Store to null will be changed to unreachable, so all instructions
after a vleff/vlsegff intrinsic call with a null new_vl output pointer
will be deleted and will cause runtime errors. With this patch, if new_vl
output pointer is null, we won't extract and store the new vl.
We will generate IR like the following pseudocode:
if (new_vl_ptr != null) { *new_vl_ptr = new_vl; } // do something.
If new_vl output pointer is known to be null or not null, the code can be
optimized and there is no impact on performance.
I don't think we usually use capital letters in basic block names.