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) 2015-2018 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 "tree.h" 33 #include "tree-core.h" 34 #include "tree-pass.h" 35 #include "target.h" 36 #include "target-globals.h" 37 #include "profile-count.h" 38 #include "cfg.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: 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: */ 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 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 * 95 make_pass_ipa_frame_header_opt (gcc::context *ctxt) 96 { 97 return new pass_ipa_frame_header_opt (ctxt); 98 } 99 100 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 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 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 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 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 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 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