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Diffstat (limited to 'js/src/frontend/TryEmitter.h')
| -rw-r--r-- | js/src/frontend/TryEmitter.h | 239 |
1 files changed, 239 insertions, 0 deletions
diff --git a/js/src/frontend/TryEmitter.h b/js/src/frontend/TryEmitter.h new file mode 100644 index 0000000000..b74157bb0e --- /dev/null +++ b/js/src/frontend/TryEmitter.h @@ -0,0 +1,239 @@ +/* -*- 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 JSOp::Goto is + // 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(); + + enum class ExceptionStack : bool { + /** + * Push only the pending exception value. + */ + No, + + /** + * Push the pending exception value and its stack. + */ + Yes, + }; + + [[nodiscard]] bool emitCatch(ExceptionStack stack = ExceptionStack::No); + + // 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 */ |