1/* Initialization of uninitialized regs.
2 Copyright (C) 2007-2017 Free Software Foundation, Inc.
3
4This file is part of GCC.
5
6GCC is free software; you can redistribute it and/or modify it under
7the terms of the GNU General Public License as published by the Free
8Software Foundation; either version 3, or (at your option) any later
9version.
10
11GCC is distributed in the hope that it will be useful, but WITHOUT ANY
12WARRANTY; without even the implied warranty of MERCHANTABILITY or
13FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14for more details.
15
16You should have received a copy of the GNU General Public License
17along 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
47static void
48initialize_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
130namespace {
131
132const 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
145class pass_initialize_regs : public rtl_opt_pass
146{
147public:
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
164rtl_opt_pass *
165make_pass_initialize_regs (gcc::context *ctxt)
166{
167 return new pass_initialize_regs (ctxt);
168}
169