llvm-project

8d9db947 - Reland "[ThinLTO] Populate declaration import status except for distributed ThinLTO under a default-off new option" (#95482)

Reland "[ThinLTO] Populate declaration import status except for distributed ThinLTO under a default-off new option" (#95482) Make `FunctionsToImportTy` an `unordered_map` rather than `DenseMap`. Credit goes to jvoung@ for the 'DenseMap -> unordered_map' change. This is a reland of https://github.com/llvm/llvm-project/pull/92718 * `DenseMap` allocates space for a large number of key/value pairs and wastes space when the number of elements are small. * While init bucket size is zero [1], it quickly allocates buckets for 64 elements [2] when the number of elements is small (for example, 3 or 4 elements). The programmer manual [3] also mentions it could waste space. * Experiments show `FunctionsToImportTy.size()` is smaller than 4 for multiple binaries with high indexing ram usage. `unordered_map` grows factor is at most 2 in llvm libc [4] for insert operations. With this change, `ComputeCrossModuleImport` ram increase is smaller than 0.5G on a couple of binaries with high indexing ram usage. A wider range of (pre-release) tests pass. [1] https://github.com/llvm/llvm-project/blob/ad79a14c9e5ec4a369eed4adf567c22cc029863f/llvm/include/llvm/ADT/DenseMap.h#L431-L432 [2] https://github.com/llvm/llvm-project/blob/ad79a14c9e5ec4a369eed4adf567c22cc029863f/llvm/include/llvm/ADT/DenseMap.h#L849 [3] https://llvm.org/docs/ProgrammersManual.html#llvm-adt-densemap-h [4] https://github.com/llvm/llvm-project/blob/ad79a14c9e5ec4a369eed4adf567c22cc029863f/libcxx/include/__hash_table#L1525-L1526 **Original commit message** The goal is to populate `declaration` import status if a new flag `-import-declaration` is on. * For in-process ThinLTO, the `declaration` status is visible to backend `function-import` pass, so `FunctionImporter::importFunctions` should read the import status and be no-op for declaration summaries. Basically, the postlink pipeline is updated to keep its current behavior (import definitions), but not updated to handle `declaration` summaries. Two use cases ([better call-graph sort](https://discourse.llvm.org/t/rfc-for-better-call-graph-sort-build-a-more-complete-call-graph-by-adding-more-indirect-call-edges/74029#support-cross-module-function-declaration-import-5) or [cross-module auto-init](https://github.com/llvm/llvm-project/pull/87597#discussion_r1556067195)) would use this bit differently. * For distributed ThinLTO, the `declaration` status is not serialized to bitcode. As discussed, https://github.com/llvm/llvm-project/pull/87600 will do this.