Improve Readme.md about compiling

[nguyenpham]

Reparagraph, add an example how to compile on Unix-like systems

[vondele]

It would be better to use make -j profile-build ARCH=x86-64-modern in the example, that will be suitable for most users.

[nguyenpham]

I use make build ARCH=x86-64 from the first example when a user types make help. Do you want me to modify Makefile too for being consistent (all will be make -j profile-build ARCH=x86-64-modern)?

[vondele]

yes, updating help would be good. Also, move profile-build to the first line of supported targets, and call it > standard build, while build could be > non-PGO build.

[nguyenpham]

I have just tried to build with all profile-build commands: make -j profile-build ARCH=x86-64-modern and make profile-build ARCH=x86-64-bmi2 COMP=gcc COMPCXX=g++-4.8. They all failed on my computer (iMac 2017, Catalina). I have called make clean before calling them to make sure they wouldn't be affected by other compiling.

I may solve/ask help to solve that problem later. However, it looks like that kind of building has a higher chance of failing for newcomers. Thus I suggest keeping the current first example (make build ARCH=x86-64) since it is the safer one.

[vondele]

OK, interesting, let's keep in the form you have right now.

Maybe file an issue for that, together with info on the compiler used, and the output of the compilation. I'm guessing this is specific to mac. Edit: or the very old gcc you have on the system.

[nguyenpham]

In my computer gcc is actually clang and it is Apple clang version 11.0.3 (clang-1103.0.32.62) - quite up to date. I guess it is not the problem of too old compilers but too new ones ;)

[vondele]

so also the g++-4.8 in the make command above links to clang? Anyway, that's most likely the reason. I can get clang to profile-build with the following:

make -j ARCH=x86-64-modern COMP=clang profile-build

with the following change to the makefile (providing the specific version of llvm-profdata, which might be an ubuntu clang installation issue):

diff --git a/src/Makefile b/src/Makefile
index 016aafec1..c42edcf4d 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -510,7 +510,7 @@ clang-profile-make:
        all
 
 clang-profile-use:
-       llvm-profdata merge -output=stockfish.profdata *.profraw
+       llvm-profdata-10 merge -output=stockfish.profdata *.profraw
        $(MAKE) ARCH=$(ARCH) COMP=$(COMP) \
        EXTRACXXFLAGS='-fprofile-instr-use=stockfish.profdata' \
        EXTRALDFLAGS='-fprofile-use ' \

[vondele]

see also #2053

[nguyenpham]

My computer links g++ to clang but doesn't know g++-4.8. Your command make -j ARCH=x86-64-modern COMP=clang profile-build failed too:

(after changing Makefile as your suggestion)

nguyenpham@iMac src % make clean  
nguyenpham@iMac src % 
nguyenpham@iMac src % make profile-build ARCH=x86-64-bmi2 COMP=gcc COMPCXX=g++-4.8
make: [.depend] Error 127 (ignored)

Config:
debug: 'no'
sanitize: 'no'
optimize: 'yes'
arch: 'x86_64'
bits: '64'
kernel: 'Darwin'
os: ''
prefetch: 'yes'
popcnt: 'yes'
sse: 'yes'
pext: 'yes'

Flags:
CXX: g++-4.8
CXXFLAGS: -Wall -Wcast-qual -fno-exceptions -std=c++11  -pedantic -Wextra -Wshadow -m64 -arch x86_64 -mmacosx-version-min=10.9 -DNDEBUG -O3 -mdynamic-no-pic -DIS_64BIT -msse -msse3 -mpopcnt -DUSE_POPCNT -DUSE_PEXT -msse4 -mbmi2 -flto
LDFLAGS:  -m64 -arch x86_64 -mmacosx-version-min=10.9 -lpthread -Wall -Wcast-qual -fno-exceptions -std=c++11  -pedantic -Wextra -Wshadow -m64 -arch x86_64 -mmacosx-version-min=10.9 -DNDEBUG -O3 -mdynamic-no-pic -DIS_64BIT -msse -msse3 -mpopcnt -DUSE_POPCNT -DUSE_PEXT -msse4 -mbmi2 -flto

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


Step 1/4. Building instrumented executable ...
/Library/Developer/CommandLineTools/usr/bin/make ARCH=x86-64-bmi2 COMP=gcc gcc-profile-make
/Library/Developer/CommandLineTools/usr/bin/make ARCH=x86-64-bmi2 COMP=gcc \
	EXTRACXXFLAGS='-fprofile-generate' \
	EXTRALDFLAGS='-lgcov' \
	all
g++-4.8 -Wall -Wcast-qual -fno-exceptions -std=c++11 -fprofile-generate -pedantic -Wextra -Wshadow -m64 -arch x86_64 -mmacosx-version-min=10.9 -DNDEBUG -O3 -mdynamic-no-pic -DIS_64BIT -msse -msse3 -mpopcnt -DUSE_POPCNT -DUSE_PEXT -msse4 -mbmi2 -flto   -c -o benchmark.o benchmark.cpp
make[2]: g++-4.8: No such file or directory
make[2]: *** [benchmark.o] Error 1
make[1]: *** [gcc-profile-make] Error 2
make: *** [profile-build] Error 2

[vondele]

yes, you'll need to figure out how to get the llvm-profdata tool to run. Seemingly doesn't work (see issue above, or workaround I posted for ubuntu).

[MichaelB7]

Make an alias called “llvm-profdata” have it set to the actual llvm-profdata exe - name will vary by version name - add the path to the folder where the exe is located on your bash profile. My guess is that you are running Catalina OS upgraded on a Mac that was running Mojave.

[vondele]

Thanks!