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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
* 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/SourceNotes.h"
#include "frontend/TDZCheckCache.h"
namespace js {
namespace frontend {
struct BytecodeEmitter;
// 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);
// emit(cond);
// ifThen.emitThen();
// emit(then_block);
// ifThen.emitEnd();
//
// `if (cond) then_block else else_block`
// IfEmitter ifThenElse(this);
// 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);
// emit(c1);
// ifThenElse.emitThenElse();
// emit(b1);
// ifThenElse.emitElseIf();
// emit(c2);
// ifThenElse.emitThenElse();
// emit(b2);
// ifThenElse.emitElseIf();
// emit(c3);
// ifThenElse.emitThenElse();
// emit(b3);
// ifThenElse.emitElse();
// emit(b4);
// ifThenElse.emitEnd();
//
// `cond ? then_expr : else_expr`
// IfEmitter condElse(this);
// emit(cond);
// condElse.emitCond();
// emit(then_block);
// condElse.emitElse();
// emit(else_block);
// condElse.emitEnd();
//
class MOZ_STACK_CLASS IfEmitter
{
public:
// 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 Kind {
// 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
};
private:
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_;
// Annotation index for IonBuilder
unsigned noteIndex_;
// 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_;
Kind kind_;
mozilla::Maybe<TDZCheckCache> tdzCache_;
#ifdef DEBUG
// The number of values pushed in the then and else blocks.
int32_t pushed_;
bool calculatedPushed_;
// The state of this emitter.
//
// +-------+ emitCond +------+ emitElse +------+ emitEnd +-----+
// | Start |-+--------->| Cond |--------->| Else |------>+------->| End |
// +-------+ | +------+ +------+ ^ +-----+
// | |
// v emitThen +------+ |
// +->+--------->| Then |------------------------>+
// ^ | +------+ ^
// | | |
// | | +---+
// | | |
// | | emitThenElse +----------+ emitElse +------+ |
// | +------------->| ThenElse |-+--------->| Else |-+
// | +----------+ | +------+
// | |
// | | emitElseIf +--------+
// | +----------->| ElseIf |-+
// | +--------+ |
// | |
// +------------------------------------------------------+
enum class State {
// The initial state.
Start,
// After calling emitThen.
Then,
// After calling emitCond.
Cond,
// After calling emitThenElse.
ThenElse,
// After calling emitElse.
Else,
// After calling emitElseIf.
ElseIf,
// After calling emitEnd.
End
};
State state_;
#endif
protected:
// For InternalIfEmitter.
IfEmitter(BytecodeEmitter* bce, Kind kind);
public:
explicit IfEmitter(BytecodeEmitter* bce);
[[nodiscard]] bool emitThen();
[[nodiscard]] bool emitCond();
[[nodiscard]] bool emitThenElse();
[[nodiscard]] bool emitElse();
[[nodiscard]] bool emitElseIf();
[[nodiscard]] bool emitEnd();
#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
private:
[[nodiscard]] bool emitIfInternal(SrcNoteType type);
void calculateOrCheckPushed();
[[nodiscard]] bool emitElseInternal();
};
// 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.
class MOZ_STACK_CLASS InternalIfEmitter : public IfEmitter
{
public:
explicit InternalIfEmitter(BytecodeEmitter* bce);
};
} /* namespace frontend */
} /* namespace js */
#endif /* frontend_IfEmitter_h */
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