[PATCH] Fix name lookup within modules during template instantiation

[Richard Smith]

Hi doug.gregor,

When we perform dependent name lookup during template instantiation, it's not sufficient to only consider names visible at the point of instantiation, because that may not include names that were visible when the template was defined. More generally, if the instantiation backtrace goes through a module M, then every declaration visible within M should be available to the instantiation. Any of those declarations might be part of the interface that M intended to export to a template that it instantiates.

The fix here has two parts:

1) If we find a non-visible declaration during name lookup during template instantiation, check whether the declaration was visible from the defining module of all entities on the active template instantiation stack. The defining module is not the owning module in all cases: we look at the module in which a template was defined, not the module in which it was first instantiated.
2) Perform pending instantiations at the end of a module, not at the end of the translation unit. This is general goodness, since it significantly cuts down the amount of redundant work that is performed in every TU importing a module, and also implicitly adds the module containing the point of instantiation to the set of modules checked for declarations in a lookup within a template instantiation.

With this change, a simple "Hello world" program now compiles with a modularized libc++ (with only one top-level module, for now -- cross-top-level-module merging of template specializations doesn't work yet).

http://llvm-reviews.chandlerc.com/D1204

Files:
  lib/Basic/Module.cpp
  lib/Sema/SemaType.cpp
  lib/Sema/SemaLookup.cpp
  lib/Sema/Sema.cpp
  test/Modules/Inputs/cxx-templates-common.h
  test/Modules/Inputs/cxx-templates-b.h
  test/Modules/Inputs/cxx-templates-b-impl.h
  test/Modules/Inputs/module.map
  test/Modules/Inputs/cxx-templates-a.h
  test/Modules/cxx-templates.cpp
  include/clang/Basic/Module.h
  include/clang/Sema/Lookup.h
  include/clang/AST/DeclBase.h
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