[LLVMdev] RFC: ThinLTO Impementation Plan

[Xinliang David Li]

On Thu, May 14, 2015 at 3:19 PM, Duncan P. N. Exon Smith <
dexonsmith at apple.com> wrote:

>
> >> On 2015-May-14, at 14:46, Eric Christopher <echristo at gmail.com> wrote:
> >>
> >> >>
> >> >> But as mentioned, ld -r can work on native object wrapped bitcode
> >> >> without a plugin as well.
> >> >>
> >> >
> >> > How? It's not like any partial linking is going to go on inside the
> bitcode
> >> > if the linker doesn't understand bitcode.
> >>
> >> It allows us to delay the actual linking until the full link step,
> >> thereby enabling ThinLTO on those modules.
> >>
> >> As we discussed offline, the current ld -r behavior with the plugin is
> >> to compile all the way down to machine code. The alternative if we use
> >> straight bitcode is to tell the plugin to stop early after combining
> >> the bitcode and emit bitcode back out, with the thinlto function info
> >> also combined.
> >
> >
> > I think this is what should happen anyhow. ld -r that doesn't do a
> partial link is misleading.
>
> FWIW, in "full" LTO on Darwin, ld64 emits bitcode from `ld -r` as long
> as all inputs are bitcode.
>

That is what need in thinLTO too.

David



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