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1 /*
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2 * Copyright 1999-2007 Sun Microsystems, Inc. All Rights Reserved.
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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4 *
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5 * This code is free software; you can redistribute it and/or modify it
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6 * under the terms of the GNU General Public License version 2 only, as
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7 * published by the Free Software Foundation.
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8 *
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9 * This code is distributed in the hope that it will be useful, but WITHOUT
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10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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12 * version 2 for more details (a copy is included in the LICENSE file that
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13 * accompanied this code).
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14 *
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15 * You should have received a copy of the GNU General Public License version
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16 * 2 along with this work; if not, write to the Free Software Foundation,
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17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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18 *
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19 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
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20 * CA 95054 USA or visit www.sun.com if you need additional information or
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21 * have any questions.
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22 *
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23 */
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24
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25 #include "incls/_precompiled.incl"
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26 #include "incls/_ciField.cpp.incl"
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27
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28 // ciField
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29 //
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30 // This class represents the result of a field lookup in the VM.
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31 // The lookup may not succeed, in which case the information in
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32 // the ciField will be incomplete.
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33
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34 // The ciObjectFactory cannot create circular data structures in one query.
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35 // To avoid vicious circularities, we initialize ciField::_type to NULL
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36 // for reference types and derive it lazily from the ciField::_signature.
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37 // Primitive types are eagerly initialized, and basic layout queries
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38 // can succeed without initialization, using only the BasicType of the field.
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39
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40 // Notes on bootstrapping and shared CI objects: A field is shared if and
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41 // only if it is (a) non-static and (b) declared by a shared instance klass.
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42 // This allows non-static field lists to be cached on shared types.
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43 // Because the _type field is lazily initialized, however, there is a
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44 // special restriction that a shared field cannot cache an unshared type.
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45 // This puts a small performance penalty on shared fields with unshared
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46 // types, such as StackTraceElement[] Throwable.stackTrace.
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47 // (Throwable is shared because ClassCastException is shared, but
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48 // StackTraceElement is not presently shared.)
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49
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50 // It is not a vicious circularity for a ciField to recursively create
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51 // the ciSymbols necessary to represent its name and signature.
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52 // Therefore, these items are created eagerly, and the name and signature
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53 // of a shared field are themselves shared symbols. This somewhat
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54 // pollutes the set of shared CI objects: It grows from 50 to 93 items,
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55 // with all of the additional 43 being uninteresting shared ciSymbols.
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56 // This adds at most one step to the binary search, an amount which
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57 // decreases for complex compilation tasks.
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58
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59 // ------------------------------------------------------------------
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60 // ciField::ciField
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61 ciField::ciField(ciInstanceKlass* klass, int index): _known_to_link_with(NULL) {
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62 ASSERT_IN_VM;
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63 CompilerThread *thread = CompilerThread::current();
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64
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65 assert(ciObjectFactory::is_initialized(), "not a shared field");
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66
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67 assert(klass->get_instanceKlass()->is_linked(), "must be linked before using its constan-pool");
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68
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69 _cp_index = index;
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70 constantPoolHandle cpool(thread, klass->get_instanceKlass()->constants());
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71
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72 // Get the field's name, signature, and type.
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73 symbolHandle name (thread, cpool->name_ref_at(index));
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74 _name = ciEnv::current(thread)->get_object(name())->as_symbol();
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75
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76 int nt_index = cpool->name_and_type_ref_index_at(index);
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77 int sig_index = cpool->signature_ref_index_at(nt_index);
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78 symbolHandle signature (thread, cpool->symbol_at(sig_index));
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79 _signature = ciEnv::current(thread)->get_object(signature())->as_symbol();
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80
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81 BasicType field_type = FieldType::basic_type(signature());
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82
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83 // If the field is a pointer type, get the klass of the
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84 // field.
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85 if (field_type == T_OBJECT || field_type == T_ARRAY) {
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86 bool ignore;
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87 // This is not really a class reference; the index always refers to the
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88 // field's type signature, as a symbol. Linkage checks do not apply.
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89 _type = ciEnv::current(thread)->get_klass_by_index(klass, sig_index, ignore);
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90 } else {
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91 _type = ciType::make(field_type);
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92 }
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93
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94 _name = (ciSymbol*)ciEnv::current(thread)->get_object(name());
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95
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96 // Get the field's declared holder.
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97 //
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98 // Note: we actually create a ciInstanceKlass for this klass,
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99 // even though we may not need to.
