af784a5c13
https://github.com/llvm/llvm-project/pull/95482 is a reland of https://github.com/llvm/llvm-project/pull/88024. https://github.com/llvm/llvm-project/pull/95482 keeps indexing memory usage reasonable by using unordered_map and doesn't make other changes to originally reviewed code. While discussing possible ways to minimize indexing memory usage, Teresa asked whether I need `ExportSetTy` as a map or a set is sufficient. This PR implements the idea. It uses a set rather than a map to track exposed ValueInfos. Currently, `ExportLists` has two use cases, and neither needs to track a ValueInfo's import/export status. So using a set is sufficient and correct. 1) In both in-process and distributed ThinLTO, it's used to decide if a function or global variable is visible [1] from another module after importing creates additional cross-module references. * If a cross-module call edge is seen today, the callee must be visible to another module without keeping track of its export status already. For instance, this [2] is how callees of direct calls get exported. 2) For in-process ThinLTO [3], it's used to compute lto cache key. * The cache key computation already hashes [4] 'ImportList' , and 'ExportList' is determined by 'ImportList'. So it's fine to not track 'import type' for export list. [1]66cd8ec4c0/llvm/lib/LTO/LTO.cpp (L1815-L1819)[2]66cd8ec4c0/llvm/lib/LTO/LTO.cpp (L1783-L1794)[3]66cd8ec4c0/llvm/lib/LTO/LTO.cpp (L1494-L1496)[4]b76100e220/llvm/lib/LTO/LTO.cpp (L194-L222)