1 files changed, 34 insertions, 7 deletions

diff --git a/lib/Transforms/IPO/GlobalDCE.cpp b/lib/Transforms/IPO/GlobalDCE.cpp
index 57481e1e42..7e7a4c0ae8 100644
--- a/lib/Transforms/IPO/GlobalDCE.cpp
+++ b/lib/Transforms/IPO/GlobalDCE.cpp
@@ -77,13 +77,19 @@ bool GlobalDCE::runOnModule(Module &M) {
   // Remove empty functions from the global ctors list.
   Changed |= optimizeGlobalCtorsList(M, isEmptyFunction);
 
+  typedef std::multimap<const Comdat *, GlobalValue *> ComdatGVPairsTy;
+  ComdatGVPairsTy ComdatGVPairs;
+
   // Loop over the module, adding globals which are obviously necessary.
   for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) {
     Changed |= RemoveUnusedGlobalValue(*I);
     // Functions with external linkage are needed if they have a body
-    if (!I->isDiscardableIfUnused() &&
-        !I->isDeclaration() && !I->hasAvailableExternallyLinkage())
-      GlobalIsNeeded(I);
+    if (!I->isDeclaration() && !I->hasAvailableExternallyLinkage()) {
+      if (!I->isDiscardableIfUnused())
+        GlobalIsNeeded(I);
+      else if (const Comdat *C = I->getComdat())
+        ComdatGVPairs.insert(std::make_pair(C, I));
+    }
   }
 
   for (Module::global_iterator I = M.global_begin(), E = M.global_end();
@@ -91,17 +97,38 @@ bool GlobalDCE::runOnModule(Module &M) {
     Changed |= RemoveUnusedGlobalValue(*I);
     // Externally visible & appending globals are needed, if they have an
     // initializer.
-    if (!I->isDiscardableIfUnused() &&
-        !I->isDeclaration() && !I->hasAvailableExternallyLinkage())
-      GlobalIsNeeded(I);
+    if (!I->isDeclaration() && !I->hasAvailableExternallyLinkage()) {
+      if (!I->isDiscardableIfUnused())
+        GlobalIsNeeded(I);
+      else if (const Comdat *C = I->getComdat())
+        ComdatGVPairs.insert(std::make_pair(C, I));
+    }
   }
 
   for (Module::alias_iterator I = M.alias_begin(), E = M.alias_end();
        I != E; ++I) {
     Changed |= RemoveUnusedGlobalValue(*I);
     // Externally visible aliases are needed.
-    if (!I->isDiscardableIfUnused())
+    if (!I->isDiscardableIfUnused()) {
       GlobalIsNeeded(I);
+    } else if (const Comdat *C = I->getComdat()) {
+      ComdatGVPairs.insert(std::make_pair(C, I));
+    }
+  }
+
+  for (ComdatGVPairsTy::iterator I = ComdatGVPairs.begin(),
+                                 E = ComdatGVPairs.end();
+       I != E;) {
+    ComdatGVPairsTy::iterator UB = ComdatGVPairs.upper_bound(I->first);
+    bool CanDiscard = std::all_of(I, UB, [](ComdatGVPairsTy::value_type Pair) {
+      return Pair.second->isDiscardableIfUnused();
+    });
+    if (!CanDiscard) {
+      std::for_each(I, UB, [this](ComdatGVPairsTy::value_type Pair) {
+        GlobalIsNeeded(Pair.second);
+      });
+    }
+    I = UB;
   }
 
   // Now that all globals which are needed are in the AliveGlobals set, we loop