[PATCH] Substantial RuntimeDyldMachO cleanup.

[Lang Hames]

Hi Philip,

Thanks for taking a look!

Answering point-by-point:

(1) These functions don't have to be defined in the headers, but that's
probably where we want them. Part of the intent of the CRTP pattern is
these definitions should be inlined into the parent class
(RuntimeDyldCRTPBase), so they need to be present when the instantiations
of the parent class are used (in RuntimeDyldMachO.cpp). That means either
putting the code for all MachO targets in to RuntimeDyldMachO.cpp, or
having one header per target. I think the latter is cleaner.

(2) Yes for now, but my plan is to start removing some of the dynamism from
the RuntimeDyldImpl class tree in the future. That work was omitted from
this patch as it was already getting large, and I wanted to clear the
general direction with the community first.

(3) I can remove the DEBUG_TYPE defines from the target-specific files if I
push the include order around in RuntimeDyldMachO.h:

>From what we have now (with the DEBUG_TYPE defined in the headers):

#include ...
#include "MachOTargets/..."
#include "MachOTargets/..."
#include ...

To:

#include ...
#include ...
// End of non-target includes.

#define DEBUG_TYPE "dyld"
#include "MachOTargets/..."
#include "MachOTargets/..."
// End target includes.

The effect is the same either way: We can use the DEBUG macro from the
target specific headers. I think I actually prefer the latter, and I'd be
happy to switch to it. Neither is canonical, but that's down to the
weirdness of the CRTP.

Cheers,
Lang.



On Fri, Jun 20, 2014 at 4:36 PM, Philip Reames <listmail at philipreames.com>
wrote:

>  The overall direction seems quite reasonable.
>
> I haven't looked at the patch in any detail under the assumption you're
> mostly just moving code around.   A couple small comments:
> - Do all these functions need to be defined in headers?
> - Do the functions on RuntimeDyldMach0 need to be marked virtual or
> override?
> - Can we move the DEBUG_TYPE macros out of the headers and into source
> files?
>
> Philip
>
>
>
>
> On 06/20/2014 01:36 PM, Lang Hames wrote:
>
> Ping?
>
>  I know Andy is out on vacation, but do any other MCJIT people have any
> thoughts on this?
>
>  Cheers,
> Lang.
>
>
>
> On Thu, Jun 12, 2014 at 1:34 PM, Lang Hames <lhames at gmail.com> wrote:
>
>> Hi All,
>>
>>  Attached is a patch that I think substantially cleans up
>> RuntimeDyldMachO and, if the general direction is agreed with, could be
>> used as a template for cleaning up RuntimeDyldELF.
>>
>>  At the moment all MCJIT relocation handling logic for MachO is
>> contained in the RuntimeDyldMachO class (see
>> lib/ExecutionEngine/RuntimeDyld/RuntimeDyldMachO.{h,cpp}). Mixing the logic
>> for all different MachO targets in a single class creates two problems:
>> (1) Poor readability/maintainability: Any change to the relocation logic
>> for a particular target has to be inspected carefully to make sure it won't
>> alter the behavior for any other target. Some of my recent patches for X86
>> have exacerbated this problem, so I'm very happy to be able to offer this
>> patch as penance.
>> (2) Poor performance: we're querying the target architecture in multiple
>> places for every relocation, despite it being a known quantity as soon as
>> we load an object file.
>>
>>  To fix these issues, this patch splits RuntimeDyldMachO's functionality
>> across the following class hierarchy:
>>
>>  RuntimeDyldMachO
>> Implemented in RuntimeDyldMachO.{h,cpp}
>> Contains logic that is completely independent of the target. This
>> consists mostly of MachO helper utilities which the derived classes use to
>> get their work done.
>>
>>  template <typename Impl>
>> RuntimeDyldMachOCRTPBase<Impl> : public RuntimeDyldMachO
>>  Implemented in RuntimeDyldMachO.h
>> Contains generic MachO algorithms/data structures that defer to the Impl
>> class for target-specific behaviors. For the curious, and as the name
>> suggests, this acts as the base of a CRTP[1] instance.
>>
>>  RuntimeDyldMachOARM : public
>> RuntimeDyldMachOCRTPBase<RuntimeDyldMachOARM>
>> RuntimeDyldMachOARM64 : public
>> RuntimeDyldMachOCRTPBase<RuntimeDyldMachOARM64>
>> RuntimeDyldMachOI386 : public
>> RuntimeDyldMachOCRTPBase<RuntimeDyldMachOI386>
>> RuntimeDyldMachOX86_64 : public
>> RuntimeDyldMachOCRTPBase<RuntimeDyldMachOX86_64>
>> Implemented in their respective *.h files in
>> lib/ExecutionEngine/RuntimeDyld/MachOTargets
>> Each of these contains the relocation logic specific to their target
>> architecture.
>>
>>  These target specific classes keep the target specific craziness
>> mercifully well contained, compared to what we have today. Each target can
>> be modified independently, without concern for breaking other targets. The
>> 'switch (Arch) ...' anti-pattern is gone, presumably with a small
>> performance benefit. There's still lots of work to do, but I think this is
>> a solid first step.
>>
>>  Please let me know what you think.
>>
>>  Cheers,
>> Lang.
>>
>>
>>  [1] http://en.wikipedia.org/wiki/Curiously_recurring_template_pattern
>>
>
>
>
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