Clean up dead code after spread desugaring

src/full-codegen/x64/full-codegen-x64.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #if V8_TARGET_ARCH_X64
 
 #include "src/ast/scopes.h"
 #include "src/code-factory.h"
 #include "src/code-stubs.h"
 #include "src/codegen.h"
@@ skipping 1643 matching lines @@
 
   bool result_saved = false;  // Is the result saved to the stack?
   ZoneList<Expression*>* subexprs = expr->values();
   int length = subexprs->length();
 
   // Emit code to evaluate all the non-constant subexpressions and to store
   // them into the newly cloned array.
   int array_index = 0;
   for (; array_index < length; array_index++) {
     Expression* subexpr = subexprs->at(array_index);
-    if (subexpr->IsSpread()) break;
+    DCHECK(!subexpr->IsSpread());
 
     // If the subexpression is a literal or a simple materialized literal it
     // is already set in the cloned array.
     if (CompileTimeValue::IsCompileTimeValue(subexpr)) continue;
 
     if (!result_saved) {
       __ Push(rax);  // array literal
       result_saved = true;
     }
     VisitForAccumulatorValue(subexpr);
@@ skipping 14 matching lines @@
   // (inclusive) and these elements gets appended to the array. Note that the
   // number elements an iterable produces is unknown ahead of time.
   if (array_index < length && result_saved) {
     __ Pop(rax);
     result_saved = false;
   }
   for (; array_index < length; array_index++) {
     Expression* subexpr = subexprs->at(array_index);
 
     __ Push(rax);
-    if (subexpr->IsSpread()) {
-      VisitForStackValue(subexpr->AsSpread()->expression());
-      __ InvokeBuiltin(Context::CONCAT_ITERABLE_TO_ARRAY_BUILTIN_INDEX,
-                       CALL_FUNCTION);
-    } else {
-      VisitForStackValue(subexpr);
-      __ CallRuntime(Runtime::kAppendElement);
-    }
+    DCHECK(!subexpr->IsSpread());
+    VisitForStackValue(subexpr);
+    __ CallRuntime(Runtime::kAppendElement);
 
     PrepareForBailoutForId(expr->GetIdForElement(array_index), NO_REGISTERS);
   }
 
   if (result_saved) {
     context()->PlugTOS();
   } else {
     context()->Plug(rax);
   }
 }
@@ skipping 3034 matching lines @@
             Assembler::target_address_at(call_target_address,
                                          unoptimized_code));
   return OSR_AFTER_STACK_CHECK;
 }
 
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_X64