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1 /* Rename SSA copies.
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2 Copyright (C) 2004, 2006, 2007, 2008 Free Software Foundation, Inc.
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3 Contributed by Andrew MacLeod <amacleod@redhat.com>
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4
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5 This file is part of GCC.
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6
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7 GCC is free software; you can redistribute it and/or modify
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8 it under the terms of the GNU General Public License as published by
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9 the Free Software Foundation; either version 3, or (at your option)
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10 any later version.
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11
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12 GCC is distributed in the hope that it will be useful,
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13 but WITHOUT ANY WARRANTY; without even the implied warranty of
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14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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15 GNU General Public License for more details.
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16
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17 You should have received a copy of the GNU General Public License
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18 along with GCC; see the file COPYING3. If not see
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19 <http://www.gnu.org/licenses/>. */
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20
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21 #include "config.h"
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22 #include "system.h"
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23 #include "coretypes.h"
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24 #include "tm.h"
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25 #include "tree.h"
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26 #include "gimple.h"
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27 #include "flags.h"
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28 #include "basic-block.h"
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29 #include "function.h"
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30 #include "diagnostic.h"
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31 #include "bitmap.h"
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32 #include "tree-flow.h"
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33 #include "gimple.h"
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34 #include "tree-inline.h"
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35 #include "timevar.h"
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36 #include "hashtab.h"
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37 #include "tree-dump.h"
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38 #include "tree-ssa-live.h"
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39 #include "tree-pass.h"
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40 #include "langhooks.h"
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41
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42 /* The following routines implement the SSA copy renaming phase.
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43
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44 This optimization looks for copies between 2 SSA_NAMES, either through a
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45 direct copy, or an implicit one via a PHI node result and its arguments.
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46
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47 Each copy is examined to determine if it is possible to rename the base
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48 variable of one of the operands to the same variable as the other operand.
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49 i.e.
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50 T.3_5 = <blah>
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51 a_1 = T.3_5
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52
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53 If this copy couldn't be copy propagated, it could possibly remain in the
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54 program throughout the optimization phases. After SSA->normal, it would
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55 become:
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56
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57 T.3 = <blah>
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58 a = T.3
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59
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60 Since T.3_5 is distinct from all other SSA versions of T.3, there is no
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61 fundamental reason why the base variable needs to be T.3, subject to
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62 certain restrictions. This optimization attempts to determine if we can
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63 change the base variable on copies like this, and result in code such as:
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64
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65 a_5 = <blah>
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66 a_1 = a_5
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67
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68 This gives the SSA->normal pass a shot at coalescing a_1 and a_5. If it is
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69 possible, the copy goes away completely. If it isn't possible, a new temp
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70 will be created for a_5, and you will end up with the exact same code:
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71
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72 a.8 = <blah>
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73 a = a.8
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74
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75 The other benefit of performing this optimization relates to what variables
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76 are chosen in copies. Gimplification of the program uses temporaries for
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77 a lot of things. expressions like
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78
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79 a_1 = <blah>
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80 <blah2> = a_1
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81
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82 get turned into
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83
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84 T.3_5 = <blah>
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85 a_1 = T.3_5
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86 <blah2> = a_1
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87
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88 Copy propagation is done in a forward direction, and if we can propagate
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89 through the copy, we end up with:
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90
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91 T.3_5 = <blah>
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92 <blah2> = T.3_5
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93
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94 The copy is gone, but so is all reference to the user variable 'a'. By
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95 performing this optimization, we would see the sequence:
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96
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97 a_5 = <blah>
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98 a_1 = a_5
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99 <blah2> = a_1
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100
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101 which copy propagation would then turn into:
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102
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103 a_5 = <blah>
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104 <blah2> = a_5
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105
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106 and so we still retain the user variable whenever possible. */
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107
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108
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109 /* Coalesce the partitions in MAP representing VAR1 and VAR2 if it is valid.
