[llvm-dev] ThinLTO naming scheme for promoted local functions

[Teresa Johnson via llvm-dev]

On Wed, Apr 6, 2016 at 12:18 PM, Peter Collingbourne <peter at pcc.me.uk>
wrote:

> Hi David,
>
> We've been considering changing the naming scheme for promoted local
> functions in ThinLTO. Currently we just prepend the file name, but that
> isn't really sound for a number of reasons (e.g. you can have the same file
> name in different directories). The alternative we've been thinking about
> is to use the hash of all external names in the module, as that is
> guaranteed to be unique within a linkage unit (otherwise the linker would
> complain).
>
> We currently (intentionally, I believe) use the same naming scheme for
> promoting local functions as we do for PGO,
>

No, we don't use this naming scheme for ThinLTO promotion. It is only used
for computation of the MD5 hash used in the function index (so that when we
want to import a function referenced by indirect call profile info which
uses this MD5 name we can find its summary).

The promotion name is based off a unique module identifier assigned at
Thin-link time (when the combined index is generated and all bitcode files
are seen).

Thanks,
Teresa

so we might need to change both. Do you see any back compat concerns with
> changing the naming scheme? I guess there are various things we can do to
> try to ensure back compat, but I wanted to get an idea of what the
> requirements are.
>
> Thanks,
> --
> --
> Peter
>



-- 
Teresa Johnson |  Software Engineer |  tejohnson at google.com |  408-460-2413
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