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 "hash-set.h"
  25 #include "vec.h"
  26 #include "input.h"
  27 #include "alias.h"
  28 #include "symtab.h"
  29 #include "inchash.h"
  30 #include "tree.h"
  31 #include "rtl.h"
  32 #include "regs.h"
  33 #include "hashtab.h"
  34 #include "hard-reg-set.h"
  35 #include "function.h"
  36 #include "flags.h"
  37 #include "statistics.h"
  38 #include "insn-config.h"
  39 #include "expmed.h"
  40 #include "dojump.h"
  41 #include "explow.h"
  42 #include "calls.h"
  43 #include "emit-rtl.h"
  44 #include "varasm.h"
  45 #include "stmt.h"
  46 #include "expr.h"
  47 #include "tree-pass.h"
  48 #include "predict.h"
  49 #include "dominance.h"
  50 #include "cfg.h"
  51 #include "basic-block.h"
  52 #include "df.h"
  53
  54 /* Check all of the uses of pseudo variables.  If any use that is MUST
  55    uninitialized, add a store of 0 immediately before it.  For
  56    subregs, this makes combine happy.  For full word regs, this makes
  57    other optimizations, like the register allocator and the reg-stack
  58    happy as well as papers over some problems on the arm and other
  59    processors where certain isa constraints cannot be handled by gcc.
  60    These are of the form where two operands to an insn my not be the
  61    same.  The ra will only make them the same if they do not
  62    interfere, and this can only happen if one is not initialized.
  63
  64    There is also the unfortunate consequence that this may mask some
  65    buggy programs where people forget to initialize stack variable.
  66    Any programmer with half a brain would look at the uninitialized
  67    variable warnings.  */
  68
  69 static void
  70 initialize_uninitialized_regs (void)
  71 {
  72   basic_block bb;
  73   bitmap already_genned = BITMAP_ALLOC (NULL);
  74
  75   if (optimize == 1)
  76     {
  77       df_live_add_problem ();
  78       df_live_set_all_dirty ();
  79     }
  80
  81   df_analyze ();
  82
  83   FOR_EACH_BB_FN (bb, cfun)
  84     {
  85       rtx_insn *insn;
  86       bitmap lr = DF_LR_IN (bb);
  87       bitmap ur = DF_LIVE_IN (bb);
  88       bitmap_clear (already_genned);
  89
  90       FOR_BB_INSNS (bb, insn)
  91         {
  92           df_ref use;
  93           if (!NONDEBUG_INSN_P (insn))
  94             continue;
  95
  96           FOR_EACH_INSN_USE (use, insn)
  97             {
  98               unsigned int regno = DF_REF_REGNO (use);
  99
 100               /* Only do this for the pseudos.  */
 101               if (regno < FIRST_PSEUDO_REGISTER)
 102                 continue;
 103
 104               /* Ignore pseudo PIC register.  */
 105               if (pic_offset_table_rtx
 106                   && regno == REGNO (pic_offset_table_rtx))
 107                 continue;
 108
 109               /* Do not generate multiple moves for the same regno.
 110                  This is common for sequences of subreg operations.
 111                  They would be deleted during combine but there is no
 112                  reason to churn the system.  */
 113               if (bitmap_bit_p (already_genned, regno))
 114                 continue;
 115
 116               /* A use is MUST uninitialized if it reaches the top of
 117                  the block from the inside of the block (the lr test)
 118                  and no def for it reaches the top of the block from
 119                  outside of the block (the ur test).  */
 120               if (bitmap_bit_p (lr, regno)
 121                   && (!bitmap_bit_p (ur, regno)))
 122                 {
 123                   rtx_insn *move_insn;
 124                   rtx reg = DF_REF_REAL_REG (use);
 125
 126                   bitmap_set_bit (already_genned, regno);
 127
 128                   start_sequence ();
 129                   emit_move_insn (reg, CONST0_RTX (GET_MODE (reg)));
 130                   move_insn = get_insns ();
 131                   end_sequence ();
 132                   emit_insn_before (move_insn, insn);
 133                   if (dump_file)
 134                     fprintf (dump_file,
 135                              "adding initialization in %s of reg %d at in block %d for insn %d.\n",
 136                              current_function_name (), regno, bb->index,
 137                              INSN_UID (insn));
 138                 }
 139             }
 140         }
 141     }
 142
 143   if (optimize == 1)
 144     {
 145       if (dump_file)
 146         df_dump (dump_file);
 147       df_remove_problem (df_live);
 148     }
 149
 150   BITMAP_FREE (already_genned);
 151 }
 152
 153 namespace {
 154
 155 const pass_data pass_data_initialize_regs =
 156 {
 157   RTL_PASS, /* type */
 158   "init-regs", /* name */
 159   OPTGROUP_NONE, /* optinfo_flags */
 160   TV_NONE, /* tv_id */
 161   0, /* properties_required */
 162   0, /* properties_provided */
 163   0, /* properties_destroyed */
 164   0, /* todo_flags_start */
 165   TODO_df_finish, /* todo_flags_finish */
 166 };
 167
 168 class pass_initialize_regs : public rtl_opt_pass
 169 {
 170 public:
 171   pass_initialize_regs (gcc::context *ctxt)
 172     : rtl_opt_pass (pass_data_initialize_regs, ctxt)
 173   {}
 174
 175   /* opt_pass methods: */
 176   virtual bool gate (function *) { return optimize > 0; }
 177   virtual unsigned int execute (function *)
 178     {
 179       initialize_uninitialized_regs ();
 180       return 0;
 181     }
 182
 183 }; // class pass_initialize_regs
 184
 185 } // anon namespace
 186
 187 rtl_opt_pass *
 188 make_pass_initialize_regs (gcc::context *ctxt)
 189 {
 190   return new pass_initialize_regs (ctxt);
 191 }