[vm/compiler] Omit implicit result type check for recognized natives.

We will still type check returns from native methods but everything
that is explicitly handled by graph builder would be trusted.

Bug: #31798
Change-Id: Ia2f5dfba63349bef7578ca4774686f47b5e484b1
Reviewed-on: https://dart-review.googlesource.com/70644
Reviewed-by: Martin Kustermann <[email protected]>
Commit-Queue: Vyacheslav Egorov <[email protected]>

Author: mraleph

runtime/vm/compiler/frontend/kernel_to_il.cc

@@ -449,13 +449,15 @@ Fragment FlowGraphBuilder::NativeCall(const String* name,
   return Fragment(call);
 }
 
-Fragment FlowGraphBuilder::Return(TokenPosition position) {
+Fragment FlowGraphBuilder::Return(TokenPosition position,
+                                  bool omit_result_type_check /* = false */) {
   Fragment instructions;
   const Function& function = parsed_function_->function();
 
   // Emit a type check of the return type in checked mode for all functions
   // and in strong mode for native functions.
-  if (I->type_checks() || (function.is_native() && I->strong())) {
+  if (!omit_result_type_check &&
+      (I->type_checks() || (function.is_native() && I->strong()))) {
     const AbstractType& return_type =
         AbstractType::Handle(Z, function.result_type());
     instructions += CheckAssignable(return_type, Symbols::FunctionResult());
@@ -741,7 +743,8 @@ Fragment FlowGraphBuilder::NativeFunctionBody(const Function& function,
   // to build these graphs so that this code is not duplicated.
 
   Fragment body;
-  MethodRecognizer::Kind kind = MethodRecognizer::RecognizeKind(function);
+  const MethodRecognizer::Kind kind = MethodRecognizer::RecognizeKind(function);
+  bool omit_result_type_check = true;
   switch (kind) {
     case MethodRecognizer::kObjectEquals:
       body += LoadLocal(scopes_->this_variable);
@@ -919,10 +922,12 @@ Fragment FlowGraphBuilder::NativeFunctionBody(const Function& function,
         body += PushArgument();
       }
       body += NativeCall(&name, &function);
+      // We typecheck results of native calls for type safety.
+      omit_result_type_check = false;
       break;
     }
   }
-  return body + Return(TokenPosition::kNoSource);
+  return body + Return(TokenPosition::kNoSource, omit_result_type_check);
 }
 
 Fragment FlowGraphBuilder::BuildImplicitClosureCreation(

runtime/vm/compiler/frontend/kernel_to_il.h

@@ -111,7 +111,7 @@ class FlowGraphBuilder : public BaseFlowGraphBuilder {
   Fragment LoadLocal(LocalVariable* variable);
   Fragment InitStaticField(const Field& field);
   Fragment NativeCall(const String* name, const Function* function);
-  Fragment Return(TokenPosition position);
+  Fragment Return(TokenPosition position, bool omit_result_type_check = false);
   Fragment CheckNull(TokenPosition position,
                      LocalVariable* receiver,
                      const String& function_name);