llvm dev - Jul 2018 - A bug-report too difficult to make

Hi all,

 

I just found out that there is an extern "C" missing on the
LLVMInitializeInstCombine function definition somewhere around this line:

 

https://github.com/llvm-mirror/llvm/blob/master/lib/Transforms/InstCombine/I
nstructionCombining.cpp#L3365

 

As a result the function name gets mangled in the .lib file and is not
accessible from LLVM C API.

 

cheers,

</wqw>

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Hi,

It looks like there's an `extern "C"` declaration in the
corresponding
header file
<https://github.com/llvm-mirror/llvm/blob/master/include/llvm-c/Initialization.h#L39>,
which appears to be sufficient <https://godbolt.org/g/UCZ3qo>. All of my
attempts to grep for `LLVMInitializeInstCombine` in my build directory are
leaving me with unmangled symbols, though I can't say the same for
`LLVMInitializeAggressiveInstCombiner`.

r336736 is an attempt to fix `LLVMInitializeAggressiveInstCombiner`. If I
missed something, please let me know. (and if you're still seeing a problem
with `LLVMInitializeInstCombine`, more details about your setup/etc. would
be appreciated.) :)

Thanks,
George

On Tue, Jul 10, 2018 at 7:23 AM Vladimir Vissoultchev via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> Hi all,
>
>
>
> I just found out that there is an *extern "C"* missing on the
> *LLVMInitializeInstCombine* function definition somewhere around this
> line:
>
>
>
>
>
https://github.com/llvm-mirror/llvm/blob/master/lib/Transforms/InstCombine/InstructionCombining.cpp#L3365
>
>
>
> As a result the function name gets mangled in the .lib file and is not
> accessible from LLVM C API.
>
>
>
> cheers,
>
> </wqw>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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Hi,

 

I think I missed the root cause of the problem the previous time. Consider your
sample code with a small tweak:

 

    extern "C" {

    void LLVMInitializeInstCombine(int);

    }

 

    char *LLVMInitializeInstCombine(int) {  return 0; }

 

This will bomb out with error C2556: 'char
*LLVMInitializeInstCombine(int)': overloaded function differs only by return
type from 'void LLVMInitializeInstCombine(int)' in MSVC

 

But when you "tweak" the same way LLVMInitializeInstCombine in
InstructionCombining.cpp the LLVMInstCombine project compiles w/ no error.

 

So the root cause here seems to be that the .h file with the extern
"C" declaration of LLVMInitializeInstCombine is not included in
InstructionCombining.cpp source, so a mismatch between declaration vs definition
is possible and is actually happening.

 

My previous fix works but probably including Initialization.h would be better
altogether.

 

cheers,

</wqw>

 

 

From: George Burgess IV [mailto:george.burgess.iv at gmail.com] 
Sent: Wednesday, July 11, 2018 1:56 AM
To: wqweto at gmail.com
Cc: llvm-dev <llvm-dev at lists.llvm.org>
Subject: Re: [llvm-dev] A bug-report too difficult to make

 

Hi,

 

It looks like there's an `extern "C"` declaration in the
corresponding header file
<https://github.com/llvm-mirror/llvm/blob/master/include/llvm-c/Initialization.h#L39>
, which appears to be sufficient <https://godbolt.org/g/UCZ3qo> . All of
my attempts to grep for `LLVMInitializeInstCombine` in my build directory are
leaving me with unmangled symbols, though I can't say the same for
`LLVMInitializeAggressiveInstCombiner`.

 

r336736 is an attempt to fix `LLVMInitializeAggressiveInstCombiner`. If I missed
something, please let me know. (and if you're still seeing a problem with
`LLVMInitializeInstCombine`, more details about your setup/etc. would be
appreciated.) :)

 

Thanks,

George

 

On Tue, Jul 10, 2018 at 7:23 AM Vladimir Vissoultchev via llvm-dev <llvm-dev
at lists.llvm.org <mailto:llvm-dev at lists.llvm.org> > wrote:

Hi all,

 

I just found out that there is an extern "C" missing on the
LLVMInitializeInstCombine function definition somewhere around this line:

 

https://github.com/llvm-mirror/llvm/blob/master/lib/Transforms/InstCombine/InstructionCombining.cpp#L3365

 

As a result the function name gets mangled in the .lib file and is not
accessible from LLVM C API.

 

cheers,

</wqw>

_______________________________________________
LLVM Developers mailing list
llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org> 
http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev

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