According to the documentation, clang supports options to emit optimisation reports:
When the pass makes a transformation (-Rpass).
When the pass fails to make a transformation (-Rpass-missed).
When the pass determines whether or not to make a transformation (-Rpass-analysis).
They provide the following example command line:
$ clang -O2 -Rpass=inline code.cc -o code
When I try this, I get an error:
$ clang src/test/tests.cpp -Rpass=inline
clang: error: unknown argument: '-Rpass=inline'
scons: *** [build/test/tests.o] Error 1
scons: building terminated because of errors.
My clang version is:
$ clang --version
Apple LLVM version 6.0 (clang-600.0.54) (based on LLVM 3.5svn)
Target: x86_64-apple-darwin14.0.0
Thread model: posix
Is this option not available on Mac OS? Is the documentation erroneous? Or am I doing it wrong? If so, how to do it right?
Works for Debian clang-3.5.0-6, so this is probably Apple clang restriction.
% clang++ -O2 -Rpass=inline foo.cpp
foo.cpp:11:2: remark: _ZN1CC2Ev inlined into main [-Rpass=inline]
P* p = new C();
^
% clang --version
Debian clang version 3.5.0-6 (tags/RELEASE_350/final) (based on LLVM 3.5.0)
Target: i386-pc-linux-gnu
Thread model: posix
Related
I'm trying to install Riak from source on macOS (https://docs.riak.com/riak/kv/2.2.3/setup/installing/mac-osx.1.html#installing-from-source).
There is a note:
Riak will not compile with Clang. Please make sure that your default
C/C++ compiler is GCC
How do I find out which compiler is the default and how to change it?
macOS Catalina (10.15.4), which command prints:
$ which clang
/usr/bin/clang
$ which gcc
/usr/bin/gcc
On macOS Catalina (and prior versions, and most likely subsequent versions too), there are two aspects to the problem and some suggested solutions.
What is the name of the compiler used by make by default?
$ mkdir junk
$ cd junk
$ > x.cpp
$ > y.c
$ make x y
c++ x.cpp -o x
cc y.c -o y
$ cd ..
$ rm -fr junk
This shows that the names used by make are cc and c++. Those are not obviously clang or clang++, but neither are they obviously gcc and g++.
$ which cc c++
/usr/bin/cc
/usr/bin/c++
$
Which compiler is it really?
Which compiler really lives behind the names cc, c++, gcc, g++, clang, and clang++? We can check which compiler these really are by getting them to identify their version:
$ for compiler in cc c++ gcc g++ clang clang++
> do
> which $compiler
> $compiler --version
> done
/usr/bin/cc
Apple clang version 11.0.0 (clang-1100.0.33.17)
Target: x86_64-apple-darwin18.7.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
/usr/bin/c++
Apple clang version 11.0.0 (clang-1100.0.33.17)
Target: x86_64-apple-darwin18.7.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
/usr/bin/gcc
Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr --with-gxx-include-dir=/usr/include/c++/4.2.1
Apple clang version 11.0.0 (clang-1100.0.33.17)
Target: x86_64-apple-darwin18.7.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
/usr/bin/g++
Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr --with-gxx-include-dir=/usr/include/c++/4.2.1
Apple clang version 11.0.0 (clang-1100.0.33.17)
Target: x86_64-apple-darwin18.7.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
/usr/bin/clang
Apple clang version 11.0.0 (clang-1100.0.33.17)
Target: x86_64-apple-darwin18.7.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
/usr/bin/clang++
Apple clang version 11.0.0 (clang-1100.0.33.17)
Target: x86_64-apple-darwin18.7.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
$
As you can see, the versions installed in /usr/bin are all the same compiler, and that compiler is clang or clang++.
This was run on a machine with macOS Mojave 10.14.6 and XCode 11.3.1. The latest version of XCode — 11.4.1 — is only available on Catalina. However, the general conclusion is the same — all the C and C++ compilers are really clang and clang++ in disguise.
How do you get GNU GCC onto your machine?
How do you get a real GNU GCC — a real GCC, not clang in disguise — onto your machine?
Use Brew to install GCC (I've not checked which version of GCC is current).
Or use MacPorts (again, I've not checked which version of GCC is current).
If you're adventuresome, do it yourself (but I've not yet succeeded at building GCC 9.3.0 on Catalina; I have a GCC 9.2.0 built on macOS Mojave 10.14.x that works OK on Catalina though — with one environment variable needed to locate the headers).
Maybe Fink — it lists GCC 8.4 as being made available in 2020; I don't know about newer versions.
Be aware that Apple has taken to hiding the system header files miles out of the way (not in /usr/include — and you can't modify that part of the file system to add a symlink to where they've hidden them):
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include
(You mean you couldn't guess that? Me neither!)
How do you change the default compiler?
Once you have GCC installed somewhere appropriate, you need to ensure you use the 'real' GCC and not the 'fake' in /usr/bin. You do that in part by ensuring that the bin directory for the 'real' GCC occurs on your PATH before /usr/bin. I have GCC 9.3.0 installed under /opt/gcc/v9.3.0, so /opt/gcc/v9.3.0/bin appears on my PATH long before /usr/bin does.
You also need to ensure that the configuration for riak (the software you're installing) uses the correct compilers. If there's a ./configure script, run it with the correct path specified for the compilers. For example, I might use:
./configure CC=/opt/gcc/v9.3.0/bin/gcc CXX=/opt/gcc/v9.3.0/bin/g++
You can also set these values as environment variables.
If it uses cmake or some other configuration package, you'll need to consult the installation instructions. That's usually README or sometimes INSTALL.
