simpler: 
$ perl -E '$x = "foo"; say for $x x= 2'

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that compiles to (only relevant part): 
BINOP (0x189a938) repeat [1] 
    UNOP (0x189a9c0) null [15] 
         SVOP (0x189aa00) gvsv  GV (0x197dac8) *x 
    SVOP (0x189a980) const  IV (0x197dae0) 2

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while 
$ perl -E '$x = "foo"; say for ($x) x= 2'

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is actually 
BINOP (0xecd938) repeat [1] 
    UNOP (0xecd8f0) null [158] 
        OP (0xecd8b8) pushmark 
        UNOP (0xecd9c0) null [15] 
            SVOP (0xecda00) gvsv  GV (0xfb0ac8) *x 
    SVOP (0xecd980) const  IV (0xfb0ae0) 2

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and 
$ perl -E '@x = (@_ = qw( a b )) x= 2'

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is 
BINOP (0x14b79b8) repeat [4] 
    UNOP (0x14b7970) null [158] 
        OP (0x14b7938) pushmark 
        BINOP (0x14b7a40) aassign [3] 
            UNOP (0x14b7b40) null [158] 
                OP (0x14b7b08) pushmark 
                SVOP (0x13ffc38) const  PV (0x159ab28) "a" 
                SVOP (0x13ffbe0) const  PV (0x159ab70) "b" 
            UNOP (0x14b7ac0) null [158] 
                OP (0x14b7a88) pushmark 
                UNOP (0x13ffc78) rv2av [2] 
                    SVOP (0x13ffcb8) gv  GV (0x13de0d0) *_ 
    SVOP (0x14b7a00) const  IV (0x159ab58) 2

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So pretty much like GrandFather said. Hopefully that answers your question. I don't think it's documented anywhere; see toke.c and perly.y if you want more details. Certainly this behaviour is subject to change without notice.

In reply to Re: ... for (@_) x= 2; by Anonymous Monk
in thread ... for (@_) x= 2; by rsFalse

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