1 | /* Initialization of uninitialized regs. |
2 | Copyright (C) 2007-2024 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 | /* 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 (stream: dump_file, |
117 | format: "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 | .type: RTL_PASS, /* type */ |
138 | .name: "init-regs" , /* name */ |
139 | .optinfo_flags: OPTGROUP_NONE, /* optinfo_flags */ |
140 | .tv_id: TV_NONE, /* tv_id */ |
141 | .properties_required: 0, /* properties_required */ |
142 | .properties_provided: 0, /* properties_provided */ |
143 | .properties_destroyed: 0, /* properties_destroyed */ |
144 | .todo_flags_start: 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: |
151 | pass_initialize_regs (gcc::context *ctxt) |
152 | : rtl_opt_pass (pass_data_initialize_regs, ctxt) |
153 | {} |
154 | |
155 | /* opt_pass methods: */ |
156 | bool gate (function *) final override { return optimize > 0; } |
157 | unsigned int execute (function *) final override |
158 | { |
159 | initialize_uninitialized_regs (); |
160 | return 0; |
161 | } |
162 | |
163 | }; // class pass_initialize_regs |
164 | |
165 | } // anon namespace |
166 | |
167 | rtl_opt_pass * |
168 | make_pass_initialize_regs (gcc::context *ctxt) |
169 | { |
170 | return new pass_initialize_regs (ctxt); |
171 | } |
172 | |