See also (increasingly older posts):
Can't compile a C program on a Mac after upgrade to Catalina
Can't compile a C program on a Mac after upgrade to Mojave
Install GNU GCC on a Mac
I can't compile with -std=c++17, I got :
error: invalid value 'c++17' in '-std=c++17'
However I update Xcode and clang.
My Clang version is:
Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr --with-gxx-include-dir=/usr/include/c++/4.2.1
Apple LLVM version 9.0.0 (clang-900.0.39.2)
Target: x86_64-apple-darwin16.7.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin`
And I load the newest header like optional, I have to do
#include <experimental/optional>
instead of
#include <optional>
Xcode brings its own complete toolchain, including headers and the actual compiler.
Apple LLVM version 9.0.0 (clang-900.0.39.2) (which ships with Xcode 9.2) does not support the usage of the flag -std=c++17 since its too old. The optional header is only included under the folder experimental/. Which is why you need to #include <experimental/optional>
In order to compile your program with c++17 support using the compiler which comes with Xcode 9.2 you need to use the -std=c++1z flag.
Xcode 9.3 will be shipped with Apple LLVM version 9.1.0 (clang-902.0.30) which has support for the -std=c++17 flag. However the optional header is as of today still under the experimental/ subdirectory. This might change during the betas.
Here is what I get with this tests:
#include <experimental/optional>
int main(int, char* []) {
return 0;
}
g++ -std=c++17 -o test test.cpp
error: invalid value 'c++17' in '-std=c++17'
g++ -std=c++1z -o test test.cpp
Did you try the c++1z argument?
Also of note my test compiles without the -std=c++1z argument provided.
I think I'm on a newer version of OSX than you:
Target: x86_64-apple-darwin17.4.0
You should use -std=c++1z as flag.
libc++ with c++17 support since macos 15
-std=c++1z also works on Apple LLVM version 8.1.0 (clang-802.0.42)
What version of LLVM does the latest emscripten use?
I googled for this quite a while but could not find any info. The background is that I've got some C++ code that requires clang-5.0 - what are the chances that it would compile with emscripten? Or at least code that needs clang-4.0?
The latest version of emscripten uses clang version 4:
$ emcc -v
emcc (Emscripten gcc/clang-like replacement + linker emulating GNU ld) 1.37.21
clang version 4.0.0 (https://github.com/kripken/emscripten-fastcomp-clang.git 974b55fd84ca447c4297fc3b00cefb6394571d18) (https://github.com/kripken/emscripten-fastcomp.git 087c6b7b18b7b769d4ad8f2ac3e0dd0ae6b924c2) (emscripten 1.37.21 : 1.37.21)
Target: x86_64-apple-darwin16.7.0
Thread model: posix
However, you can build WebAssembly without emscripten, by using the clang, llc, s2wasm and wasm tools separately as documented in this gist.
Another good alternative is the wasm-toolchain project:
https://github.com/tpimh/wasm-toolchain
With this installed, I have clang version 6:
$ ./clang --version
clang version 6.0.0 (http://llvm.org/git/clang.git 9411957410813aeefc1bb299abcb856ce1ef8aae) (http://llvm.org/git/llvm.git 68b21d6108df63d65d6735e9686d53cca844e37a)
Target: x86_64-apple-darwin16.7.0
Thread model: posix
I'm working on LLVM/Clang fork (for AVR). How can i force Clang Driver to use LLVM assembler instead of system one?
MBA-Anton:bin asmirnov$ ./clang++
-I/Applications/avr.app/Contents/Resources/Java/hardware/avr/cores/avr -I/Applications/avr.app/Contents/Resources/Java/hardware/avr/variants/standard
/var/folders/64/fwfkm1k51zbd4_c5lwpsbljh0000gn/T/build5450310618632673119.tmp/Blink.cpp
-o /tmp/Blink.avr.hex -I /Applications/avr.app//Contents/Resources/Java/hardware/tools/avr/avr/include/
--target=avr -O1 -v
And it uses LLVM clang compiler (not system, correct):
clang version 3.6.0 (https://github.com/4ntoine/clang.git 0d08deedd548d964f63cf896ae9acb8d878a5fd8) (https://github.com/dylanmckay/avr-llvm.git 447b58bced825fa7bea31f3882f277535cc9fca6)
Target: avr
Thread model: posix
"/Users/asmirnov/Documents/dev/src/llvm_dylan/installed/bin/clang" -cc1 ...
But system assembler (incorrect):
"/usr/bin/as" -o ...
It should use LLVM's llvm-as as it "knows" AVR target (opcodes, etc). How can i force it use LLVM's assembler?
You can use clang to emit LLVM IR code by using the option -emit-llvm.
Let's say you want to compile a C file into LLVM IR:
clang -emit-llvm -c file.c
It will create a LLVM bytecode file file.bc. You will be able to compile the file with llc.
Originally, I used clang++ with -std=c++11 compile my C++11 code, everything was OK. Recently, I updated the Xcode in AppStore, I compiled the SAME program in command line again, it doesn't work anymore, it shows errors like below:
/usr/include/c++/4.2.1/bits/stl_construct.h:81:38: error: no matching
constructor for initialization of
'std::basic_string'
::new(static_cast(__p)) T1(_value);
It seems the clang++ is using gcc's header files, apparently, gcc's version is very old. However, if I compile the same program by using Xcode, everything is fine.
It seems, at command line , the clang++ can't find the correct header files anymore.
More information, running command clang++ --version, following output:
Apple LLVM version 5.0 (clang-500.2.79) (based on LLVM 3.3svn)
Target: x86_64-apple-darwin12.5.0 Thread model: posix
which clang++
/usr/bin/clang++
RESOLVED with option -stdlib=libc++