2 files changed, 75 insertions, 4 deletions

diff --git a/llvm/lib/Transforms/IPO/FunctionImport.cpp b/llvm/lib/Transforms/IPO/FunctionImport.cpp
index 3f0d2624f5d..ec82248d78b 100644
--- a/llvm/lib/Transforms/IPO/FunctionImport.cpp
+++ b/llvm/lib/Transforms/IPO/FunctionImport.cpp
@@ -75,6 +75,69 @@ static std::unique_ptr<Module> loadFile(const std::string &FileName,
 
 namespace {
 
+// Return true if the Summary describes a GlobalValue that can be externally
+// referenced, i.e. it does not need renaming (linkage is not local) or renaming
+// is possible (does not have a section for instance).
+static bool canBeExternallyReferenced(const GlobalValueSummary &Summary) {
+  if (!Summary.needsRenaming())
+    return true;
+
+  if (Summary.hasSection())
+    // Can't rename a global that needs renaming if has a section.
+    return false;
+
+  return true;
+}
+
+// Return true if \p GUID describes a GlobalValue that can be externally
+// referenced, i.e. it does not need renaming (linkage is not local) or
+// renaming is possible (does not have a section for instance).
+static bool canBeExternallyReferenced(const ModuleSummaryIndex &Index,
+                                      GlobalValue::GUID GUID) {
+  auto Summaries = Index.findGlobalValueSummaryList(GUID);
+  if (Summaries == Index.end())
+    return true;
+  if (Summaries->second.size() != 1)
+    // If there are multiple globals with this GUID, then we know it is
+    // not a local symbol, and it is necessarily externally referenced.
+    return true;
+
+  // We don't need to check for the module path, because if it can't be
+  // externally referenced and we call it, it is necessarilly in the same
+  // module
+  return canBeExternallyReferenced(**Summaries->second.begin());
+}
+
+// Return true if the global described by \p Summary can be imported in another
+// module.
+static bool eligibleForImport(const ModuleSummaryIndex &Index,
+                              const GlobalValueSummary &Summary) {
+  if (!canBeExternallyReferenced(Summary))
+    // Can't import a global that needs renaming if has a section for instance.
+    // FIXME: we may be able to import it by copying it without promotion.
+    return false;
+
+  // Check references (and potential calls) in the same module. If the current
+  // value references a global that can't be externally referenced it is not
+  // eligible for import.
+  bool AllRefsCanBeExternallyReferenced =
+      llvm::all_of(Summary.refs(), [&](const ValueInfo &VI) {
+        return canBeExternallyReferenced(Index, VI.getGUID());
+      });
+  if (!AllRefsCanBeExternallyReferenced)
+    return false;
+
+  if (auto *FuncSummary = dyn_cast<FunctionSummary>(&Summary)) {
+    bool AllCallsCanBeExternallyReferenced = llvm::all_of(
+        FuncSummary->calls(), [&](const FunctionSummary::EdgeTy &Edge) {
+          return canBeExternallyReferenced(Index, Edge.first.getGUID());
+        });
+    if (!AllCallsCanBeExternallyReferenced)
+      return false;
+  }
+  return true;
+}
+
 /// Given a list of possible callee implementation for a call site, select one
 /// that fits the \p Threshold.
 ///
@@ -86,7 +149,8 @@ namespace {
 /// - One that has PGO data attached.
 /// - [insert you fancy metric here]
 static const GlobalValueSummary *
-selectCallee(const GlobalValueSummaryList &CalleeSummaryList,
+selectCallee(const ModuleSummaryIndex &Index,
+             const GlobalValueSummaryList &CalleeSummaryList,
              unsigned Threshold) {
   auto It = llvm::find_if(
       CalleeSummaryList,
@@ -111,6 +175,9 @@ selectCallee(const GlobalValueSummaryList &CalleeSummaryList,
         if (Summary->instCount() > Threshold)
           return false;
 
+        if (!eligibleForImport(Index, *Summary))
+          return false;
+
         return true;
       });
   if (It == CalleeSummaryList.end())
@@ -125,10 +192,9 @@ static const GlobalValueSummary *selectCallee(GlobalValue::GUID GUID,
                                               unsigned Threshold,
                                               const ModuleSummaryIndex &Index) {
   auto CalleeSummaryList = Index.findGlobalValueSummaryList(GUID);
-  if (CalleeSummaryList == Index.end()) {
+  if (CalleeSummaryList == Index.end())
     return nullptr; // This function does not have a summary
-  }
-  return selectCallee(CalleeSummaryList->second, Threshold);
+  return selectCallee(Index, CalleeSummaryList->second, Threshold);
 }
 
 /// Mark the global \p GUID as export by module \p ExportModulePath if found in
diff --git a/llvm/lib/Transforms/Utils/FunctionImportUtils.cpp b/llvm/lib/Transforms/Utils/FunctionImportUtils.cpp
index f1d12bce06c..4280e96841e 100644
--- a/llvm/lib/Transforms/Utils/FunctionImportUtils.cpp
+++ b/llvm/lib/Transforms/Utils/FunctionImportUtils.cpp
@@ -64,6 +64,11 @@ bool FunctionImportGlobalProcessing::doPromoteLocalToGlobal(
   if (GVar && GVar->isConstant() && GVar->hasUnnamedAddr())
     return false;
 
+  if (GVar && GVar->hasSection())
+    // Some sections like "__DATA,__cfstring" are "magic" and promotion is not
+    // allowed. Just disable promotion on any GVar with sections right now.
+    return false;
+
   // Eventually we only need to promote functions in the exporting module that
   // are referenced by a potentially exported function (i.e. one that is in the
   // summary index).