[llvm-dev] Deleting function IR after codegen

[Quentin Colombet via llvm-dev]

> On Mar 8, 2016, at 11:50 AM, Eric Christopher <echristo at gmail.com> wrote:
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> I could attach a patch, but first i’d really like to know if anyone is fundamentally opposed to this.
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> Not necessarily. I think that any information that isn't being serialized in MI right now for a function could be as well. Definitely something for GlobalISel to keep in mind.

+1.
That’s basically where I would like to go with MachineModule/MachineModulePass.
http://lists.llvm.org/pipermail/llvm-dev/2016-January/094426.html

Cheers,
-Quentin
>  
> I should note, a couple of issues have come up in the prototype.
> - llvm::getDISubprogram was walking the function body to find the subprogram.  This is trivial to fix as functions now have !dbg on them.
> 
> This is definitely worth it, please go ahead and do this.
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> - The AsmPrinter is calling canBeOmittedFromSymbolTable on GlobalValue’s which then walks all their uses.  I think this should be done earlier in codegen as an analysis whose results are available to the AsmPrinter.
> 
> I think this makes sense, but I worry about late added GlobalValues during code gen? How would we cope with that? Example: Let's say we start lowering a target specific construct as an MI pass etc and it constructs a global value, when do we run the analysis to make sure that all such things happen? Late as possible I'd assume. Maybe this isn't an issue, but thought I'd bring it up. At any rate, could you provide a bit more detail here?
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> - BB’s whose addresses are taken, i.e. jump tables, can’t be deleted.  Those functions will just keep their IR around so no changes there.
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> Oh well. Conveniently there aren't a lot of these.
> 
> -eric
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