Assert that the VISC launch's streaming value is a defined constant.

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

@@ -943,6 +943,7 @@ bool GenVISC::runOnModule(Module &M) {
         Constant* F = ConstantExpr::getPointerCast(graphFunc, Type::getInt8PtrTy(Ctx));
 
         ConstantInt* Op = cast<ConstantInt>(CI->getArgOperand(0));
+	assert(Op && "VISC launch's streaming argument is a constant value.");
         Value* isStreaming = Op->isZero()? ConstantInt::getFalse(Ctx)
                              : ConstantInt::getTrue(Ctx);