Re: JIT compiling with LLVM v9.0

On Fri, Feb 2, 2018 at 2:05 PM, Andres Freund <andres(at)anarazel(dot)de> wrote:
> On 2018-02-01 09:32:17 -0800, Jeff Davis wrote:
>> On Wed, Jan 31, 2018 at 12:03 AM, Konstantin Knizhnik
>> <k(dot)knizhnik(at)postgrespro(dot)ru> wrote:
>> > The same problem takes place with old versions of GCC: I have to upgrade GCC
>> > to 7.2 to make it possible to compile this code.
>> > The problem in not in compiler itself, but in libc++ headers.
>>
>> How can I get this branch to compile on ubuntu 16.04? I have llvm-5.0
>> and gcc-5.4 installed. Do I need to compile with clang or gcc? Any
>> CXXFLAGS required?
>
> Just to understand: You're running in the issue with the header being
> included from within the extern "C" {}? Hm, I've pushed a quick fix for
> that.

That change wasn't quite enough: to get this building against libc++
(Clang's native stdlb) I also needed this change to llvmjit.h so that
<llvm-c/Types.h> wouldn't be included with the wrong linkage (perhaps
you can find a less ugly way):

+#ifdef __cplusplus
+}
+#endif
#include <llvm-c/Types.h>
+#ifdef __cplusplus
+extern "C"
+{
+#endif

> Other than that, you can compile with both gcc or clang, but clang needs
> to be available. Will be guessed from PATH if clang clang-5.0 clang-4.0
> (in that order) exist, similar with llvm-config llvm-config-5.0 being
> guessed. LLVM_CONFIG/CLANG/CXX= as an argument to configure overrides
> both of that. E.g.
> ./configure --with-llvm LLVM_CONFIG=~/build/llvm/5/opt/install/bin/llvm-config
> is what I use, although I also add:
> LDFLAGS='-Wl,-rpath,/home/andres/build/llvm/5/opt/install/lib'
> so I don't have to install llvm anywhere the system knows about.

BTW if you're building with clang (vendor compiler on at least macOS
and FreeBSD) you'll probably need CXXFLAGS=-std=c++11 (or later
standard) because it's still defaulting to '98.

--
Thomas Munro
http://www.enterprisedb.com