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| -rw-r--r-- | js/src/frontend/IfEmitter.h | 311 |
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diff --git a/js/src/frontend/IfEmitter.h b/js/src/frontend/IfEmitter.h new file mode 100644 index 0000000000..eaf4e2d8f4 --- /dev/null +++ b/js/src/frontend/IfEmitter.h @@ -0,0 +1,311 @@ +/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- + * vim: set ts=8 sts=2 et sw=2 tw=80: + * This Source Code Form is subject to the terms of the Mozilla Public + * License, v. 2.0. If a copy of the MPL was not distributed with this + * file, You can obtain one at http://mozilla.org/MPL/2.0/. */ + +#ifndef frontend_IfEmitter_h +#define frontend_IfEmitter_h + +#include "mozilla/Attributes.h" +#include "mozilla/Maybe.h" + +#include <stdint.h> + +#include "frontend/JumpList.h" +#include "frontend/TDZCheckCache.h" + +namespace js { +namespace frontend { + +struct BytecodeEmitter; + +class MOZ_STACK_CLASS BranchEmitterBase { + protected: + BytecodeEmitter* bce_; + + // Jump around the then clause, to the beginning of the else clause. + JumpList jumpAroundThen_; + + // Jump around the else clause, to the end of the entire branch. + JumpList jumpsAroundElse_; + + // The stack depth before emitting the then block. + // Used for restoring stack depth before emitting the else block. + // Also used for assertion to make sure then and else blocks pushed the + // same number of values. + int32_t thenDepth_ = 0; + + enum class ConditionKind { Positive, Negative }; + + // Whether the then-clause, the else-clause, or else-if condition may + // contain declaration or access to lexical variables, which means they + // should have their own TDZCheckCache. Basically TDZCheckCache should be + // created for each basic block, which then-clause, else-clause, and + // else-if condition are, but for internally used branches which are + // known not to touch lexical variables we can skip creating TDZCheckCache + // for them. + // + // See the comment for TDZCheckCache class for more details. + enum class LexicalKind { + // For syntactic branches (if, if-else, and conditional expression), + // which basically may contain declaration or accesses to lexical + // variables inside then-clause, else-clause, and else-if condition. + MayContainLexicalAccessInBranch, + + // For internally used branches which don't touch lexical variables + // inside then-clause, else-clause, nor else-if condition. + NoLexicalAccessInBranch + }; + LexicalKind lexicalKind_; + + mozilla::Maybe<TDZCheckCache> tdzCache_; + +#ifdef DEBUG + // The number of values pushed in the then and else blocks. + int32_t pushed_ = 0; + bool calculatedPushed_ = false; +#endif + + protected: + BranchEmitterBase(BytecodeEmitter* bce, LexicalKind lexicalKind); + + [[nodiscard]] bool emitThenInternal(ConditionKind conditionKind); + void calculateOrCheckPushed(); + [[nodiscard]] bool emitElseInternal(); + [[nodiscard]] bool emitEndInternal(); + + public: +#ifdef DEBUG + // Returns the number of values pushed onto the value stack inside + // `then_block` and `else_block`. + // Can be used in assertion after emitting if-then-else. + int32_t pushed() const { return pushed_; } + + // Returns the number of values popped onto the value stack inside + // `then_block` and `else_block`. + // Can be used in assertion after emitting if-then-else. + int32_t popped() const { return -pushed_; } +#endif +}; + +// Class for emitting bytecode for blocks like if-then-else. +// +// This class can be used to emit single if-then-else block, or cascading +// else-if blocks. +// +// Usage: (check for the return value is omitted for simplicity) +// +// `if (cond) then_block` +// IfEmitter ifThen(this); +// ifThen.emitIf(Some(offset_of_if)); +// emit(cond); +// ifThen.emitThen(); +// emit(then_block); +// ifThen.emitEnd(); +// +// `if (!cond) then_block` +// IfEmitter ifThen(this); +// ifThen.emitIf(Some(offset_of_if)); +// emit(cond); +// ifThen.emitThen(IfEmitter::ConditionKind::Negative); +// emit(then_block); +// ifThen.emitEnd(); +// +// `if (cond) then_block else else_block` +// IfEmitter ifThenElse(this); +// ifThen.emitIf(Some(offset_of_if)); +// emit(cond); +// ifThenElse.emitThenElse(); +// emit(then_block); +// ifThenElse.emitElse(); +// emit(else_block); +// ifThenElse.emitEnd(); +// +// `if (c1) b1 else if (c2) b2 else if (c3) b3 else b4` +// IfEmitter