+
+ /* Hmm, this is a bit paradoxical. We know that INSN is a valid insn
+ in MD. But if there is no optab to generate the insn, we can not
+ perform the variable expansion. This can happen if an MD provides
+ an insn but not a named pattern to generate it, for example to avoid
+ producing code that needs additional mode switches like for x87/mmx.
+
+ So we check have_insn_for which looks for an optab for the operation
+ in SRC. If it doesn't exist, we can't perform the expansion even
+ though INSN is valid. */
+ if (!have_insn_for (GET_CODE (src), GET_MODE (src)))
+ return NULL;
+