1 /* Initialization of uninitialized regs. 2 Copyright (C) 2007-2018 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 } 169