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      1 /*
      2  * Copyright 2016 Google Inc.
      3  *
      4  * Use of this source code is governed by a BSD-style license that can be
      5  * found in the LICENSE file.
      6  */
      7 
      8 #ifndef SKSL_VARIABLE
      9 #define SKSL_VARIABLE
     10 
     11 #include "SkSLModifiers.h"
     12 #include "SkSLPosition.h"
     13 #include "SkSLSymbol.h"
     14 #include "SkSLType.h"
     15 
     16 namespace SkSL {
     17 
     18 struct Expression;
     19 
     20 /**
     21  * Represents a variable, whether local, global, or a function parameter. This represents the
     22  * variable itself (the storage location), which is shared between all VariableReferences which
     23  * read or write that storage location.
     24  */
     25 struct Variable : public Symbol {
     26     enum Storage {
     27         kGlobal_Storage,
     28         kLocal_Storage,
     29         kParameter_Storage
     30     };
     31 
     32     Variable(int offset, Modifiers modifiers, StringFragment name, const Type& type,
     33              Storage storage, Expression* initialValue = nullptr)
     34     : INHERITED(offset, kVariable_Kind, name)
     35     , fModifiers(modifiers)
     36     , fType(type)
     37     , fStorage(storage)
     38     , fInitialValue(initialValue)
     39     , fReadCount(0)
     40     , fWriteCount(initialValue ? 1 : 0) {}
     41 
     42     ~Variable() override {
     43         // can't destroy a variable while there are remaining references to it
     44         if (fInitialValue) {
     45             --fWriteCount;
     46         }
     47         ASSERT(!fReadCount && !fWriteCount);
     48     }
     49 
     50     virtual String description() const override {
     51         return fModifiers.description() + fType.fName + " " + fName;
     52     }
     53 
     54     bool dead() const {
     55         return !fWriteCount || (!fReadCount && !(fModifiers.fFlags & Modifiers::kOut_Flag));
     56     }
     57 
     58     mutable Modifiers fModifiers;
     59     const Type& fType;
     60     const Storage fStorage;
     61 
     62     Expression* fInitialValue = nullptr;
     63 
     64     // Tracks how many sites read from the variable. If this is zero for a non-out variable (or
     65     // becomes zero during optimization), the variable is dead and may be eliminated.
     66     mutable int fReadCount;
     67     // Tracks how many sites write to the variable. If this is zero, the variable is dead and may be
     68     // eliminated.
     69     mutable int fWriteCount;
     70 
     71     typedef Symbol INHERITED;
     72 };
     73 
     74 } // namespace SkSL
     75 
     76 #endif
     77