1 /* Discover if the stack pointer is modified in a function.
2 Copyright (C) 2007-2014 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 "tm.h"
24 #include "tree.h"
25 #include "rtl.h"
26 #include "regs.h"
27 #include "expr.h"
28 #include "tree-pass.h"
29 #include "basic-block.h"
30 #include "flags.h"
31 #include "output.h"
32 #include "df.h"
33
34 /* Determine if the stack pointer is constant over the life of the function.
35 Only useful before prologues have been emitted. */
36
37 static void
notice_stack_pointer_modification_1(rtx x,const_rtx pat ATTRIBUTE_UNUSED,void * data ATTRIBUTE_UNUSED)38 notice_stack_pointer_modification_1 (rtx x, const_rtx pat ATTRIBUTE_UNUSED,
39 void *data ATTRIBUTE_UNUSED)
40 {
41 if (x == stack_pointer_rtx
42 /* The stack pointer is only modified indirectly as the result
43 of a push until later. See the comments in rtl.texi
44 regarding Embedded Side-Effects on Addresses. */
45 || (MEM_P (x)
46 && GET_RTX_CLASS (GET_CODE (XEXP (x, 0))) == RTX_AUTOINC
47 && XEXP (XEXP (x, 0), 0) == stack_pointer_rtx))
48 crtl->sp_is_unchanging = 0;
49 }
50
51 static void
notice_stack_pointer_modification(void)52 notice_stack_pointer_modification (void)
53 {
54 basic_block bb;
55 rtx insn;
56
57 /* Assume that the stack pointer is unchanging if alloca hasn't
58 been used. */
59 crtl->sp_is_unchanging = !cfun->calls_alloca;
60 if (crtl->sp_is_unchanging)
61 FOR_EACH_BB_FN (bb, cfun)
62 FOR_BB_INSNS (bb, insn)
63 {
64 if (INSN_P (insn))
65 {
66 /* Check if insn modifies the stack pointer. */
67 note_stores (PATTERN (insn),
68 notice_stack_pointer_modification_1,
69 NULL);
70 if (! crtl->sp_is_unchanging)
71 return;
72 }
73 }
74
75 /* The value coming into this pass was 0, and the exit block uses
76 are based on this. If the value is now 1, we need to redo the
77 exit block uses. */
78 if (df && crtl->sp_is_unchanging)
79 df_update_exit_block_uses ();
80 }
81
82 /* Some targets can emit simpler epilogues if they know that sp was
83 not ever modified during the function. After reload, of course,
84 we've already emitted the epilogue so there's no sense searching. */
85
86 static unsigned int
rest_of_handle_stack_ptr_mod(void)87 rest_of_handle_stack_ptr_mod (void)
88 {
89 notice_stack_pointer_modification ();
90 return 0;
91 }
92
93 namespace {
94
95 const pass_data pass_data_stack_ptr_mod =
96 {
97 RTL_PASS, /* type */
98 "*stack_ptr_mod", /* name */
99 OPTGROUP_NONE, /* optinfo_flags */
100 false, /* has_gate */
101 true, /* has_execute */
102 TV_NONE, /* tv_id */
103 0, /* properties_required */
104 0, /* properties_provided */
105 0, /* properties_destroyed */
106 0, /* todo_flags_start */
107 0, /* todo_flags_finish */
108 };
109
110 class pass_stack_ptr_mod : public rtl_opt_pass
111 {
112 public:
pass_stack_ptr_mod(gcc::context * ctxt)113 pass_stack_ptr_mod (gcc::context *ctxt)
114 : rtl_opt_pass (pass_data_stack_ptr_mod, ctxt)
115 {}
116
117 /* opt_pass methods: */
execute()118 unsigned int execute () { return rest_of_handle_stack_ptr_mod (); }
119
120 }; // class pass_stack_ptr_mod
121
122 } // anon namespace
123
124 rtl_opt_pass *
make_pass_stack_ptr_mod(gcc::context * ctxt)125 make_pass_stack_ptr_mod (gcc::context *ctxt)
126 {
127 return new pass_stack_ptr_mod (ctxt);
128 }
129