[llvm-dev] DWARF Fission + ThinLTO

[Teresa Johnson via llvm-dev]

On Thu, May 4, 2017 at 7:22 AM, Rafael Avila de Espindola via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> David Blaikie via llvm-dev <llvm-dev at lists.llvm.org> writes:
>
> > So Dehao and I have been dealing with some of the nitty gritty details of
> > debug info with ThinLTO, specifically with Fission(Split DWARF).
> >
> > This applies to LTO as well, so I won't single out ThinLTO here.
>
> When are the .dwo files produced? If at link time, what is the advantage
> of using fission? Normally the advantage is the faster link, but if it
> is the linker producing them, what is left?
>

For ThinLTO they are produced by the backends, and only the split .o part
needs to be linked. I think that benefit would occur with in-process
ThinLTO as well (the .o files handed back to the linker are smaller), but
for us where we have a distributed ThinLTO build, the backends are
producing split .o and .dwo files and so the final native link process gets
all the normal advantages of fission.

For regular LTO, I suppose the same benefit could occur - the backend
produces a split .o and .dwo file and only passes the split .o file to the
link.

Teresa


> Cheers,
> Rafael
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-- 
Teresa Johnson |  Software Engineer |  tejohnson at google.com |  408-460-2413
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