We shouldn't throw under FLAG_debug_code, rather abort.

src/ia32/full-codegen-ia32.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 3393 matching lines @@
 
   VisitForStackValue(args->at(1));  // index
   VisitForStackValue(args->at(2));  // value
   VisitForAccumulatorValue(args->at(0));  // string
 
   __ pop(value);
   __ pop(index);
 
   if (FLAG_debug_code) {
     __ test(value, Immediate(kSmiTagMask));
-    __ ThrowIf(not_zero, kNonSmiValue);
+    __ Check(zero, kNonSmiValue);
     __ test(index, Immediate(kSmiTagMask));
-    __ ThrowIf(not_zero, kNonSmiValue);
+    __ Check(zero, kNonSmiValue);
   }
 
   __ SmiUntag(value);
   __ SmiUntag(index);
 
   if (FLAG_debug_code) {
     static const uint32_t one_byte_seq_type = kSeqStringTag | kOneByteStringTag;
     __ EmitSeqStringSetCharCheck(string, index, value, one_byte_seq_type);
   }
 
@@ skipping 12 matching lines @@
   Register value = ecx;
 
   VisitForStackValue(args->at(1));  // index
   VisitForStackValue(args->at(2));  // value
   VisitForAccumulatorValue(args->at(0));  // string
   __ pop(value);
   __ pop(index);
 
   if (FLAG_debug_code) {
     __ test(value, Immediate(kSmiTagMask));
-    __ ThrowIf(not_zero, kNonSmiValue);
+    __ Check(zero, kNonSmiValue);
     __ test(index, Immediate(kSmiTagMask));
-    __ ThrowIf(not_zero, kNonSmiValue);
+    __ Check(zero, kNonSmiValue);
     __ SmiUntag(index);
     static const uint32_t two_byte_seq_type = kSeqStringTag | kTwoByteStringTag;
     __ EmitSeqStringSetCharCheck(string, index, value, two_byte_seq_type);
     __ SmiTag(index);
   }
 
   __ SmiUntag(value);
   // No need to untag a smi for two-byte addressing.
   __ mov_w(FieldOperand(string, index, times_1, SeqTwoByteString::kHeaderSize),
            value);
@@ skipping 1432 matching lines @@
 
   ASSERT_EQ(isolate->builtins()->OsrAfterStackCheck()->entry(),
             Assembler::target_address_at(call_target_address));
   return OSR_AFTER_STACK_CHECK;
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_IA32