Desugar async/await to create the resulting Promise upfront

src/full-codegen/full-codegen.cc

Index: src/full-codegen/full-codegen.cc
diff --git a/src/full-codegen/full-codegen.cc b/src/full-codegen/full-codegen.cc
index a227137b4a3bb1e7c1021c71b8d5faaa8b32983c..2d9db83bf7d2811c2f03d2c5598d70d5a4516edb 100644
--- a/src/full-codegen/full-codegen.cc
+++ b/src/full-codegen/full-codegen.cc
@@ -896,6 +896,7 @@ void FullCodeGenerator::EmitContinue(Statement* target) {
   // accumulator on the stack.
   ClearAccumulator();
   while (!current->IsContinueTarget(target)) {
+    if (HasStackOverflow()) return;

[adamk, 2016/08/22 18:47:39]

These additional HasStackOverflow() are surprising, since there's currently only
a single explicit check for this in full-codegen.cc right now. Why did they get
added?

[Dan Ehrenberg, 2016/08/22 19:01:10]

The new desugaring ends up making some significant finally blocks. It turns out
that finally blocks trigger recursion in fullcodegen in a different way from
what the AstVisitor is already testing for. As a result, leaving out these
checks led to corruption in fullcodegen's datastructures. I only needed one of
these (IIRC EmitUnwindAndReturn) but it seemed reasonable to add the others by
analogy, even if we don't currently have a desugaring that would lead to an
overflow in this case.

     if (current->IsTryFinally()) {
       Comment cmnt(masm(), "[ Deferred continue through finally");
       current->Exit(&context_length);
@@ -936,6 +937,7 @@ void FullCodeGenerator::EmitBreak(Statement* target) {
   // accumulator on the stack.
   ClearAccumulator();
   while (!current->IsBreakTarget(target)) {
+    if (HasStackOverflow()) return;
     if (current->IsTryFinally()) {
       Comment cmnt(masm(), "[ Deferred break through finally");
       current->Exit(&context_length);
@@ -971,6 +973,7 @@ void FullCodeGenerator::EmitUnwindAndReturn() {
   NestedStatement* current = nesting_stack_;
   int context_length = 0;
   while (current != NULL) {
+    if (HasStackOverflow()) return;
     if (current->IsTryFinally()) {
       Comment cmnt(masm(), "[ Deferred return through finally");
       current->Exit(&context_length);