Re: To-Be-Closed For-In-Loop Variable has Problems with Tailcalls
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- Subject: Re: To-Be-Closed For-In-Loop Variable has Problems with Tailcalls
- From: Andrew Gierth <andrew@...>
- Date: 2021年3月31日 23:17:37 +0100
>>>>> "Xmilia" == Xmilia Hermit <xmilia.hermit@gmail.com> writes:
Xmilia> Hi,
Xmilia> I think I just found a bug regarding to-be-closed variables.
Xmilia> For some reason the forth to-be-closed variable of a for-in
Xmilia> loop has problems to close with a tailcall as can be seen in
Xmilia> the following example.
Yes, this is definitely a bug. I think the problem is that the compiler
is not recognizing that return tail() should not actually be a tail call
(since a toclose variable is in scope) and is compiling it as if it is,
which leaves the stack and its to-close marks in an inconsistent state.
Specifically the test() bytecode is:
function <l2.lua:17,21> (10 instructions at 0x800a32280)
0 params, 7 slots, 2 upvalues, 5 locals, 0 constants, 0 functions
1 [18] GETUPVAL 0 0 ; pairs_with_close
2 [18] CALL 0 1 5 ; 0 in 4 out
3 [18] TFORPREP 0 3 ; to 7
4 [19] GETUPVAL 5 1 ; tail
5 [19] TAILCALL 5 1 0 ; 0 in
6 [19] RETURN 5 0 0 ; all out
7 [18] TFORCALL 0 1
8 [18] TFORLOOP 0 5 ; to 4
9 [20] CLOSE 0
10 [21] RETURN 0 1 0 ; 0 out
This looks like a simple oversight in forlist() in lparser.c, which is
calling markupval on the close variable but not setting bl->insidetbc to
signal that a close var is in scope.
--
Andrew.