Lower the select instruction when the operands are of vector type.

src/IceInstX8632.cpp

Index: src/IceInstX8632.cpp
diff --git a/src/IceInstX8632.cpp b/src/IceInstX8632.cpp
index f1a68da1da65423e572551f478a50b9ad99c769b..93a872ca2475548c1fe5c31a63a0ba57b3594856 100644
--- a/src/IceInstX8632.cpp
+++ b/src/IceInstX8632.cpp
@@ -458,6 +458,7 @@ template <> const char *InstX8632Sbb::Opcode = "sbb";
 template <> const char *InstX8632Psub::Opcode = "psub";
 template <> const char *InstX8632And::Opcode = "and";
 template <> const char *InstX8632Pand::Opcode = "pand";
+template <> const char *InstX8632Pandn::Opcode = "pandn";
 template <> const char *InstX8632Or::Opcode = "or";
 template <> const char *InstX8632Por::Opcode = "por";
 template <> const char *InstX8632Xor::Opcode = "xor";