Assert that the VISC launch's function argument is a defined constant.

llvm/tools/hpvm/lib/Transforms/GenVISC/GenVISC.cpp

@@ -941,6 +941,7 @@ bool GenVISC::runOnModule(Module &M) {
         Function* graphFunc = cast<Function>(CI->getArgOperand(1));
         graphFunc = transformReturnTypeToStruct(graphFunc);
         Constant* F = ConstantExpr::getPointerCast(graphFunc, Type::getInt8PtrTy(Ctx));
+	assert(F && "Function invoked by VISC launch has to be define and constant.");
 
         ConstantInt* Op = cast<ConstantInt>(CI->getArgOperand(0));
 	assert(Op && "VISC launch's streaming argument is a constant value.");