[ThinLTO] Import only necessary DICompileUnit fields

Summary:
As discussed on mailing list, for ThinLTO importing we don't need
to import all the fields of the DICompileUnit. Don't import enums,
macros, retained types lists. Also only import local scoped imported
entities. Since we don't currently import any global variables,
we also don't need to import the list of global variables (added an
assert to verify none are being imported).

This is being done by pre-populating the value map entries to map
the unneeded metadata to nullptr. For the imported entities, we can
simply replace the source module's list with a new list containing
only those needed imported entities. This is done in the IRLinker
constructor so that value mapping automatically does the desired
mapping.

Reviewers: mehdi_amini, dexonsmith, dblaikie, aprantl

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D27635

llvm-svn: 289441

1 files changed, 2 insertions, 1 deletions

diff --git a/llvm/lib/Linker/LinkModules.cpp b/llvm/lib/Linker/LinkModules.cpp
index cf4826f4c02..cf2c4ccf523 100644
--- a/llvm/lib/Linker/LinkModules.cpp
+++ b/llvm/lib/Linker/LinkModules.cpp
@@ -583,7 +583,8 @@ bool ModuleLinker::run() {
                            [this](GlobalValue &GV, IRMover::ValueAdder Add) {
                              addLazyFor(GV, Add);
                            },
-                           !isPerformingImport())) {
+                           /* LinkModuleInlineAsm */ !isPerformingImport(),
+                           /* IsPerformingImport */ isPerformingImport())) {
     handleAllErrors(std::move(E), [&](ErrorInfoBase &EIB) {
       DstM.getContext().diagnose(LinkDiagnosticInfo(DS_Error, EIB.message()));
       HasErrors = true;