[vm] Set WasCompiled at safepoint

Setting WasCompiled on a function after unoptimized compilation in the
background thread could race with other modifications of function tags.

To avoid this potential problem, setting of WasCompiled is moved to
FinalizeCompilation which is called at safepoint.

This is a possible fix for flaky assertion failure
../../runtime/vm/compiler/jit/compiler.cc: 901: error: expected: !optimized || function.WasCompiled()
on dartkb/debug bots.

Change-Id: Ia38ddf892438be3314e181cd77c8f8d6cf69978d
Reviewed-on: https://dart-review.googlesource.com/c/80381
Auto-Submit: Alexander Markov <alexmarkov@google.com>
Reviewed-by: Siva Annamalai <asiva@google.com>
Commit-Queue: Alexander Markov <alexmarkov@google.com>

Author: alexmarkov

runtime/vm/compiler/jit/compiler.cc

@@ -675,6 +675,7 @@ RawCode* CompileParsedFunctionHelper::FinalizeCompilation(
     }
     function.set_unoptimized_code(code);
     function.AttachCode(code);
+    function.SetWasCompiled(true);
   }
   if (parsed_function()->HasDeferredPrefixes()) {
     ASSERT(!FLAG_load_deferred_eagerly);
@@ -947,11 +948,7 @@ static RawObject* CompileFunctionHelper(CompilationPipeline* pipeline,
 
     const Code& result = Code::Handle(helper.Compile(pipeline));
 
-    if (!result.IsNull()) {
-      if (!optimized) {
-        function.SetWasCompiled(true);
-      }
-    } else {
+    if (result.IsNull()) {
       if (Compiler::IsBackgroundCompilation()) {
         // Try again later, background compilation may abort because of
         // state change during compilation.
@@ -1216,7 +1213,8 @@ RawObject* Compiler::CompileOptimizedFunction(Thread* thread,
 
   // If running with interpreter, do the unoptimized compilation first.
   const bool optimized = !FLAG_enable_interpreter ||
-                         (function.unoptimized_code() != Object::null());
+                         ((function.unoptimized_code() != Object::null()) &&
+                          function.WasCompiled());
 
   // If we are in the optimizing in the mutator/Dart thread, then
   // this is either an OSR compilation or background compilation is