Serializing mixed gimple data from a plugin in LTO?

[Basile Starynkevitch <basile at starynkevitch dot net>]

Hello All,

Let's imagine someone is writing a plugin (or a MELT extension...) which computes some complex information around gimple in a pass before LTO serialization and re-uses that information in a later pass after LTO serialization. A possible way to associate data inside a plugin to some gimples would be to have hash tables (keys being Gimple, associated value being some complex information specific to the plugin). The the plugin would compute & serialize [i.e. write or output] data in a pass before LTO and deserialize [re-read or input] that data at LTO time.

The writing happens in the write_summary and write_optimization_summary hooks of struct ipa_opt_pass_d of file tree-pass.h. The reading happens in read_summary & read_optimization_summary hooks.

But what I cannot understand is how can such a plugin know what are the gimple involved. Since the plugin needs to persist (i.e. serialize into LTO stream & de-serialize) an hash table mapping some gimples to its data, the plugin need to know what gimples are serialized & deserialized, to restore at LTO streaming read the common gimple pointers (the same gimple pointer should appear in the function & the hash table)....

I would imagine gcc/lto-streamer-out.c would have a plugin hook inside output_gimple_stmt but this is not the case...

I admit I don't have a clear picture of LTO streams usage (& customization) from plugins. 
Or perhaps it is not possible yet???

Regards.
-- 
Basile STARYNKEVITCH         http://starynkevitch.net/Basile/
email: basile<at>starynkevitch<dot>net mobile: +33 6 8501 2359
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