Looking at the definition of ENTER and LEAVE I see:

#define ENTER push_scope()
#define LEAVE pop_scope()
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And SAVETMPS and FREETMPS are:

#define SAVETMPS save_int((int*)&PL_tmps_floor), PL_tmps_floor = PL_tm
+ps_ix
#define FREETMPS if (PL_tmps_ix > PL_tmps_floor) free_tmps()
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So ENTER/LEAVE is responsible for managing the scope stack (growing it, adjusting pointers) and SAVETMPS/FREETMPS just handles the temp stack, and calls free_tmps() if needed.

I imagine that leaves you with more questions than you came in with, but I'll have to leave it at that. No time to dig further now...

-sam