[PPC] Use alias symbols in address computation.

This seems to match what gcc does for ppc and what every other llvm
backend does.

This is a fixed version of r209638. The difference is to avoid any change
in behavior for functions. The logic for using constant pools for function
addresseses is spread over a few places and we have to keep them in sync.

llvm-svn: 209821
diff --git a/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp b/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
index f6e075d..b8f5957 100644
--- a/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
+++ b/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
@@ -1472,17 +1472,9 @@
 
     if (GlobalAddressSDNode *G = dyn_cast<GlobalAddressSDNode>(GA)) {
       const GlobalValue *GValue = G->getGlobal();
-      const GlobalAlias *GAlias = dyn_cast<GlobalAlias>(GValue);
-      const GlobalValue *RealGValue = GAlias ? GAlias->getAliasee() : GValue;
-      const GlobalVariable *GVar = dyn_cast<GlobalVariable>(RealGValue);
-      assert((GVar || isa<Function>(RealGValue)) &&
-             "Unexpected global value subclass!");
-
-      // An external variable is one without an initializer.  For these,
-      // for variables with common linkage, and for Functions, generate
-      // the LDtocL form.
-      if (!GVar || !GVar->hasInitializer() || RealGValue->hasCommonLinkage() ||
-          RealGValue->hasAvailableExternallyLinkage())
+      if (GValue->getType()->getElementType()->isFunctionTy() ||
+          GValue->isDeclaration() || GValue->hasCommonLinkage() ||
+          GValue->hasAvailableExternallyLinkage())
         return CurDAG->getMachineNode(PPC::LDtocL, dl, MVT::i64, GA,
                                       SDValue(Tmp, 0));
     }