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| -rw-r--r-- | js/src/frontend/SwitchEmitter.h | 474 |
1 files changed, 474 insertions, 0 deletions
diff --git a/js/src/frontend/SwitchEmitter.h b/js/src/frontend/SwitchEmitter.h new file mode 100644 index 0000000000..59d45fc71c --- /dev/null +++ b/js/src/frontend/SwitchEmitter.h @@ -0,0 +1,474 @@ +/* -*- 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_SwitchEmitter_h +#define frontend_SwitchEmitter_h + +#include "mozilla/Assertions.h" // MOZ_ASSERT +#include "mozilla/Attributes.h" // MOZ_STACK_CLASS +#include "mozilla/Maybe.h" // mozilla::Maybe + +#include <stddef.h> // size_t +#include <stdint.h> // int32_t, uint32_t + +#include "frontend/BytecodeControlStructures.h" // BreakableControl +#include "frontend/EmitterScope.h" // EmitterScope +#include "frontend/JumpList.h" // JumpList, JumpTarget +#include "frontend/TDZCheckCache.h" // TDZCheckCache +#include "js/AllocPolicy.h" // SystemAllocPolicy +#include "js/Value.h" // JSVAL_INT_MAX, JSVAL_INT_MIN +#include "js/Vector.h" // Vector +#include "vm/Scope.h" // LexicalScope + +namespace js { +namespace frontend { + +struct BytecodeEmitter; + +// Class for emitting bytecode for switch-case-default block. +// +// Usage: (check for the return value is omitted for simplicity) +// +// `switch (discriminant) { case c1_expr: c1_body; }` +// SwitchEmitter se(this); +// se.emitDiscriminant(offset_of_switch); +// emit(discriminant); +// +// se.validateCaseCount(1); +// se.emitCond(); +// +// se.prepareForCaseValue(); +// emit(c1_expr); +// se.emitCaseJump(); +// +// se.emitCaseBody(); +// emit(c1_body); +// +// se.emitEnd(); +// +// `switch (discriminant) { case c1_expr: c1_body; case c2_expr: c2_body; +// default: def_body; }` +// SwitchEmitter se(this); +// se.emitDiscriminant(offset_of_switch); +// emit(discriminant); +// +// se.validateCaseCount(2); +// se.emitCond(); +// +// se.prepareForCaseValue(); +// emit(c1_expr); +// se.emitCaseJump(); +// +// se.prepareForCaseValue(); +// emit(c2_expr); +// se.emitCaseJump(); +// +// se.emitCaseBody(); +// emit(c1_body); +// +// se.emitCaseBody(); +// emit(c2_body); +// +// se.emitDefaultBody(); +// emit(def_body); +// +// se.emitEnd(); +// +// `switch (discriminant) { case c1_expr: c1_body; case c2_expr: c2_body; }` +// with Table Switch +// SwitchEmitter::TableGenerator tableGen(this); +// tableGen.addNumber(c1_expr_value); +// tableGen.addNumber(c2_expr_value); +// tableGen.finish(2); +// +// // If `!tableGen.isValid()` here, `emitCond` should be used instead. +// +// SwitchEmitter se(this); +// se.emitDiscriminant(offset_of_switch); +// emit(discriminant); +// se.validateCaseCount(2); +// se.emitTable(tableGen); +// +// se.emitCaseBody(c1_expr_value, tableGen); +// emit(c1_body); +// +// se.emitCaseBody(c2_expr_value, tableGen); +// emit(c2_body); +// +// se.emitEnd(); +// +// `switch (discriminant) { case c1_expr: c1_body; case c2_expr: c2_body; +// default: def_body; }` +// with Table Switch +// SwitchEmitter::TableGenerator tableGen(bce); +// tableGen.addNumber(c1_expr_value); +// tableGen.addNumber(c2_expr_value); +// tableGen.finish(2); +// +// // If `!tableGen.isValid()` here, `emitCond` should be used instead. +// +// SwitchEmitter se(this); +// se.emitDiscriminant(offset_of_switch); +// emit(discriminant); +// se.validateCaseCount(2); +// se.emitTable(tableGen); +// +// se.emitCaseBody(c1_expr_value, tableGen); +// emit(c1_body); +// +// se.emitCaseBody(c2_expr_value, tableGen); +// emit(c2_body); +// +// se.emitDefaultBody(); +// emit(def_body); +// +// se.emitEnd(); +// +// `switch (discriminant) { case c1_expr: c1_body; }` +// in case c1_body contains lexical bindings +// SwitchEmitter se(this); +// se.emitDiscriminant(offset_of_switch); +// emit(discriminant); +// +// se.validateCaseCount(1); +// +// se.emitLexical(bindings); +// +// se.emitCond(); +// +// se.prepareForCaseValue(); +// emit(c1_expr); +// se.emitCaseJump(); +// +// se.emitCaseBody(); +// emit(c1_body); +// +// se.emitEnd(); +// +// `switch (discriminant) { case c1_expr: c1_body; }` +// in case