Add ExternalStringResourceBase::IsCompressible

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index 732477cd81ff9852091de87e7a262a58e2bcecfc..db7c09138c43967e9ce9fb78d2bb52156482a1b4 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -1687,7 +1687,7 @@ bool String::MakeExternal(v8::String::ExternalStringResource* resource) {
   // the field caching the address of the backing store.  When we encounter
   // short external strings in generated code, we need to bailout to runtime.
   Map* new_map;
-  if (size < ExternalString::kSize) {
+  if (size < ExternalString::kSize || resource->isCompressible()) {

[Yang, 2015/12/17 11:41:53]

Is this necessary? For source strings, we always create external strings from
scratch, and do not turn V8 strings into external strings, right? Can we instead
assert that resource is not compressible?

[hajimehoshi, 2016/01/05 08:07:44]

I meant compressible string should use short_*_map to avoid caching in the same
way we did in factory.cc. Am I missing something?

     new_map = is_internalized
         ? (is_one_byte
            ? heap->short_external_internalized_string_with_one_byte_data_map()
@@ -1753,7 +1753,7 @@ bool String::MakeExternal(v8::String::ExternalOneByteStringResource* resource) {
   // the field caching the address of the backing store.  When we encounter
   // short external strings in generated code, we need to bailout to runtime.
   Map* new_map;
-  if (size < ExternalString::kSize) {
+  if (size < ExternalString::kSize || resource->isCompressible()) {
     new_map = is_internalized
                   ? heap->short_external_one_byte_internalized_string_map()
                   : heap->short_external_one_byte_string_map();