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) 2015-2020 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 #define IN_TARGET_CODE 1
27
28 #include "config.h"
29 #include "system.h"
30 #include "context.h"
31 #include "coretypes.h"
32 #include "backend.h"
33 #include "tree.h"
34 #include "tree-core.h"
35 #include "tree-pass.h"
36 #include "target.h"
37 #include "target-globals.h"
38 #include "profile-count.h"
39 #include "cgraph.h"
40 #include "function.h"
41 #include "basic-block.h"
42 #include "gimple.h"
43 #include "gimple-iterator.h"
44 #include "gimple-walk.h"
45
46 static unsigned int frame_header_opt (void);
47
48 namespace {
49
50 const pass_data pass_data_ipa_frame_header_opt =
51 {
52 IPA_PASS, /* type */
53 "frame-header-opt", /* name */
54 OPTGROUP_NONE, /* optinfo_flags */
55 TV_CGRAPHOPT, /* tv_id */
56 0, /* properties_required */
57 0, /* properties_provided */
58 0, /* properties_destroyed */
59 0, /* todo_flags_start */
60 0, /* todo_flags_finish */
61 };
62
63 class pass_ipa_frame_header_opt : public ipa_opt_pass_d
64 {
65 public:
pass_ipa_frame_header_opt(gcc::context * ctxt)66 pass_ipa_frame_header_opt (gcc::context *ctxt)
67 : ipa_opt_pass_d (pass_data_ipa_frame_header_opt, ctxt,
68 NULL, /* generate_summary */
69 NULL, /* write_summary */
70 NULL, /* read_summary */
71 NULL, /* write_optimization_summary */
72 NULL, /* read_optimization_summary */
73 NULL, /* stmt_fixup */
74 0, /* function_transform_todo_flags_start */
75 NULL, /* function_transform */
76 NULL) /* variable_transform */
77 {}
78
79 /* opt_pass methods: */
gate(function *)80 virtual bool gate (function *)
81 {
82 /* This optimization has no affect if TARGET_NEWABI. If optimize
83 is not at least 1 then the data needed for the optimization is
84 not available and nothing will be done anyway. */
85 return TARGET_OLDABI && flag_frame_header_optimization && optimize > 0;
86 }
87
execute(function *)88 virtual unsigned int execute (function *) { return frame_header_opt (); }
89
90 }; // class pass_ipa_frame_header_opt
91
92 } // anon namespace
93
94 static ipa_opt_pass_d *
make_pass_ipa_frame_header_opt(gcc::context * ctxt)95 make_pass_ipa_frame_header_opt (gcc::context *ctxt)
96 {
97 return new pass_ipa_frame_header_opt (ctxt);
98 }
99
100 void
mips_register_frame_header_opt(void)101 mips_register_frame_header_opt (void)
102 {
103 opt_pass *p = make_pass_ipa_frame_header_opt (g);
104 struct register_pass_info f = { p, "comdats", 1, PASS_POS_INSERT_AFTER };
105 register_pass (&f);
106 }
107
108
109 /* Return true if it is certain that this is a leaf function. False if it is
110 not a leaf function or if it is impossible to tell. */
111
112 static bool
is_leaf_function(function * fn)113 is_leaf_function (function *fn)
114 {
115 basic_block bb;
116 gimple_stmt_iterator gsi;
117
118 /* If we do not have a cfg for this function be conservative and assume
119 it is not a leaf function. */
120 if (fn->cfg == NULL)
121 return false;
122
123 FOR_EACH_BB_FN (bb, fn)
124 for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
125 if (is_gimple_call (gsi_stmt (gsi)))
126 return false;
127 return true;
128 }
129
130 /* Return true if this function has inline assembly code or if we cannot
131 be certain that it does not. False if we know that there is no inline
132 assembly. */
133
134 static bool
has_inlined_assembly(function * fn)135 has_inlined_assembly (function *fn)
136 {
137 basic_block bb;
138 gimple_stmt_iterator gsi;
139
140 /* If we do not have a cfg for this function be conservative and assume
141 it is may have inline assembly. */
142 if (fn->cfg == NULL)
143 return true;
144
145 FOR_EACH_BB_FN (bb, fn)
146 for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
147 if (gimple_code (gsi_stmt (gsi)) == GIMPLE_ASM)
148 return true;
149
150 return false;
151 }
152
153 /* Return true if this function will use the stack space allocated by its
154 caller or if we cannot determine for certain that it does not. */
155
156 static bool
needs_frame_header_p(function * fn)157 needs_frame_header_p (function *fn)
158 {
159 tree t;
160
161 if (fn->decl == NULL)
162 return true;
163
164 if (fn->stdarg)
165 return true;
166
167 for (t = DECL_ARGUMENTS (fn->decl); t; t = TREE_CHAIN (t))
168 {
169 if (!use_register_for_decl (t))
170 return true;
171
172 /* Some 64-bit types may get copied to general registers using the frame
173 header, see mips_output_64bit_xfer. Checking for SImode only may be
174 overly restrictive but it is guaranteed to be safe. */
175 if (DECL_MODE (t) != SImode)
176 return true;
177 }
178
179 return false;
180 }
181
182 /* Return true if the argument stack space allocated by function FN is used.