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110 Choose a representative for the partition, and send debug info to DEBUG. */
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111
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112 static bool
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113 copy_rename_partition_coalesce (var_map map, tree var1, tree var2, FILE *debug)
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114 {
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115 int p1, p2, p3;
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116 tree root1, root2;
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117 tree rep1, rep2;
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118 var_ann_t ann1, ann2, ann3;
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119 bool ign1, ign2, abnorm;
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120
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121 gcc_assert (TREE_CODE (var1) == SSA_NAME);
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122 gcc_assert (TREE_CODE (var2) == SSA_NAME);
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123
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124 register_ssa_partition (map, var1);
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125 register_ssa_partition (map, var2);
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126
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127 p1 = partition_find (map->var_partition, SSA_NAME_VERSION (var1));
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128 p2 = partition_find (map->var_partition, SSA_NAME_VERSION (var2));
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129
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130 if (debug)
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131 {
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132 fprintf (debug, "Try : ");
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133 print_generic_expr (debug, var1, TDF_SLIM);
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134 fprintf (debug, "(P%d) & ", p1);
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135 print_generic_expr (debug, var2, TDF_SLIM);
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136 fprintf (debug, "(P%d)", p2);
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137 }
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138
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139 gcc_assert (p1 != NO_PARTITION);
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140 gcc_assert (p2 != NO_PARTITION);
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141
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142 rep1 = partition_to_var (map, p1);
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143 rep2 = partition_to_var (map, p2);
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144 root1 = SSA_NAME_VAR (rep1);
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145 root2 = SSA_NAME_VAR (rep2);
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146
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147 ann1 = var_ann (root1);
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148 ann2 = var_ann (root2);
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149
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150 if (p1 == p2)
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151 {
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152 if (debug)
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153 fprintf (debug, " : Already coalesced.\n");
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154 return false;
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155 }
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156
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157 /* Don't coalesce if one of the variables occurs in an abnormal PHI. */
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158 abnorm = (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (rep1)
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159 || SSA_NAME_OCCURS_IN_ABNORMAL_PHI (rep2));
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160 if (abnorm)
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161 {
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162 if (debug)
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163 fprintf (debug, " : Abnormal PHI barrier. No coalesce.\n");
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164 return false;
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165 }
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166
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167 /* Partitions already have the same root, simply merge them. */
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168 if (root1 == root2)
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169 {
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170 p1 = partition_union (map->var_partition, p1, p2);
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171 if (debug)
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172 fprintf (debug, " : Same root, coalesced --> P%d.\n", p1);
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173 return false;
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174 }
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175
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176 /* Never attempt to coalesce 2 difference parameters. */
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177 if (TREE_CODE (root1) == PARM_DECL && TREE_CODE (root2) == PARM_DECL)
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178 {
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179 if (debug)
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180 fprintf (debug, " : 2 different PARM_DECLS. No coalesce.\n");
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181 return false;
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182 }
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183
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184 if ((TREE_CODE (root1) == RESULT_DECL) != (TREE_CODE (root2) == RESULT_DECL))
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185 {
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186 if (debug)
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187 fprintf (debug, " : One root a RESULT_DECL. No coalesce.\n");
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188 return false;
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189 }
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190
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191 ign1 = TREE_CODE (root1) == VAR_DECL && DECL_IGNORED_P (root1);
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192 ign2 = TREE_CODE (root2) == VAR_DECL && DECL_IGNORED_P (root2);
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193
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194 /* Never attempt to coalesce 2 user variables unless one is an inline
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195 variable. */
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196 if (!ign1 && !ign2)
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197 {
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198 if (DECL_FROM_INLINE (root2))
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199 ign2 = true;
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200 else if (DECL_FROM_INLINE (root1))
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201 ign1 = true;
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202 else
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203 {
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204 if (debug)
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205 fprintf (debug, " : 2 different USER vars. No coalesce.\n");
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206 return false;
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207 }
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208 }
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209
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210 /* Don't coalesce if there are two different memory tags. */
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211 if (ann1->symbol_mem_tag
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212 && ann2->symbol_mem_tag
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213 && ann1->symbol_mem_tag != ann2->symbol_mem_tag)
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214 {
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215 if (debug)
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216 fprintf (debug, " : 2 memory tags. No coalesce.\n");
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217 return false;
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218 }
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219
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220 /* If both values have default defs, we can't coalesce. If only one has a
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221 tag, make sure that variable is the new root partition. */
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222 if (gimple_default_def (cfun, root1))
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223 {
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224 if (gimple_default_def (cfun, root2))
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225 {
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226 if (debug)
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227 fprintf (debug, " : 2 default defs. No coalesce.\n");
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228 return false;
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229 }
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230 else
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231 {
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232 ign2 = true;
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233 ign1 = false;
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234 }
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235 }
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236 else if (gimple_default_def (cfun, root2))
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237 {
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238 ign1 = true;
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239 ign2 = false;
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240 }
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241
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242 /* Don't coalesce if the two variables aren't type compatible. */
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243 if (!types_compatible_p (TREE_TYPE (root1), TREE_TYPE (root2)))
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244 {
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245 if (debug)
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246 fprintf (debug, " : Incompatible types. No coalesce.\n");
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247 return false;
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248 }
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249
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250 /* Don't coalesce if the aliasing sets of the types are different. */
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251 if (POINTER_TYPE_P (TREE_TYPE (root1))
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252 && POINTER_TYPE_P (TREE_TYPE (root2))
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253 && ((get_alias_set (TREE_TYPE (TREE_TYPE (root1)))
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254 != get_alias_set (TREE_TYPE (TREE_TYPE (root2))))
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255 || ((DECL_P (root1) && !MTAG_P (root1))
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256 && (DECL_P (root2) && !MTAG_P (root2))
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257 && DECL_NO_TBAA_P (root1) != DECL_NO_TBAA_P (root2))))
