[compiler] Remove bailout in ast-numbering's VisitYield.

It's sufficient to bailout when seeing that the function literal is a
generator or async function, as those are the only cases in which there can be
yields.

Also: add a comment on --turbo-from-bytecode and Ignition generators.

R=mstarzinger@chromium.org
BUG=

Review-Url: https://codereview.chromium.org/2060843002
Cr-Commit-Position: refs/heads/master@{#36930}

src/ast/ast-numbering.cc

@@ -220,7 +220,6 @@ void AstNumberingVisitor::VisitYield(Yield* node) {
   node->set_yield_id(yield_count_);
   yield_count_++;
   IncrementNodeCount();
-  DisableOptimization(kYield);
   ReserveFeedbackSlots(node);
   node->set_base_id(ReserveIdRange(Yield::num_ids()));
   Visit(node->generator_object());
@@ -580,6 +579,9 @@ bool AstNumberingVisitor::Renumber(FunctionLiteral* node) {
   }
 
   if (IsGeneratorFunction(node->kind()) || IsAsyncFunction(node->kind())) {
+    // TODO(neis): We may want to allow Turbofan optimization here if
+    // --turbo-from-bytecode is set and we know that Ignition is used.
+    // Unfortunately we can't express that here.
     DisableOptimization(kGenerator);
   }
 

src/bailout-reason.h

@@ -267,8 +267,7 @@ namespace internal {
   V(kWrongArgumentCountForInvokeIntrinsic,                                     \
     "Wrong number of arguments for intrinsic")                                 \
   V(kShouldNotDirectlyEnterOsrFunction,                                        \
-    "Should not directly enter OSR-compiled function")                         \
-  V(kYield, "Yield")
+    "Should not directly enter OSR-compiled function")
 
 #define ERROR_MESSAGES_CONSTANTS(C, T) C,
 enum BailoutReason {