Implement the isSafeToDiscardIfUnused predicate and use it in globalopt and
globaldce. Globaldce was already removing linkonce globals, but globalopt was
not.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@158476 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/IPO/GlobalDCE.cpp b/lib/Transforms/IPO/GlobalDCE.cpp
index 2b427aa..18c1c7b 100644
--- a/lib/Transforms/IPO/GlobalDCE.cpp
+++ b/lib/Transforms/IPO/GlobalDCE.cpp
@@ -65,7 +65,7 @@
   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->hasLocalLinkage() && !I->hasLinkOnceLinkage() &&
+    if (!I->isDiscardableIfUnused() &&
         !I->isDeclaration() && !I->hasAvailableExternallyLinkage())
       GlobalIsNeeded(I);
   }
@@ -75,7 +75,7 @@
     Changed |= RemoveUnusedGlobalValue(*I);
     // Externally visible & appending globals are needed, if they have an
     // initializer.
-    if (!I->hasLocalLinkage() && !I->hasLinkOnceLinkage() &&
+    if (!I->isDiscardableIfUnused() &&
         !I->isDeclaration() && !I->hasAvailableExternallyLinkage())
       GlobalIsNeeded(I);
   }
@@ -84,7 +84,7 @@
        I != E; ++I) {
     Changed |= RemoveUnusedGlobalValue(*I);
     // Externally visible aliases are needed.
-    if (!I->hasLocalLinkage() && !I->hasLinkOnceLinkage())
+    if (!I->isDiscardableIfUnused())
       GlobalIsNeeded(I);
   }