[vm/intrinsics] Introduce dart:_internal.uncheckedCast.

This function can be used to avoid checked down casts in the parts
of the code where we know by construction that the type of the
value matches expectations.

Use it to avoid down-cast in the _LinkedHashMap.operator[].

Bug: #31798
Change-Id: I80949bfb84dde7716fc23aeba311931970ce16aa
Reviewed-on: https://dart-review.googlesource.com/70511
Commit-Queue: Vyacheslav Egorov <[email protected]>
Reviewed-by: Alexander Markov <[email protected]>

Author: mraleph

runtime/lib/compact_hash.dart

@@ -344,7 +344,7 @@ abstract class _LinkedHashMapMixin<K, V> implements _HashBase {
 
   V operator [](Object key) {
     var v = _getValueOrData(key);
-    return identical(_data, v) ? null : v;
+    return identical(_data, v) ? null : internal.unsafeCast<V>(v);
   }
 
   bool containsValue(Object value) {

runtime/lib/internal_patch.dart

@@ -110,3 +110,10 @@ Int32List _growRegExpStack(Int32List stack) {
   }
   return newStack;
 }
+
+// This function can be used to skip implicit or explicit checked down casts in
+// the parts of the core library implementation where we know by construction the
+// type of a value.
+//
+// Important: this is unsafe and must be used with care.
+T unsafeCast<T>(Object v) native "Internal_unsafeCast";

runtime/lib/object.cc

@@ -319,6 +319,11 @@ DEFINE_NATIVE_ENTRY(Internal_inquireIs64Bit, 0) {
 #endif  // defined(ARCH_IS_64_BIT)
 }
 
+DEFINE_NATIVE_ENTRY(Internal_unsafeCast, 1) {
+  UNREACHABLE();  // Should be erased at Kernel translation time.
+  return arguments->NativeArgAt(0);
+}
+
 static bool ExtractInterfaceTypeArgs(Zone* zone,
                                      const Class& instance_cls,
                                      const TypeArguments& instance_type_args,

runtime/vm/bootstrap_natives.h

@@ -307,6 +307,7 @@ namespace dart {
   V(GrowableList_getCapacity, 1)                                               \
   V(GrowableList_setLength, 2)                                                 \
   V(GrowableList_setData, 2)                                                   \
+  V(Internal_unsafeCast, 1)                                                    \
   V(Internal_makeListFixedLength, 1)                                           \
   V(Internal_makeFixedListUnmodifiable, 1)                                     \
   V(Internal_inquireIs64Bit, 0)                                                \

runtime/vm/compiler/frontend/kernel_binary_flowgraph.cc

@@ -3867,9 +3867,16 @@ Fragment StreamingFlowGraphBuilder::BuildStaticInvocation(bool is_const,
   Fragment instructions;
   LocalVariable* instance_variable = NULL;
 
-  bool special_case_identical = klass.IsTopLevel() &&
-                                (klass.library() == Library::CoreLibrary()) &&
-                                (target.name() == Symbols::Identical().raw());
+  const bool special_case_unchecked_cast =
+      klass.IsTopLevel() && (klass.library() == Library::InternalLibrary()) &&
+      (target.name() == Symbols::UnsafeCast().raw());
+
+  const bool special_case_identical =
+      klass.IsTopLevel() && (klass.library() == Library::CoreLibrary()) &&
+      (target.name() == Symbols::Identical().raw());
+
+  const bool special_case =
+      special_case_identical || special_case_unchecked_cast;
 
   // If we cross the Kernel -> VM core library boundary, a [StaticInvocation]
   // can appear, but the thing we're calling is not a static method, but a
@@ -3905,7 +3912,7 @@ Fragment StreamingFlowGraphBuilder::BuildStaticInvocation(bool is_const,
     const TypeArguments& type_arguments = PeekArgumentsInstantiatedType(klass);
     instructions += TranslateInstantiatedTypeArguments(type_arguments);
     instructions += PushArgument();
-  } else if (!special_case_identical && I->reify_generic_functions()) {
+  } else if (!special_case && I->reify_generic_functions()) {
     AlternativeReadingScope alt(&reader_);
     ReadUInt();                               // read argument count.
     intptr_t list_length = ReadListLength();  // read types list length.
@@ -3921,7 +3928,7 @@ Fragment StreamingFlowGraphBuilder::BuildStaticInvocation(bool is_const,
   Array& argument_names = Array::ZoneHandle(Z);
   instructions += BuildArguments(&argument_names, NULL /* arg count */,
                                  NULL /* positional arg count */,
-                                 special_case_identical);  // read arguments.
+                                 special_case);  // read arguments.
   ASSERT(target.AreValidArguments(type_args_len, argument_count, argument_names,
                                   NULL));
 
@@ -3931,6 +3938,8 @@ Fragment StreamingFlowGraphBuilder::BuildStaticInvocation(bool is_const,
   if (special_case_identical) {
     ASSERT(argument_count == 2);
     instructions += StrictCompare(Token::kEQ_STRICT, /*number_check=*/true);
+  } else if (special_case_unchecked_cast) {
+    // Simply do nothing: the result value is already pushed on the stack.
   } else {
     instructions += StaticCall(position, target, argument_count, argument_names,
                                ICData::kStatic, &result_type, type_args_len);

runtime/vm/kernel_loader.cc

@@ -1652,6 +1652,8 @@ void KernelLoader::LoadProcedure(const Library& library,
     expression_evaluation_function_ = function.raw();
   }
   function.set_kernel_offset(procedure_offset);
+  function.set_is_reflectable(function.is_reflectable() &&
+                              library.raw() != Library::InternalLibrary());
 
   ActiveMemberScope active_member(&active_class_, &function);
 

runtime/vm/parser.cc

@@ -6100,7 +6100,9 @@ void Parser::ParseTopLevelFunction(TopLevel* top_level,
   result_type.SetScopeFunction(func);
   func.set_end_token_pos(function_end_pos);
   func.set_modifier(func_modifier);
-  if (library_.is_dart_scheme() && library_.IsPrivate(func_name)) {
+  if (library_.is_dart_scheme() &&
+      (library_.IsPrivate(func_name) ||
+       library_.raw() == Library::InternalLibrary())) {
     func.set_is_reflectable(false);
   }
   if (is_native) {
@@ -11759,6 +11761,11 @@ AstNode* Parser::ParseStaticCall(const Class& cls,
                                   InvocationMirror::kMethod,
                                   NULL,  // No existing function.
                                   prefix);
+  } else if (cls.IsTopLevel() &&
+             (cls.library() == Library::InternalLibrary()) &&
+             (func.name() == Symbols::UnsafeCast().raw())) {
+    ASSERT(num_arguments == 1);
+    return arguments->NodeAt(0);
   } else if (cls.IsTopLevel() && (cls.library() == Library::CoreLibrary()) &&
              (func.name() == Symbols::Identical().raw()) &&
              func_type_args.IsNull()) {

runtime/vm/symbols.h

@@ -25,6 +25,7 @@ class ObjectPointerVisitor;
   V(TruncDivOperator, "~/")                                                    \
   V(UnaryMinus, "unary-")                                                      \
   V(Identical, "identical")                                                    \
+  V(UnsafeCast, "unsafeCast")                                                  \
   V(Length, "length")                                                          \
   V(_setLength, "_setLength")                                                  \
   V(IndexToken, "[]")                                                          \