Re: [Tarantool-patches] [PATCH luajit] Prevent compile of __concat with tailcall to fast function.

[Sergey Bronnikov via Tarantool-patches <tarantool-patches@dev.tarantool.org>]

Hi, Max!

Thanks for the patch! LGTM

see my minor comments below

On 10/25/23 14:40, Maksim Kokryashkin wrote:
> From: Mike Pall <mike>
<snipped>
> diff --git a/test/tarantool-tests/lj-690-concat-tail-call.test.lua b/test/tarantool-tests/lj-690-concat-tail-call.test.lua
> new file mode 100644
> index 00000000..20775417
> --- /dev/null
> +++ b/test/tarantool-tests/lj-690-concat-tail-call.test.lua
> @@ -0,0 +1,34 @@
> +local tap = require('tap')
> +local test = tap.test('lj-690-concat-tail-call'):skipcond({
> +  ['Test requires JIT enabled'] = not jit.status(),
> +})
> +
> +test:plan(1)
> +
> +-- XXX: Test execution results in an `unbalanced stack after
> +-- hot instruction` assertion fail, only if the LuaJIT is built
> +-- with assertion support. Otherwise, the behavior is undefined
> +-- (it usually fails with a bus error instead).
> +
> +-- The 'setmetatable' tailcall is delayed, but the non-trivial
> +-- MM_concat continuation is not delayed, and recording fails
> +-- since there is no metatable with a defined concat for one of
> +-- the arguments. During the continuation processing, the stack
> +-- delta is altered and fixed up after the continuation frame
> +-- recording. Since continuation frame recording fails, the
> +-- stack delta is not restored, and the stack becomes unbalanced.
> +
> +local t = {}
> +t.__concat = function ()

excess whitespace after "function"


> +  return setmetatable({}, t)
> +end
> +local a = setmetatable({}, t)
> +
> +jit.opt.start('hotloop=1')
> +for _ = 1, 4 do
> +  -- XXX: Extra concat is needed for a non-trivial continuation.
> +  local _ =  '' .. '' .. a
> +end
> +
> +test:ok(true, 'stack is balanced')
> +test:done(true)
> --
> 2.39.3 (Apple Git-145)
>