We shouldn't throw under FLAG_debug_code, rather abort.

src/mips/macro-assembler-mips.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 5032 matching lines @@
 }
 
 
 void MacroAssembler::EmitSeqStringSetCharCheck(Register string,
                                                Register index,
                                                Register value,
                                                Register scratch,
                                                uint32_t encoding_mask) {
   Label is_object;
   SmiTst(string, at);
-  ThrowIf(eq, kNonObject, at, Operand(zero_reg));
+  Check(ne, kNonObject, at, Operand(zero_reg));
 
   lw(at, FieldMemOperand(string, HeapObject::kMapOffset));
   lbu(at, FieldMemOperand(at, Map::kInstanceTypeOffset));
 
   andi(at, at, kStringRepresentationMask | kStringEncodingMask);
   li(scratch, Operand(encoding_mask));
-  ThrowIf(ne, kUnexpectedStringType, at, Operand(scratch));
+  Check(eq, kUnexpectedStringType, at, Operand(scratch));
 
   // 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.
   Label index_tag_ok, index_tag_bad;
   TrySmiTag(index, scratch, &index_tag_bad);
   Branch(&index_tag_ok);
   bind(&index_tag_bad);
-  Throw(kIndexIsTooLarge);
+  Abort(kIndexIsTooLarge);
   bind(&index_tag_ok);
 
   lw(at, FieldMemOperand(string, String::kLengthOffset));
-  ThrowIf(ge, kIndexIsTooLarge, index, Operand(at));
+  Check(lt, kIndexIsTooLarge, index, Operand(at));
 
   ASSERT(Smi::FromInt(0) == 0);
-  ThrowIf(lt, kIndexIsNegative, index, Operand(zero_reg));
+  Check(ge, kIndexIsNegative, index, Operand(zero_reg));
 
   SmiUntag(index, index);
 }
 
 
 void MacroAssembler::PrepareCallCFunction(int num_reg_arguments,
                                           int num_double_arguments,
                                           Register scratch) {
   int frame_alignment = ActivationFrameAlignment();
 
@@ skipping 658 matching lines @@
        opcode == BGTZL);
   opcode = (cond == eq) ? BEQ : BNE;
   instr = (instr & ~kOpcodeMask) | opcode;
   masm_.emit(instr);
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_MIPS