[all-commits] [llvm/llvm-project] 729530: -fmodules-codegen should not emit extern templates

[Luboš Luňák via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: 729530f68fe135ad41d470fbed019cc5e31ac8a5
      https://github.com/llvm/llvm-project/commit/729530f68fe135ad41d470fbed019cc5e31ac8a5
  Author: Luboš Luňák <l.lunak at centrum.cz>
  Date:   2020-01-14 (Tue, 14 Jan 2020)

  Changed paths:
    M clang/lib/Serialization/ASTWriterDecl.cpp
    A clang/test/Modules/codegen-extern-template.cpp
    A clang/test/Modules/codegen-extern-template.h
    A clang/test/Modules/codegen-extern-template.modulemap

  Log Message:
  -----------
  -fmodules-codegen should not emit extern templates

If a header contains 'extern template', then the template should be provided
somewhere by an explicit instantiation, so it is not necessary to generate
a copy. Worse, this can lead to an unresolved symbol, because the codegen's
object file will not actually contain functions from such a template
because of the GVA_AvailableExternally, but the object file for the explicit
instantiation will not contain them either because it will be blocked
by the information provided by the module.

Differential Revision: https://reviews.llvm.org/D69779