ifThenElse(this); +// ifThen.emitIf(Some(offset_of_if)); +// emit(c1); +// ifThenElse.emitThenElse(); +// emit(b1); +// ifThenElse.emitElseIf(Some(offset_of_if)); +// emit(c2); +// ifThenElse.emitThenElse(); +// emit(b2); +// ifThenElse.emitElseIf(Some(offset_of_if)); +// emit(c3); +// ifThenElse.emitThenElse(); +// emit(b3); +// ifThenElse.emitElse(); +// emit(b4); +// ifThenElse.emitEnd(); +// +class MOZ_STACK_CLASS IfEmitter : public BranchEmitterBase { + public: + using ConditionKind = BranchEmitterBase::ConditionKind; + + protected: +#ifdef DEBUG + // The state of this emitter. + // + // +-------+ emitIf +----+ + // | Start |------->| If |-+ + // +-------+ +----+ | + // | + // +--------------------+ + // | + // v emitThen +------+ emitEnd +-----+ + // +->+--------->| Then |---------------------------->+-------->| End | + // ^ | +------+ ^ +-----+ + // | | | + // | | | + // | | | + // | | emitThenElse +----------+ emitElse +------+ | + // | +------------->| ThenElse |-+--------->| Else |-+ + // | +----------+ | +------+ + // | | + // | | emitElseIf +--------+ + // | +----------->| ElseIf |-+ + // | +--------+ | + // | | + // +------------------------------------------------------+ + enum class State { + // The initial state. + Start, + + // After calling emitIf. + If, + + // After calling emitThen. + Then, + + // After calling emitThenElse. + ThenElse, + + // After calling emitElse. + Else, + + // After calling emitElseIf. + ElseIf, + + // After calling emitEnd. + End + }; + State state_ = State::Start; +#endif + + protected: + // For InternalIfEmitter. + IfEmitter(BytecodeEmitter* bce, LexicalKind lexicalKind); + + public: + explicit IfEmitter(BytecodeEmitter* bce); + + // `ifPos` is the offset in the source code for the character below: + // + // if ( cond ) { ... } else if ( cond2 ) { ... } + // ^ ^ + // | | + // | ifPos for emitElseIf + // | + // ifPos for emitIf + // + // Can be Nothing() if not available. + [[nodiscard]] bool emitIf(const mozilla::Maybe<uint32_t>& ifPos); + + [[nodiscard]] bool emitThen( + ConditionKind conditionKind = ConditionKind::Positive); + [[nodiscard]] bool emitThenElse( + ConditionKind conditionKind = ConditionKind::Positive); + + [[nodiscard]] bool emitElseIf(const mozilla::Maybe<uint32_t>& ifPos); + [[nodiscard]] bool emitElse(); + + [[nodiscard]] bool emitEnd(); +}; + +// Class for emitting bytecode for blocks like if-then-else which doesn't touch +// lexical variables. +// +// See the comments above NoLexicalAccessInBranch for more details when to use +// this instead of IfEmitter. +// Compared to IfEmitter, this class doesn't have emitIf method, given that +// it doesn't have syntactic `if`, and also the `cond` value can be already +// on the stack. +// +// Usage: (check for the return value is omitted for simplicity) +// +// `if (cond) then_block else else_block` (effectively) +// emit(cond); +// InternalIfEmitter ifThenElse(this); +// ifThenElse.emitThenElse(); +// emit(then_block); +// ifThenElse.emitElse(); +// emit(else_block); +// ifThenElse.emitEnd(); +// +class MOZ_STACK_CLASS InternalIfEmitter : public IfEmitter { + public: + explicit InternalIfEmitter(BytecodeEmitter* bce); +}; + +// Class for emitting bytecode for conditional expression. +// +// Usage: (check for the return value is omitted for simplicity) +// +// `cond ? then_expr : else_expr` +// CondEmitter condElse(this); +// condElse.emitCond(); +// emit(cond); +// condElse.emitThenElse(); +// emit(then_expr); +// condElse.emitElse(); +// emit(else_expr); +// condElse.emitEnd(); +// +class MOZ_STACK_CLASS CondEmitter : public BranchEmitterBase { +#ifdef DEBUG + // The state of this emitter. + // + // +-------+ emitCond +------+ emitThenElse +----------+ + // | Start |--------->| Cond |------------->| ThenElse |-+ + // +-------+ +------+ +----------+ | + // | + // +-----------------+ + // | + // | emitElse +------+ emitEnd +-----+ + // +--------->| Else |-------->| End | + // +------+ +-----+ + enum class State { + // The initial state. + Start, + + // After calling emitCond. + Cond, + + // After calling emitThenElse. + ThenElse, + + // After calling emitElse. + Else, + + // After calling emitEnd. + End + }; + State state_ = State::Start; +#endif + + public: + explicit CondEmitter(BytecodeEmitter* bce); + + [[nodiscard]] bool emitCond(); + [[nodiscard]] bool emitThenElse( + ConditionKind conditionKind = ConditionKind::Positive); + [[nodiscard]] bool emitElse(); + [[nodiscard]] bool emitEnd(); +}; + +} /* namespace frontend */ +} /* namespace js */ + +#endif /* frontend_IfEmitter_h */ |