1 /* Initialization of uninitialized regs.
2 Copyright (C) 2007 Free Software Foundation,
5 This file is part of GCC.
7 GCC is free software; you can redistribute it and/or modify it under
8 the terms of the GNU General Public License as published by the Free
9 Software Foundation; either version 2, or (at your option) any later
12 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
13 WARRANTY; without even the implied warranty of MERCHANTABILITY or
14 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
17 You should have received a copy of the GNU General Public License
18 along with GCC; see the file COPYING. If not, write to the Free
19 Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA
24 #include "coretypes.h"
30 #include "tree-pass.h"
31 #include "basic-block.h"
35 /* Check all of the uses of pseudo variables. If any use that is MUST
36 uninitialized, add a store of 0 immediately before it. For
37 subregs, this makes combine happy. For full word regs, this makes
38 other optimizations, like the register allocator and the reg-stack
39 happy as well as papers over some problems on the arm and other
40 processors where certain isa constraints cannot be handled by gcc.
41 These are of the form where two operands to an insn my not be the
42 same. The ra will only make them the same if they do not
43 interfere, and this can only happen if one is not initialized.
45 There is also the unfortunate consequence that this may mask some
46 buggy programs where people forget to initialize stack variable.
47 Any programmer with half a brain would look at the uninitialized
51 initialize_uninitialized_regs (void)
54 bitmap already_genned = BITMAP_ALLOC (NULL);
58 df_live_add_problem ();
59 df_live_set_all_dirty ();
67 bitmap lr = DF_LR_IN (bb);
68 bitmap ur = DF_LIVE_IN (bb);
69 bitmap_clear (already_genned);
71 FOR_BB_INSNS (bb, insn)
73 unsigned int uid = INSN_UID (insn);
74 struct df_ref **use_rec;
78 for (use_rec = DF_INSN_UID_USES (uid); *use_rec; use_rec++)
80 struct df_ref *use = *use_rec;
81 unsigned int regno = DF_REF_REGNO (use);
83 /* Only do this for the pseudos. */
84 if (regno < FIRST_PSEUDO_REGISTER)
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))
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)))
102 rtx reg = DF_REF_REAL_REG (use);
104 bitmap_set_bit (already_genned, regno);
107 emit_move_insn (reg, CONST0_RTX (GET_MODE (reg)));
108 move_insn = get_insns ();
110 add_insn_before (move_insn, insn, bb);
113 "adding initialization in %s of reg %d at in block %d for insn %d.\n",
114 current_function_name (), regno, bb->index, uid);
121 df_remove_problem (df_live);
123 BITMAP_FREE (already_genned);
127 gate_initialize_regs (void)
133 rest_of_handle_initialize_regs (void)
136 initialize_uninitialized_regs ();
141 struct tree_opt_pass pass_initialize_regs =
143 "init-regs", /* name */
144 gate_initialize_regs, /* gate */
145 rest_of_handle_initialize_regs, /* execute */
148 0, /* static_pass_number */
150 0, /* properties_required */
151 0, /* properties_provided */
152 0, /* properties_destroyed */
153 0, /* todo_flags_start */
155 TODO_df_finish, /* todo_flags_finish */