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1 /* Initialization of uninitialized regs.
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2 Copyright (C) 2007, 2008 Free Software Foundation, Inc.
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3
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4 This file is part of GCC.
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5
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6 GCC is free software; you can redistribute it and/or modify it under
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7 the terms of the GNU General Public License as published by the Free
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8 Software Foundation; either version 3, or (at your option) any later
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9 version.
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10
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11 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
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12 WARRANTY; without even the implied warranty of MERCHANTABILITY or
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13 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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14 for more details.
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15
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16 You should have received a copy of the GNU General Public License
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17 along with GCC; see the file COPYING3. If not see
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18 <http://www.gnu.org/licenses/>. */
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19
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20 #include "config.h"
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21 #include "system.h"
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22 #include "coretypes.h"
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23 #include "tm.h"
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24 #include "tree.h"
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25 #include "rtl.h"
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26 #include "regs.h"
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27 #include "expr.h"
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28 #include "tree-pass.h"
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29 #include "basic-block.h"
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30 #include "flags.h"
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31 #include "df.h"
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32
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33 /* Check all of the uses of pseudo variables. If any use that is MUST
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34 uninitialized, add a store of 0 immediately before it. For
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35 subregs, this makes combine happy. For full word regs, this makes
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36 other optimizations, like the register allocator and the reg-stack
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37 happy as well as papers over some problems on the arm and other
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38 processors where certain isa constraints cannot be handled by gcc.
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39 These are of the form where two operands to an insn my not be the
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40 same. The ra will only make them the same if they do not
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41 interfere, and this can only happen if one is not initialized.
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42
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43 There is also the unfortunate consequence that this may mask some
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44 buggy programs where people forget to initialize stack variable.
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45 Any programmer with half a brain would look at the uninitialized
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46 variable warnings. */
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47
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48 static void
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49 initialize_uninitialized_regs (void)
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50 {
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51 basic_block bb;
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52 bitmap already_genned = BITMAP_ALLOC (NULL);
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53
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54 if (optimize == 1)
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55 {
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56 df_live_add_problem ();
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57 df_live_set_all_dirty ();
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58 }
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59
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60 df_analyze ();
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61
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62 FOR_EACH_BB (bb)
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63 {
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64 rtx insn;
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65 bitmap lr = DF_LR_IN (bb);
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66 bitmap ur = DF_LIVE_IN (bb);
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67 bitmap_clear (already_genned);
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68
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69 FOR_BB_INSNS (bb, insn)
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70 {
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71 unsigned int uid = INSN_UID (insn);
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72 df_ref *use_rec;
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73 if (!INSN_P (insn))
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74 continue;
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75
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76 for (use_rec = DF_INSN_UID_USES (uid); *use_rec; use_rec++)
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77 {
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78 df_ref use = *use_rec;
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79 unsigned int regno = DF_REF_REGNO (use);
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80
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81 /* Only do this for the pseudos. */
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82 if (regno < FIRST_PSEUDO_REGISTER)
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83 continue;
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84
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85 /* Do not generate multiple moves for the same regno.
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86 This is common for sequences of subreg operations.
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87 They would be deleted during combine but there is no
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88 reason to churn the system. */
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89 if (bitmap_bit_p (already_genned, regno))
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90 continue;
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91
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92 /* A use is MUST uninitialized if it reaches the top of
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93 the block from the inside of the block (the lr test)
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94 and no def for it reaches the top of the block from
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95 outside of the block (the ur test). */
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96 if (bitmap_bit_p (lr, regno)
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97 && (!bitmap_bit_p (ur, regno)))
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98 {
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99 rtx move_insn;
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100 rtx reg = DF_REF_REAL_REG (use);
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101
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102 bitmap_set_bit (already_genned, regno);
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103
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104 start_sequence ();
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105 emit_move_insn (reg, CONST0_RTX (GET_MODE (reg)));
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106 move_insn = get_insns ();
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107 end_sequence ();
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108 emit_insn_before (move_insn, insn);
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109 if (dump_file)
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110 fprintf (dump_file,
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111 "adding initialization in %s of reg %d at in block %d for insn %d.\n",
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112 current_function_name (), regno, bb->index, uid);
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113 }
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114 }
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115 }
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116 }
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117
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118 if (optimize == 1)
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119 {
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120 if (dump_file)
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121 df_dump (dump_file);
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122 df_remove_problem (df_live);
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123 }
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124
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125 BITMAP_FREE (already_genned);
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126 }
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127
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128 static bool
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129 gate_initialize_regs (void)
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130 {
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131 return optimize > 0;
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132 }
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133
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134 static unsigned int
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135 rest_of_handle_initialize_regs (void)
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136 {
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137 initialize_uninitialized_regs ();
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138 return 0;
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139 }
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140
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141 struct rtl_opt_pass pass_initialize_regs =
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142 {
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143 {
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144 RTL_PASS,
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145 "init-regs", /* name */
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146 gate_initialize_regs, /* gate */
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147 rest_of_handle_initialize_regs, /* execute */
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148 NULL, /* sub */
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149 NULL, /* next */
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150 0, /* static_pass_number */
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151 0, /* tv_id */
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152 0, /* properties_required */
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153 0, /* properties_provided */
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154 0, /* properties_destroyed */
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155 0, /* todo_flags_start */
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156 TODO_dump_func |
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157 TODO_df_finish /* todo_flags_finish */
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158 }
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159 };
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