gcc/init-regs.c

   1 /* Initialization of uninitialized regs.
   2    Copyright (C) 2007-2020 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 "rtl.h"
  25 #include "tree.h"
  26 #include "df.h"
  27 #include "memmodel.h"
  28 #include "emit-rtl.h"
  29 #include "expr.h"
  30 #include "tree-pass.h"
  31
  32 /* Check all of the uses of pseudo variables.  If any use that is MUST
  33    uninitialized, add a store of 0 immediately before it.  For
  34    subregs, this makes combine happy.  For full word regs, this makes
  35    other optimizations, like the register allocator and the reg-stack
  36    happy as well as papers over some problems on the arm and other
  37    processors where certain isa constraints cannot be handled by gcc.
  38    These are of the form where two operands to an insn my not be the
  39    same.  The ra will only make them the same if they do not
  40    interfere, and this can only happen if one is not initialized.
  41
  42    There is also the unfortunate consequence that this may mask some
  43    buggy programs where people forget to initialize stack variable.
  44    Any programmer with half a brain would look at the uninitialized
  45    variable warnings.  */
  46
  47 static void
  48 initialize_uninitialized_regs (void)
  49 {
  50   basic_block bb;
  51   auto_bitmap already_genned;
  52
  53   if (optimize == 1)
  54     {
  55       df_live_add_problem ();
  56       df_live_set_all_dirty ();
  57     }
  58
  59   df_analyze ();
  60
  61   FOR_EACH_BB_FN (bb, cfun)
  62     {
  63       rtx_insn *insn;
  64       bitmap lr = DF_LR_IN (bb);
  65       bitmap ur = DF_LIVE_IN (bb);
  66       bitmap_clear (already_genned);
  67
  68       FOR_BB_INSNS (bb, insn)
  69         {
  70           df_ref use;
  71           if (!NONDEBUG_INSN_P (insn))
  72             continue;
  73
  74           FOR_EACH_INSN_USE (use, insn)
  75             {
  76               unsigned int regno = DF_REF_REGNO (use);
  77
  78               /* Only do this for the pseudos.  */
  79               if (regno < FIRST_PSEUDO_REGISTER)
  80                 continue;
  81
  82               /* Ignore pseudo PIC register.  */
  83               if (pic_offset_table_rtx
  84                   && regno == REGNO (pic_offset_table_rtx))
  85                 continue;
  86
  87               /* Do not generate multiple moves for the same regno.
  88                  This is common for sequences of subreg operations.
  89                  They would be deleted during combine but there is no
  90                  reason to churn the system.  */
  91               if (bitmap_bit_p (already_genned, regno))
  92                 continue;
  93
  94               /* A use is MUST uninitialized if it reaches the top of
  95                  the block from the inside of the block (the lr test)
  96                  and no def for it reaches the top of the block from
  97                  outside of the block (the ur test).  */
  98               if (bitmap_bit_p (lr, regno)
  99                   && (!bitmap_bit_p (ur, regno)))
 100                 {
 101                   rtx_insn *move_insn;
 102                   rtx reg = DF_REF_REAL_REG (use);
 103
 104                   bitmap_set_bit (already_genned, regno);
 105
 106                   start_sequence ();
 107                   emit_clobber (reg);
 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
 130 namespace {
 131
 132 const pass_data pass_data_initialize_regs =
 133 {
 134   RTL_PASS, /* type */
 135   "init-regs", /* name */
 136   OPTGROUP_NONE, /* optinfo_flags */
 137   TV_NONE, /* tv_id */
 138   0, /* properties_required */
 139   0, /* properties_provided */
 140   0, /* properties_destroyed */
 141   0, /* todo_flags_start */
 142   TODO_df_finish, /* todo_flags_finish */
 143 };
 144
 145 class pass_initialize_regs : public rtl_opt_pass
 146 {
 147 public:
 148   pass_initialize_regs (gcc::context *ctxt)
 149     : rtl_opt_pass (pass_data_initialize_regs, ctxt)
 150   {}
 151
 152   /* opt_pass methods: */
 153   virtual bool gate (function *) { return optimize > 0; }
 154   virtual unsigned int execute (function *)
 155     {
 156       initialize_uninitialized_regs ();
 157       return 0;
 158     }
 159
 160 }; // class pass_initialize_regs
 161
 162 } // anon namespace
 163
 164 rtl_opt_pass *
 165 make_pass_initialize_regs (gcc::context *ctxt)
 166 {
 167   return new pass_initialize_regs (ctxt);
 168 }