OpenMandriva, the first Clang-built Linux distribution

Re:OpenMandriva, the first Clang-built Linux distribution by rurban on Sunday June 16, 2019 @02:03PM (#20196911)

No, GCC has serious shortcomings in certain areas. -flto=thin is better, autofdo/bolt is better, the jit is better, but the most important point are C constexpr which are implemented as in C++, but with GCC you cannot decide at compile-time if a constexpr is constant, so it misses out on many optimizations. It only has _Static_assert, but no usable __builtin_constant_p. With GCC it errors at compile-time, with clang it returns 0. clang also has diagnose_if, e.g. to match user-defined compile-time warnings with user-defined run-time warnings.

e.g. the clang memcpy can be 100x faster than the gcc memcpy, when the size and alignment is known.

And gcc-9 added serious regressions on some platforms, that you need to blacklist it. gcc-10 probably not being better.

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Re:OpenMandriva, the first Clang-built Linux distribution by BurningCycles on Monday June 17, 2019 @04:41AM (#20201023)

I have to disagree, -flto=thin is faster in compile time, but in performance I get better results with -flto=n in GCC.

Also with FDO I get better results with GCC over Clang/LLVM, my main test subjects are rendering (Blender), archivers, encoders and emulation.

However with straight up -O2/-O3 I very often get better performance with Clang/LLVM. I haven't benchmarked on ARM though, my results may be very different there.

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Re:OpenMandriva, the first Clang-built Linux distribution by astrange on Sunday June 16, 2019 @07:55PM (#20198699)

Where do clang and gcc implement memcpy? That's part of the C library.

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