1/* Discover if the stack pointer is modified in a function.
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 "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
33static void
34notice_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
51namespace {
52
53const pass_data pass_data_stack_ptr_mod =
54{
55 RTL_PASS, /* type */
56 "*stack_ptr_mod", /* name */
57 OPTGROUP_NONE, /* optinfo_flags */
58 TV_NONE, /* tv_id */
59 0, /* properties_required */
60 0, /* properties_provided */
61 0, /* properties_destroyed */
62 0, /* todo_flags_start */
63 0, /* todo_flags_finish */
64};
65
66class pass_stack_ptr_mod : public rtl_opt_pass
67{
68public:
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 virtual unsigned int execute (function *);
75
76}; // class pass_stack_ptr_mod
77
78unsigned int
79pass_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 (PATTERN (insn),
95 notice_stack_pointer_modification_1,
96 NULL);
97 if (! crtl->sp_is_unchanging)
98 return 0;
99 }
100 }
101
102 /* The value coming into this pass was 0, and the exit block uses
103 are based on this. If the value is now 1, we need to redo the
104 exit block uses. */
105 if (df && crtl->sp_is_unchanging)
106 df_update_exit_block_uses ();
107
108 return 0;
109}
110
111} // anon namespace
112
113rtl_opt_pass *
114make_pass_stack_ptr_mod (gcc::context *ctxt)
115{
116 return new pass_stack_ptr_mod (ctxt);
117}
118