1 /* Initialization of uninitialized regs. 2 Copyright (C) 2007, 2008, 2009 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 "tree.h" 25 #include "rtl.h" 26 #include "regs.h" 27 #include "expr.h" 28 #include "tree-pass.h" 29 #include "basic-block.h" 30 #include "flags.h" 31 #include "df.h" 32 33 /* Check all of the uses of pseudo variables. If any use that is MUST 34 uninitialized, add a store of 0 immediately before it. For 35 subregs, this makes combine happy. For full word regs, this makes 36 other optimizations, like the register allocator and the reg-stack 37 happy as well as papers over some problems on the arm and other 38 processors where certain isa constraints cannot be handled by gcc. 39 These are of the form where two operands to an insn my not be the 40 same. The ra will only make them the same if they do not 41 interfere, and this can only happen if one is not initialized. 42 43 There is also the unfortunate consequence that this may mask some 44 buggy programs where people forget to initialize stack variable. 45 Any programmer with half a brain would look at the uninitialized 46 variable warnings. */ 47 48 static void 49 initialize_uninitialized_regs (void) 50 { 51 basic_block bb; 52 bitmap already_genned = BITMAP_ALLOC (NULL); 53 54 if (optimize == 1) 55 { 56 df_live_add_problem (); 57 df_live_set_all_dirty (); 58 } 59 60 df_analyze (); 61 62 FOR_EACH_BB (bb) 63 { 64 rtx insn; 65 bitmap lr = DF_LR_IN (bb); 66 bitmap ur = DF_LIVE_IN (bb); 67 bitmap_clear (already_genned); 68 69 FOR_BB_INSNS (bb, insn) 70 { 71 unsigned int uid = INSN_UID (insn); 72 df_ref *use_rec; 73 if (!NONDEBUG_INSN_P (insn)) 74 continue; 75 76 for (use_rec = DF_INSN_UID_USES (uid); *use_rec; use_rec++) 77 { 78 df_ref use = *use_rec; 79 unsigned int regno = DF_REF_REGNO (use); 80 81 /* Only do this for the pseudos. */ 82 if (regno < FIRST_PSEUDO_REGISTER) 83 continue; 84 85 /* Do not generate multiple moves for the same regno. 86 This is common for sequences of subreg operations. 87 They would be deleted during combine but there is no 88 reason to churn the system. */ 89 if (bitmap_bit_p (already_genned, regno)) 90 continue; 91 92 /* A use is MUST uninitialized if it reaches the top of 93 the block from the inside of the block (the lr test) 94 and no def for it reaches the top of the block from 95 outside of the block (the ur test). */ 96 if (bitmap_bit_p (lr, regno) 97 && (!bitmap_bit_p (ur, regno))) 98 { 99 rtx move_insn; 100 rtx reg = DF_REF_REAL_REG (use); 101 102 bitmap_set_bit (already_genned, regno); 103 104 start_sequence (); 105 emit_move_insn (reg, CONST0_RTX (GET_MODE (reg))); 106 move_insn = get_insns (); 107 end_sequence (); 108 emit_insn_before (move_insn, insn); 109 if (dump_file) 110 fprintf (dump_file, 111 "adding initialization in %s of reg %d at in block %d for insn %d.\n", 112 current_function_name (), regno, bb->index, uid); 113 } 114 } 115 } 116 } 117 118 if (optimize == 1) 119 { 120 if (dump_file) 121 df_dump (dump_file); 122 df_remove_problem (df_live); 123 } 124 125 BITMAP_FREE (already_genned); 126 } 127 128 static bool 129 gate_initialize_regs (void) 130 { 131 return optimize > 0; 132 } 133 134 static unsigned int 135 rest_of_handle_initialize_regs (void) 136 { 137 initialize_uninitialized_regs (); 138 return 0; 139 } 140 141 struct rtl_opt_pass pass_initialize_regs = 142 { 143 { 144 RTL_PASS, 145 "init-regs", /* name */ 146 gate_initialize_regs, /* gate */ 147 rest_of_handle_initialize_regs, /* execute */ 148 NULL, /* sub */ 149 NULL, /* next */ 150 0, /* static_pass_number */ 151 TV_NONE, /* tv_id */ 152 0, /* properties_required */ 153 0, /* properties_provided */ 154 0, /* properties_destroyed */ 155 0, /* todo_flags_start */ 156 TODO_df_finish /* todo_flags_finish */ 157 } 158 }; 159