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111
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1 /* Analyze functions to determine if callers need to allocate a frame header
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2 on the stack. The frame header is used by callees to save their arguments.
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3 This optimization is specific to TARGET_OLDABI targets. For TARGET_NEWABI
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4 targets, if a frame header is required, it is allocated by the callee.
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5
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6
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7 Copyright (C) 2015-2017 Free Software Foundation, Inc.
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8
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9 This file is part of GCC.
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10
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11 GCC is free software; you can redistribute it and/or modify it
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12 under the terms of the GNU General Public License as published by the
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13 Free Software Foundation; either version 3, or (at your option) any
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14 later version.
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15
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16 GCC is distributed in the hope that it will be useful, but WITHOUT
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17 ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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18 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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19 for more details.
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20
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21 You should have received a copy of the GNU General Public License
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22 along with GCC; see the file COPYING3. If not see
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23 <http://www.gnu.org/licenses/>. */
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24
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25
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26 #include "config.h"
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27 #include "system.h"
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28 #include "context.h"
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29 #include "coretypes.h"
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30 #include "tree.h"
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31 #include "tree-core.h"
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32 #include "tree-pass.h"
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33 #include "target.h"
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34 #include "target-globals.h"
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35 #include "profile-count.h"
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36 #include "cfg.h"
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37 #include "cgraph.h"
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38 #include "function.h"
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39 #include "basic-block.h"
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40 #include "gimple.h"
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41 #include "gimple-iterator.h"
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42 #include "gimple-walk.h"
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43
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44 static unsigned int frame_header_opt (void);
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45
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46 namespace {
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47
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48 const pass_data pass_data_ipa_frame_header_opt =
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49 {
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50 IPA_PASS, /* type */
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51 "frame-header-opt", /* name */
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52 OPTGROUP_NONE, /* optinfo_flags */
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53 TV_CGRAPHOPT, /* tv_id */
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54 0, /* properties_required */
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55 0, /* properties_provided */
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56 0, /* properties_destroyed */
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57 0, /* todo_flags_start */
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58 0, /* todo_flags_finish */
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59 };
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60
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61 class pass_ipa_frame_header_opt : public ipa_opt_pass_d
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62 {
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63 public:
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64 pass_ipa_frame_header_opt (gcc::context *ctxt)
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65 : ipa_opt_pass_d (pass_data_ipa_frame_header_opt, ctxt,
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66 NULL, /* generate_summary */
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67 NULL, /* write_summary */
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68 NULL, /* read_summary */
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69 NULL, /* write_optimization_summary */
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70 NULL, /* read_optimization_summary */
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71 NULL, /* stmt_fixup */
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72 0, /* function_transform_todo_flags_start */
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73 NULL, /* function_transform */
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74 NULL) /* variable_transform */
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75 {}
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76
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77 /* opt_pass methods: */
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78 virtual bool gate (function *)
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79 {
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80 /* This optimization has no affect if TARGET_NEWABI. If optimize
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81 is not at least 1 then the data needed for the optimization is
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82 not available and nothing will be done anyway. */
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83 return TARGET_OLDABI && flag_frame_header_optimization && optimize > 0;
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84 }
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85
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86 virtual unsigned int execute (function *) { return frame_header_opt (); }
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87
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88 }; // class pass_ipa_frame_header_opt
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89
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90 } // anon namespace
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91
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92 static ipa_opt_pass_d *
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93 make_pass_ipa_frame_header_opt (gcc::context *ctxt)
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94 {
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95 return new pass_ipa_frame_header_opt (ctxt);
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96 }
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97
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98 void
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99 mips_register_frame_header_opt (void)
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100 {
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101 opt_pass *p = make_pass_ipa_frame_header_opt (g);
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102 static struct register_pass_info f =
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103 {p, "comdats", 1, PASS_POS_INSERT_AFTER };
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104 register_pass (&f);
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105 }
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106
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107
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108 /* Return true if it is certain that this is a leaf function. False if it is
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109 not a leaf function or if it is impossible to tell. */
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110
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111 static bool
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112 is_leaf_function (function *fn)
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113 {
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114 basic_block bb;
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115 gimple_stmt_iterator gsi;
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116
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117 /* If we do not have a cfg for this function be conservative and assume
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118 it is not a leaf function. */
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119 if (fn->cfg == NULL)
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120 return false;
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121
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122 FOR_EACH_BB_FN (bb, fn)
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123 for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
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124 if (is_gimple_call (gsi_stmt (gsi)))
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125 return false;
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126 return true;
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127 }
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128
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129 /* Return true if this function has inline assembly code or if we cannot
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130 be certain that it does not. False if we know that there is no inline
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131 assembly. */
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132
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133 static bool
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134 has_inlined_assembly (function *fn)
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135 {
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136 basic_block bb;
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137 gimple_stmt_iterator gsi;
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138
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139 /* If we do not have a cfg for this function be conservative and assume
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140 it is may have inline assembly. */
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141 if (fn->cfg == NULL)
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142 return true;
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143
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144 FOR_EACH_BB_FN (bb, fn)
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145 for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
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146 if (gimple_code (gsi_stmt (gsi)) == GIMPLE_ASM)
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147 return true;
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148
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149 return false;
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150 }
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151
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152 /* Return true if this function will use the stack space allocated by its
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153 caller or if we cannot determine for certain that it does not. */
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154
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155 static bool
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156 needs_frame_header_p (function *fn)
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157 {
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158 tree t;
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159
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160 if (fn->decl == NULL)
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161 return true;
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162
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163 if (fn->stdarg)
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164 return true;
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165
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166 for (t = DECL_ARGUMENTS (fn->decl); t; t = TREE_CHAIN (t))
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167 {
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168 if (!use_register_for_decl (t))
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169 return true;
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170
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171 /* Some 64-bit types may get copied to general registers using the frame
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172 header, see mips_output_64bit_xfer. Checking for SImode only may be
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173 overly restrictive but it is guaranteed to be safe. */
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174 if (DECL_MODE (t) != SImode)
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175 return true;
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176 }
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177
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178 return false;
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179 }
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180
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181 /* Return true if the argument stack space allocated by function FN is used.
