[VM] Use Symbols::Empty() when there is no source for a script instead of creating new empty string objects.

a-siva · commit-bot@chromium.org · commit a933f42b9e3b · 2018-10-10T21:25:46.000Z
Change-Id: I8ec6702557b07c4c4ede2aece5a3f25b4cde1a5b Reviewed-on: https://dart-review.googlesource.com/c/79060 Reviewed-by: Ryan Macnak <rmacnak@google.com> Commit-Queue: Siva Annamalai <asiva@google.com>
diff --git a/runtime/vm/compiler/frontend/kernel_translation_helper.cc b/runtime/vm/compiler/frontend/kernel_translation_helper.cc
@@ -2507,12 +2507,17 @@ String& KernelReaderHelper::SourceTableUriFor(intptr_t index) {
   return H.DartString(reader_.BufferAt(ReaderOffset()), size, Heap::kOld);
 }
 
-String& KernelReaderHelper::GetSourceFor(intptr_t index) {
+const String& KernelReaderHelper::GetSourceFor(intptr_t index) {
   AlternativeReadingScope alt(&reader_);
   SetOffset(GetOffsetForSourceInfo(index));
   SkipBytes(ReadUInt());       // skip uri.
   intptr_t size = ReadUInt();  // read source List<byte> size.
-  return H.DartString(reader_.BufferAt(ReaderOffset()), size, Heap::kOld);
+  ASSERT(size >= 0);
+  if (size == 0) {
+    return Symbols::Empty();
+  } else {
+    return H.DartString(reader_.BufferAt(ReaderOffset()), size, Heap::kOld);
+  }
 }
 
 RawTypedData* KernelReaderHelper::GetLineStartsFor(intptr_t index) {
diff --git a/runtime/vm/compiler/frontend/kernel_translation_helper.h b/runtime/vm/compiler/frontend/kernel_translation_helper.h
@@ -1028,7 +1028,7 @@ class KernelReaderHelper {
   intptr_t SourceTableSize();
   intptr_t GetOffsetForSourceInfo(intptr_t index);
   String& SourceTableUriFor(intptr_t index);
-  String& GetSourceFor(intptr_t index);
+  const String& GetSourceFor(intptr_t index);
   RawTypedData* GetLineStartsFor(intptr_t index);
 
   Zone* zone_;
diff --git a/runtime/vm/kernel_loader.cc b/runtime/vm/kernel_loader.cc
@@ -1776,11 +1776,12 @@ const Object& KernelLoader::ClassForScriptAt(const Class& klass,
 
 RawScript* KernelLoader::LoadScriptAt(intptr_t index) {
   const String& uri_string = helper_.SourceTableUriFor(index);
-  String& sources = helper_.GetSourceFor(index);
+  const String& script_source = helper_.GetSourceFor(index);
+  String& sources = String::Handle(Z);
   TypedData& line_starts =
       TypedData::Handle(Z, helper_.GetLineStartsFor(index));
-  if (sources.Length() == 0 && line_starts.Length() == 0 &&
-      uri_string.Length() > 0) {
+  if (script_source.raw() == Symbols::Empty().raw() &&
+      line_starts.Length() == 0 && uri_string.Length() > 0) {
     // Entry included only to provide URI - actual source should already exist
     // in the VM, so try to find it.
     Library& lib = Library::Handle(Z);
@@ -1796,6 +1797,8 @@ RawScript* KernelLoader::LoadScriptAt(intptr_t index) {
         break;
       }
     }
+  } else {
+    sources = script_source.raw();
   }
 
   const Script& script = Script::Handle(
@@ -1805,8 +1808,8 @@ RawScript* KernelLoader::LoadScriptAt(intptr_t index) {
   script.set_kernel_script_index(index);
   script.set_kernel_program_info(kernel_program_info_);
   script.set_line_starts(line_starts);
-  script.set_debug_positions(Array::Handle(Array::null()));
-  script.set_yield_positions(Array::Handle(Array::null()));
+  script.set_debug_positions(Array::null_array());
+  script.set_yield_positions(Array::null_array());
   return script.raw();
 }
 
