char t = Wrapper.basicTypeChar(c);
mv = cw.visitMethod(NOT_ACC_PUBLIC + ACC_FINAL, "cloneExtend" + t, makeSignature(String.valueOf(t), false), null, E_THROWABLE);
mv.visitCode();
// return SPECIES_DATA.extendWithIndex(extensionIndex(t)).constructor[0].invokeBasic(mt, lf, argL0, ..., narg)
// obtain constructor
mv.visitFieldInsn(GETSTATIC, className, "SPECIES_DATA", SPECIES_DATA_SIG);
int iconstInsn = ICONST_0 + extensionIndex(t);
assert(iconstInsn <= ICONST_5);
mv.visitInsn(iconstInsn);
mv.visitMethodInsn(INVOKEVIRTUAL, SPECIES_DATA, "extendWithIndex", BMHSPECIES_DATA_EWI_SIG);
mv.visitFieldInsn(GETFIELD, SPECIES_DATA, "constructor", "[" + MH_SIG);