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 Strange think about Clang compiler

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Dann Corbit




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Join date : 2020-11-26

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PostSubject: Strange think about Clang compiler   Strange think about Clang compiler EmptyFri May 28, 2021 10:57 pm

Why is it that the special Clang linker (lld) does not come with Clang?
It seems bizarre that I have to install and maintain it separately.
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Dann Corbit




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Join date : 2020-11-26

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PostSubject: Re: Strange think about Clang compiler   Strange think about Clang compiler EmptyFri May 28, 2021 11:16 pm

After adding the right linker, I still cannot do a profile build:
lld-link: error: could not open 'C:/msys64/mingw64/lib/clang/12.0.0/lib/windows/libclang_rt.profile-x86_64.a': No such file or directory
clang++: error: linker command failed with exit code 1 (use -v to see invocation)

It seems that if you want to do that, you have to build the compiler yourself from scratch:
https://stackoverflow.com/questions/29392702/missing-libclang-rt-san-x86-64-a-file-for-llvm-compiler-rt

It also fails to build with a non-profile build (config sanity check fails):
dannc@DESKTOP-426Q3JG MINGW64 /c/users/dannc/chess/stockfish-master/src
$ make build arch=x86-64-avx512 COMP=clang
Default net: nn-7756374aaed3.nnue
Already available.

Config:
debug: 'no'
sanitize: 'no'
optimize: 'yes'
arch: 'x86-64-avx512'
bits: '64'
kernel: 'MINGW64_NT-10.0-19041'
os: 'Windows_NT'
prefetch: 'yes'
popcnt: 'yes'
pext: 'no'
sse: 'yes'
mmx: 'no'
sse2: 'yes'
ssse3: 'yes'
sse41: 'yes'
avx2: 'no'
avx512: 'no'
vnni256: 'no'
vnni512: 'no'
neon: 'no'

Flags:
CXX: clang++
CXXFLAGS: -Wall -Wcast-qual -fno-exceptions -std=c++17 -pedantic -Wextra -Wshadow -m64 -DUSE_PTHREADS -DNDEBUG -O3 -mtune=native -fexperimental-new-pass-manager -DIS_64BIT -msse -msse3 -mpopcnt -DUSE_POPCNT -DUSE_SSE41 -msse4.1 -DUSE_SSSE3 -mssse3 -DUSE_SSE2 -msse2 -flto -fuse-ld=lld
LDFLAGS: -latomic -m64 -lpthread -Wall -Wcast-qual -fno-exceptions -std=c++17 -pedantic -Wextra -Wshadow -m64 -DUSE_PTHREADS -DNDEBUG -O3 -mtune=native -fexperimental-new-pass-manager -DIS_64BIT -msse -msse3 -mpopcnt -DUSE_POPCNT -DUSE_SSE41 -msse4.1 -DUSE_SSSE3 -mssse3 -DUSE_SSE2 -msse2 -flto -fuse-ld=lld

Testing config sanity. If this fails, try 'make help' ...

make: *** [Makefile:841: config-sanity] Error 1

From this I conclude that they do not test at all with clang on Windows using msys2
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TheSelfImprover

TheSelfImprover


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PostSubject: Re: Strange think about Clang compiler   Strange think about Clang compiler EmptyFri May 28, 2021 11:28 pm

Do you get better compiled code from CLang than from other C compilers?
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Dann Corbit




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PostSubject: Re: Strange think about Clang compiler   Strange think about Clang compiler EmptyFri May 28, 2021 11:57 pm

TheSelfImprover wrote:
Do you get better compiled code from CLang than from other C compilers?

Back when it used to work, the answer was "sometimes" (depending on what engine I was building and other factors).
The thing I liked most about clang was the compiler diagnostics, which are better than gcc (or at least they were, not sure today).
However, I have not been able to build Stockfish with Clang for two or three years now.
I quit trying for about 6 months, but today I got an update to Clang to version 12:
$ clang --version
clang version 12.0.0
Target: x86_64-w64-windows-gnu
Thread model: posix
InstalledDir: C:/msys64/mingw64/bin

So I thought I would give it another try. My guess is that it works great on Linux and it might work on Windows if we had a workable configuration in the makefile.
But the makefile that comes with SF simply does not work with clang on Windows using msys2 (at least on my system).
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j.t.




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Join date : 2021-07-09
Age : 24
Location : Berlin

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PostSubject: Re: Strange think about Clang compiler   Strange think about Clang compiler EmptyFri Jul 09, 2021 2:11 am

TheSelfImprover wrote:
Do you get better compiled code from CLang than from other C compilers?

I noticed very significant improvements of using Clang over GCC when also compiling with -flto (quick unscientific test, running both versions at the same time: clang + LTO -> 1820 knps, gcc + LTO -> 1560 knps). Though the reason for this big difference could be that I am writing the code in Nim and then the Nim compiler translates this into weird, human-untypical C code.
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TheSelfImprover

TheSelfImprover


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PostSubject: Re: Strange think about Clang compiler   Strange think about Clang compiler EmptyFri Jul 09, 2021 12:57 pm

j.t. wrote:
...I am writing the code in Nim and then the Nim compiler translates this into weird, human-untypical C code.


Arrggghhhhh - there are too many languages!!!  Shocked

I hadn't heard of Nim: it's good that it transpiles into other languages like C and JavaScript - but I suspect that more and more transpilers are being written for other languages anyway.
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