What happened to IBM XL C/C++ preprocessor macros?

Question

I'm working on GCC112 from the compile farm, which is a Linux ppc64-le machine. I'm testing IBM XL C/C++ and catching a compile failure on some AES code that uses POWER8. The code has worked for the last couple of years. The failure is new.

The compile failure is:

$ CXX=xlC make aes-simd.o
xlC -DNDEBUG -g2 -O3 -qrtti -qpic -qarch=pwr8 -qaltivec -c aes-simd.cpp
In file included from aes-simd.cpp:29:
./ppc-simd.h:443:16: error: use of undeclared identifier
      '__builtin_crypto_vcipher'; did you mean '__builtin_vec_vcipher'?
    return (T1)__builtin_crypto_vcipher((uint64x2_p)state, (uint64x2_p)key);

__builtin_crypto_vcipher is a GCC builtin. The only way to get into that path is if __xlc__ and __xlC__ are not defined:

template <class T1, class T2>
inline T1 VectorEncrypt(const T1& state, const T2& key)
{
#if defined(__xlc__) || defined(__xlC__)
    return (T1)__vcipher((uint8x16_p)state, (uint8x16_p)key);
#elif defined(__GNUC__)
    return (T1)__builtin_crypto_vcipher((uint64x2_p)state, (uint64x2_p)key);
#else
    _ASSERT(0);
#endif
}

Checking preprocessor macros:

$ xlC -qshowmacros -qarch=pwr8 -qaltivec -E aes-simd.cpp | grep -i xlc
#define __XLC_BUILTIN_VAARG__ 1

It looks like nearly all the preprocessor macros have disappeared. A single macro of __XLC_BUILTIN_VAARG__ is not correct.

What happened to the IBM XL C/C++ preprocessor macros, and how do I get them back?

$ xlC -qversion
IBM XL C/C++ for Linux, V13.1.6 (Community Edition)
Version: 13.01.0006.0001
/opt/ibm/xlC/13.1.6/bin/.orig/xlC

score 1 · Accepted Answer · answered Jul 31 '18 at 02:09

IBM XL C/C++ for Linux V13.1.6 does not define __xlc__ or __xlC__ by default, but you can get the compiler to define them by using -qxlcompatmacros. You may be able to make use of the other macros it defines like __ibmxl__; see this Knowledge Center page for more information.

I know the GCC compile farm admins recently upgraded to 13.1.6 at the request of one of XL's other users, but I believe IBM XL C/C++ for Linux (for little endian distributions) has always had this same behaviour.

IBM XL C/C++ for Linux (for big endian distributions) and IBM XL C/C++ for AIX behave differently and define __xlc__ or __xlC__ by default.

Thanks @Nicole. I should have known it was LLVM and their stupid trick of pretending to be another compiler but failing to consume the program. — jww, Jul 31 '18 at 02:23

What happened to IBM XL C/C++ preprocessor macros?

1 Answers1