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

[Maxim Kokryashkin]

Hi!
Thanks for the fixes!
LGTM
--
Best regards,
Maxim Kokryashkin
 
 
> 
>>Hi, Maxim!
>>Thanks for the review!
>>Fixed your comments on the branch!
>>
>>On 16.06.23, Maxim Kokryashkin wrote:
>>>
>>> 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/
>>
>>Fixed.
>>
>>> >>non-vararg parameters as dead slots due to early return for BC_RET
>>> >Typo: s/due to/due to the/
>>
>>Fixed.
>>
>>> >Also, it’d be nice to mention the exact spot where the early return
>>> >is use-def analysis happens.
>>
>>Added.
>>
>>> >>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/
>>
>>Fixed.
>>
>>> >>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`?
>>
>>Added the comment.
>>
>>> >>+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?
>>
>>Unfortunately no, because we want to record not wrap function (at the
>>second test), but the one is pcall-ed.
>>Added the comment.
>>
>>> >>+
>>> >>+-- 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
>>> > 
>>
>>--
>>Best regards,
>>Sergey Kaplun
> 
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