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

[Teresa Johnson via llvm-dev]

On Wed, Apr 20, 2016 at 12:28 PM, Rafael Espíndola <
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 |  408-460-2413
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