Missing/wrong build dependencies for inline functions in HotSpot

[Volker Simonis]

I found the problem!

It's related to the use of precompiled headers. We need to use
'-fpch-deps' in order to get the full dependencies, otherwise all the
dependencies from the pch file are omitted.

I'm currently preparing a webrev which fixes  the problem. It would be
nice if somebody could meanwhile open a bug for the problem (e.g.
"Usage of gcc with precompiled headers produces wrong build
dependencies") and provide a bug-id.

Regards,
Volker


On Fri, Jun 8, 2012 at 7:50 PM, Volker Simonis <volker.simonis at gmail.com> wrote:
> Yes, that's really strange. You're right, the dependency file should
> contain ".. the names of all the included files" (gcc -man page).
>
> So it seems to be a bug in gcc and how it handles '-MMD' although I
> couldn't find a bug report for it and I can't believe that nobody else
> has noticed this before. I've tried gcc 4.4.3 and 4.1.2 and they both
> produce a wrong dependency file which only contains the direct
> includes of the processed .cpp file (with "-c -MMD -MP -MF
> ../generated/dependencies/frame.o.d -o frame.o").
>
> If I compile with "-c -MM -MP -MF ../generated/dependencies/frame.o.d
> -o frame.o" the generated dependency file is much bigger and looks ok,
> but of course I get no object file. I also get he same wrong behavior
> for -MD vs -M. The only reason behind -MD and -MMD is that it "..can
> be used to generate a dependency output file as a side-effect of the
> compilation process" (from the GCC man page) - but that doesn't seem
> to work..
>
> Does anybody has an explanation for this behavior?
>
> Regards,
> Volker
>
> On Fri, Jun 8, 2012 at 6:25 PM, Keith McGuigan
> <keith.mcguigan at oracle.com> wrote:
>>
>> I don't understand why gcc doesn't put frame_x86.inline.hpp into the
>> generated/dependencies/frame.o.d file.  Isn't the point of -MMD to calculate
>> the full closer of header files used for listing as a dependency?  Is this a
>> bug in gcc or are we using it wrong?
>>
>> I notice that Sun Studio compiler does put the arch-specific header file in
>> the generated dependency file.  Weird.
>>
>> --
>> - Keith
>>
>>
>> On 6/8/2012 11:58 AM, Volker Simonis wrote:
>>>
>>> Hi,
>>>
>>> I've just stumbled across the problem that changing the implementation
>>> of an inline function in HotSpot does not necessarily rebuild all the
>>> call sites of that function. This is because because of the way how
>>> the build dependencies are handled within the HotSpot. As an example
>>> you may have a look at frame.cpp:
>>>
>>> frame.cpp includes frame.inline.hpp
>>> frame.inline.hpp includes frame_x86.inline.hpp
>>>
>>> However frame.cpp only depends on frame.inline.hpp directly (i.e.
>>> frame.cpp only includes frame.inline.hpp directly and this is where
>>> the dependencies generated by gcc with '-MMD' are computed from).
>>> So if an inline function in frame_x86.inline.hpp will be changed (e.g.
>>> the constructor frame::frame()), frame.cpp will not be recompiled in
>>> an incremental build, although it uses the constructor frame::frame().
>>> This makes incremental builds useless (or dangerous, depending on the
>>> view point) when inline functions are changed.
>>>
>>> I think this is a non-trivial problem which is deeply rooted in the
>>> way how C++ implements inlining and the way how inline functions are
>>> defined in HotSpot (i.e. .hpp, .inline.hpp,  _<cpu>.hpp and
>>> _<cpu>.inline.hpp files). I don't have a solution for it but just
>>> wanted to ask if somebody else already stumbled upon this problem
>>> and/or has solution for it?
>>>
>>> Regards,
>>> Volker