Fix llvm_unreachable being tripped in ExecutionEngine

[bmoody]

Summary

Add handling for GlobalAliases in ExecutionEngine::getConstantValue.

[lhames]

Looks good to me. Do you have commit access? If not I can commit on your behalf.

[bmoody]

I don't have commit access, you're welcome to commit on my behalf. Thanks!

[lhames]

Committed in r333217. Thanks Brad!

lib/ExecutionEngine/ExecutionEngine.cpp

GenericValue ExecutionEngine::getConstantValue(const Constant *C) {
   case Type::FP128TyID:
   case Type::PPC_FP128TyID:
     Result.IntVal = cast <ConstantFP>(C)->getValueAPF().bitcastToAPInt();
     break;
   case Type::IntegerTyID:
     Result.IntVal = cast<ConstantInt>(C)->getValue();
     break;
   case Type::PointerTyID:
+    while (auto *A = dyn_cast<GlobalAlias>(C)) {
+      C = A->getAliasee();
+    }
     if (isa<ConstantPointerNull>(C))
       Result.PointerVal = nullptr;
     else if (const Function *F = dyn_cast<Function>(C))
       Result = PTOGV(getPointerToFunctionOrStub(const_cast<Function*>(F)));
     else if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(C))
       Result = PTOGV(getOrEmitGlobalVariable(const_cast<GlobalVariable*>(GV)));
     else
       llvm_unreachable("Unknown constant pointer type!");

test/ExecutionEngine/Interpreter/alias.ll

+; RUN: %lli -force-interpreter %s
+
+define i32 @func() {
+entry:
+  ret i32 0
+}
+
+@alias = alias i32 (), i32 ()* @func
+
+define i32 @main() {
+entry:
+  %call = call i32 @alias()
+  ret i32 %call
+}