We shouldn't throw under FLAG_debug_code, rather abort.

src/mips/full-codegen-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 3482 matching lines @@
   Register index = a1;
   Register value = a2;
 
   VisitForStackValue(args->at(1));  // index
   VisitForStackValue(args->at(2));  // value
   VisitForAccumulatorValue(args->at(0));  // string
   __ Pop(index, value);
 
   if (FLAG_debug_code) {
     __ SmiTst(value, at);
-    __ ThrowIf(ne, kNonSmiValue, at, Operand(zero_reg));
+    __ Check(eq, kNonSmiValue, at, Operand(zero_reg));
     __ SmiTst(index, at);
-    __ ThrowIf(ne, kNonSmiIndex, at, Operand(zero_reg));
+    __ Check(eq, kNonSmiIndex, at, Operand(zero_reg));
     __ SmiUntag(index, index);
     static const uint32_t one_byte_seq_type = kSeqStringTag | kOneByteStringTag;
     Register scratch = t5;
     __ EmitSeqStringSetCharCheck(
         string, index, value, scratch, one_byte_seq_type);
     __ SmiTag(index, index);
   }
 
   __ SmiUntag(value, value);
   __ Addu(at,
@@ skipping 14 matching lines @@
   Register index = a1;
   Register value = a2;
 
   VisitForStackValue(args->at(1));  // index
   VisitForStackValue(args->at(2));  // value
   VisitForAccumulatorValue(args->at(0));  // string
   __ Pop(index, value);
 
   if (FLAG_debug_code) {
     __ SmiTst(value, at);
-    __ ThrowIf(ne, kNonSmiValue, at, Operand(zero_reg));
+    __ Check(eq, kNonSmiValue, at, Operand(zero_reg));
     __ SmiTst(index, at);
-    __ ThrowIf(ne, kNonSmiIndex, at, Operand(zero_reg));
+    __ Check(eq, kNonSmiIndex, at, Operand(zero_reg));
     __ SmiUntag(index, index);
     static const uint32_t two_byte_seq_type = kSeqStringTag | kTwoByteStringTag;
     Register scratch = t5;
     __ EmitSeqStringSetCharCheck(
         string, index, value, scratch, two_byte_seq_type);
     __ SmiTag(index, index);
   }
 
   __ SmiUntag(value, value);
   __ Addu(at,
@@ skipping 1408 matching lines @@
       Assembler::target_address_at(pc_immediate_load_address)) ==
          reinterpret_cast<uint32_t>(
              isolate->builtins()->OsrAfterStackCheck()->entry()));
   return OSR_AFTER_STACK_CHECK;
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_MIPS