1 files changed, 142 insertions, 0 deletions
diff --git a/js/src/frontend/OptionalEmitter.cpp b/js/src/frontend/OptionalEmitter.cpp
new file mode 100644
index 0000000000..6fe5924099
--- /dev/null
+++ b/js/src/frontend/OptionalEmitter.cpp
@@ -0,0 +1,142 @@
+/* -*- 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/OptionalEmitter.h"
+
+#include "frontend/BytecodeEmitter.h"
+#include "frontend/IfEmitter.h"  // IfEmitter, InternalIfEmitter, CondEmitter
+#include "vm/Opcodes.h"
+
+using namespace js;
+using namespace js::frontend;
+
+OptionalEmitter::OptionalEmitter(BytecodeEmitter* bce, int32_t initialDepth)
+    : bce_(bce), tdzCache_(bce), initialDepth_(initialDepth) {}
+
+bool OptionalEmitter::emitJumpShortCircuit() {
+  MOZ_ASSERT(state_ == State::Start || state_ == State::ShortCircuit ||
+             state_ == State::ShortCircuitForCall);
+  MOZ_ASSERT(initialDepth_ + 1 == bce_->bytecodeSection().stackDepth());
+
+  if (!bce_->emit1(JSOp::IsNullOrUndefined)) {
+    //              [stack] OBJ NULL-OR-UNDEF
+    return false;
+  }
+  if (!bce_->emitJump(JSOp::JumpIfTrue, &jumpShortCircuit_)) {
+    //              [stack] OBJ
+    return false;
+  }
+
+#ifdef DEBUG
+  state_ = State::ShortCircuit;
+#endif
+  return true;
+}
+
+bool OptionalEmitter::emitJumpShortCircuitForCall() {
+  MOZ_ASSERT(state_ == State::Start || state_ == State::ShortCircuit ||
+             state_ == State::ShortCircuitForCall);
+  int32_t depth = bce_->bytecodeSection().stackDepth();
+  MOZ_ASSERT(initialDepth_ + 2 == depth);
+  if (!bce_->emit1(JSOp::Swap)) {
+    //              [stack] THIS CALLEE
+    return false;
+  }
+
+  InternalIfEmitter ifEmitter(bce_);
+  if (!bce_->emit1(JSOp::IsNullOrUndefined)) {
+    //              [stack] THIS CALLEE NULL-OR-UNDEF
+    return false;
+  }
+
+  if (!ifEmitter.emitThen()) {
+    //              [stack] THIS CALLEE
+    return false;
+  }
+
+  if (!bce_->emit1(JSOp::Pop)) {
+    //              [stack] THIS
+    return false;
+  }
+
+  if (!bce_->emitJump(JSOp::Goto, &jumpShortCircuit_)) {
+    //              [stack] THIS
+    return false;
+  }
+
+  if (!ifEmitter.emitEnd()) {
+    return false;
+  }
+
+  bce_->bytecodeSection().setStackDepth(depth);
+
+  if (!bce_->emit1(JSOp::Swap)) {
+    //              [stack] THIS CALLEE
+    return false;
+  }
+#ifdef DEBUG
+  state_ = State::ShortCircuitForCall;
+#endif
+  return true;
+}
+
+bool OptionalEmitter::emitOptionalJumpTarget(JSOp op,
+                                             Kind kind /* = Kind::Other */) {
+#ifdef DEBUG
+  int32_t depth = bce_->bytecodeSection().stackDepth();
+#endif
+  MOZ_ASSERT(state_ == State::ShortCircuit ||
+             state_ == State::ShortCircuitForCall);
+
+  // if we get to this point, it means that the optional chain did not short
+  // circuit, so we should skip the short circuiting bytecode.
+  if (!bce_->emitJump(JSOp::Goto, &jumpFinish_)) {
+    //              [stack] RESULT
+    return false;
+  }
+
+  if (!bce_->emitJumpTargetAndPatch(jumpShortCircuit_)) {
+    //              [stack] # if call
+    //              [stack] THIS
+    //              [stack] # otherwise
+    //              [stack] OBJ
+    return false;
+  }
+
+  // reset stack depth to the depth when we jumped
+  bce_->bytecodeSection().setStackDepth(initialDepth_ + 1);
+
+  if (!bce_->emit1(JSOp::Pop)) {
+    //              [stack]
+    return false;
+  }
+
+  if (!bce_->emit1(op)) {
+    //              [stack] JSOP
+    return false;
+  }
+
+  if (kind == Kind::Reference) {
+    if (!bce_->emit1(op)) {
+      //            [stack] JSOP JSOP
+      return false;
+    }
+  }
+
+  MOZ_ASSERT(depth == bce_->bytecodeSection().stackDepth());
+
+  if (!bce_->emitJumpTargetAndPatch(jumpFinish_)) {
+    //              [stack] # if call
+    //              [stack] CALLEE THIS
+    //              [stack] # otherwise
+    //              [stack] VAL
+    return false;
+  }
+#ifdef DEBUG
+  state_ = State::JumpEnd;
+#endif
+  return true;
+}