183 Return false if the space is needed or if the need for the space cannot
184 be determined. */
185
186 static bool
callees_functions_use_frame_header(function * fn)187 callees_functions_use_frame_header (function *fn)
188 {
189 basic_block bb;
190 gimple_stmt_iterator gsi;
191 gimple *stmt;
192 tree called_fn_tree;
193 function *called_fn;
194
195 if (fn->cfg == NULL)
196 return true;
197
198 FOR_EACH_BB_FN (bb, fn)
199 {
200 for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
201 {
202 stmt = gsi_stmt (gsi);
203 if (is_gimple_call (stmt))
204 {
205 called_fn_tree = gimple_call_fndecl (stmt);
206 if (called_fn_tree != NULL)
207 {
208 called_fn = DECL_STRUCT_FUNCTION (called_fn_tree);
209 if (called_fn == NULL
210 || DECL_WEAK (called_fn_tree)
211 || has_inlined_assembly (called_fn)
212 || !is_leaf_function (called_fn)
213 || !called_fn->machine->does_not_use_frame_header)
214 return true;
215 }
216 else
217 return true;
218 }
219 }
220 }
221 return false;
222 }
223
224 /* Set the callers_may_not_allocate_frame flag for any function which
225 function FN calls because FN may not allocate a frame header. */
226
227 static void
set_callers_may_not_allocate_frame(function * fn)228 set_callers_may_not_allocate_frame (function *fn)
229 {
230 basic_block bb;
231 gimple_stmt_iterator gsi;
232 gimple *stmt;
233 tree called_fn_tree;
234 function *called_fn;
235
236 if (fn->cfg == NULL)
237 return;
238
239 FOR_EACH_BB_FN (bb, fn)
240 {
241 for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
242 {
243 stmt = gsi_stmt (gsi);
244 if (is_gimple_call (stmt))
245 {
246 called_fn_tree = gimple_call_fndecl (stmt);
247 if (called_fn_tree != NULL)
248 {
249 called_fn = DECL_STRUCT_FUNCTION (called_fn_tree);
250 if (called_fn != NULL)
251 called_fn->machine->callers_may_not_allocate_frame = true;
252 }
253 }
254 }
255 }
256 return;
257 }
258
259 /* Scan each function to determine those that need its frame headers. Perform
260 a second scan to determine if the allocation can be skipped because none of
261 their callees require the frame header. */
262
263 static unsigned int
frame_header_opt()264 frame_header_opt ()
265 {
266 struct cgraph_node *node;
267 function *fn;
268
269 FOR_EACH_DEFINED_FUNCTION (node)
270 {
271 fn = node->get_fun ();
272 if (fn != NULL)
273 fn->machine->does_not_use_frame_header = !needs_frame_header_p (fn);
274 }
275
276 FOR_EACH_DEFINED_FUNCTION (node)
277 {
278 fn = node->get_fun ();
279 if (fn != NULL)
280 fn->machine->optimize_call_stack
281 = !callees_functions_use_frame_header (fn) && !is_leaf_function (fn);
282 }
283
284 FOR_EACH_DEFINED_FUNCTION (node)
285 {
286 fn = node->get_fun ();
287 if (fn != NULL && fn->machine->optimize_call_stack)
288 set_callers_may_not_allocate_frame (fn);
289 }
290
291 return 0;
292 }
293