Class description
An instruction for inserting a write barrier. This instruction is almost always inserted after a ##set-slot instruction. If the container object is in an older generation than the item inserted, this instruction guarantees that the item will not be garbage collected. It has the following slots:
srcObject to which the writer barrier refers.
slotSlot index of the object.
scaleNo idea.
tagType tag for obj.
temp1First temporary register to clobber.
temp2Second temporary register to clobber.


TUPLE: ##write-barrier < vreg-insn
src slot scale tag temp1 temp2 insn# ;