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182 Return false if the space is needed or if the need for the space cannot
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183 be determined. */
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184
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185 static bool
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186 callees_functions_use_frame_header (function *fn)
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187 {
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188 basic_block bb;
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189 gimple_stmt_iterator gsi;
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190 gimple *stmt;
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191 tree called_fn_tree;
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192 function *called_fn;
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193
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194 if (fn->cfg == NULL)
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195 return true;
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196
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197 FOR_EACH_BB_FN (bb, fn)
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198 {
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199 for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
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200 {
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201 stmt = gsi_stmt (gsi);
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202 if (is_gimple_call (stmt))
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203 {
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204 called_fn_tree = gimple_call_fndecl (stmt);
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205 if (called_fn_tree != NULL)
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206 {
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207 called_fn = DECL_STRUCT_FUNCTION (called_fn_tree);
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208 if (called_fn == NULL
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209 || DECL_WEAK (called_fn_tree)
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210 || has_inlined_assembly (called_fn)
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211 || !is_leaf_function (called_fn)
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212 || !called_fn->machine->does_not_use_frame_header)
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213 return true;
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214 }
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215 else
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216 return true;
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217 }
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218 }
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219 }
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220 return false;
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221 }
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222
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223 /* Set the callers_may_not_allocate_frame flag for any function which
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224 function FN calls because FN may not allocate a frame header. */
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225
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226 static void
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227 set_callers_may_not_allocate_frame (function *fn)
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228 {
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229 basic_block bb;
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230 gimple_stmt_iterator gsi;
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231 gimple *stmt;
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232 tree called_fn_tree;
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233 function *called_fn;
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234
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235 if (fn->cfg == NULL)
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236 return;
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237
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238 FOR_EACH_BB_FN (bb, fn)
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239 {
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240 for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
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241 {
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242 stmt = gsi_stmt (gsi);
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243 if (is_gimple_call (stmt))
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244 {
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245 called_fn_tree = gimple_call_fndecl (stmt);
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246 if (called_fn_tree != NULL)
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247 {
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248 called_fn = DECL_STRUCT_FUNCTION (called_fn_tree);
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249 if (called_fn != NULL)
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250 called_fn->machine->callers_may_not_allocate_frame = true;
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251 }
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252 }
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253 }
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254 }
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255 return;
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256 }
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257
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258 /* Scan each function to determine those that need its frame headers. Perform
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259 a second scan to determine if the allocation can be skipped because none of
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260 their callees require the frame header. */
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261
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262 static unsigned int
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263 frame_header_opt ()
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264 {
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265 struct cgraph_node *node;
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266 function *fn;
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267
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268 FOR_EACH_DEFINED_FUNCTION (node)
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269 {
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270 fn = node->get_fun ();
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271 if (fn != NULL)
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272 fn->machine->does_not_use_frame_header = !needs_frame_header_p (fn);
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273 }
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274
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275 FOR_EACH_DEFINED_FUNCTION (node)
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276 {
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277 fn = node->get_fun ();
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278 if (fn != NULL)
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279 fn->machine->optimize_call_stack
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280 = !callees_functions_use_frame_header (fn) && !is_leaf_function (fn);
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281 }
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282
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283 FOR_EACH_DEFINED_FUNCTION (node)
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284 {
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285 fn = node->get_fun ();
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286 if (fn != NULL && fn->machine->optimize_call_stack)
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287 set_callers_may_not_allocate_frame (fn);
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288 }
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289
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290 return 0;
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291 }
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