[ThinLTO] Remove functions resolved to available_externally from comdats

Summary:
thinLTOResolveWeakForLinkerModule needs to drop any preempted weak symbols
that were converted to available_externally from comdats, otherwise we
will get a verification failure (since available_externally is a
declaration for the linker, and no declarations can be in a comdat).

Reviewers: mehdi_amini

Subscribers: llvm-commits, mehdi_amini

Differential Revision: https://reviews.llvm.org/D23015

llvm-svn: 278739

1 files changed, 9 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/IPO/FunctionImport.cpp b/llvm/lib/Transforms/IPO/FunctionImport.cpp
index c9d008ebd38..4b429d88215 100644
--- a/llvm/lib/Transforms/IPO/FunctionImport.cpp
+++ b/llvm/lib/Transforms/IPO/FunctionImport.cpp
@@ -493,6 +493,15 @@ void llvm::thinLTOResolveWeakForLinkerModule(
     DEBUG(dbgs() << "ODR fixing up linkage for `" << GV.getName() << "` from "
                  << GV.getLinkage() << " to " << NewLinkage << "\n");
     GV.setLinkage(NewLinkage);
+    // Remove functions converted to available_externally from comdats,
+    // as this is a declaration for the linker, and will be dropped eventually.
+    // It is illegal for comdats to contain declarations.
+    auto *GO = dyn_cast_or_null<GlobalObject>(&GV);
+    if (GO && GO->isDeclarationForLinker() && GO->hasComdat()) {
+      assert(GO->hasAvailableExternallyLinkage() &&
+             "Expected comdat on definition (possibly available external)");
+      GO->setComdat(nullptr);
+    }
   };
 
   // Process functions and global now