1 /* Initialization of uninitialized regs.
2 Copyright (C) 2007-2021 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
initialize_uninitialized_regs(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 /* PR98872: Only emit an initialization if MODE has a
109 CONST0_RTX defined. */
110 if (CONST0_RTX (GET_MODE (reg)))
111 emit_move_insn (reg, CONST0_RTX (GET_MODE (reg)));
112 move_insn = get_insns ();
113 end_sequence ();
114 emit_insn_before (move_insn, insn);
115 if (dump_file)
116 fprintf (dump_file,
117 "adding initialization in %s of reg %d at in block %d for insn %d.\n",
118 current_function_name (), regno, bb->index,
119 INSN_UID (insn));
120 }
121 }
122 }
123 }
124
125 if (optimize == 1)
126 {
127 if (dump_file)
128 df_dump (dump_file);
129 df_remove_problem (df_live);
130 }
131 }
132
133 namespace {
134
135 const pass_data pass_data_initialize_regs =
136 {
137 RTL_PASS, /* type */
138 "init-regs", /* name */
139 OPTGROUP_NONE, /* optinfo_flags */
140 TV_NONE, /* tv_id */
141 0, /* properties_required */
142 0, /* properties_provided */
143 0, /* properties_destroyed */
144 0, /* todo_flags_start */
145 TODO_df_finish, /* todo_flags_finish */
146 };
147
148 class pass_initialize_regs : public rtl_opt_pass
149 {
150 public:
pass_initialize_regs(gcc::context * ctxt)151 pass_initialize_regs (gcc::context *ctxt)
152 : rtl_opt_pass (pass_data_initialize_regs, ctxt)
153 {}
154
155 /* opt_pass methods: */
gate(function *)156 virtual bool gate (function *) { return optimize > 0; }
execute(function *)157 virtual unsigned int execute (function *)
158 {
159 initialize_uninitialized_regs ();
160 return 0;
161 }
162
163 }; // class pass_initialize_regs
164
165 } // anon namespace
166
167 rtl_opt_pass *
make_pass_initialize_regs(gcc::context * ctxt)168 make_pass_initialize_regs (gcc::context *ctxt)
169 {
170 return new pass_initialize_regs (ctxt);
171 }
172