[openmp] [runtime] Disable KMP_HAVE_QUAD on NetBSD gcc

[mgorny]

Summary

Disable KMP_HAVE_QUAD when building via gcc on NetBSD system,
as the build fails due to unimplemented builtins:

.../kmp_atomic.cpp.o: In function `__kmpc_atomic_cmplx16_mul':
.../kmp_atomic.cpp:1332: undefined reference to `__multc3'
.../kmp_atomic.cpp.o: In function `__kmpc_atomic_cmplx16_div':
.../kmp_atomic.cpp:1334: undefined reference to `__divtc3'
...

[krytarowski]

I propose to detect it based on _GLIBCXX_USE_FLOAT128 && __GLIBCXX__.

Is float128 in libc++ with GCC?

[krytarowski]

Hmm on the other hand, we enable _GLIBCXX_USE_FLOAT128 on NetBSD for i386/amd64.. however it doesn't work here. Can we add a feature detection?

[mgorny]

In D55478#1324490, @krytarowski wrote:

Hmm on the other hand, we enable _GLIBCXX_USE_FLOAT128 on NetBSD for i386/amd64.. however it doesn't work here. Can we add a feature detection?

What should it detect? If using __float128 works?

[krytarowski]

In D55478#1327056, @mgorny wrote:

In D55478#1324490, @krytarowski wrote:

Hmm on the other hand, we enable _GLIBCXX_USE_FLOAT128 on NetBSD for i386/amd64.. however it doesn't work here. Can we add a feature detection?

What should it detect? If using __float128 works?

Yes, and whether _Complex __float128 works in particular.

[krytarowski]

After some more analysis, this is not trivial to check dynamically right now and unless there is support in the toolchain, we can get this patch as is and move on.

openmp/trunk/runtime/src/kmp_os.h

 /* _Quad is already defined for icc */
 #undef KMP_HAVE_QUAD
 #define KMP_HAVE_QUAD 1
 #elif KMP_COMPILER_CLANG
 /* Clang doesn't support a software-implemented
    128-bit extended precision type yet */
 typedef long double _Quad;
 #elif KMP_COMPILER_GCC
+/* GCC on NetBSD lacks __multc3/__divtc3 builtins needed for quad */
+#if !KMP_OS_NETBSD
 typedef __float128 _Quad;
 #undef KMP_HAVE_QUAD
 #define KMP_HAVE_QUAD 1
+#endif
 #elif KMP_COMPILER_MSVC
 typedef long double _Quad;
 #endif
 #else
 #if __LDBL_MAX_EXP__ >= 16384 && KMP_COMPILER_GCC
 typedef long double _Quad;
 #undef KMP_HAVE_QUAD
 #define KMP_HAVE_QUAD 1