[Tarantool-patches] [PATCH luajit v1] Fix BC_UCLO insertion for returns.

[Sergey Bronnikov]

Hi, Max!


Thanks for review! Added more comments to the test and commit message.

New changes force-pushed to the branch. Please take a look.


S.

On 6/7/23 14:35, Maxim Kokryashkin wrote:
> Hi, Sergey and Sergey!
>
>         Hi, Sergey!
>         Thanks for the patch!
>         Please, consider my comments below.
>
>         On 30.05.23, Sergey Bronnikov wrote:
>         > From: Sergey Bronnikov <sergeyb at tarantool.org
>         </compose?To=sergeyb at tarantool.org>>
>         >
>         > Contributed by XmiliaH.
>         >
>         > (cherry-picked from commit
>         93a65d3cc263aef2d2feb3d7ff2206aca3bee17e)
>         >
>         > After emitting bytecode instruction BC_FNEW fixup is not
>         required,
>
>     Typo: s/bytecode/the bytecode
>
Fixed, thanks!


>         > because FuncState will set a flag PROTO_CHILD that will
>         trigger emitting
>         > a pair of instructions BC_UCLO and BC_RET (see
>         <src/lj_parse.c:2355>)
>         > and BC_RET will close all upvalues from base equal to 0.
>
>         This part describes why replacing UCLO with FNEW is good
>         enough and
>         better than just deleting
>         | case BC_UCLO: return;
>         But the original problem is that some of BC_RET are not
>         fixup-ed, due to
>         early return, if UCLO is obtained before, those leads to VM
>         inconsistency after return from the function. Please, mention
>         this too.
>
>     Agree here, it is hard to get what the patch is about from that
>     description,
>     without diving into the changes.
>
Added more details.


<snipped>
>
>         Also, before the patch I got the following assertion in JIT:
>
>         | LUA_PATH="src/?.lua;;" src/luajit -Ohotloop=1 -e '
>         |
>         | local function missing_uclo()
>         | while true do -- luacheck: ignore
>         | local f
>         | if false then break end
>         | while true do
>         | if f then
>         | return f
>         | end
>         | f = function()
>         | return f
>         | end
>         | end
>         | end
>         | end
>         | f = missing_uclo()
>         | print(f())
>         | f = missing_uclo()
>         | print(f())
>         | '
>         | 3.1002202036551
>         | luajit:
>         /home/burii/reviews/luajit/lj-819-missing-uclo/src/lj_record.c:135:
>         rec_check_slots: Assertion `((((((tr))>>24) & IRT_TYPE) -
>         (TRef)(IRT_NUM) <= (TRef)
>         | (IRT_INT-IRT_NUM)))' failed.
>         | Aborted
>
>         I don't sure that we should test this particular failure too,
>         since the
>         origin of the problem is the incorrect emitted bytecode.
>
>         Thoughts?
>
>     We should not, because it is most likely caused by the issue
>     that was fixed in the LuaJIT/LuaJIT at 5c46f477.
>

assert in rec_check_slots could be for many reasons, so I added a 
testcase for compiler too.


>
>         > --
>         > 2.34.1
>         >
>
>         --
>         Best regards,
>         Sergey Kaplun
>
>     --
>     Best regards,
>     Maxim Kokryashkin
>
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