>
> > >>+-- reduces `jitdump()` output for reader significantly.
> > >>+local fmod = math.fmod
> > >>+local pcall = pcall
> > >>+
> > >>+-- Use the 2 values for `fmod()` to produce non-zero value for
> > >>+-- the call on trace (the last one call).
> > >>+local ARG_ON_RECORDING = 6
> > >>+local ON_TRACE_VALUE = ARG_ON_RECORDING + 1
> > >Why are they exactly 6 and 7? Please drop a comment.
>
> No special meaning, added a comment.
>
> > >>+
> > >>+-- The `jitdump()` output was like the following before the patch:
> > >>+-- 0003 > num SLOAD #1 T
> > >>+-- .... SNAP #1 [`wrap()`|---- pcall|`varg()`|----]
> > >>+-- 0004 } tab TNEW #3 #0
> > >>+-- 0005 > num SLOAD #4 T
> > >>+-- 0006 p32 FLOAD 0004 tab.array
> > >>+-- 0007 p32 AREF 0006 +1
> > >>+-- 0008 } num ASTORE 0007 0005
> > >>+-- .... SNAP #2 [`wrap()`|---- pcall|math.fmod|+6 0005]
> > >>+--
> > >>+-- The first snapshot misses the 0003 IR in the last slot to be
> > >>+-- used in the `fmod()` later, so it leads to the additional
> > >>+-- 0005 SLOAD #4, and storing it in the second snapshot.
> > >>+--
> > >>+-- The correct snapshot content after the patch is the following:
> > >>+-- .... SNAP #1 [`wrap()`|---- pcall|`varg()`|0003]
> > >>+-- ....
> > >>+-- .... SNAP #2 [`wrap()`|---- pcall|math.fmod|+6 0003]
> > >>+local function varg(...)
> > >>+ -- Generate snapshot after `pcall()` with missing slot.
> > >>+ -- The snapshot is generated before each TNEW after the commit
> > >>+ -- 7505e78bd6c24cac6e93f5163675021734801b65 ("Handle on-trace
> > >>+ -- OOM errors from helper functions.")
> > >>+ local slot = ({...})[1]
> > >>+ -- Forcify stitch and usage of vararg slot.
> > >>+ return fmod(ARG_ON_RECORDING, slot)
> > >Are there any reasons behind the `fmod` choice? If so, please drop a comment.
>
> No, added the comment.
>
> > >>+end
> > >>+
> > >>+jit.opt.start('hotloop=1')
> > >>+
> > >>+local _, result
> > >>+local function wrap(arg)
> > >>+ -- `pcall()` is needed to emit snapshot to handle on-trace
> > >>+ -- errors.
> > >Maybe it is worth mentioning Mike’s original comment[1] here.
> > >Feel free to ignore.
>
> I just added the reference to the issue in the header, the comment above
> is about the same as Mike's but more verbose.
>
> ===================================================================
> diff --git a/test/tarantool-tests/lj-704-bc-varg-use-def.test.lua b/test/tarantool-tests/lj-704-bc-varg-use-def.test.lua
> index c3ba65dd..3608ea4e 100644
> --- a/test/tarantool-tests/lj-704-bc-varg-use-def.test.lua
> +++ b/test/tarantool-tests/lj-704-bc-varg-use-def.test.lua
> @@ -8,13 +8,13 @@ local test = tap.test('lj-704-bc-varg-use-def'):skipcond({
>
> test:plan(1)
>
> --- XXX: we don't really need to store this builtins, but this is
> +-- XXX: we don't really need to store these builtins, but this is
> -- reduces `jitdump()` output for reader significantly.
> local fmod = math.fmod
> local pcall = pcall
>
> -- Use the 2 values for `fmod()` to produce non-zero value for
> --- the call on trace (the last one call).
> +-- the call on trace (the last one call). No special meaning.
> local ARG_ON_RECORDING = 6
> local ON_TRACE_VALUE = ARG_ON_RECORDING + 1
>
> @@ -42,23 +42,23 @@ local function varg(...)
> -- 7505e78bd6c24cac6e93f5163675021734801b65 ("Handle on-trace
> -- OOM errors from helper functions.")
> local slot = ({...})[1]
> - -- Forcify stitch and usage of vararg slot.
> + -- Forcify stitch and usage of vararg slot. Any NIY is OK here.
> return fmod(ARG_ON_RECORDING, slot)
> end
>
> jit.opt.start('hotloop=1')
>
> local _, result
> -local function wrap(arg)
> +local function wrap(func, arg)
> -- `pcall()` is needed to emit snapshot to handle on-trace
> -- errors.
> - _, result = pcall(varg, arg)
> + _, result = pcall(func, arg)
> end
> -- Record trace with the 0 result.
> -wrap(ARG_ON_RECORDING)
> -wrap(ARG_ON_RECORDING)
> +wrap(varg, ARG_ON_RECORDING)
> +wrap(varg, ARG_ON_RECORDING)
> -- Record trace with the non-zero result.
> -wrap(ON_TRACE_VALUE)
> +wrap(varg, ON_TRACE_VALUE)
Brr, acturally, we need to separate two `wrap()` functions - to prevent
compilation for the `wrap()` itself as non pcall-ed fixed-arg function.
Added the comment.
>
> test:ok(result ~= 0, 'use-def analysis for BC_VARG')
> ===================================================================
>
> I also modify `wrap()` function to get the function to call considering
> your comments in the next patch.
>
> > >>+ _, result = pcall(varg, arg)
> > >>+end
> > >>+-- Record trace with the 0 result.
> > >>+wrap(ARG_ON_RECORDING)
> > >>+wrap(ARG_ON_RECORDING)
> > >>+-- Record trace with the non-zero result.
> > >>+wrap(ON_TRACE_VALUE)
> > >>+
> > >>+test:ok(result ~= 0, 'use-def analysis for BC_VARG')
> > >>+
> > >>+os.exit(test:check() and 0 or 1)
> > >>--
> > >>2.34.1
> > >[1]:
https://github.com/LuaJIT/LuaJIT/issues/704> > >--
> > >Best regards,
> > >Maxim Kokryashkin
>
> --
> Best regards,
> Sergey Kaplun
--
Best regards,
Sergey Kaplun