Re: [Tarantool-patches] [PATCH luajit 2/2] Fix use-def analysis for vararg functions.

[Maxim Kokryashkin via Tarantool-patches <tarantool-patches@dev.tarantool.org>]

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Hi, Sergey!
Thanks for the patch!
Please consider my comments below.
 
> 
>>From: Mike Pall <mike>
>>
>>Reported by Shmuel Zeigerman.
>>
>>(cherry-picked from commit 0e53a314d7910898e1ea5ba90385d43e8a6c5e57)
>>
>>Use-def analysis for BC_FUNCV may consider slots greater than amount of
>Typo: s/than/than the/
>>non-vararg parameters as dead slots due to early return for BC_RET
>Typo: s/due to/due to the/
>Also, it’d be nice to mention the exact spot where the early return
>is use-def analysis happens.
>>emitted before usage of BC_VARG. This patch restricts the maxslot to be
>>analyzed in such case with amount of parameters for the prototype of the
>Typo: s/with/with the/
>>current function being recorded.
>>
>>Sergey Kaplun:
>>* added the description and the test for the problem
>>
>>Part of tarantool/tarantool#8516
>>Relates to tarantool/tarantool#8718
>>---
>> src/lj_snap.c | 6 +++--
>> .../lj-704-bc-varg-use-def.test.lua | 27 ++++++++++++++++++-
>> 2 files changed, 30 insertions(+), 3 deletions(-)
>>
>>diff --git a/src/lj_snap.c b/src/lj_snap.c
>>index 5bbe8498..a063c316 100644
>>--- a/src/lj_snap.c
>>+++ b/src/lj_snap.c
>>@@ -301,8 +301,10 @@ static BCReg snap_usedef(jit_State *J, uint8_t *udf,
>> void lj_snap_purge(jit_State *J)
>> {
>>   uint8_t udf[SNAP_USEDEF_SLOTS];
>>- BCReg maxslot = J->maxslot;
>>- BCReg s = snap_usedef(J, udf, J->pc, maxslot);
>>+ BCReg s, maxslot = J->maxslot;
>>+ if (bc_op(*J->pc) == BC_FUNCV && maxslot > J->pt->numparams)
>>+ maxslot = J->pt->numparams;
>>+ s = snap_usedef(J, udf, J->pc, maxslot);
>>   for (; s < maxslot; s++)
>>     if (udf[s] != 0)
>>       J->base[s] = 0; /* Purge dead slots. */
>>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..38606686 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
>>@@ -6,7 +6,7 @@ local test = tap.test('lj-704-bc-varg-use-def'):skipcond({
>>   ['Test requires JIT enabled'] = not jit.status(),
>> })
>> 
>>-test:plan(1)
>>+test:plan(2)
>> 
>> -- XXX: we don't really need to store this builtins, but this is
>> -- reduces `jitdump()` output for reader significantly.
>>@@ -62,4 +62,29 @@ wrap(ON_TRACE_VALUE)
>> 
>> test:ok(result ~= 0, 'use-def analysis for BC_VARG')
>> 
>>+-- Now check the same case, but with BC_RET before the BC_VARG,
>>+-- so use-def analysis will take early return case.
>Same as in the commit message, please mention the exact spot.
>>+-- See `snap_usedef()` in <src/lj_snap.c> for details.
>>+-- The test checks that slots greater than `numparams` are not
>>+-- purged.
>>+local function varg_ret_bc(...)
>>+ -- XXX: This branch contains BC_RET. See the comment above.
>>+ -- luacheck: ignore
>>+ if false then else end
>>+ local slot = ({...})[1]
>>+ return fmod(ARG_ON_RECORDING, slot)
>Is there any reason why it has to be `fmod`?
>>+end
>>+
>>+local function wrap_ret_bc(arg)
>>+ _, result = pcall(varg_ret_bc, arg)
>>+end
>Is it possible to adapt the `wrap` function from the test
>for the previous patch, so it can be used for both tests?
>>+
>>+-- Record trace with the 0 result.
>>+wrap_ret_bc(ARG_ON_RECORDING)
>>+wrap_ret_bc(ARG_ON_RECORDING)
>>+-- Record trace with the non-zero result.
>>+wrap_ret_bc(ON_TRACE_VALUE)
>>+
>>+test:ok(result ~= 0, 'use-def analysis for FUNCV with return before BC_VARG')
>>+
>> os.exit(test:check() and 0 or 1)
>>--
>>2.34.1
>--
>Best regards,
>Maxim Kokryashkin
> 

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