[llvm-dev] distinct DISubprograms hindering sharing inlined subprogram descriptions

[Reid Kleckner via llvm-dev]

Sorry for derailing into your aside, but...

On Fri, Oct 15, 2021 at 12:07 PM David Blaikie <dblaikie at gmail.com> wrote:

> (side note: Anyone interested in making ThinLTO home type definitions?
> That'd be great to reduce type duplication - would mean ThinLTO could turn
> off type units and/or that .o/.dwo/etc files would just generally be
> smaller anyway)
>

Hey, I think that is a great idea! ThinLTO tends to be used in release
build configurations, which tend to have debug info enabled. The size of
symbols in release build config matters a lot because it is typically
archived for a long time.

COFF & MachO platforms have other ways to deduplicate types (PDBs &
dsymutil), but less duplicate stuff always makes things faster.

For ELF users already using type units, this optimization will only allow
us to recover the overhead of type units, which I recall is significant. In
our evaluation of the feature for Chrome, we found it increased the final
binary size significantly: crbug.com/1031936#c4
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