It might be interesting to test happens if "calleeAddrs" had just an alias of a function and not the original function (right now both large_indirect_callee and large_indirect_callee_alias are there?), but could be okay to test that later too.

Can you add a documentation for the DecSummaries parameter here too? (similar to the ThinLTOCodeGenerator.h comment, might be useful to indicate it's a subset of ModuleToSummariesForIndex).

nit: maybe indicate "When writing a subset of the index" also?

Not a big issue, but was wondering if the module path is needed or if a set instead of map would work? It seemed like each GlobalValueSummary* would only be imported from one module for declaration. Or is it possible that for a particular GVS_i ? mod_A -> GVS_i mod_B -> GVS_i Otherwise, the map does match the gatherImportedSummariesForModule more closely.