Instead of special casing one-element interpolations, just generate a static call to _interpolateSi…

runtime/vm/intermediate_language.cc

Index: runtime/vm/intermediate_language.cc
diff --git a/runtime/vm/intermediate_language.cc b/runtime/vm/intermediate_language.cc
index 9cb25e2fef815f5449b3b4506049f20ab10d0fc3..45fbf8823af8a4127cf7aaa7b6f968ebf50061a7 100644
--- a/runtime/vm/intermediate_language.cc
+++ b/runtime/vm/intermediate_language.cc
@@ -2886,9 +2886,7 @@ const Function& StringInterpolateInstr::CallFunction() const {
     function_ =
         Resolver::ResolveStatic(
             cls,
-            is_singleton_
-                ? Library::PrivateCoreLibName(Symbols::InterpolateSingle())
-                : Library::PrivateCoreLibName(Symbols::Interpolate()),
+            Library::PrivateCoreLibName(Symbols::Interpolate()),
             kNumberOfArguments,
             kNoArgumentNames);
   }
@@ -2907,35 +2905,12 @@ Definition* StringInterpolateInstr::Canonicalize(FlowGraph* flow_graph) {
   //   StoreIndexed(v2, v3, v4)   -- v3:constant index, v4: value.
   //   ..
   //   v8 <- StringInterpolate(v2)
-  // or for a single element:
-  //   v2 <- StringInterpolateSingle(v0)
 
   // Don't compile-time fold when optimizing the interpolation function itself.
   if (flow_graph->parsed_function().function().raw() == CallFunction().raw()) {
     return this;
   }
 
-  if (is_singleton_) {
-    Value* value = this->value();
-    if (!value->definition()->IsConstant()) return this;
-    const Object& obj = value->definition()->AsConstant()->value();
-    if (!obj.IsNumber() && !obj.IsString() && !obj.IsBool() && !obj.IsNull()) {
-      return this;
-    }
-    // This is only really useful for numbers, so we don't bother optimizing
-    // for strings, bool or null.
-    const Array& interpolate_arg = Array::Handle(Array::New(1));
-    interpolate_arg.SetAt(0, obj);
-    const Object& result = Object::Handle(
-        DartEntry::InvokeFunction(CallFunction(), interpolate_arg));
-    if (result.IsUnhandledException()) {
-      return this;
-    }
-    ASSERT(result.IsString());
-    const String& converted =
-        String::ZoneHandle(Symbols::New(String::Cast(result)));
-    return flow_graph->GetConstant(converted);
-  }
   CreateArrayInstr* create_array = value()->definition()->AsCreateArray();
   ASSERT(create_array != NULL);
   // Check if the string interpolation has only constant inputs.