We shouldn't throw under FLAG_debug_code, rather abort.

src/x64/macro-assembler-x64.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 4587 matching lines @@
 #endif
 }
 
 
 void MacroAssembler::EmitSeqStringSetCharCheck(Register string,
                                                Register index,
                                                Register value,
                                                uint32_t encoding_mask) {
   Label is_object;
   JumpIfNotSmi(string, &is_object);
-  Throw(kNonObject);
+  Abort(kNonObject);
   bind(&is_object);
 
   push(value);
   movp(value, FieldOperand(string, HeapObject::kMapOffset));
   movzxbq(value, FieldOperand(value, Map::kInstanceTypeOffset));
 
   andb(value, Immediate(kStringRepresentationMask | kStringEncodingMask));
   cmpq(value, Immediate(encoding_mask));
   pop(value);
-  ThrowIf(not_equal, kUnexpectedStringType);
+  Check(equal, kUnexpectedStringType);
 
   // The index is assumed to be untagged coming in, tag it to compare with the
   // string length without using a temp register, it is restored at the end of
   // this function.
   Integer32ToSmi(index, index);
   SmiCompare(index, FieldOperand(string, String::kLengthOffset));
-  ThrowIf(greater_equal, kIndexIsTooLarge);
+  Check(less, kIndexIsTooLarge);
 
   SmiCompare(index, Smi::FromInt(0));
-  ThrowIf(less, kIndexIsNegative);
+  Check(greater_equal, kIndexIsNegative);
 
   // Restore the index
   SmiToInteger32(index, index);
 }
 
 
 void MacroAssembler::PrepareCallCFunction(int num_arguments) {
   int frame_alignment = OS::ActivationFrameAlignment();
   ASSERT(frame_alignment != 0);
   ASSERT(num_arguments >= 0);
@@ skipping 354 matching lines @@
   j(equal, found);
   movp(current, FieldOperand(current, Map::kPrototypeOffset));
   CompareRoot(current, Heap::kNullValueRootIndex);
   j(not_equal, &loop_again);
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64