Reland "[ThinLTO] Populate declaration import status except for distributed ThinLTO under a default-off new option" - #95482
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…eSummary::GVFlags - This change doesn't set the bit in the summaries, just make the code changes.
Update this one accordingly
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…97360) #95482 is a reland of #88024. #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] https://github.com/llvm/llvm-project/blob/66cd8ec4c08252ebc73c82e4883a8da247ed146b/llvm/lib/LTO/LTO.cpp#L1815-L1819 [2] https://github.com/llvm/llvm-project/blob/66cd8ec4c08252ebc73c82e4883a8da247ed146b/llvm/lib/LTO/LTO.cpp#L1783-L1794 [3] https://github.com/llvm/llvm-project/blob/66cd8ec4c08252ebc73c82e4883a8da247ed146b/llvm/lib/LTO/LTO.cpp#L1494-L1496 [4] https://github.com/llvm/llvm-project/blob/b76100e220591fab2bf0a4917b216439f7aa4b09/llvm/lib/LTO/LTO.cpp#L194-L222
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#87600 was reverted in order to revert 6262763. Now #95482 is fix forward for 6262763. This patch is a reland for #87600 **Changes on top of original patch** In `llvm/include/llvm/IR/ModuleSummaryIndex.h`, make the type of `GVSummaryPtrSet` an `unordered_set` which is more memory efficient when the number of elements is smaller than 128 [1] **Original commit message** For distributed ThinLTO, the LTO indexing step generates combined summary for each module, and postlink pipeline reads the combined summary which stores the information for link-time optimization. This patch populates the 'import type' of a summary in bitcode, and updates bitcode reader to parse the bit correctly. [1] https://github.com/llvm/llvm-project/blob/393eff4e02e7ab3d234d246a8d6912c8e745e6f9/llvm/lib/Support/SmallPtrSet.cpp#L43
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…ibuted ThinLTO under a default-off new option" (llvm#95482) Make `FunctionsToImportTy` an `unordered_map` rather than `DenseMap`. Credit goes to jvoung@ for the 'DenseMap -> unordered_map' change. This is a reland of llvm#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](llvm#87597 (comment))) would use this bit differently. * For distributed ThinLTO, the `declaration` status is not serialized to bitcode. As discussed, llvm#87600 will do this.
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llvm#87600 was reverted in order to revert llvm@6262763. Now llvm#95482 is fix forward for llvm@6262763. This patch is a reland for llvm#87600 **Changes on top of original patch** In `llvm/include/llvm/IR/ModuleSummaryIndex.h`, make the type of `GVSummaryPtrSet` an `unordered_set` which is more memory efficient when the number of elements is smaller than 128 [1] **Original commit message** For distributed ThinLTO, the LTO indexing step generates combined summary for each module, and postlink pipeline reads the combined summary which stores the information for link-time optimization. This patch populates the 'import type' of a summary in bitcode, and updates bitcode reader to parse the bit correctly. [1] https://github.com/llvm/llvm-project/blob/393eff4e02e7ab3d234d246a8d6912c8e745e6f9/llvm/lib/Support/SmallPtrSet.cpp#L43
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Make
FunctionsToImportTyanunordered_maprather thanDenseMap. Credit goes to jvoung@ for the 'DenseMap -> unordered_map' change. This is a reland of #92718DenseMapallocates space for a large number of key/value pairs and wastes space when the number of elements are small.FunctionsToImportTy.size()is smaller than 4 for multiple binaries with high indexing ram usage.unordered_mapgrows factor is at most 2 in llvm libc for insert operations.With this change,
ComputeCrossModuleImportram increase is smaller than 0.5G on a couple of binaries with high indexing ram usage. A wider range of (pre-release) tests pass.Original commit message
The goal is to populate
declarationimport status if a new flag-import-declarationis on.For in-process ThinLTO, the
declarationstatus is visible to backendfunction-importpass, soFunctionImporter::importFunctionsshould 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 handledeclarationsummaries. Two use cases (better call-graph sort or cross-module auto-init) would use this bit differently.For distributed ThinLTO, the
declarationstatus is not serialized to bitcode. As discussed, [ThinLTO][Bitcode] Generate import type in bitcode #87600 will do this.