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/* -*- 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_TryEmitter_h
#define frontend_TryEmitter_h
#include "mozilla/Attributes.h" // MOZ_STACK_CLASS
#include "mozilla/Maybe.h" // mozilla::Maybe, mozilla::Nothing
#include <stdint.h> // uint32_t
#include "frontend/BytecodeControlStructures.h" // TryFinallyControl
#include "frontend/BytecodeOffset.h" // BytecodeOffset
#include "frontend/JumpList.h" // JumpList, JumpTarget
namespace js {
namespace frontend {
struct BytecodeEmitter;
// Class for emitting bytecode for blocks like try-catch-finally.
//
// Usage: (check for the return value is omitted for simplicity)
//
// `try { try_block } catch (ex) { catch_block }`
// TryEmitter tryCatch(this, TryEmitter::Kind::TryCatch,
// TryEmitter::ControlKind::Syntactic);
// tryCatch.emitTry();
// emit(try_block);
// tryCatch.emitCatch();
// emit(catch_block); // Pending exception is on stack
// tryCatch.emitEnd();
//
// `try { try_block } finally { finally_block }`
// TryEmitter tryCatch(this, TryEmitter::Kind::TryFinally,
// TryEmitter::ControlKind::Syntactic);
// tryCatch.emitTry();
// emit(try_block);
// // finally_pos: The "{" character's position in the source code text.
// tryCatch.emitFinally(Some(finally_pos));
// emit(finally_block);
// tryCatch.emitEnd();
//
// `try { try_block } catch (ex) {catch_block} finally { finally_block }`
// TryEmitter tryCatch(this, TryEmitter::Kind::TryCatchFinally,
// TryEmitter::ControlKind::Syntactic);
// tryCatch.emitTry();
// emit(try_block);
// tryCatch.emitCatch();
// emit(catch_block);
// tryCatch.emitFinally(Some(finally_pos));
// emit(finally_block);
// tryCatch.emitEnd();
//
class MOZ_STACK_CLASS TryEmitter {
public:
enum class Kind { TryCatch, TryCatchFinally, TryFinally };
// Syntactic try-catch-finally and internally used non-syntactic
// try-catch-finally behave differently for 2 points.
//
// The first one is whether TryFinallyControl is used or not.
// See the comment for `controlInfo_`.
//
// The second one is whether the catch and finally blocks handle the frame's
// return value. For syntactic try-catch-finally, the bytecode marked with
// "*" are emitted to clear return value with `undefined` before the catch
// block and the finally block, and also to save/restore the return value
// before/after the finally block. Note that these instructions are not
// emitted for noScriptRval scripts that don't track the return value.
//
// JSOp::Try offsetOf(jumpToEnd)
//
// try_body...
//
// JSOp::Goto finally
// JSOp::JumpTarget
// jumpToEnd:
// JSOp::Goto end:
//
// catch:
// JSOp::JumpTarget
// * JSOp::Undefined
// * JSOp::SetRval
//
// catch_body...
//
// JSOp::Goto finally
// JSOp::JumpTarget
// JSOp::Goto end
//
// finally:
// JSOp::JumpTarget
// * JSOp::GetRval
// * JSOp::Undefined
// * JSOp::SetRval
//
// finally_body...
//
// * JSOp::SetRval
// JSOp::Nop
//
// end:
// JSOp::JumpTarget
//
// For syntactic try-catch-finally, Syntactic should be used.
// For non-syntactic try-catch-finally, NonSyntactic should be used.
enum class ControlKind { Syntactic, NonSyntactic };
private:
BytecodeEmitter* bce_;
Kind kind_;
ControlKind controlKind_;
// Tracks jumps to the finally block for later fixup.
//
// When a finally block is active, non-local jumps (including
// jumps-over-catches) result in a goto being written into the bytecode
// stream and fixed-up later.
//
// For non-syntactic try-catch-finally, all that handling is skipped.
// The non-syntactic try-catch-finally must:
// * have only one catch block
// * have JSOp::Goto at the end of catch-block
// * have no non-local-jump
// * don't use finally block for normal completion of try-block and
// catch-block
//
// Additionally, a finally block may be emitted for non-syntactic
// try-catch-finally, even if the kind is TryCatch, because GOSUBs are not
// emitted.
mozilla::Maybe<TryFinallyControl> controlInfo_;
// The stack depth before emitting JSOp::Try.
int depth_;
// The offset of the JSOp::Try op.
BytecodeOffset tryOpOffset_;
// JSOp::JumpTarget after the entire try-catch-finally block.
JumpList catchAndFinallyJump_;
// The offset of JSOp::Goto at the end of the try block.
JumpTarget tryEnd_;
// The offset of JSOp::JumpTarget at the beginning of the finally block.
JumpTarget finallyStart_;
#ifdef DEBUG
// The state of this emitter.
//
// +-------+ emitTry +-----+ emitCatch +-------+ emitEnd +-----+
// | Start |-------->| Try |-+---------->| Catch |-+->+--------->| End |
// +-------+ +-----+ | +-------+ | ^ +-----+
// | | |
// | +------------------+ +----+
// | | |
// | v emitFinally +---------+ |
// +->+------------>| Finally |--+
// +---------+
enum class State {
// The initial state.
Start,
// After calling emitTry.
Try,
// After calling emitCatch.
Catch,
// After calling emitFinally.
Finally,
// After calling emitEnd.
End
};
State state_;
#endif
bool hasCatch() const {
return kind_ == Kind::TryCatch || kind_ == Kind::TryCatchFinally;
}
bool hasFinally() const {
return kind_ == Kind::TryCatchFinally || kind_ == Kind::TryFinally;
}
BytecodeOffset offsetAfterTryOp() const {
return tryOpOffset_ + BytecodeOffsetDiff(JSOpLength_Try);
}
// Returns true if catch and finally blocks should handle the frame's
// return value.
bool shouldUpdateRval() const;
// Jump to the finally block. After the finally block executes,
// fall through to the code following the finally block.
[[nodiscard]] bool emitJumpToFinallyWithFallthrough();
public:
TryEmitter(BytecodeEmitter* bce, Kind kind, ControlKind controlKind);
[[nodiscard]] bool emitTry();
[[nodiscard]] bool emitCatch();
// If `finallyPos` is specified, it's an offset of the finally block's
// "{" character in the source code text, to improve line:column number in
// the error reporting.
// For non-syntactic try-catch-finally, `finallyPos` can be omitted.
[[nodiscard]] bool emitFinally(
const mozilla::Maybe<uint32_t>& finallyPos = mozilla::Nothing());
[[nodiscard]] bool emitEnd();
private:
[[nodiscard]] bool emitTryEnd();
[[nodiscard]] bool emitCatchEnd();
[[nodiscard]] bool emitFinallyEnd();
};
} /* namespace frontend */
} /* namespace js */
#endif /* frontend_TryEmitter_h */
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