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258 {
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259 if (debug)
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260 fprintf (debug, " : 2 different aliasing sets. No coalesce.\n");
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261 return false;
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262 }
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263
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264
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265 /* Merge the two partitions. */
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266 p3 = partition_union (map->var_partition, p1, p2);
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267
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268 /* Set the root variable of the partition to the better choice, if there is
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269 one. */
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270 if (!ign2)
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271 replace_ssa_name_symbol (partition_to_var (map, p3), root2);
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272 else if (!ign1)
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273 replace_ssa_name_symbol (partition_to_var (map, p3), root1);
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274
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275 /* Update the various flag widgitry of the current base representative. */
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276 ann3 = var_ann (SSA_NAME_VAR (partition_to_var (map, p3)));
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277 if (ann1->symbol_mem_tag)
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278 ann3->symbol_mem_tag = ann1->symbol_mem_tag;
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279 else
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280 ann3->symbol_mem_tag = ann2->symbol_mem_tag;
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281
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282 if (debug)
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283 {
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284 fprintf (debug, " --> P%d ", p3);
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285 print_generic_expr (debug, SSA_NAME_VAR (partition_to_var (map, p3)),
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286 TDF_SLIM);
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287 fprintf (debug, "\n");
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288 }
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289 return true;
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290 }
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291
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292
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293 /* This function will make a pass through the IL, and attempt to coalesce any
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294 SSA versions which occur in PHI's or copies. Coalescing is accomplished by
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295 changing the underlying root variable of all coalesced version. This will
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296 then cause the SSA->normal pass to attempt to coalesce them all to the same
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297 variable. */
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298
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299 static unsigned int
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300 rename_ssa_copies (void)
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301 {
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302 var_map map;
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303 basic_block bb;
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304 gimple_stmt_iterator gsi;
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305 tree var, part_var;
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306 gimple stmt, phi;
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307 unsigned x;
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308 FILE *debug;
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309 bool updated = false;
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310
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311 if (dump_file && (dump_flags & TDF_DETAILS))
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312 debug = dump_file;
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313 else
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314 debug = NULL;
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315
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316 map = init_var_map (num_ssa_names + 1);
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317
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318 FOR_EACH_BB (bb)
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319 {
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320 /* Scan for real copies. */
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321 for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
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322 {
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323 stmt = gsi_stmt (gsi);
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324 if (gimple_assign_ssa_name_copy_p (stmt))
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325 {
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326 tree lhs = gimple_assign_lhs (stmt);
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327 tree rhs = gimple_assign_rhs1 (stmt);
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328
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329 updated |= copy_rename_partition_coalesce (map, lhs, rhs, debug);
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330 }
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331 }
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332 }
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333
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334 FOR_EACH_BB (bb)
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335 {
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336 /* Treat PHI nodes as copies between the result and each argument. */
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337 for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi))
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338 {
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339 size_t i;
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340 tree res;
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341
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342 phi = gsi_stmt (gsi);
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343 res = gimple_phi_result (phi);
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344
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345 /* Do not process virtual SSA_NAMES. */
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346 if (!is_gimple_reg (SSA_NAME_VAR (res)))
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347 continue;
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348
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349 for (i = 0; i < gimple_phi_num_args (phi); i++)
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350 {
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351 tree arg = gimple_phi_arg (phi, i)->def;
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352 if (TREE_CODE (arg) == SSA_NAME)
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353 updated |= copy_rename_partition_coalesce (map, res, arg, debug);
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354 }
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355 }
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356 }
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357
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358 if (debug)
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359 dump_var_map (debug, map);
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360
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361 /* Now one more pass to make all elements of a partition share the same
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362 root variable. */
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363
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364 for (x = 1; x <= num_ssa_names; x++)
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365 {
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366 part_var = partition_to_var (map, x);
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367 if (!part_var)
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368 continue;
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369 var = map->partition_to_var[x];
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370 if (debug)
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371 {
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372 if (SSA_NAME_VAR (var) != SSA_NAME_VAR (part_var))
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373 {
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374 fprintf (debug, "Coalesced ");
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375 print_generic_expr (debug, var, TDF_SLIM);
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376 fprintf (debug, " to ");
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377 print_generic_expr (debug, part_var, TDF_SLIM);
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378 fprintf (debug, "\n");
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379 }
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380 }
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381 replace_ssa_name_symbol (var, SSA_NAME_VAR (part_var));
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382 }
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383
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384 delete_var_map (map);
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385 return updated ? TODO_remove_unused_locals : 0;
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386 }
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387
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388 /* Return true if copy rename is to be performed. */
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389
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390 static bool
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391 gate_copyrename (void)
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392 {
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393 return flag_tree_copyrename != 0;
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394 }
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395
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396 struct gimple_opt_pass pass_rename_ssa_copies =
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397 {
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398 {
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399 GIMPLE_PASS,
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400 "copyrename", /* name */
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401 gate_copyrename, /* gate */
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402 rename_ssa_copies, /* execute */
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403 NULL, /* sub */
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404 NULL, /* next */
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405 0, /* static_pass_number */
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406 TV_TREE_COPY_RENAME, /* tv_id */
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407 PROP_cfg | PROP_ssa, /* properties_required */
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408 0, /* properties_provided */
|
|
|
409 0, /* properties_destroyed */
|
|
|
410 0, /* todo_flags_start */
|
|
|
411 TODO_dump_func | TODO_verify_ssa /* todo_flags_finish */
|
|
|
412 }
|
|
|
413 };
|
