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List:       gcc-bugs
Subject:    [Bug c++/104712] -fkeep-inline-functions causing link errors  (debian but not godbolt?)
From:       ajrh at ajrh dot net via Gcc-bugs <gcc-bugs () gcc ! gnu ! org>
Date:       2022-02-28 15:42:52
Message-ID: bug-104712-4-U95oOIW3ZS () http ! gcc ! gnu ! org/bugzilla/
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104712

ajrh at ajrh dot net changed:

           What    |Removed                     |Added
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                 CC|                            |ajrh at ajrh dot net

--- Comment #6 from ajrh at ajrh dot net ---
Created attachment 52525
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=52525&action=edit
mention -ffunction-sections -Wl,-gc-sections in gcov manual

On deeper investigation the original code had lots of unused inlined explicit
template specializations, and a few of these had constants missing the 'inline'
keyword.   So gcc is behaving perfectly.    Apologies for the misleading
testcase.

I understand better now:    --keep-inline-functions is  correctly generating
lots of otherwise dead code,  and of course some of it might not link.   
Though I only wanted to link it in order to run gcov to find and remove all the
dead code, an amusing catch-22.

Am I correct that a good way to fix this sometimes will be to use
-ffunction-sections -Wl,-gc-sections ?    E.g. in the example below:

----

extern int i;

inline int f(const char *x)
{
    return i;
}

int main(int argc, char *argv[])
{
    return !!argc;
}

----

 gcc -o x --coverage x.cpp && {x; gcov x}
File 'x.cpp'
Lines executed:100.00% of 2

gcc -o x --coverage -fkeep-inline-functions x.cpp && {x; gcov x}
x.cpp:(.text._Z1fPKc[_Z1fPKc]+0x1c): undefined reference to `i'

g++ -o x --coverage -fkeep-inline-functions -ffunction-sections
-Wl,-gc-sections x.cpp && {x; gcov x} 
File 'x.cpp'
Lines executed:50.00% of 4

----

If that's right it might be useful to  mention as a hint in the manual.   
Attached a texi patch if so.

Thank you all for the help.=
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