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1 | /* Initialization of uninitialized regs. | |
2 | Copyright (C) 2007-2019 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 | 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 | ||
130 | namespace { | |
131 | ||
132 | const 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 | ||
145 | class pass_initialize_regs : public rtl_opt_pass | |
146 | { | |
147 | public: | |
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 | ||
164 | rtl_opt_pass * | |
165 | make_pass_initialize_regs (gcc::context *ctxt) | |
166 | { | |
167 | return new pass_initialize_regs (ctxt); | |
168 | } |