1 | /* Discover if the stack pointer is modified in a function. |
2 | Copyright (C) 2007-2023 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 "df.h" |
26 | #include "memmodel.h" |
27 | #include "emit-rtl.h" |
28 | #include "tree-pass.h" |
29 | |
30 | /* Determine if the stack pointer is constant over the life of the function. |
31 | Only useful before prologues have been emitted. */ |
32 | |
33 | static void |
34 | notice_stack_pointer_modification_1 (rtx x, const_rtx pat ATTRIBUTE_UNUSED, |
35 | void *data ATTRIBUTE_UNUSED) |
36 | { |
37 | if (x == stack_pointer_rtx |
38 | /* The stack pointer is only modified indirectly as the result |
39 | of a push until later. See the comments in rtl.texi |
40 | regarding Embedded Side-Effects on Addresses. */ |
41 | || (MEM_P (x) |
42 | && GET_RTX_CLASS (GET_CODE (XEXP (x, 0))) == RTX_AUTOINC |
43 | && XEXP (XEXP (x, 0), 0) == stack_pointer_rtx)) |
44 | crtl->sp_is_unchanging = 0; |
45 | } |
46 | |
47 | /* Some targets can emit simpler epilogues if they know that sp was |
48 | not ever modified during the function. After reload, of course, |
49 | we've already emitted the epilogue so there's no sense searching. */ |
50 | |
51 | namespace { |
52 | |
53 | const pass_data pass_data_stack_ptr_mod = |
54 | { |
55 | .type: RTL_PASS, /* type */ |
56 | .name: "*stack_ptr_mod" , /* name */ |
57 | .optinfo_flags: OPTGROUP_NONE, /* optinfo_flags */ |
58 | .tv_id: TV_NONE, /* tv_id */ |
59 | .properties_required: 0, /* properties_required */ |
60 | .properties_provided: 0, /* properties_provided */ |
61 | .properties_destroyed: 0, /* properties_destroyed */ |
62 | .todo_flags_start: 0, /* todo_flags_start */ |
63 | .todo_flags_finish: 0, /* todo_flags_finish */ |
64 | }; |
65 | |
66 | class pass_stack_ptr_mod : public rtl_opt_pass |
67 | { |
68 | public: |
69 | pass_stack_ptr_mod (gcc::context *ctxt) |
70 | : rtl_opt_pass (pass_data_stack_ptr_mod, ctxt) |
71 | {} |
72 | |
73 | /* opt_pass methods: */ |
74 | unsigned int execute (function *) final override; |
75 | |
76 | }; // class pass_stack_ptr_mod |
77 | |
78 | unsigned int |
79 | pass_stack_ptr_mod::execute (function *fun) |
80 | { |
81 | basic_block bb; |
82 | rtx_insn *insn; |
83 | |
84 | /* Assume that the stack pointer is unchanging if alloca hasn't |
85 | been used. */ |
86 | crtl->sp_is_unchanging = !fun->calls_alloca; |
87 | if (crtl->sp_is_unchanging) |
88 | FOR_EACH_BB_FN (bb, fun) |
89 | FOR_BB_INSNS (bb, insn) |
90 | { |
91 | if (INSN_P (insn)) |
92 | { |
93 | /* Check if insn modifies the stack pointer. */ |
94 | note_stores (insn, notice_stack_pointer_modification_1, NULL); |
95 | if (! crtl->sp_is_unchanging) |
96 | return 0; |
97 | } |
98 | } |
99 | |
100 | /* The value coming into this pass was 0, and the exit block uses |
101 | are based on this. If the value is now 1, we need to redo the |
102 | exit block uses. */ |
103 | if (df && crtl->sp_is_unchanging) |
104 | df_update_exit_block_uses (); |
105 | |
106 | return 0; |
107 | } |
108 | |
109 | } // anon namespace |
110 | |
111 | rtl_opt_pass * |
112 | make_pass_stack_ptr_mod (gcc::context *ctxt) |
113 | { |
114 | return new pass_stack_ptr_mod (ctxt); |
115 | } |
116 | |