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1 | /* Analyze functions to determine if callers need to allocate a frame header |
2 | on the stack. The frame header is used by callees to save their arguments. | |
3 | This optimization is specific to TARGET_OLDABI targets. For TARGET_NEWABI | |
4 | targets, if a frame header is required, it is allocated by the callee. | |
5 | ||
6 | ||
7 | Copyright (C) 2015 Free Software Foundation, Inc. | |
8 | ||
9 | This file is part of GCC. | |
10 | ||
11 | GCC is free software; you can redistribute it and/or modify it | |
12 | under the terms of the GNU General Public License as published by the | |
13 | Free Software Foundation; either version 3, or (at your option) any | |
14 | later version. | |
15 | ||
16 | GCC is distributed in the hope that it will be useful, but WITHOUT | |
17 | ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | |
18 | FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | |
19 | for more details. | |
20 | ||
21 | You should have received a copy of the GNU General Public License | |
22 | along with GCC; see the file COPYING3. If not see | |
23 | <http://www.gnu.org/licenses/>. */ | |
24 | ||
25 | ||
26 | #include "config.h" | |
27 | #include "system.h" | |
28 | #include "context.h" | |
29 | #include "coretypes.h" | |
30 | #include "tree.h" | |
31 | #include "tree-core.h" | |
32 | #include "tree-pass.h" | |
33 | #include "target.h" | |
34 | #include "target-globals.h" | |
35 | #include "cfg.h" | |
36 | #include "cgraph.h" | |
37 | #include "function.h" | |
38 | #include "basic-block.h" | |
39 | #include "gimple.h" | |
40 | #include "gimple-iterator.h" | |
41 | #include "gimple-walk.h" | |
42 | ||
43 | static unsigned int frame_header_opt (void); | |
44 | ||
45 | namespace { | |
46 | ||
47 | const pass_data pass_data_ipa_frame_header_opt = | |
48 | { | |
49 | IPA_PASS, /* type */ | |
50 | "frame-header-opt", /* name */ | |
51 | OPTGROUP_NONE, /* optinfo_flags */ | |
52 | TV_CGRAPHOPT, /* tv_id */ | |
53 | 0, /* properties_required */ | |
54 | 0, /* properties_provided */ | |
55 | 0, /* properties_destroyed */ | |
56 | 0, /* todo_flags_start */ | |
57 | 0, /* todo_flags_finish */ | |
58 | }; | |
59 | ||
60 | class pass_ipa_frame_header_opt : public ipa_opt_pass_d | |
61 | { | |
62 | public: | |
63 | pass_ipa_frame_header_opt (gcc::context *ctxt) | |
64 | : ipa_opt_pass_d (pass_data_ipa_frame_header_opt, ctxt, | |
65 | NULL, /* generate_summary */ | |
66 | NULL, /* write_summary */ | |
67 | NULL, /* read_summary */ | |
68 | NULL, /* write_optimization_summary */ | |
69 | NULL, /* read_optimization_summary */ | |
70 | NULL, /* stmt_fixup */ | |
71 | 0, /* function_transform_todo_flags_start */ | |
72 | NULL, /* function_transform */ | |
73 | NULL) /* variable_transform */ | |
74 | {} | |
75 | ||
76 | /* opt_pass methods: */ | |
77 | virtual bool gate (function *) | |
78 | { | |
79 | /* This optimization has no affect if TARGET_NEWABI. If optimize | |
80 | is not at least 1 then the data needed for the optimization is | |
81 | not available and nothing will be done anyway. */ | |
82 | return TARGET_OLDABI && flag_frame_header_optimization; | |
83 | } | |
84 | ||
85 | virtual unsigned int execute (function *) { return frame_header_opt (); } | |
86 | ||
87 | }; // class pass_ipa_frame_header_opt | |
88 | ||
89 | } // anon namespace | |
90 | ||
91 | static ipa_opt_pass_d * | |
92 | make_pass_ipa_frame_header_opt (gcc::context *ctxt) | |
93 | { | |
94 | return new pass_ipa_frame_header_opt (ctxt); | |
95 | } | |
96 | ||
97 | void | |
98 | mips_register_frame_header_opt (void) | |
