valgrind error with __builtin_ctz

我想分析我的代码，但遇到了问题。

如果我运行以下代码:

#include <iostream>
int main() {
    size_t val = 8;
    std::cout << sizeof(val) << std::endl;
    std::cout << __builtin_ctz(val) << std::endl;
}

按预期返回

8
3

如果我对它运行valgrind，它返回:

==28602== Memcheck, a memory error detector
==28602== Copyright (C) 2002-2011, and GNU GPL'd, by Julian Seward et al.
==28602== Using Valgrind-3.7.0 and LibVEX; rerun with -h for copyright info
==28602== Command: ./test
==28602== 
8
vex amd64->IR: unhandled instruction bytes: 0xF3 0xF 0xBC 0xC0 0x89 0xC6 0xBF 0x60
==28602== valgrind: Unrecognised instruction at address 0x400890.
==28602==    at 0x400890: main (in /home/magu_/sod/test/test)
==28602== Your program just tried to execute an instruction that Valgrind
==28602== did not recognise.  There are two possible reasons for this.
==28602== 1. Your program has a bug and erroneously jumped to a non-code
==28602==    location.  If you are running Memcheck and you just saw a
==28602==    warning about a bad jump, it's probably your program's fault.
==28602== 2. The instruction is legitimate but Valgrind doesn't handle it,
==28602==    i.e. it's Valgrind's fault.  If you think this is the case or
==28602==    you are not sure, please let us know and we'll try to fix it.
==28602== Either way, Valgrind will now raise a SIGILL signal which will
==28602== probably kill your program.
==28602== 
==28602== Process terminating with default action of signal 4 (SIGILL)
==28602==  Illegal opcode at address 0x400890
==28602==    at 0x400890: main (in /home/magu_/sod/test/test)
==28602== 
==28602== HEAP SUMMARY:
==28602==     in use at exit: 0 bytes in 0 blocks
==28602==   total heap usage: 0 allocs, 0 frees, 0 bytes allocated
==28602== 
==28602== All heap blocks were freed -- no leaks are possible
==28602== 
==28602== For counts of detected and suppressed errors, rerun with: -v
==28602== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 2 from 2)
Illegal instruction (core dumped)

这是valgrind的bug还是我不应该在我的计算机上使用__builtin_ctz ?__builtin_popcount不抛出任何错误

g++ (Ubuntu 4.8.1-2ubuntu1~12.04) 4.8.1
CPU : Intel Core Duo T7500