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100 int holder_index = cpool->klass_ref_index_at(index);
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101 bool holder_is_accessible;
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102 ciInstanceKlass* declared_holder =
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103 ciEnv::current(thread)->get_klass_by_index(klass, holder_index,
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104 holder_is_accessible)
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105 ->as_instance_klass();
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106
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107 // The declared holder of this field may not have been loaded.
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108 // Bail out with partial field information.
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109 if (!holder_is_accessible) {
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110 // _cp_index and _type have already been set.
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111 // The default values for _flags and _constant_value will suffice.
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112 // We need values for _holder, _offset, and _is_constant,
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113 _holder = declared_holder;
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114 _offset = -1;
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115 _is_constant = false;
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116 return;
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117 }
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118
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119 instanceKlass* loaded_decl_holder = declared_holder->get_instanceKlass();
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120
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121 // Perform the field lookup.
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122 fieldDescriptor field_desc;
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123 klassOop canonical_holder =
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124 loaded_decl_holder->find_field(name(), signature(), &field_desc);
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125 if (canonical_holder == NULL) {
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126 // Field lookup failed. Will be detected by will_link.
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127 _holder = declared_holder;
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128 _offset = -1;
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129 _is_constant = false;
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130 return;
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131 }
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132
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133 assert(canonical_holder == field_desc.field_holder(), "just checking");
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134 initialize_from(&field_desc);
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135 }
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136
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137 ciField::ciField(fieldDescriptor *fd): _known_to_link_with(NULL) {
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138 ASSERT_IN_VM;
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139
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140 _cp_index = -1;
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141
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142 // Get the field's name, signature, and type.
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143 ciEnv* env = CURRENT_ENV;
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144 _name = env->get_object(fd->name())->as_symbol();
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145 _signature = env->get_object(fd->signature())->as_symbol();
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146
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147 BasicType field_type = fd->field_type();
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148
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149 // If the field is a pointer type, get the klass of the
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150 // field.
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151 if (field_type == T_OBJECT || field_type == T_ARRAY) {
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152 _type = NULL; // must call compute_type on first access
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153 } else {
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154 _type = ciType::make(field_type);
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155 }
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156
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157 initialize_from(fd);
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158
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159 // Either (a) it is marked shared, or else (b) we are done bootstrapping.
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160 assert(is_shared() || ciObjectFactory::is_initialized(),
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161 "bootstrap classes must not create & cache unshared fields");
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162 }
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163
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164 void ciField::initialize_from(fieldDescriptor* fd) {
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165 // Get the flags, offset, and canonical holder of the field.
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166 _flags = ciFlags(fd->access_flags());
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167 _offset = fd->offset();
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168 _holder = CURRENT_ENV->get_object(fd->field_holder())->as_instance_klass();
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169
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170 // Check to see if the field is constant.
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171 if (_holder->is_initialized() &&
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172 this->is_final() && this->is_static()) {
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173 // This field just may be constant. The only cases where it will
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174 // not be constant are:
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175 //
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176 // 1. The field holds a non-perm-space oop. The field is, strictly
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177 // speaking, constant but we cannot embed non-perm-space oops into
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178 // generated code. For the time being we need to consider the
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179 // field to be not constant.
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180 // 2. The field is a *special* static&final field whose value
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181 // may change. The three examples are java.lang.System.in,
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182 // java.lang.System.out, and java.lang.System.err.
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183
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184 klassOop k = _holder->get_klassOop();
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185 assert( SystemDictionary::system_klass() != NULL, "Check once per vm");
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186 if( k == SystemDictionary::system_klass() ) {
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187 // Check offsets for case 2: System.in, System.out, or System.err
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188 if( _offset == java_lang_System::in_offset_in_bytes() ||
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189 _offset == java_lang_System::out_offset_in_bytes() ||
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190 _offset == java_lang_System::err_offset_in_bytes() ) {
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191 _is_constant = false;
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192 return;
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193 }
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194 }
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195
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196 _is_constant = true;
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197 switch(type()->basic_type()) {
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198 case T_BYTE:
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199 _constant_value = ciConstant(type()->basic_type(), k->byte_field(_offset));
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200 break;
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201 case T_CHAR:
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202 _constant_value = ciConstant(type()->basic_type(), k->char_field(_offset));
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203 break;
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204 case T_SHORT:
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205 _constant_value = ciConstant(type()->basic_type(), k->short_field(_offset));
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206 break;
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207 case T_BOOLEAN:
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208 _constant_value = ciConstant(type()->basic_type(), k->bool_field(_offset));
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209 break;
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210 case T_INT:
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211 _constant_value = ciConstant(type()->basic_type(), k->int_field(_offset));
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212 break;
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213 case T_FLOAT:
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214 _constant_value = ciConstant(k->float_field(_offset));
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215 break;
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216 case T_DOUBLE:
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217 _constant_value = ciConstant(k->double_field(_offset));
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218 break;
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219 case T_LONG:
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220 _constant_value = ciConstant(k->long_field(_offset));
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221 break;
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222 case T_OBJECT:
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223 case T_ARRAY:
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224 {
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225 oop o = k->obj_field(_offset);
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226
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227 // A field will be "constant" if it is known always to be
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228 // a non-null reference to an instance of a particular class,
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229 // or to a particular array. This can happen even if the instance
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230 // or array is not perm. In such a case, an "unloaded" ciArray
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231 // or ciInstance is created. The compiler may be able to use
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232 // information about the object's class (which is exact) or length.
