[llvm-dev] Lazily Loaded Modules and Linker::LinkOnlyNeeded

[Neil Henning via llvm-dev]

Hey all,

For LinkModules, /*dest*/ is a fully materialized module, /*src*/ is a 
lazily loaded module.

 From what I understood, getLinkedToGlobal() is finding the function in 
/*src*/ that matches some function declaration in /*dest*/, and given 
that /*src*/ is lazily loaded it could be un-materialized.

The functions I need brought in from /*src*//**/ into /*dest*/ are 
always declarations in /*dest*/. The problem is that (for some reason) 
the combination of Linker::LinkOnlyNeeded and a function that is not 
materialized will not copy the function body from /*src*/ into /*dest*/.

Cheers,
-Neil.

On 20/04/16 20:39, Teresa Johnson wrote:
>
>
> On Wed, Apr 20, 2016 at 12:28 PM, Rafael Espíndola 
> <rafael.espindola at gmail.com <mailto:rafael.espindola at gmail.com>> wrote:
>
>
>         I understood from his description that he reversed the
>         destination and source so that destination is the user code.
>         I assumed it was not lazy loaded, but that would explain the
>         question then :)
>
>         Neil: can you clarify? If Teresa is right, why aren't you
>         materializing the destination module entirely?
>
>
>
>     I don't think it has ever been tried to use a lazy destination.
>     Having said that, I don't think isMaterializable should return
>     true for a declaration.
>
>
> Looking at isMaterializable, I'm now a little confused about Neil's 
> case - the materializable bit is set to true only when 
> the MODULE_CODE_FUNCTION indicated that it was !isproto, which means 
> it should have a definition in that module. So I agree with you that 
> isMaterializable shouldn't be returning true when the symbol is only 
> available as a declaration.
>
> Neil - what case are you trying to handle here? If there is a 
> materializable definition in the dest module, wouldn't you want to use 
> that instead of linking one in from the source module?
>
> Teresa
>
>
>
>         Even materializing functions from the source module on the fly
>         isn't supported right now, is it?
>
>     It is.
>
>     Neil, the flag is linked to llvm-link's -only-needed command line
>     option. At least for simple cases it seems to be working. Given
>
>     declare void @g()
>     define void @f() {
>       call void @g()
>       ret void
>     }
>
>     and
>
>     define void @g() {
>       ret void
>     }
>     define void @h() {
>       ret void
>     }
>
>
>     linking with "llvm-link -only-needed test1.bc test2.bc" will bring
>     in g, but not h. Can you write a testcase showing what you were
>     expecting it to do but it is not?
>
>     Cheers,
>     Rafael
>
>
>
>
> -- 
> Teresa Johnson | 	 Software Engineer | 	tejohnson at google.com 
> <mailto:tejohnson at google.com> | 	 408-460-2413
>

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