[ThinLTO] Rename COMDATs for COFF when promoting/renaming COMDAT leader

Summary:
COFF requires that COMDAT name match that of the leader. When we promote
and rename an internal leader in ThinLTO due to an import, ensure we
subsequently rename the associated COMDAT. Similar to D31963 which did
this during ThinLTO module splitting.

Fixes PR40414.

Reviewers: pcc, inglorion

Subscribers: mehdi_amini, dexonsmith, dmajor, llvm-commits

Differential Revision: https://reviews.llvm.org/D57395

llvm-svn: 352763

1 files changed, 17 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Utils/FunctionImportUtils.cpp b/llvm/lib/Transforms/Utils/FunctionImportUtils.cpp
index a122b28e52e..84c360a17b5 100644
--- a/llvm/lib/Transforms/Utils/FunctionImportUtils.cpp
+++ b/llvm/lib/Transforms/Utils/FunctionImportUtils.cpp
@@ -248,6 +248,7 @@ void FunctionImportGlobalProcessing::processGlobalForThinLTO(GlobalValue &GV) {
   bool DoPromote = false;
   if (GV.hasLocalLinkage() &&
       ((DoPromote = shouldPromoteLocalToGlobal(&GV)) || isPerformingImport())) {
+    auto Name = GV.getName();
     // Once we change the name or linkage it is difficult to determine
     // again whether we should promote since shouldPromoteLocalToGlobal needs
     // to locate the summary (based on GUID from name and linkage). Therefore,
@@ -256,6 +257,12 @@ void FunctionImportGlobalProcessing::processGlobalForThinLTO(GlobalValue &GV) {
     GV.setLinkage(getLinkage(&GV, DoPromote));
     if (!GV.hasLocalLinkage())
       GV.setVisibility(GlobalValue::HiddenVisibility);
+
+    // If we are renaming a COMDAT leader, ensure that we record the COMDAT
+    // for later renaming as well. This is required for COFF.
+    if (const auto *C = GV.getComdat())
+      if (C->getName() == Name)
+        RenamedComdats.try_emplace(C, M.getOrInsertComdat(GV.getName()));
   } else
     GV.setLinkage(getLinkage(&GV, /* DoPromote */ false));
 
@@ -280,6 +287,16 @@ void FunctionImportGlobalProcessing::processGlobalsForThinLTO() {
     processGlobalForThinLTO(SF);
   for (GlobalAlias &GA : M.aliases())
     processGlobalForThinLTO(GA);
+
+  // Replace any COMDATS that required renaming (because the COMDAT leader was
+  // promoted and renamed).
+  if (!RenamedComdats.empty())
+    for (auto &GO : M.global_objects())
+      if (auto *C = GO.getComdat()) {
+        auto Replacement = RenamedComdats.find(C);
+        if (Replacement != RenamedComdats.end())
+          GO.setComdat(Replacement->second);
+      }
 }
 
 bool FunctionImportGlobalProcessing::run() {