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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         kInterfaceBlock_Storage,
     29         kLocal_Storage,
     30         kParameter_Storage
     31     };
     32 
     33     Variable(int offset, Modifiers modifiers, StringFragment name, const Type& type,
     34              Storage storage, Expression* initialValue = nullptr)
     35     : INHERITED(offset, kVariable_Kind, name)
     36     , fModifiers(modifiers)
     37     , fType(type)
     38     , fStorage(storage)
     39     , fInitialValue(initialValue)
     40     , fReadCount(0)
     41     , fWriteCount(initialValue ? 1 : 0) {}
     42 
     43     ~Variable() override {
     44         // can't destroy a variable while there are remaining references to it
     45         if (fInitialValue) {
     46             --fWriteCount;
     47         }
     48         SkASSERT(!fReadCount && !fWriteCount);
     49     }
     50 
     51     virtual String description() const override {
     52         return fModifiers.description() + fType.fName + " " + fName;
     53     }
     54 
     55     bool dead() const {
     56         return !fWriteCount || (!fReadCount && !(fModifiers.fFlags & (Modifiers::kOut_Flag |
     57                                                                       Modifiers::kPLS_Flag |
     58                                                                       Modifiers::kPLSOut_Flag)));
     59     }
     60 
     61     mutable Modifiers fModifiers;
     62     const Type& fType;
     63     const Storage fStorage;
     64 
     65     Expression* fInitialValue = nullptr;
     66 
     67     // Tracks how many sites read from the variable. If this is zero for a non-out variable (or
     68     // becomes zero during optimization), the variable is dead and may be eliminated.
     69     mutable int fReadCount;
     70     // Tracks how many sites write to the variable. If this is zero, the variable is dead and may be
     71     // eliminated.
     72     mutable int fWriteCount;
     73 
     74     typedef Symbol INHERITED;
     75 };
     76 
     77 } // namespace SkSL
     78 
     79 #endif
     80