getBranch :: NInst -> [Int]
getBranch (Source s, size, IF_ICMP _ t) = [addW16Signed s t, s+size]
getBranch (Source s, size, GOTO t) = [addW16Signed s t]
+getBranch (Source s, size, IRETURN ) = [0] --actually wrong
getBranch _ = []
-- a version of Prelude.span whereby the first element