c1_body contains hosted functions +// SwitchEmitter se(this); +// se.emitDiscriminant(offset_of_switch); +// emit(discriminant); +// +// se.validateCaseCount(1); +// +// se.emitLexical(bindings); +// emit(hosted functions); +// +// se.emitCond(); +// +// se.prepareForCaseValue(); +// emit(c1_expr); +// se.emitCaseJump(); +// +// se.emitCaseBody(); +// emit(c1_body); +// +// se.emitEnd(); +// +class MOZ_STACK_CLASS SwitchEmitter { + // Bytecode for each case. + // + // Cond Switch (uses an equality comparison for each case) + // {discriminant} + // + // {c1_expr} + // JSOp::Case c1 + // + // JSOp::JumpTarget + // {c2_expr} + // JSOp::Case c2 + // + // ... + // + // JSOp::JumpTarget + // JSOp::Default default + // + // c1: + // JSOp::JumpTarget + // {c1_body} + // JSOp::Goto end + // + // c2: + // JSOp::JumpTarget + // {c2_body} + // JSOp::Goto end + // + // default: + // end: + // JSOp::JumpTarget + // + // Table Switch + // {discriminant} + // JSOp::TableSwitch c1, c2, ... + // + // c1: + // JSOp::JumpTarget + // {c1_body} + // JSOp::Goto end + // + // c2: + // JSOp::JumpTarget + // {c2_body} + // JSOp::Goto end + // + // ... + // + // end: + // JSOp::JumpTarget + + public: + enum class Kind { Table, Cond }; + + // Class for generating optimized table switch data. + class MOZ_STACK_CLASS TableGenerator { + BytecodeEmitter* bce_; + + // Bit array for given numbers. + mozilla::Maybe<js::Vector<size_t, 128, SystemAllocPolicy>> intmap_; + + // The length of the intmap_. + int32_t intmapBitLength_ = 0; + + // The length of the table. + uint32_t tableLength_ = 0; + + // The lower and higher bounds of the table. + int32_t low_ = JSVAL_INT_MAX, high_ = JSVAL_INT_MIN; + + // Whether the table is still valid. + bool valid_ = true; + +#ifdef DEBUG + bool finished_ = false; +#endif + + public: + explicit TableGenerator(BytecodeEmitter* bce) : bce_(bce) {} + + void setInvalid() { valid_ = false; } + [[nodiscard]] bool isValid() const { return valid_; } + [[nodiscard]] bool isInvalid() const { return !valid_; } + + // Add the given number to the table. The number is the value of + // `expr` for `case expr:` syntax. + [[nodiscard]] bool addNumber(int32_t caseValue); + + // Finish generating the table. + // `caseCount` should be the number of cases in the switch statement, + // excluding the default case. + void finish(uint32_t caseCount); + + private: + friend SwitchEmitter; + + // The following methods can be used only after calling `finish`. + + // Returns the lower bound of the added numbers. + int32_t low() const { + MOZ_ASSERT(finished_); + return low_; + } + + // Returns the higher bound of the numbers. + int32_t high() const { + MOZ_ASSERT(finished_); + return high_; + } + + // Returns the index in SwitchEmitter.caseOffsets_ for table switch. + uint32_t toCaseIndex(int32_t caseValue) const; + + // Returns the length of the table. + // This method can be called only if `isValid()` is true. + uint32_t tableLength() const; + }; + + private: + BytecodeEmitter* bce_; + + // `kind_` should be set to the correct value in emitCond/emitTable. + Kind kind_ = Kind::Cond; + + // True if there's explicit default case. + bool hasDefault_ = false; + + // The number of cases in the switch statement, excluding the default case. + uint32_t caseCount_ = 0; + + // Internal index for case jump and case body, used by cond switch. + uint32_t caseIndex_ = 0; + + // Bytecode offset after emitting `discriminant`. + BytecodeOffset top_; + + // Bytecode offset of the previous JSOp::Case. + BytecodeOffset lastCaseOffset_; + + // Bytecode offset of the JSOp::JumpTarget for default body. + JumpTarget defaultJumpTargetOffset_; + + // Bytecode offset of the JSOp::Default. + JumpList condSwitchDefaultOffset_; + + // Instantiated when there's lexical scope for entire switch. + mozilla::Maybe<TDZCheckCache> tdzCacheLexical_; + mozilla::Maybe<EmitterScope> emitterScope_; + + // Instantiated while emitting case expression and case/default body. + mozilla::Maybe<TDZCheckCache> tdzCacheCaseAndBody_; + + // Control for switch. + mozilla::Maybe<BreakableControl> controlInfo_; + + uint32_t