1/*
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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24
25#ifndef SHARE_UTILITIES_FAKERTTISUPPORT_HPP
26#define SHARE_UTILITIES_FAKERTTISUPPORT_HPP
27
28#include "utilities/globalDefinitions.hpp"
29#include "utilities/debug.hpp"
30
31// Provides support for checked downcasts in a hierarchy of classes.
32// The base class provides a member of this type, specialized on that
33// base class and an associated tag type. Tags are small non-negative
34// integer values uniquely associated with distinct classes in the
35// hierarchy. A tag type is often an enum type.
36//
37// The concrete class specifies the concrete tag.
38//
39// The tag set specifies the set of classes in the derivation
40// sequence. Classes in the derivation sequence add their associated
41// tag during construction. Given the tag associated with a class, an
42// object is an instance of that class if the tag is included in the
43// object's set of recorded tags.
44//
45// A tag T is present in a tag set if the T'th bit of the tag set is
46// one.
47//
48// Note: The representation of a tag set being uintx sets an upper
49// bound on the size of a class hierarchy this utility can be used
50// with.
51template<typename T, typename TagType>
52class FakeRttiSupport {
53 friend class VMStructs;
54public:
55 // Construct with the indicated concrete tag, and include the
56 // concrete tag in the associated tag set.
57 explicit FakeRttiSupport(TagType concrete_tag) :
58 _tag_set(tag_bit(concrete_tag)), _concrete_tag(concrete_tag) { }
59
60 // Construct with the indicated concrete tag and tag set.
61 // Note: This constructor is public only to allow clients to set up
62 // "unusual" (or perhaps buggy) fake RTTI configurations.
63 FakeRttiSupport(TagType concrete_tag, uintx tag_set) :
64 _tag_set(tag_set), _concrete_tag(validate_tag(concrete_tag)) { }
65
66 // Get the concrete tag.
67 TagType concrete_tag() const { return _concrete_tag; }
68
69 // Test whether tag is in the tag set.
70 bool has_tag(TagType tag) const {
71 return (_tag_set & tag_bit(tag)) != 0;
72 }
73
74 // Return a new support object which is the same as this, except tag
75 // has been added to the tag set. The tag must not already be
76 // present in the tag set.
77 FakeRttiSupport add_tag(TagType tag) const {
78 uintx tbit = tag_bit(tag);
79 assert((_tag_set & tbit) == 0,
80 "Tag " UINTX_FORMAT " is already present in tag set: " UINTX_FORMAT,
81 (uintx)tag, _tag_set);
82 return FakeRttiSupport(_concrete_tag, _tag_set | tbit);
83 }
84
85private:
86 uintx _tag_set;
87 TagType _concrete_tag;
88
89 static uintx tag_bit(TagType tag) {
90 return ((uintx)1) << validate_tag(tag);
91 }
92
93 static TagType validate_tag(TagType tag) {
94 assert(0 <= tag, "Tag " INTX_FORMAT " is negative", (intx)tag);
95 assert(tag < BitsPerWord,
96 "Tag " UINTX_FORMAT " is too large", (uintx)tag);
97 return tag;
98 }
99};
100
101#endif // SHARE_UTILITIES_FAKERTTISUPPORT_HPP
102