[llvm-dev] Getting Object Files During LTO

[Quentin Colombet via llvm-dev]

I believe the ordering should be deterministic between two runs, but
not necessarily in the order of the input files.

That said, Steven's answer is probably more interesting to you:
> For both thinLTO and fullLTO, there exists APIs to write object file output before sending it to the linker. Depending on which linker you use, linker might provide you with different options.

2018-08-06 16:52 GMT-07:00 Bill Wendling <isanbard at gmail.com>:
> On Mon, Aug 6, 2018 at 4:30 PM Quentin Colombet <quentin.colombet at gmail.com>
> wrote:
>>
>> Hi Bill,
>>
>>
>> 2018-08-06 16:13 GMT-07:00 Bill Wendling via llvm-dev
>> <llvm-dev at lists.llvm.org>:
>> > Is there a way to get object files from the LTO step before the linker
>> > performs the final link phase? What I'd like to do is given these
>> > bitcode
>> > files:
>> >
>> >   a.lto.o, b.lto.o, c.lto.o
>> >
>> > run LTO on them and get out the object files:
>> >
>> >   a.o, b.o, c.o
>> >
>> > (These .o files hold the code that is sent directly to the final link
>> > phase.)
>> >
>> > If there doesn't currently exist a way, is such a thing possible?
>>
>> I don't think that's possible, because basically the LTO pipeline will
>> put all the input files into one module and we have no way to track
>> back what came from what, nor it made much sense after LTO does
>> inlining and such.
>> That said, for thin-LTO we may still have some of the information around.
>>
>> + Teresa, she should know.
>>
> That's what I feared might be the answer. Another question then, would the
> function ordering be deterministic? I.e., if a.o had functions "foo", "bar",
> and "baz", and b.o had functions "mux", "nux", and bork", would the function
> order before it went off to the final link phase be:
>
>   foo, bar, baz, mux, nux, bork
>
> (This assumes that none of those functions were inlined or otherwise
> deleted.)
>
> -bw