99 | { | |
100 | opt_pass *p = make_pass_ipa_frame_header_opt (g); | |
101 | static struct register_pass_info f = | |
102 | {p, "comdats", 1, PASS_POS_INSERT_AFTER }; | |
103 | register_pass (&f); | |
104 | } | |
105 | ||
106 | ||
107 | /* Return true if it is certain that this is a leaf function. False if it is | |
108 | not a leaf function or if it is impossible to tell. */ | |
109 | ||
110 | static bool | |
111 | is_leaf_function (function *fn) | |
112 | { | |
113 | basic_block bb; | |
114 | gimple_stmt_iterator gsi; | |
115 | ||
116 | /* If we do not have a cfg for this function be conservative and assume | |
117 | it is not a leaf function. */ | |
118 | if (fn->cfg == NULL) | |
119 | return false; | |
120 | ||
121 | FOR_EACH_BB_FN (bb, fn) | |
122 | for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi)) | |
123 | if (is_gimple_call (gsi_stmt (gsi))) | |
124 | return false; | |
125 | return true; | |
126 | } | |
127 | ||
128 | /* Return true if this function will use the stack space allocated by its | |
129 | caller or if we cannot determine for certain that it does not. */ | |
130 | ||
131 | static bool | |
132 | needs_frame_header_p (function *fn) | |
133 | { | |
134 | tree t; | |
135 | ||
136 | if (fn->decl == NULL) | |
137 | return true; | |
138 | ||
139 | if (fn->stdarg || !is_leaf_function (fn)) | |
140 | return true; | |
141 | ||
142 | for (t = DECL_ARGUMENTS (fn->decl); t; t = TREE_CHAIN (t)) | |
143 | { | |
144 | if (!use_register_for_decl (t)) | |
145 | return true; | |
146 | } | |
147 | ||
148 | return false; | |
149 | } | |
150 | ||
151 | /* Returns TRUE if the argument stack space allocated by function FN is used. | |
152 | Returns FALSE if the space is needed or if the need for the space cannot | |
153 | be determined. */ | |
154 | ||
155 | static bool | |
156 | callees_functions_use_frame_header (function *fn) | |
157 | { | |
158 | basic_block bb; | |
159 | gimple_stmt_iterator gsi; | |
160 | gimple *stmt; | |
161 | tree called_fn_tree; | |
162 | function *called_fn; | |
163 | ||
164 | if (fn->cfg == NULL) | |
165 | return true; | |
166 | ||
167 | FOR_EACH_BB_FN (bb, fn) | |
168 | { | |
169 | for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi)) | |
170 | { | |
171 | stmt = gsi_stmt (gsi); | |
172 | if (is_gimple_call (stmt)) | |
173 | { | |
174 | called_fn_tree = gimple_call_fndecl (stmt); | |
175 | if (called_fn_tree != NULL) | |
176 | { | |
177 | called_fn = DECL_STRUCT_FUNCTION (called_fn_tree); | |
178 | if (called_fn == NULL | |
179 | || DECL_WEAK (called_fn_tree) | |
180 | || !called_fn->machine->does_not_use_frame_header) | |
181 | return true; | |
182 | } | |
183 | else | |
184 | return true; | |
185 | } | |
186 | } | |
187 | } | |
188 | return false; | |
189 | } | |
190 | ||
191 | /* Scan each function to determine those that need its frame headers. Perform | |
192 | a second scan to determine if the allocation can be skipped because none of | |
193 | their callees require the frame header. */ | |
194 | ||
195 | static unsigned int | |
196 | frame_header_opt () | |
197 | { | |
198 | struct cgraph_node *node; | |
199 | function *fn; | |
200 | ||
201 | FOR_EACH_DEFINED_FUNCTION (node) | |
202 | { | |
203 | fn = node->get_fun (); | |
204 | if (fn != NULL) | |
205 | fn->machine->does_not_use_frame_header = !needs_frame_header_p (fn); | |
206 | } | |
207 | ||
208 | FOR_EACH_DEFINED_FUNCTION (node) | |
209 | { | |
210 | fn = node->get_fun (); | |
211 | if (fn != NULL) | |
212 | fn->machine->optimize_call_stack | |
213 | = !callees_functions_use_frame_header (fn); | |
214 | } | |
215 | return 0; | |
216 | } |