[llvm-dev] Issue with BUILD_SHARED_LIBS=ON

[Jakub (Kuba) Kuderski via llvm-dev]

Hi Roger,

I think it was me who introduced the change from `() { }` to `() = default`
for a couple of dominators-related classes during the major refactoring I
did in the summer. We got reports of very similar compiler/linker failures
with gcc and older versions of clang, and I thought I reverted most of them
to `() {}` as a workaround. Fell free to do the same with this one.

Best regards,
Kuba

On Fri, Dec 8, 2017 at 1:04 PM, David Blaikie via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Keeping the shared library build working's probably a fine idea, though
> working around GCC bugs (depending on how ubiquitous they are) might be
> less so.
>
> I'd be fine with this patch going in for this case, though. For a one line
> change there's no need to send a phab review, someone (probably me, I
> guess) can just apply/commit this directly.
>
> On Fri, Dec 8, 2017 at 1:37 AM Roger Ferrer Ibanez via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> Dear all,
>>
>> while trying to build llvm with shared libraries using GCC (tested both in
>> Ubuntu 14.04 and Ubuntu 16.04) as in
>>
>>   cmake -G Ninja -DBUILD_SHARED_LIBS=ON
>>
>> I run into the following link error
>>
>>    lib/Transforms/IPO/CMakeFiles/LLVMipo.dir/PartialInlining.cpp.o: In
>> function `llvm::ForwardDominanceFrontierBase<llvm::BasicBlock>::
>> ForwardDominanceFrontierBase()':
>>    <path>/llvm/include/llvm/Analysis/DominanceFrontier.h:122: undefined
>> reference to `llvm::DominanceFrontierBase<llvm::BasicBlock,
>> false>::DominanceFrontierBase()'
>>
>> This change
>>
>>    diff --git a/include/llvm/Analysis/DominanceFrontier.h
>> b/include/llvm/Analysis/DominanceFrontier.h
>>    index a304dff..e743d2d 100644
>>    --- a/include/llvm/Analysis/DominanceFrontier.h
>>    +++ b/include/llvm/Analysis/DominanceFrontier.h
>>    @@ -52,7 +52,7 @@ protected:
>>       static constexpr bool IsPostDominators = IsPostDom;
>>
>>     public:
>>    -  DominanceFrontierBase() = default;
>>    +  DominanceFrontierBase() { }
>>
>>       /// getRoots - Return the root blocks of the current CFG.  This may
>> include
>>       /// multiple blocks if we are computing post dominators.  For
>> forward
>>
>> seems to fix the problem and I think is related to this GCC defect
>>
>>    https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57728
>>
>> I'm unsure about the level of interest in the community when it comes to
>> builds
>> using shared libraries.  I personally use them because for debug builds,
>> at
>> link time, they are less demanding in memory. However that alone might
>> not be
>> enough to justify this change as there are valid workarounds (like not
>> using
>> shared libraries, building clang with clang, using lld, etc).
>>
>> Thoughts? If this is reasonable I will create a Phabricator.
>>
>> Kind regards,
>> Roger
>> _______________________________________________
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>> llvm-dev at lists.llvm.org
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>>
>
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>


-- 
Jakub Kuderski
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