+
+# Some comments about 'T' opcode classifier:
+
+# Safe to set if the ppcode uses:
+# tryAMAGICbin, tryAMAGICun, SETn, SETi, SETu, PUSHn, PUSHTARG, SETTARG,
+# SETs(TARG), XPUSHn, XPUSHu,
+
+# Unsafe to set if the ppcode uses dTARG or [X]RETPUSH[YES|NO|UNDEF]
+
+# lt and friends do SETs (including ncmp, but not scmp)
+
+# Additional mode of failure: the opcode can modify TARG before it "used"
+# all the arguments (or may call an external function which does the same).
+# If the target coincides with one of the arguments ==> kaboom.
+
+# pp.c pos substr each not OK (RETPUSHUNDEF)
+# substr vec also not OK due to LV to target (are they???)
+# ref not OK (RETPUSHNO)
+# trans not OK (dTARG; TARG = sv_newmortal();)
+# ucfirst etc not OK: TMP arg processed inplace
+# quotemeta not OK (unsafe when TARG == arg)
+# each repeat not OK too due to list context
+# pack split - unknown whether they are safe
+# sprintf: is calling do_sprintf(TARG,...) which can act on TARG
+# before other args are processed.
+
+# Suspicious wrt "additional mode of failure" (and only it):
+# schop, chop, postinc/dec, bit_and etc, negate, complement.
+
+# Also suspicious: 4-arg substr, sprintf, uc/lc (POK_only), reverse, pack.
+
+# substr/vec: doing TAINT_off()???
+
+# pp_hot.c
+# readline - unknown whether it is safe
+# match subst not OK (dTARG)
+# grepwhile not OK (not always setting)
+# join not OK (unsafe when TARG == arg)
+
+# Suspicious wrt "additional mode of failure": concat (dealt with
+# in ck_sassign()), join (same).
+
+# pp_ctl.c
+# mapwhile flip caller not OK (not always setting)
+
+# pp_sys.c
+# backtick glob warn die not OK (not always setting)
+# warn not OK (RETPUSHYES)
+# open fileno getc sysread syswrite ioctl accept shutdown
+# ftsize(etc) readlink telldir fork alarm getlogin not OK (RETPUSHUNDEF)
+# umask select not OK (XPUSHs(&PL_sv_undef);)
+# fileno getc sysread syswrite tell not OK (meth("FILENO" "GETC"))
+# sselect shm* sem* msg* syscall - unknown whether they are safe
+# gmtime not OK (list context)
+
+# Suspicious wrt "additional mode of failure": warn, die, select.
+