llvm dev - Jul 2017 - Compiling LLVM to LLVM IR

Hello everyone,

I'm trying to compile LLVM and Clang into LLVM IR with debug info. I know
that clang++ -g2 -S -emit-llvm <filename> does this, but I'm
unfamiliar with CMake.

I tried changing CMAKE_CXX_FLAGS in CMakeCache.txt to "clang++ -g2 -S
-emit-llvm," "-g2 -S -emit-llvm," and "-emit-llvm," but
everything I tried resulted in a failed build, and/or .o files that didn't
look like LLVM IR files when I opened them up. Where is the right place to pass
these flags in?

Thanks,
Mackenzie

Hi Mackenzie,

The trick is to use LTO.
Here is a set of commands you need to run in order to prepare build system:

$ mkdir build
$ cd build
$ export CFLAGS="-flto -g "
$ export CXXFLAGS="-flto -g "
$ export CPPFLAGS="-flto -g "
$ cmake ../llvm

Now you can build any target you want, for instance:

$ make LLVMSupport -j8

When it's done you will have bunch of .o files, which are actually LLVM
bitcode files:

$ find ./ -name "*.o" | xargs file
.//CMakeFiles/test.o:                                                           
LLVM bitcode, wrapper x86_64
.//lib/Support/CMakeFiles/LLVMSupport.dir/Allocator.cpp.o:                      
LLVM bitcode, wrapper x86_64
.//lib/Support/CMakeFiles/LLVMSupport.dir/APFloat.cpp.o:                        
LLVM bitcode, wrapper x86_64
.//lib/Support/CMakeFiles/LLVMSupport.dir/APInt.cpp.o:                          
LLVM bitcode, wrapper x86_64
.//lib/Support/CMakeFiles/LLVMSupport.dir/APSInt.cpp.o:                         
LLVM bitcode, wrapper x86_64
.//lib/Support/CMakeFiles/LLVMSupport.dir/ARMAttributeParser.cpp.o:             
LLVM bitcode, wrapper x86_64
....

If you need a human readable IR, then you can convert them into .ll using
llvm-dis:

$ llvm-dis .//lib/Support/CMakeFiles/LLVMSupport.dir/Allocator.cpp.o
$ file .//lib/Support/CMakeFiles/LLVMSupport.dir/Allocator.cpp.o.ll
.//lib/Support/CMakeFiles/LLVMSupport.dir/Allocator.cpp.o.ll: ASCII text, with
very long lines

I hope that helps.

Cheers,
Alex.
> On 29. Jul 2017, at 10:32, Mackenzie Moore via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> 
> Hello everyone,
> 
> I'm trying to compile LLVM and Clang into LLVM IR with debug info. I
know that clang++ -g2 -S -emit-llvm <filename> does this, but I'm
unfamiliar with CMake.
> 
> I tried changing CMAKE_CXX_FLAGS in CMakeCache.txt to "clang++ -g2 -S
-emit-llvm," "-g2 -S -emit-llvm," and "-emit-llvm," but
everything I tried resulted in a failed build, and/or .o files that didn't
look like LLVM IR files when I opened them up. Where is the right place to pass
these flags in?
> 
> Thanks,
> Mackenzie
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
--
AlexDenisov
Software Engineer, https://lowlevelbits.org

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2017-07-29 2:50 GMT-07:00 Alex Denisov via llvm-dev <llvm-dev at
lists.llvm.org
>:
> Hi Mackenzie,
>
> The trick is to use LTO.
> Here is a set of commands you need to run in order to prepare build system:
>
> $ mkdir build
> $ cd build
> $ export CFLAGS="-flto -g "
> $ export CXXFLAGS="-flto -g "
> $ export CPPFLAGS="-flto -g "
> $ cmake ../llvm
>
Shorter:

```cmake  ../llvm -DLLVM_ENABLE_LTO=YES```

Note that LTO implies a different optimization pipeline. If you just want
IR without changing anything else, the exact command line flag is
`-emit-llvm` I believe.

Best,

-- 
Mehdi




>
> Now you can build any target you want, for instance:
>
> $ make LLVMSupport -j8
>
> When it's done you will have bunch of .o files, which are actually LLVM
> bitcode files:
>
> $ find ./ -name "*.o" | xargs file
> .//CMakeFiles/test.o:
>       LLVM bitcode, wrapper x86_64
> .//lib/Support/CMakeFiles/LLVMSupport.dir/Allocator.cpp.o:
>        LLVM bitcode, wrapper x86_64
> .//lib/Support/CMakeFiles/LLVMSupport.dir/APFloat.cpp.o:
>        LLVM bitcode, wrapper x86_64
> .//lib/Support/CMakeFiles/LLVMSupport.dir/APInt.cpp.o:
>        LLVM bitcode, wrapper x86_64
> .//lib/Support/CMakeFiles/LLVMSupport.dir/APSInt.cpp.o:
>         LLVM bitcode, wrapper x86_64
> .//lib/Support/CMakeFiles/LLVMSupport.dir/ARMAttributeParser.cpp.o:
>         LLVM bitcode, wrapper x86_64
> ....
>
> If you need a human readable IR, then you can convert them into .ll using
> llvm-dis:
>
> $ llvm-dis .//lib/Support/CMakeFiles/LLVMSupport.dir/Allocator.cpp.o
> $ file .//lib/Support/CMakeFiles/LLVMSupport.dir/Allocator.cpp.o.ll
> .//lib/Support/CMakeFiles/LLVMSupport.dir/Allocator.cpp.o.ll: ASCII text,
> with very long lines
>
> I hope that helps.
>
> Cheers,
> Alex.
>
> > On 29. Jul 2017, at 10:32, Mackenzie Moore via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
> >
> > Hello everyone,
> >
> > I'm trying to compile LLVM and Clang into LLVM IR with debug info.
I
> know that clang++ -g2 -S -emit-llvm <filename> does this, but I'm
> unfamiliar with CMake.
> >
> > I tried changing CMAKE_CXX_FLAGS in CMakeCache.txt to "clang++
-g2 -S
> -emit-llvm," "-g2 -S -emit-llvm," and
"-emit-llvm," but everything I tried
> resulted in a failed build, and/or .o files that didn't look like LLVM
IR
> files when I opened them up. Where is the right place to pass these flags
> in?
> >
> > Thanks,
> > Mackenzie
> > _______________________________________________
> > LLVM Developers mailing list
> > llvm-dev at lists.llvm.org
> > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
> --
> AlexDenisov
> Software Engineer, https://lowlevelbits.org
>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>
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