Avoid a warning in clang that IS_64BIT is already defined

[maximmasiutin]

We avoid a warning in clang (LLVM) compiler that IS_64BIT is already defined by checking whether IS_64BIT was defined earlier. If it was already defined, we do not define it again, thus avoiding the warning.

To reproduce it, run make.exe build ARCH=x86-64-vnni512 COMP=clang or make.exe build ARCH=x86-64-vnni512 COMP=icx under Windows. Prerequisite: LLVM Windows binary, Cygwin make.

[vondele]

The comment above says // No Makefile used and so assumes that if _MSC_VER is defined no Makefile is used. I don't think silencing of warnings this way is helpful. The question why is there a warning, what's the assumption that is wrong, and that can be addressed or not.

[maximmasiutin]

The Makefile is used. I run the command make.exe build ARCH=x86-64-vnni512 COMP=clang under Windows ang get this warning. I use native Windows binary for clang.exe and CygWin makefile. The same error happens in COMP=icx for Windows. If you think that we should modify the Makefile rather than the .h file, let me know. The Clang compiler (and the icx) define _MSC_VER for compatibility.

[maximmasiutin]

This is how clang is called:

clang++  -Wall -Wcast-qual -fno-exceptions -std=c++17 -DNDEBUG -O3 -DIS_64BIT -msse -msse3 -mpopcnt -DUSE_POPCNT -DUSE_AVX2 -mavx -mavx2 -mbmi -DUSE_AVX512 -mavx512f -mavx512bw -DUSE_VNNI -mavx512f -mavx512bw -mavx512vnni -mavx512dq -mavx512vl -mprefer-vector-width=512 -DUSE_SSE41 -msse4.1 -DUSE_SSSE3 -mssse3 -DUSE_SSE2 -msse2 -DUSE_PEXT -mbmi2 -DGIT_SHA=6e830117 -DGIT_DATE=20230401 -c -o benchmark.o benchmark.cpp

As you see, make somehow adds the -DIS_64BIT command line parameter for some reason. Do you think that we should remove it?

[vondele]

No, the problem is we're trying to have some code trying to support compiling without Makefile / supporting MSCV, other compilers trying to behave like MSCV while using Makefile.

[maximmasiutin]

What if we define something like GENUINE_MSVC in an appropriate .h file that will be only defined if _MSC_VER is defined but not __llvm__ or __clang__ or Intel's defines are defined, so that we will avoid clashes like we had with incbin and with that one? It will also resolve displaying proper compiler name. I had such code but didn't create a pull request for that since there were already too many pull requests.

[snicolet]

Can we instead modify line 66 to read like that?

   #if defined(_WIN64) && defined(_MSC_VER) && !defined(__clang__)  // No Makefile used

[snicolet]

@maximmasiutin what would you think about the above solution? :-)

[maximmasiutin]

I am OK with any solution as long as there will be no warning in clang that IS_64BIT is already defined.

[snicolet]

Can you confirm that this would fix the warning for you? :-)