1// Copyright 2006-2008 the V8 project authors. All rights reserved.
2// Redistribution and use in source and binary forms, with or without
3// modification, are permitted provided that the following conditions are
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5//
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8//     * Redistributions in binary form must reproduce the above
9//       copyright notice, this list of conditions and the following
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11//       with the distribution.
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13//       contributors may be used to endorse or promote products derived
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15//
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17// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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20// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
21// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
22// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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26// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
27
28#ifndef V8_VARIABLES_H_
29#define V8_VARIABLES_H_
30
31#include "zone.h"
32
33namespace v8 {
34namespace internal {
35
36class UseCount BASE_EMBEDDED {
37 public:
38  UseCount();
39
40  // Inform the node of a "use". The weight can be used to indicate
41  // heavier use, for instance if the variable is accessed inside a loop.
42  void RecordRead(int weight);
43  void RecordWrite(int weight);
44  void RecordAccess(int weight);  // records a read & write
45  void RecordUses(UseCount* uses);
46
47  int nreads() const  { return nreads_; }
48  int nwrites() const  { return nwrites_; }
49  int nuses() const  { return nreads_ + nwrites_; }
50
51  bool is_read() const  { return nreads() > 0; }
52  bool is_written() const  { return nwrites() > 0; }
53  bool is_used() const  { return nuses() > 0; }
54
55#ifdef DEBUG
56  void Print();
57#endif
58
59 private:
60  int nreads_;
61  int nwrites_;
62};
63
64
65// Variables and AST expression nodes can track their "type" to enable
66// optimizations and removal of redundant checks when generating code.
67
68class StaticType {
69 public:
70  enum Kind {
71    UNKNOWN,
72    LIKELY_SMI
73  };
74
75  StaticType() : kind_(UNKNOWN) {}
76
77  bool Is(Kind kind) const { return kind_ == kind; }
78
79  bool IsKnown() const { return !Is(UNKNOWN); }
80  bool IsUnknown() const { return Is(UNKNOWN); }
81  bool IsLikelySmi() const { return Is(LIKELY_SMI); }
82
83  void CopyFrom(StaticType* other) {
84    kind_ = other->kind_;
85  }
86
87  static const char* Type2String(StaticType* type);
88
89  // LIKELY_SMI accessors
90  void SetAsLikelySmi() {
91    kind_ = LIKELY_SMI;
92  }
93
94  void SetAsLikelySmiIfUnknown() {
95    if (IsUnknown()) {
96      SetAsLikelySmi();
97    }
98  }
99
100 private:
101  Kind kind_;
102
103  DISALLOW_COPY_AND_ASSIGN(StaticType);
104};
105
106
107// The AST refers to variables via VariableProxies - placeholders for the actual
108// variables. Variables themselves are never directly referred to from the AST,
109// they are maintained by scopes, and referred to from VariableProxies and Slots
110// after binding and variable allocation.
111
112class Variable: public ZoneObject {
113 public:
114  enum Mode {
115    // User declared variables:
116    VAR,       // declared via 'var', and 'function' declarations
117
118    CONST,     // declared via 'const' declarations
119
120    // Variables introduced by the compiler:
121    DYNAMIC,         // always require dynamic lookup (we don't know
122                     // the declaration)
123
124    DYNAMIC_GLOBAL,  // requires dynamic lookup, but we know that the
125                     // variable is global unless it has been shadowed
126                     // by an eval-introduced variable
127
128    DYNAMIC_LOCAL,   // requires dynamic lookup, but we know that the
129                     // variable is local and where it is unless it
130                     // has been shadowed by an eval-introduced
131                     // variable
132
133    INTERNAL,        // like VAR, but not user-visible (may or may not
134                     // be in a context)
135
136    TEMPORARY        // temporary variables (not user-visible), never
137                     // in a context
138  };
139
140  enum Kind {
141    NORMAL,
142    THIS,
143    ARGUMENTS
144  };
145
146  Variable(Scope* scope,
147           Handle<String> name,
148           Mode mode,
149           bool is_valid_lhs,
150           Kind kind);
151
152  // Printing support
153  static const char* Mode2String(Mode mode);
154
155  // Type testing & conversion
156  Property* AsProperty();
157  Variable* AsVariable();
158  bool IsValidLeftHandSide() { return is_valid_LHS_; }
159
160  // The source code for an eval() call may refer to a variable that is
161  // in an outer scope about which we don't know anything (it may not
162  // be the global scope). scope() is NULL in that case. Currently the
163  // scope is only used to follow the context chain length.
164  Scope* scope() const  { return scope_; }
165
166  Handle<String> name() const  { return name_; }
167  Mode mode() const  { return mode_; }
168  bool is_accessed_from_inner_scope() const  {
169    return is_accessed_from_inner_scope_;
170  }
171  UseCount* var_uses()  { return &var_uses_; }
172  UseCount* obj_uses()  { return &obj_uses_; }
173
174  bool IsVariable(Handle<String> n) const {
175    return !is_this() && name().is_identical_to(n);
176  }
177
178  bool is_dynamic() const {
179    return (mode_ == DYNAMIC ||
180            mode_ == DYNAMIC_GLOBAL ||
181            mode_ == DYNAMIC_LOCAL);
182  }
183
184  bool is_global() const;
185  bool is_this() const { return kind_ == THIS; }
186  bool is_arguments() const { return kind_ == ARGUMENTS; }
187
188  // True if the variable is named eval and not known to be shadowed.
189  bool is_possibly_eval() const {
190    return IsVariable(Factory::eval_symbol()) &&
191        (mode_ == DYNAMIC || mode_ == DYNAMIC_GLOBAL);
192  }
193
194  Variable* local_if_not_shadowed() const {
195    ASSERT(mode_ == DYNAMIC_LOCAL && local_if_not_shadowed_ != NULL);
196    return local_if_not_shadowed_;
197  }
198
199  void set_local_if_not_shadowed(Variable* local) {
200    local_if_not_shadowed_ = local;
201  }
202
203  Expression* rewrite() const  { return rewrite_; }
204  Slot* slot() const;
205
206  StaticType* type() { return &type_; }
207
208 private:
209  Scope* scope_;
210  Handle<String> name_;
211  Mode mode_;
212  bool is_valid_LHS_;
213  Kind kind_;
214
215  Variable* local_if_not_shadowed_;
216
217  // Usage info.
218  bool is_accessed_from_inner_scope_;  // set by variable resolver
219  UseCount var_uses_;  // uses of the variable value
220  UseCount obj_uses_;  // uses of the object the variable points to
221
222  // Static type information
223  StaticType type_;
224
225  // Code generation.
226  // rewrite_ is usually a Slot or a Property, but may be any expression.
227  Expression* rewrite_;
228
229  friend class Scope;  // Has explicit access to rewrite_.
230};
231
232
233} }  // namespace v8::internal
234
235#endif  // V8_VARIABLES_H_
236