annotate src/share/vm/oops/arrayOop.hpp @ 10185:d50cc62e94ff

8012715: G1: GraphKit accesses PtrQueue::_index as int but is size_t Summary: In graphKit INT operations were generated to access PtrQueue::_index which has type size_t. This is 64 bit on 64-bit machines. No problems occur on little endian machines as long as the index fits into 32 bit, but on big endian machines the upper part is read, which is zero. This leads to unnecessary branches to the slow path in the runtime. Reviewed-by: twisti, johnc Contributed-by: Martin Doerr <martin.doerr@sap.com>
author johnc
date Wed, 24 Apr 2013 14:48:43 -0700
parents da91efe96a93
children 7944aba7ba41
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1 /*
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2 * Copyright (c) 1997, 2012, Oracle and/or its affiliates. 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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20 * or visit www.oracle.com if you need additional information or have any
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21 * questions.
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22 *
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23 */
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24
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25 #ifndef SHARE_VM_OOPS_ARRAYOOP_HPP
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26 #define SHARE_VM_OOPS_ARRAYOOP_HPP
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27
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28 #include "memory/universe.inline.hpp"
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29 #include "oops/oop.hpp"
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30
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31 // arrayOopDesc is the abstract baseclass for all arrays. It doesn't
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32 // declare pure virtual to enforce this because that would allocate a vtbl
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33 // in each instance, which we don't want.
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34
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35 // The layout of array Oops is:
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36 //
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37 // markOop
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38 // Klass* // 32 bits if compressed but declared 64 in LP64.
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39 // length // shares klass memory or allocated after declared fields.
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40
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41
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42 class arrayOopDesc : public oopDesc {
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43 friend class VMStructs;
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44
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45 // Interpreter/Compiler offsets
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46
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47 // Header size computation.
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48 // The header is considered the oop part of this type plus the length.
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49 // Returns the aligned header_size_in_bytes. This is not equivalent to
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50 // sizeof(arrayOopDesc) which should not appear in the code.
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51 static int header_size_in_bytes() {
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52 size_t hs = align_size_up(length_offset_in_bytes() + sizeof(int),
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53 HeapWordSize);
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54 #ifdef ASSERT
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55 // make sure it isn't called before UseCompressedOops is initialized.
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56 static size_t arrayoopdesc_hs = 0;
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57 if (arrayoopdesc_hs == 0) arrayoopdesc_hs = hs;
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58 assert(arrayoopdesc_hs == hs, "header size can't change");
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59 #endif // ASSERT
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60 return (int)hs;
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61 }
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63 public:
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64 // The _length field is not declared in C++. It is allocated after the
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65 // declared nonstatic fields in arrayOopDesc if not compressed, otherwise
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66 // it occupies the second half of the _klass field in oopDesc.
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67 static int length_offset_in_bytes() {
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68 return UseCompressedKlassPointers ? klass_gap_offset_in_bytes() :
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69 sizeof(arrayOopDesc);
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70 }
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71
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72 // Returns the offset of the first element.
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73 static int base_offset_in_bytes(BasicType type) {
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74 return header_size(type) * HeapWordSize;
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75 }
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77 // Returns the address of the first element.
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78 void* base(BasicType type) const {
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79 return (void*) (((intptr_t) this) + base_offset_in_bytes(type));
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80 }
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81
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82 // Tells whether index is within bounds.
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83 bool is_within_bounds(int index) const { return 0 <= index && index < length(); }
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84
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85 // Accessors for instance variable which is not a C++ declared nonstatic
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86 // field.
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87 int length() const {
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88 return *(int*)(((intptr_t)this) + length_offset_in_bytes());
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89 }
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90 void set_length(int length) {
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91 *(int*)(((intptr_t)this) + length_offset_in_bytes()) = length;
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92 }
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93
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94 // Should only be called with constants as argument
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95 // (will not constant fold otherwise)
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96 // Returns the header size in words aligned to the requirements of the
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97 // array object type.
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98 static int header_size(BasicType type) {
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99 size_t typesize_in_bytes = header_size_in_bytes();
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100 return (int)(Universe::element_type_should_be_aligned(type)
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101 ? align_object_offset(typesize_in_bytes/HeapWordSize)
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102 : typesize_in_bytes/HeapWordSize);
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103 }
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104
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105 // Return the maximum length of an array of BasicType. The length can passed
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106 // to typeArrayOop::object_size(scale, length, header_size) without causing an
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107 // overflow. We also need to make sure that this will not overflow a size_t on
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108 // 32 bit platforms when we convert it to a byte size.
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109 static int32_t max_array_length(BasicType type) {
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110 assert(type >= 0 && type < T_CONFLICT, "wrong type");
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111 assert(type2aelembytes(type) != 0, "wrong type");
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112
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113 const size_t max_element_words_per_size_t =
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114 align_size_down((SIZE_MAX/HeapWordSize - header_size(type)), MinObjAlignment);
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115 const size_t max_elements_per_size_t =
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116 HeapWordSize * max_element_words_per_size_t / type2aelembytes(type);
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117 if ((size_t)max_jint < max_elements_per_size_t) {
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118 // It should be ok to return max_jint here, but parts of the code
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119 // (CollectedHeap, Klass::oop_oop_iterate(), and more) uses an int for
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120 // passing around the size (in words) of an object. So, we need to avoid
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121 // overflowing an int when we add the header. See CRs 4718400 and 7110613.
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122 return align_size_down(max_jint - header_size(type), MinObjAlignment);
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123 }
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124 return (int32_t)max_elements_per_size_t;
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125 }
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126
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127 // for unit testing
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128 #ifndef PRODUCT
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129 static bool check_max_length_overflow(BasicType type);
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130 static int32_t old_max_array_length(BasicType type);
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131 static void test_max_array_length();
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132 #endif
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133 };
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134
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135 #endif // SHARE_VM_OOPS_ARRAYOOP_HPP