[Tarantool-patches] [PATCH] Mark CONV as non-weak, to prevent elimination of its side-effect.
Maksim Kokryashkin
max.kokryashkin at gmail.com
Wed Jul 12 12:52:10 MSK 2023
From: Mike Pall <mike>
An unused guarded CONV int.num cannot be omitted in general.
(cherry-picked from commit 881d02d3117838acaf4fb844332c8e33cc95c8c5)
In some cases, an unused `CONV` omission may lead to a guard
absence, resulting in invalid control flow branching and
undefined behavior. For a comprehensive example of
the described situation, please refer to the comment
in `test/tarantool-tests/mark-conv-non-weak.test.lua`.
Maxim Kokryashkin:
* added the description and the test for the problem
Part of tarantool/tarantool#8825
---
src/lj_ir.h | 2 +-
.../mark-conv-non-weak.test.lua | 58 +++++++++++++++++++
2 files changed, 59 insertions(+), 1 deletion(-)
create mode 100644 test/tarantool-tests/mark-conv-non-weak.test.lua
diff --git a/src/lj_ir.h b/src/lj_ir.h
index e8bca275..bf9b9292 100644
--- a/src/lj_ir.h
+++ b/src/lj_ir.h
@@ -132,7 +132,7 @@
_(XBAR, S , ___, ___) \
\
/* Type conversions. */ \
- _(CONV, NW, ref, lit) \
+ _(CONV, N , ref, lit) \
_(TOBIT, N , ref, ref) \
_(TOSTR, N , ref, lit) \
_(STRTO, N , ref, ___) \
diff --git a/test/tarantool-tests/mark-conv-non-weak.test.lua b/test/tarantool-tests/mark-conv-non-weak.test.lua
new file mode 100644
index 00000000..aad39058
--- /dev/null
+++ b/test/tarantool-tests/mark-conv-non-weak.test.lua
@@ -0,0 +1,58 @@
+local tap = require('tap')
+local test = tap.test('mark-conv-non-weak'):skipcond({
+ ['Test requires JIT enabled'] = not jit.status(),
+})
+
+test:plan(1)
+
+local data = {0.1, 0, 0.1, 0, 0 / 0}
+local sum = 0
+
+jit.opt.start('hotloop=1', 'hotexit=1')
+
+-- When the last trace is recorded, the traced bytecode
+-- is the following before the patch:
+-- ---- TRACE 4 start 2/3 test.lua:6
+-- 0018 ADDVV 1 1 6
+-- 0019 ITERC 5 3 3
+-- 0000 . FUNCC ; ipairs_aux
+-- 0020 JITERL 5 1
+-- 0021 GGET 2 7 ; "assert"
+-- 0022 ISEQV 1 1
+-- 0023 JMP 4 => 0026
+-- 0024 KPRI 4 1
+-- 0025 JMP 5 => 0027
+-- 0027 CALL 2 1 2
+-- 0000 . FUNCC ; assert
+--
+-- And the following after the patch:
+-- ---- TRACE 4 start 2/2 test.lua:5
+-- 0016 ISNEV 6 6
+-- 0017 JMP 7 => 0019
+-- 0019 ITERC 5 3 3
+-- 0000 . FUNCC ; ipairs_aux
+-- 0020 JITERL 5 1
+-- 0021 GGET 2 7 ; "assert"
+-- 0022 ISEQV 1 1
+-- 0023 JMP 4 => 0026
+-- 0026 KPRI 4 2
+-- 0027 CALL 2 1 2
+-- 0000 . FUNCC ; assert
+-- 0028 RET0 0 1
+--
+-- The crucial difference here is the abscent
+-- `ISNEV` in the first case, which produces the
+-- desired guarded `CONV`, when translated to IR.
+--
+-- Since there is no guard, NaN is added to the sum,
+-- despite the test case logic.
+
+for _, val in ipairs(data) do
+ if val == val then
+ sum = sum + val
+ end
+end
+
+test:ok(sum == sum, 'NaN check was not omitted')
+
+os.exit(test:check() and 0 or 1)
--
2.39.2 (Apple Git-143)
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