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233
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234 if (o == NULL) {
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235 _constant_value = ciConstant(type()->basic_type(), ciNullObject::make());
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236 } else {
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237 _constant_value = ciConstant(type()->basic_type(), CURRENT_ENV->get_object(o));
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238 assert(_constant_value.as_object() == CURRENT_ENV->get_object(o), "check interning");
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239 }
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240 }
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241 }
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242 } else {
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243 _is_constant = false;
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244 }
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245 }
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246
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247 // ------------------------------------------------------------------
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248 // ciField::compute_type
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249 //
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250 // Lazily compute the type, if it is an instance klass.
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251 ciType* ciField::compute_type() {
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252 GUARDED_VM_ENTRY(return compute_type_impl();)
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253 }
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254
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255 ciType* ciField::compute_type_impl() {
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256 ciKlass* type = CURRENT_ENV->get_klass_by_name_impl(_holder, _signature, false);
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257 if (!type->is_primitive_type() && is_shared()) {
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258 // We must not cache a pointer to an unshared type, in a shared field.
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259 bool type_is_also_shared = false;
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260 if (type->is_type_array_klass()) {
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261 type_is_also_shared = true; // int[] etc. are explicitly bootstrapped
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262 } else if (type->is_instance_klass()) {
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263 type_is_also_shared = type->as_instance_klass()->is_shared();
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264 } else {
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265 // Currently there is no 'shared' query for array types.
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266 type_is_also_shared = !ciObjectFactory::is_initialized();
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267 }
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268 if (!type_is_also_shared)
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269 return type; // Bummer.
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270 }
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271 _type = type;
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272 return type;
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273 }
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274
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275
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276 // ------------------------------------------------------------------
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277 // ciField::will_link
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278 //
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279 // Can a specific access to this field be made without causing
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280 // link errors?
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281 bool ciField::will_link(ciInstanceKlass* accessing_klass,
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282 Bytecodes::Code bc) {
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283 VM_ENTRY_MARK;
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284 if (_offset == -1) {
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285 // at creation we couldn't link to our holder so we need to
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286 // maintain that stance, otherwise there's no safe way to use this
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287 // ciField.
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288 return false;
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289 }
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290
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291 if (_known_to_link_with == accessing_klass) {
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292 return true;
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293 }
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294
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295 FieldAccessInfo result;
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296 constantPoolHandle c_pool(THREAD,
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297 accessing_klass->get_instanceKlass()->constants());
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298 LinkResolver::resolve_field(result, c_pool, _cp_index,
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299 Bytecodes::java_code(bc),
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300 true, false, KILL_COMPILE_ON_FATAL_(false));
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301
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302 // update the hit-cache, unless there is a problem with memory scoping:
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303 if (accessing_klass->is_shared() || !is_shared())
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304 _known_to_link_with = accessing_klass;
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305
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306 return true;
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307 }
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308
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309 // ------------------------------------------------------------------
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310 // ciField::print
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311 void ciField::print() {
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312 tty->print("<ciField ");
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313 _holder->print_name();
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314 tty->print(".");
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315 _name->print_symbol();
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316 tty->print(" offset=%d type=", _offset);
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317 if (_type != NULL) _type->print_name();
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318 else tty->print("(reference)");
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319 tty->print(" is_constant=%s", bool_to_str(_is_constant));
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320 if (_is_constant) {
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321 tty->print(" constant_value=");
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322 _constant_value.print();
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323 }
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324 tty->print(">");
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325 }
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326
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327 // ------------------------------------------------------------------
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328 // ciField::print_name_on
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329 //
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330 // Print the name of this field
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331 void ciField::print_name_on(outputStream* st) {
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332 name()->print_symbol_on(st);
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333 }
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