1 files changed, 291 insertions, 0 deletions
diff --git a/js/src/frontend/TryEmitter.cpp b/js/src/frontend/TryEmitter.cpp
new file mode 100644
index 0000000000..1004f4ce25
--- /dev/null
+++ b/js/src/frontend/TryEmitter.cpp
@@ -0,0 +1,291 @@
+/* -*- 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/TryEmitter.h"
+
+#include "mozilla/Assertions.h"  // MOZ_ASSERT
+
+#include "frontend/BytecodeEmitter.h"  // BytecodeEmitter
+#include "frontend/SharedContext.h"    // StatementKind
+#include "vm/JSScript.h"               // JSTRY_CATCH, JSTRY_FINALLY
+#include "vm/Opcodes.h"                // JSOp
+
+using namespace js;
+using namespace js::frontend;
+
+using mozilla::Maybe;
+
+TryEmitter::TryEmitter(BytecodeEmitter* bce, Kind kind, ControlKind controlKind)
+    : bce_(bce),
+      kind_(kind),
+      controlKind_(controlKind),
+      depth_(0),
+      tryOpOffset_(0)
+#ifdef DEBUG
+      ,
+      state_(State::Start)
+#endif
+{
+  if (controlKind_ == ControlKind::Syntactic) {
+    controlInfo_.emplace(
+        bce_, hasFinally() ? StatementKind::Finally : StatementKind::Try);
+  }
+}
+
+bool TryEmitter::emitTry() {
+  MOZ_ASSERT(state_ == State::Start);
+
+  // Since an exception can be thrown at any place inside the try block,
+  // we need to restore the stack and the scope chain before we transfer
+  // the control to the exception handler.
+  //
+  // For that we store in a try note associated with the catch or
+  // finally block the stack depth upon the try entry. The interpreter
+  // uses this depth to properly unwind the stack and the scope chain.
+  depth_ = bce_->bytecodeSection().stackDepth();
+
+  tryOpOffset_ = bce_->bytecodeSection().offset();
+  if (!bce_->emit1(JSOp::Try)) {
+    return false;
+  }
+
+#ifdef DEBUG
+  state_ = State::Try;
+#endif
+  return true;
+}
+
+bool TryEmitter::emitTryEnd() {
+  MOZ_ASSERT(state_ == State::Try);
+  MOZ_ASSERT(depth_ == bce_->bytecodeSection().stackDepth());
+
+  // Gosub to finally, if present.
+  if (hasFinally() && controlInfo_) {
+    if (!bce_->emitGoSub(&controlInfo_->gosubs)) {
+      return false;
+    }
+  }
+
+  // Emit jump over catch and/or finally.
+  if (!bce_->emitJump(JSOp::Goto, &catchAndFinallyJump_)) {
+    return false;
+  }
+
+  if (!bce_->emitJumpTarget(&tryEnd_)) {
+    return false;
+  }
+
+  return true;
+}
+
+bool TryEmitter::emitCatch() {
+  MOZ_ASSERT(state_ == State::Try);
+  if (!emitTryEnd()) {
+    return false;
+  }
+
+  MOZ_ASSERT(bce_->bytecodeSection().stackDepth() == depth_);
+
+  if (controlKind_ == ControlKind::Syntactic) {
+    // Clear the frame's return value that might have been set by the
+    // try block:
+    //
+    //   eval("try { 1; throw 2 } catch(e) {}"); // undefined, not 1
+    if (!bce_->emit1(JSOp::Undefined)) {
+      return false;
+    }
+    if (!bce_->emit1(JSOp::SetRval)) {
+      return false;
+    }
+  }
+
+  if (!bce_->emit1(JSOp::Exception)) {
+    return false;
+  }
+
+  if (!instrumentEntryPoint()) {
+    return false;
+  }
+
+#ifdef DEBUG
+  state_ = State::Catch;
+#endif
+  return true;
+}
+
+bool TryEmitter::emitCatchEnd() {
+  MOZ_ASSERT(state_ == State::Catch);
+
+  if (!controlInfo_) {
+    return true;
+  }
+
+  // gosub <finally>, if required.
+  if (hasFinally()) {
+    if (!bce_->emitGoSub(&controlInfo_->gosubs)) {
+      return false;
+    }
+    MOZ_ASSERT(bce_->bytecodeSection().stackDepth() == depth_);
+
+    // Jump over the finally block.
+    if (!bce_->emitJump(JSOp::Goto, &catchAndFinallyJump_)) {
+      return false;
+    }
+  }
+
+  return true;
+}
+
+bool TryEmitter::emitFinally(
+    const Maybe<uint32_t>& finallyPos /* = Nothing() */) {
+  // If we are using controlInfo_ (i.e., emitting a syntactic try
+  // blocks), we must have specified up front if there will be a finally
+  // close. For internal non-syntactic try blocks, like those emitted for
+  // yield* and IteratorClose inside for-of loops, we can emitFinally even
+  // without specifying up front, since the internal non-syntactic try
+  // blocks emit no GOSUBs.
