1 files changed, 215 insertions, 0 deletions
diff --git a/js/src/frontend/AsyncEmitter.cpp b/js/src/frontend/AsyncEmitter.cpp
new file mode 100644
index 0000000000..bee6b804f1
--- /dev/null
+++ b/js/src/frontend/AsyncEmitter.cpp
@@ -0,0 +1,215 @@
+/* -*- 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/. */
+
+#include "frontend/AsyncEmitter.h"
+
+#include "mozilla/Assertions.h"  // MOZ_ASSERT
+
+#include "frontend/BytecodeEmitter.h"  // BytecodeEmitter
+#include "frontend/NameOpEmitter.h"    // NameOpEmitter
+#include "frontend/ParserAtom.h"       // TaggedParserAtomIndex
+#include "vm/Opcodes.h"                // JSOp
+
+using namespace js;
+using namespace js::frontend;
+
+bool AsyncEmitter::prepareForParamsWithExpressionOrDestructuring() {
+  MOZ_ASSERT(state_ == State::Start);
+#ifdef DEBUG
+  state_ = State::Parameters;
+#endif
+
+  rejectTryCatch_.emplace(bce_, TryEmitter::Kind::TryCatch,
+                          TryEmitter::ControlKind::NonSyntactic);
+  return rejectTryCatch_->emitTry();
+}
+
+bool AsyncEmitter::prepareForParamsWithoutExpressionOrDestructuring() {
+  MOZ_ASSERT(state_ == State::Start);
+#ifdef DEBUG
+  state_ = State::Parameters;
+#endif
+  return true;
+}
+
+bool AsyncEmitter::emitParamsEpilogue() {
+  MOZ_ASSERT(state_ == State::Parameters);
+
+  if (rejectTryCatch_) {
+    // If we get here, we need to reset the TryEmitter. Parameters can't reuse
+    // the reject try-catch block from the function body, because the body
+    // may have pushed an additional var-environment. This messes up scope
+    // resolution for the |.generator| variable, because we'd need different
+    // hops to reach |.generator| depending on whether the error was thrown
+    // from the parameters or the function body.
+    if (!emitRejectCatch()) {
+      return false;
+    }
+  }
+
+#ifdef DEBUG
+  state_ = State::PostParams;
+#endif
+  return true;
+}
+
+bool AsyncEmitter::prepareForModule() {
+  // Unlike functions, modules do not have params that we need to worry about.
+  // Instead, this code is for setting up the required generator that will be
+  // used for top level await. Before we can start using top-level await in
+  // modules, we need to emit a
+  // |.generator| which we can use to pause and resume execution.
+  MOZ_ASSERT(state_ == State::Start);
+  MOZ_ASSERT(
+      bce_->lookupName(TaggedParserAtomIndex::WellKnown::dot_generator_())
+          .hasKnownSlot());
+
+  NameOpEmitter noe(bce_, TaggedParserAtomIndex::WellKnown::dot_generator_(),
+                    NameOpEmitter::Kind::Initialize);
+  if (!noe.prepareForRhs()) {
+    //              [stack]
+    return false;
+  }
+  if (!bce_->emit1(JSOp::Generator)) {
+    //              [stack] GEN
+    return false;
+  }
+  if (!noe.emitAssignment()) {
+    //              [stack] GEN
+    return false;
+  }
+  if (!bce_->emit1(JSOp::Pop)) {
+    //              [stack]
+    return false;
+  }
+
+#ifdef DEBUG
+  state_ = State::ModulePrologue;
+#endif
+
+  return true;
+}
+
+bool AsyncEmitter::prepareForBody() {
+  MOZ_ASSERT(state_ == State::PostParams || state_ == State::ModulePrologue);
+
+  rejectTryCatch_.emplace(bce_, TryEmitter::Kind::TryCatch,
+                          TryEmitter::ControlKind::NonSyntactic);
+#ifdef DEBUG
+  state_ = State::Body;
+#endif
+  return rejectTryCatch_->emitTry();
+}
+
+bool AsyncEmitter::emitEndFunction() {
+#ifdef DEBUG
+  MOZ_ASSERT(state_ == State::Body);
+#endif
+
+  // The final yield has already been emitted
+  // by FunctionScriptEmitter::emitEndBody().
+
+  if (!emitRejectCatch()) {
+    return false;
+  }
+
+#ifdef DEBUG
+  state_ = State::End;
+#endif
+  return true;
+}
+
+bool AsyncEmitter::emitEndModule() {
+#ifdef DEBUG
+  MOZ_ASSERT(state_ == State::Body);
+#endif
+
+  if (!emitFinalYield()) {
+    return false;
+  }
+
+  if (!emitRejectCatch()) {
+    return false;
+  }
+
+#ifdef DEBUG
+  state_ = State::End;
+#endif
+  return true;
+}
+
+bool AsyncEmitter::emitFinalYield() {
+  if (!bce_->emit1(JSOp::Undefined)) {
+    //              [stack] UNDEF
+    return false;
+  }
+
+  if (!bce_->emitGetDotGeneratorInInnermostScope()) {
+    //              [stack] UNDEF GEN
+    return false;
+  }
+
+  if (!bce_->emit1(JSOp::AsyncResolve)) {
+    //              [stack] PROMISE
+    return false;
+  }
+
+  if (!bce_->emit1(JSOp::SetRval)) {
+    //              [stack]
+    return false;
+  }
+
+  if (!bce_->emitGetDotGeneratorInInnermostScope()) {
+    //              [stack] GEN
+    return false;
+  }
+
+  if (!bce_->emitYieldOp(JSOp::FinalYieldRval)) {
+    //              [stack]
+    return false;
+  }
+
+  return true;
+}
+
+bool AsyncEmitter::emitRejectCatch() {
+  if (!rejectTryCatch_->emitCatch(TryEmitter::ExceptionStack::Yes)) {
+    //              [stack] EXC STACK
+    return false;
+  }
+
+  if (!bce_->emitGetDotGeneratorInInnermostScope()) {
+    //              [stack] EXC STACK GEN
+    return false;
+  }
+
+  if (!bce_->emit1(JSOp::AsyncReject)) {
+    //              [stack] PROMISE
+    return false;
+  }
+
+  if (!bce_->emit1(JSOp::SetRval)) {
+    //              [stack]
+    return false;
+  }
+
+  if (!bce_->emitGetDotGeneratorInInnermostScope()) {
+    //              [stack] GEN
+    return false;
+  }
+
+  if (!bce_->emitYieldOp(JSOp::FinalYieldRval)) {
+    //              [stack]
+    return false;
+  }
+
+  if (!rejectTryCatch_->emitEnd()) {
+    return false;
+  }
+
+  rejectTryCatch_.reset();
+  return true;
+}