switchPos_ = 0; + + // Cond Switch: + // Offset of each JSOp::Case. + // Table Switch: + // Offset of each JSOp::JumpTarget for case. + js::Vector<BytecodeOffset, 32, SystemAllocPolicy> caseOffsets_; + + // The state of this emitter. + // + // +-------+ emitDiscriminant +--------------+ + // | Start |----------------->| Discriminant |-+ + // +-------+ +--------------+ | + // | + // +-------------------------------------------+ + // | + // | validateCaseCount +-----------+ + // +->+------------------------>+------------------>| CaseCount |-+ + // | ^ +-----------+ | + // | emitLexical +---------+ | | + // +------------>| Lexical |-+ | + // +---------+ | + // | + // +--------------------------------------------------------------+ + // | + // | emitTable +-------+ + // +---------->| Table |----------------------------------->+-+ + // | +-------+ ^ | + // | | | + // | emitCond +------+ | | + // +---------->| Cond |-+------------------------------->+->+ | + // +------+ | ^ | + // | | | + // +------------------+ | | + // | | | + // |prepareForCaseValue +-----------+ | | + // +----------+--------->| CaseValue | | | + // ^ +-----------+ | | + // | | | | + // | | emitCaseJump +------+ | | + // | +------------->| Case |->+-+ | + // | +------+ | | + // | | | + // +--------------------------------------+ | + // | + // +----------------------------------------------------------+ + // | + // | emitEnd +-----+ + // +-+----------------------------------------->+-------->| End | + // | ^ +-----+ + // | emitCaseBody +----------+ | + // +->+-+---------------->| CaseBody |--->+-+-+ + // ^ | +----------+ ^ | + // | | | | + // | | emitDefaultBody +-------------+ | | + // | +---------------->| DefaultBody |-+ | + // | +-------------+ | + // | | + // +-------------------------------------+ + // + protected: + enum class State { + // The initial state. + Start, + + // After calling emitDiscriminant. + Discriminant, + + // After calling validateCaseCount. + CaseCount, + + // After calling emitLexical. + Lexical, + + // After calling emitCond. + Cond, + + // After calling emitTable. + Table, + + // After calling prepareForCaseValue. + CaseValue, + + // After calling emitCaseJump. + Case, + + // After calling emitCaseBody. + CaseBody, + + // After calling emitDefaultBody. + DefaultBody, + + // After calling emitEnd. + End + }; + State state_ = State::Start; + + public: + explicit SwitchEmitter(BytecodeEmitter* bce); + + // `switchPos` is the offset in the source code for the character below: + // + // switch ( cond ) { ... } + // ^ + // | + // switchPos + [[nodiscard]] bool emitDiscriminant(uint32_t switchPos); + + // `caseCount` should be the number of cases in the switch statement, + // excluding the default case. + [[nodiscard]] bool validateCaseCount(uint32_t caseCount); + + // `bindings` is a lexical scope for the entire switch, in case there's + // let/const effectively directly under case or default blocks. + [[nodiscard]] bool emitLexical(LexicalScope::ParserData* bindings); + + [[nodiscard]] bool emitCond(); + [[nodiscard]] bool emitTable(const TableGenerator& tableGen); + + [[nodiscard]] bool prepareForCaseValue(); + [[nodiscard]] bool emitCaseJump(); + + [[nodiscard]] bool emitCaseBody(); + [[nodiscard]] bool emitCaseBody(int32_t caseValue, + const TableGenerator& tableGen); + [[nodiscard]] bool emitDefaultBody(); + [[nodiscard]] bool emitEnd(); + + private: + [[nodiscard]] bool emitCaseOrDefaultJump(uint32_t caseIndex, bool isDefault); + [[nodiscard]] bool emitImplicitDefault(); +}; + +// Class for emitting bytecode for switch-case-default block that doesn't +// correspond to a syntactic `switch`. +// Compared to SwitchEmitter, this class doesn't require `emitDiscriminant`, +// and the discriminant can already be on the stack. Usage is otherwise +// the same as SwitchEmitter. +class MOZ_STACK_CLASS InternalSwitchEmitter : public SwitchEmitter { + public: + explicit InternalSwitchEmitter(BytecodeEmitter* bce); +}; + +} /* namespace frontend */ +} /* namespace js */ + +#endif /* frontend_SwitchEmitter_h */ |