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

[Igor Munkin]

Sergey,

Thanks for the patch! LGTM, considering the fixes made to resolve the
comments left by Max. I also applied the changes we discussed offline.

On 09.06.23, Sergey Kaplun via Tarantool-patches wrote:
> 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
> non-vararg parameters as dead slots due to early return for BC_RET

Side note: mentioned BC_JMP here too.

> 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
> 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(-)
> 

<snipped>

> 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.
> +-- 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)
> +end
> +
> +local function wrap_ret_bc(arg)
> +  _, result = pcall(varg_ret_bc, arg)
> +end
> +
> +-- 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')

Side note: Applied the changes we've discussed. The diff is below:

================================================================================

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 36fa450a..e6a0973b 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
@@ -62,17 +62,17 @@ 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,
+-- Now check the same case, but with BC_JMP before the BC_VARG,
 -- so use-def analysis will take early return case for BCMlit.
 -- 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.
+  -- XXX: This branch contains BC_JMP. See the comment above.
   -- luacheck: ignore
   if false then else end
   local slot = ({...})[1]
-  -- Forcify stitch and usage of vararg slot. Any NIY is OK here.
+  -- Forcify stitch and usage of vararg slot. Any NYI is OK here.
   return fmod(ARG_ON_RECORDING, slot)
 end
 
@@ -88,6 +88,6 @@ 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')
+test:ok(result ~= 0, 'use-def analysis for FUNCV with jump before BC_VARG')
 
 os.exit(test:check() and 0 or 1)

================================================================================

> +
>  os.exit(test:check() and 0 or 1)
> -- 
> 2.34.1
> 

-- 
Best regards,
IM