+  if (!controlInfo_) {
+    if (kind_ == Kind::TryCatch) {
+      kind_ = Kind::TryCatchFinally;
+    }
+  } else {
+    MOZ_ASSERT(hasFinally());
+  }
+
+  if (!hasCatch()) {
+    MOZ_ASSERT(state_ == State::Try);
+    if (!emitTryEnd()) {
+      return false;
+    }
+  } else {
+    MOZ_ASSERT(state_ == State::Catch);
+    if (!emitCatchEnd()) {
+      return false;
+    }
+  }
+
+  MOZ_ASSERT(bce_->bytecodeSection().stackDepth() == depth_);
+
+  if (!bce_->emitJumpTarget(&finallyStart_)) {
+    return false;
+  }
+
+  if (controlInfo_) {
+    // Fix up the gosubs that might have been emitted before non-local
+    // jumps to the finally code.
+    bce_->patchJumpsToTarget(controlInfo_->gosubs, finallyStart_);
+
+    // Indicate that we're emitting a subroutine body.
+    controlInfo_->setEmittingSubroutine();
+  }
+  if (finallyPos) {
+    if (!bce_->updateSourceCoordNotes(finallyPos.value())) {
+      return false;
+    }
+  }
+  if (!bce_->emit1(JSOp::Finally)) {
+    return false;
+  }
+
+  if (controlKind_ == ControlKind::Syntactic) {
+    if (!bce_->emit1(JSOp::GetRval)) {
+      return false;
+    }
+
+    // Clear the frame's return value to make break/continue return
+    // correct value even if there's no other statement before them:
+    //
+    //   eval("x: try { 1 } finally { break x; }"); // undefined, not 1
+    if (!bce_->emit1(JSOp::Undefined)) {
+      return false;
+    }
+    if (!bce_->emit1(JSOp::SetRval)) {
+      return false;
+    }
+  }
+
+  if (!instrumentEntryPoint()) {
+    return false;
+  }
+
+#ifdef DEBUG
+  state_ = State::Finally;
+#endif
+  return true;
+}
+
+bool TryEmitter::emitFinallyEnd() {
+  MOZ_ASSERT(state_ == State::Finally);
+
+  if (controlKind_ == ControlKind::Syntactic) {
+    if (!bce_->emit1(JSOp::SetRval)) {
+      return false;
+    }
+  }
+
+  if (!bce_->emit1(JSOp::Retsub)) {
+    return false;
+  }
+
+  bce_->hasTryFinally = true;
+  return true;
+}
+
+bool TryEmitter::emitEnd() {
+  if (!hasFinally()) {
+    MOZ_ASSERT(state_ == State::Catch);
+    if (!emitCatchEnd()) {
+      return false;
+    }
+  } else {
+    MOZ_ASSERT(state_ == State::Finally);
+    if (!emitFinallyEnd()) {
+      return false;
+    }
+  }
+
+  MOZ_ASSERT(bce_->bytecodeSection().stackDepth() == depth_);
+
+  // Fix up the end-of-try/catch jumps to come here.
+  if (!bce_->emitJumpTargetAndPatch(catchAndFinallyJump_)) {
+    return false;
+  }
+
+  // Add the try note last, to let post-order give us the right ordering
+  // (first to last for a given nesting level, inner to outer by level).
+  if (hasCatch()) {
+    if (!bce_->addTryNote(TryNoteKind::Catch, depth_, offsetAfterTryOp(),
+                          tryEnd_.offset)) {
+      return false;
+    }
+  }
+
+  // If we've got a finally, mark try+catch region with additional
+  // trynote to catch exceptions (re)thrown from a catch block or
+  // for the try{}finally{} case.
+  if (hasFinally()) {
+    if (!bce_->addTryNote(TryNoteKind::Finally, depth_, offsetAfterTryOp(),
+                          finallyStart_.offset)) {
+      return false;
+    }
+  }
+
+#ifdef DEBUG
+  state_ = State::End;
+#endif
+  return true;
+}
+
+bool TryEmitter::instrumentEntryPoint() {
+  // Frames for async functions can resume execution at catch or finally blocks
+  // if an await operation threw an exception. While the frame might already be
+  // on the stack, the Entry instrumentation kind only indicates that a new
+  // frame *might* have been pushed.
+  if (bce_->sc->isFunctionBox() && bce_->sc->asFunctionBox()->isAsync()) {
+    return bce_->emitInstrumentation(InstrumentationKind::Entry);
+  }
+  return true;
+}