js/src/frontend/ExpressionStatementEmitter.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
   2  * vim: set ts=8 sts=2 et sw=2 tw=80:
   3  * This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #ifndef frontend_ExpressionStatementEmitter_h
   8 #define frontend_ExpressionStatementEmitter_h
   9
  10 #include "mozilla/Attributes.h"
  11
  12 #include <stdint.h>
  13
  14 #include "frontend/ValueUsage.h"
  15
  16 namespace js {
  17 namespace frontend {
  18
  19 struct BytecodeEmitter;
  20
  21 // Class for emitting bytecode for expression statement.
  22 //
  23 // Usage: (check for the return value is omitted for simplicity)
  24 //
  25 //   `expr;`
  26 //     // IgnoreValue if this is in normal script.
  27 //     // WantValue if this is in eval script.
  28 //     ValueUsage valueUsage = ...;
  29 //
  30 //     ExpressionStatementEmitter ese(this, valueUsage);
  31 //     ese.prepareForExpr(offset_of_expr);
  32 //     emit(expr);
  33 //     ese.emitEnd();
  34 //
  35 class MOZ_STACK_CLASS ExpressionStatementEmitter {
  36   BytecodeEmitter* bce_;
  37
  38 #ifdef DEBUG
  39   // The stack depth before emitting expression.
  40   int32_t depth_;
  41 #endif
  42
  43   // The usage of the value of the expression.
  44   ValueUsage valueUsage_;
  45
  46 #ifdef DEBUG
  47   // The state of this emitter.
  48   //
  49   // +-------+ prepareForExpr +------+ emitEnd +-----+
  50   // | Start |--------------->| Expr |-------->| End |
  51   // +-------+                +------+         +-----+
  52   enum class State {
  53     // The initial state.
  54     Start,
  55
  56     // After calling prepareForExpr.
  57     Expr,
  58
  59     // After calling emitEnd.
  60     End
  61   };
  62   State state_ = State::Start;
  63 #endif
  64
  65  public:
  66   ExpressionStatementEmitter(BytecodeEmitter* bce, ValueUsage valueUsage);
  67
  68   // Parameters are the offset in the source code for each character below:
  69   //
  70   //   expr;
  71   //   ^
  72   //   |
  73   //   beginPos
  74   [[nodiscard]] bool prepareForExpr(uint32_t beginPos);
  75   [[nodiscard]] bool emitEnd();
  76 };
  77
  78 }  // namespace frontend
  79 }  // namespace js
  80
  81 #endif /* frontend_ExpressionStatementEmitter_h */