[perl #44967] Using a freed variable (Coverity CID 98)

[via RT]

# New Ticket Created by  Paul Cochrane 
# Please include the string:  [perl #44967]
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# <URL: http://rt.perl.org/rt3/Ticket/Display.html?id=44967 >


While having a look through some of the static analysis output
provided by Coverity Prevent I stumbled across this code (in
compilers/imcc/optimizer.c:633):

                            if (found) {
                                prev = ins2->prev;
                                if (prev) {
                                    subst_ins(unit, ins2, tmp, 1);
                                    any = 1;
                                    IMCC_debug(interp, DEBUG_OPT2,
                                            " reduced to %I\n", tmp);
                                    ins2 = prev->next;
                                }
                            }

The variable ins2 is freed by the call to subst_ins() but is then
later assigned to later in the if-block.  Um, this isn't a good idea
is it?  The variable shouldn't be freed in subst_ins() I don't think,
so shouldn't we instead have the line:

                                    subst_ins(unit, ins2, tmp, 0);

(where setting the argument to 0 means *not* freeing the variable).

Is this the right thing to do?  Just wanted to ask the opinion of our
resident gurus before I went and broke something...

Thanks!

Paul