[all-commits] [llvm/llvm-project] 8de789: [ThinLTO] Populate declaration import status excep...

[Mingming Liu via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 8de7890572296830b27b6e6db39b36810bc98c31
      https://github.com/llvm/llvm-project/commit/8de7890572296830b27b6e6db39b36810bc98c31
  Author: Mingming Liu <mingmingl at google.com>
  Date:   2024-05-19 (Sun, 19 May 2024)

  Changed paths:
    M llvm/include/llvm/IR/ModuleSummaryIndex.h
    M llvm/include/llvm/Transforms/IPO/FunctionImport.h
    M llvm/lib/LTO/LTO.cpp
    M llvm/lib/LTO/LTOBackend.cpp
    M llvm/lib/Transforms/IPO/FunctionImport.cpp
    M llvm/test/ThinLTO/X86/funcimport-stats.ll
    A llvm/test/ThinLTO/X86/import_callee_declaration.ll
    M llvm/test/Transforms/FunctionImport/funcimport.ll
    M llvm/tools/llvm-link/llvm-link.cpp

  Log Message:
  -----------
  [ThinLTO] Populate declaration import status except for distributed ThinLTO under a default-off new option (#88024)

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 and cross-module auto-init)
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.

[1] 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
[2] https://github.com/llvm/llvm-project/pull/87597#discussion_r1556067195



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