From the looks of this B::Terse output it doesn't look like any optimisation is performed in this case 
my $very = { nested => { hash => } };
$$very{nested}{hash} = "something" 
   unless exists $$very{nested}{hash};
LISTOP (0x8109128) leave [1]
    OP (0x816c108) enter
    COP (0x81090f0) nextstate
    BINOP (0x8195f40) sassign
        UNOP (0x81090d0) srefgen
            UNOP (0x8195f18) null [141]
                LISTOP (0x8195ef0) anonhash
                    OP (0x8109a48) pushmark
                    SVOP (0x8109f20) const  PV (0x8107d6c) "nested"
                    UNOP (0x8109a68) srefgen
                        UNOP (0x8104058) null [141]
                            LISTOP (0x81872f0) anonhash
                                OP (0x8187318) pushmark
                                SVOP (0x81872d0) const  PV (0x8107d90)
+ "hash"
        OP (0x8180df8) padsv [1]
    COP (0x816c0d0) nextstate
    UNOP (0x816c0b0) null
        LOGOP (0x816c088) or
            UNOP (0x816c068) exists
                UNOP (0x8109968) null [135]
                    UNOP (0x8109948) rv2hv [3]
                        BINOP (0x8109900) helem
                            UNOP (0x81098c0) rv2hv
                                OP (0x81098a0) padsv [1]
                            SVOP (0x81098e0) const  PV (0x8107dc0) "ne
+sted"
                    SVOP (0x8109928) const  PV (0x8107dd8) "hash"
            BINOP (0x8109878) sassign
                SVOP (0x8109858) const  PV (0x8107de4) "something"
                BINOP (0x8187c38) helem
                    UNOP (0x8187c18) rv2hv [2]
                        BINOP (0x8187bd0) helem
                            UNOP (0x8187b90) rv2hv
                                OP (0x8187b70) padsv [1]
                            SVOP (0x8187bb0) const  PV (0x8107d84) "ne
+sted"
                    SVOP (0x8187bf8) const  PV (0x8107d78) "hash"
- syntax OK

[download]

HTH

_________
broquaint

In reply to Re: Are common access expressions optimized? by broquaint
in thread Are common access expressions optimized? by John M. Dlugosz

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