[compiler] Ensure the function is compiled after CompileOptimized

The Code object returned by CompileOptimized runtime functions is
tail-called to continue execution. This Code object should not be the
CompileLazy builtin.

We ran into this case when the requested code kind was available, but
not attached - here we returned early from Compiler::CompileOptimized
without doing anything.

To satisfy the postcondition, this CL removes the early exit and lets
GetOptimizedCode handle the cached cases (both the FeedbackVector's
optimized code cache, and the isolate cache).

Bug: v8:8888
Change-Id: Ie60e6cf27b697ea6685441184b65f28f3583f75a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2557500Reviewed-by: Mythri Alle <mythria@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71358}

src/codegen/compiler.cc

@@ -1927,9 +1927,6 @@ bool Compiler::CompileOptimized(Handle<JSFunction> function,
                                 ConcurrencyMode mode, CodeKind code_kind) {
   DCHECK(CodeKindIsOptimizedJSFunction(code_kind));
 
-  // If the requested code kind is already available, do nothing.
-  if (function->HasAvailableCodeKind(code_kind)) return true;
-
   Isolate* isolate = function->GetIsolate();
   DCHECK(AllowCompilation::IsAllowed(isolate));
 

src/runtime/runtime-compiler.cc

@@ -65,6 +65,8 @@ Object CompileOptimized(Isolate* isolate, Handle<JSFunction> function,
     return ReadOnlyRoots(isolate).exception();
   }
 
+  // As a post-condition of CompileOptimized, the function *must* be compiled,
+  // i.e. the installed Code object must not be the CompileLazy builtin.
   DCHECK(function->is_compiled());
   return function->code();
 }