR_EACH_INSN_USE (use, insn)
  92             {
  93               unsigned int regno = DF_REF_REGNO (use);
  94
  95               /* Only do this for the pseudos.  */
  96               if (regno < FIRST_PSEUDO_REGISTER)
  97                 continue;
  98
  99               /* Ignore pseudo PIC register.  */
 100               if (pic_offset_table_rtx
 101                   && regno == REGNO (pic_offset_table_rtx))
 102                 continue;
 103
 104               /* Do not generate multiple moves for the same regno.
 105                  This is common for sequences of subreg operations.
 106                  They would be deleted during combine but there is no
 107                  reason to churn the system.  */
 108               if (bitmap_bit_p (already_genned, regno))
 109                 continue;
 110
 111               /* A use is MUST uninitialized if it reaches the top of
 112                  the block from the inside of the block (the lr test)
 113                  and no def for it reaches the top of the block from
 114                  outside of the block (the ur test).  */
 115               if (bitmap_bit_p (lr, regno)
 116                   && (!bitmap_bit_p (ur, regno)))
 117                 {
 118                   rtx_insn *move_insn;
 119                   rtx reg = DF_REF_REAL_REG (use);
 120
 121                   bitmap_set_bit (already_genned, regno);
 122
 123                   start_sequence ();
 124                   emit_move_insn (reg, CONST0_RTX (GET_MODE (reg)));
 125                   move_insn = get_insns ();
 126                   end_sequence ();
 127                   emit_insn_before (move_insn, insn);
 128                   if (dump_file)
 129                     fprintf (dump_file,
 130                              "adding initialization in %s of reg %d at in block %d for insn %d.\n",
 131                              current_function_name (), regno, bb->index,
 132                              INSN_UID (insn));
 133                 }
 134             }
 135         }
 136     }
 137
 138   if (optimize == 1)
 139     {
 140       if (dump_file)
 141         df_dump (dump_file);
 142       df_remove_problem (df_live);
 143     }
 144
 145   BITMAP_FREE (already_genned);
 146 }
 147
 148 namespace {
 149
 150 const pass_data pass_data_initialize_regs =
 151 {
 152   RTL_PASS, /* type */
 153   "init-regs", /* name */
 154   OPTGROUP_NONE, /* optinfo_flags */
 155   TV_NONE, /* tv_id */
 156   0, /* properties_required */
 157   0, /* properties_provided */
 158   0, /* properties_destroyed */
 159   0, /* todo_flags_start */
 160   TODO_df_finish, /* todo_flags_finish */
 161 };
 162
 163 class pass_initialize_regs : public rtl_opt_pass
 164 {
 165 public:
 166   pass_initialize_regs (gcc::context *ctxt)
 167     : rtl_opt_pass (pass_data_initialize_regs, ctxt)
 168   {}
 169
 170   /* opt_pass methods: */
 171   virtual bool gate (function *) { return optimize > 0; }
 172   virtual unsigned int execute (function *)
 173     {
 174       initialize_uninitialized_regs ();
 175       return 0;
 176     }
 177
 178 }; // class pass_initialize_regs
 179
 180 } // anon namespace
 181
 182 rtl_opt_pass *
 183 make_pass_initialize_regs (gcc::context *ctxt)
 184 {
 185   return new pass_initialize_regs (ctxt);
 186 }