[PATCH] D75382: [lld] Initial commit for new Mach-O backend

[Rui Ueyama via Phabricator via llvm-commits]

ruiu added inline comments.


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Comment at: lld/MachO/OutputSegment.cpp:16
+
+std::vector<OutputSegment *> macho::outputSegments;
+
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MaskRay wrote:
> alexshap wrote:
> > @ruiu, @pcc - just curious, would you mind adding some comments regarding the design considerations which motivated this approach (using global variables to store various parts of the object file, storing the state globally etc) ? 
> I started to be heavily involved in lld/ELF since mid 2018. I do not know much about the previous history.
> 
> You find the discussions in D70421 and https://reviews.llvm.org/D70766#1761624 helpful. If we can avoid global variables, that will be nice.
This variable is essentially a singleton, as you need only one list of output segments for each instance of the linker, and in many places you'll need to access it, so I decided to make it a global variable. Other singletons are also represented by global variables. In addition to that, this code is simply written in an old-fashioned way to reflect my taste, which shouldn't be necessarily bad. Actually I'm fairly satisfied with this design as it is pretty straightforward.

An alternative design is to define a "context" object and make that object to have all singletons like this. That design isn't bad too and is perhaps arguably better, but if you do that you'll end up having to add one extra parameter to virtually all functions.

Anyway, this topic tends to become a bikesheddy, so I'd focus on bringing up the mach-o linker while reusing the exact same design as the other ports.


Repository:
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  https://reviews.llvm.org/D75382/new/

https://reviews.llvm.org/D75382