1 /* Initialization of uninitialized regs. 2 Copyright (C) 2007-2016 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 "emit-rtl.h" 28 #include "expr.h" 29 #include "tree-pass.h" 30 31 /* Check all of the uses of pseudo variables. If any use that is MUST 32 uninitialized, add a store of 0 immediately before it. For 33 subregs, this makes combine happy. For full word regs, this makes 34 other optimizations, like the register allocator and the reg-stack 35 happy as well as papers over some problems on the arm and other 36 processors where certain isa constraints cannot be handled by gcc. 37 These are of the form where two operands to an insn my not be the 38 same. The ra will only make them the same if they do not 39 interfere, and this can only happen if one is not initialized. 40 41 There is also the unfortunate consequence that this may mask some 42 buggy programs where people forget to initialize stack variable. 43 Any programmer with half a brain would look at the uninitialized 44 variable warnings. */ 45 46 static void 47 initialize_uninitialized_regs (void) 48 { 49 basic_block bb; 50 bitmap already_genned = BITMAP_ALLOC (NULL); 51 52 if (optimize == 1) 53 { 54 df_live_add_problem (); 55 df_live_set_all_dirty (); 56 } 57 58 df_analyze (); 59 60 FOR_EACH_BB_FN (bb, cfun) 61 { 62 rtx_insn *insn; 63 bitmap lr = DF_LR_IN (bb); 64 bitmap ur = DF_LIVE_IN (bb); 65 bitmap_clear (already_genned); 66 67 FOR_BB_INSNS (bb, insn) 68 { 69 df_ref use; 70 if (!NONDEBUG_INSN_P (insn)) 71 continue; 72 73 FOR_EACH_INSN_USE (use, insn) 74 { 75 unsigned int regno = DF_REF_REGNO (use); 76 77 /* Only do this for the pseudos. */ 78 if (regno < FIRST_PSEUDO_REGISTER) 79 continue; 80 81 /* Ignore pseudo PIC register. */ 82 if (pic_offset_table_rtx 83 && regno == REGNO (pic_offset_table_rtx)) 84 continue; 85 86 /* Do not generate multiple moves for the same regno. 87 This is common for sequences of subreg operations. 88 They would be deleted during combine but there is no 89 reason to churn the system. */ 90 if (bitmap_bit_p (already_genned, regno)) 91 continue; 92 93 /* A use is MUST uninitialized if it reaches the top of 94 the block from the inside of the block (the lr test) 95 and no def for it reaches the top of the block from 96 outside of the block (the ur test). */ 97 if (bitmap_bit_p (lr, regno) 98 && (!bitmap_bit_p (ur, regno))) 99 { 100 rtx_insn *move_insn; 101 rtx reg = DF_REF_REAL_REG (use); 102 103 bitmap_set_bit (already_genned, regno); 104 105 start_sequence (); 106 emit_move_insn (reg, CONST0_RTX (GET_MODE (reg))); 107 move_insn = get_insns (); 108 end_sequence (); 109 emit_insn_before (move_insn, insn); 110 if (dump_file) 111 fprintf (dump_file, 112 "adding initialization in %s of reg %d at in block %d for insn %d.\n", 113 current_function_name (), regno, bb->index, 114 INSN_UID (insn)); 115 } 116 } 117 } 118 } 119 120 if (optimize == 1) 121 { 122 if (dump_file) 123 df_dump (dump_file); 124 df_remove_problem (df_live); 125 } 126 127 BITMAP_FREE (already_genned); 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 } 169