[cfe-dev] Problems compiling clang 3.7.0 with gcc 4.9

[Craig Rodrigues via cfe-dev]

On Wed, Oct 7, 2015 at 1:23 PM, Richard Smith <richard at metafoo.co.uk> wrote:

> On Wed, Oct 7, 2015 at 4:47 AM, Craig Rodrigues <rodrigc at freebsd.org>
> wrote:
>
>> Hi,
>>
>> I recently tried to compile clang 3.7.0 with gcc 4.9
>> under FreeBSD.  I reproduced the problem with gcc 5.0.
>>
>> The full build error is here:
>> https://jenkins.freebsd.org/job/FreeBSD_HEAD_amd64_gcc4.9/617/console
>>
>> The error of interest is:
>>
>>
>> --- Module.o ---
>> /usr/local/bin/x86_64-portbld-freebsd10.1-g++
>> -isystem
>> /builds/FreeBSD_HEAD_amd64_gcc4.9/obj/builds/FreeBSD_HEAD_amd64_gcc4.9/tmp/usr/include
>> -L/builds/FreeBSD_HEAD_amd64_gcc4.9/obj/builds/FreeBSD_HEAD_amd64_gcc4.9/tmp/usr/lib
>> --sysroot=/builds/FreeBSD_HEAD_amd64_gcc4.9/obj/builds/FreeBSD_HEAD_amd64_gcc4.9/tmp
>> -B/usr/local/x86_64-freebsd/bin/
>> -I/builds/FreeBSD_HEAD_amd64_gcc4.9/obj/builds/FreeBSD_HEAD_amd64_gcc4.9/tmp/usr/include/c++/v1
>> -std=gnu++11
>> -L/builds/FreeBSD_HEAD_amd64_gcc4.9/obj/builds/FreeBSD_HEAD_amd64_gcc4.9/tmp/../lib/libc++
>> --sysroot=/builds/FreeBSD_HEAD_amd64_gcc4.9/obj/builds/FreeBSD_HEAD_amd64_gcc4.9/tmp
>> -B/usr/local/x86_64-freebsd/bin/  -O2 -pipe
>> -I/builds/FreeBSD_HEAD_amd64_gcc4.9/lib/clang/libclangbasic/../../../contrib/llvm/include
>> -I/builds/FreeBSD_HEAD_amd64_gcc4.9/lib/clang/libclangbasic/../../../contrib/llvm/tools/clang/include
>> -I/builds/FreeBSD_HEAD_amd64_gcc4.9/lib/clang/libclangbasic/../../../contrib/llvm/tools/clang/lib/Basic
>> -I.
>> -I/builds/FreeBSD_HEAD_amd64_gcc4.9/lib/clang/libclangbasic/../../../contrib/llvm/../../lib/clang/include
>> -DLLVM_ON_UNIX -DLLVM_ON_FREEBSD -D__STDC_LIMIT_MACROS
>> -D__STDC_CONSTANT_MACROS -DCLANG_ENABLE_ARCMT
>> -DCLANG_ENABLE_STATIC_ANALYZER -fno-strict-aliasing
>> -DLLVM_DEFAULT_TARGET_TRIPLE=\"x86_64-unknown-freebsd11.0\"
>> -DLLVM_HOST_TRIPLE=\"x86_64-unknown-freebsd11.0\" -DDEFAULT_SYSROOT=\"\"
>> -fstack-protector-strong  -std=c++11 -fno-exceptions -fno-rtti  -c
>> /builds/FreeBSD_HEAD_amd64_gcc4.9/lib/clang/libclangbasic/../../../contrib/llvm/tools/clang/lib/Basic/Module.cpp
>> -o Module.o
>> In file included from
>> /builds/FreeBSD_HEAD_amd64_gcc4.9/lib/clang/libclangbasic/../../../contrib/llvm/tools/clang/include/clang/Basic/SourceLocation.h:22:0,
>>                  from
>>                  /builds/FreeBSD_HEAD_amd64_gcc4.9/lib/clang/libclangbasic/../../../contrib/llvm/tools/clang/include/clang/Basic/Module.h:18,
>>                  from
>>                  /builds/FreeBSD_HEAD_amd64_gcc4.9/lib/clang/libclangbasic/../../../contrib/llvm/tools/clang/lib/Basic/Module.cpp:15:
>> /builds/FreeBSD_HEAD_amd64_gcc4.9/obj/builds/FreeBSD_HEAD_amd64_gcc4.9/tmp/usr/include/c++/v1/functional:1322:17:
>> error: '_Rp std::__1::__function::__base<_Rp(_ArgTypes
>> ...)>::operator()(_ArgTypes&& ...) [with _Rp = void; _ArgTypes =
>> {clang::VisibleModuleSet::setVisible(clang::Module*, clang::SourceLocation,
>> clang::VisibleModuleSet::VisibleCallback,
>> clang::VisibleModuleSet::ConflictCallback)::Visiting}]', declared
>> using local type 'clang::VisibleModuleSet::setVisible(clang::Module*,
>> clang::SourceLocation, clang::VisibleModuleSet::VisibleCallback,
>> clang::VisibleModuleSet::ConflictCallback)::Visiting', is used but
>> never defined [-fpermissive]
>>      virtual _Rp operator()(_ArgTypes&& ...) = 0;
>>                  ^
>>
>> This looks like a GCC bug. I'm not sure why it imagines that this pure
> virtual function is used; did it produce any note indicating that?
>

There was no note to indicate why GCC thought that this pure virtual
function is used.
The only thing I could think of was maybe there was something in the llvm
implementation of
std::function that caused this to happen.



> In any case, given that the link succeeds if you move the struct
> definition outside of the function (so it's not able to detect the problem
> during compilation any more), this function is very likely not actually
> used, and thus the diagnostic here is wrong.
>
> One more thing that's worth checking: if you build with -fpermissive, does
> the compile and link succeed?
>
>
I added -fpermissive to the command-line, and the compile and link
succeeded.

If this looks like a GCC bug, I can submit something to them.

--
Craig
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