From: Sergey Kaplun via Tarantool-patches <tarantool-patches@dev.tarantool.org> To: Maxim Kokryashkin <m.kokryashkin@tarantool.org>, Sergey Bronnikov <sergeyb@tarantool.org> Cc: tarantool-patches@dev.tarantool.org Subject: [Tarantool-patches] [PATCH luajit 2/2] FFI: Fix 64 bit shift fold rules. Date: Wed, 2 Oct 2024 11:09:06 +0300 [thread overview] Message-ID: <7531b1a6a3f39f8f2d83a54befdc67af987cebaf.1727855711.git.skaplun@tarantool.org> (raw) In-Reply-To: <cover.1727855711.git.skaplun@tarantool.org> From: Mike Pall <mike> Thanks to Peter Cawley. (cherry picked from commit 9e0437240f1fb4bfa7248f6ec8be0e3181016119) For `IR_BSHR`, `IR_BROL`, `IR_BROR` during `kfold_int64arith()` the left argument is truncated down to 32 bits, which leads to incorrect results if the right argument is >= 32. Also, `IR_BSAR` does an unsigned shift rather than a signed shift, but since this case branch is unreachable, it is harmless for now. This patch fixes all misbehaviours (including possible for `IR_BSAR`) to preserve IR semantics. Sergey Kaplun: * added the description and the test for the problem Part of tarantool/tarantool#10199 --- src/lj_opt_fold.c | 8 +- .../lj-1079-fix-64-bitshift-folds.test.lua | 74 +++++++++++++++++++ 2 files changed, 78 insertions(+), 4 deletions(-) create mode 100644 test/tarantool-tests/lj-1079-fix-64-bitshift-folds.test.lua diff --git a/src/lj_opt_fold.c b/src/lj_opt_fold.c index e2171e1b..2702f79f 100644 --- a/src/lj_opt_fold.c +++ b/src/lj_opt_fold.c @@ -382,10 +382,10 @@ static uint64_t kfold_int64arith(jit_State *J, uint64_t k1, uint64_t k2, case IR_BOR: k1 |= k2; break; case IR_BXOR: k1 ^= k2; break; case IR_BSHL: k1 <<= (k2 & 63); break; - case IR_BSHR: k1 = (int32_t)((uint32_t)k1 >> (k2 & 63)); break; - case IR_BSAR: k1 >>= (k2 & 63); break; - case IR_BROL: k1 = (int32_t)lj_rol((uint32_t)k1, (k2 & 63)); break; - case IR_BROR: k1 = (int32_t)lj_ror((uint32_t)k1, (k2 & 63)); break; + case IR_BSHR: k1 >>= (k2 & 63); break; + case IR_BSAR: k1 = (uint64_t)((int64_t)k1 >> (k2 & 63)); break; + case IR_BROL: k1 = lj_rol(k1, (k2 & 63)); break; + case IR_BROR: k1 = lj_ror(k1, (k2 & 63)); break; default: lj_assertJ(0, "bad IR op %d", op); break; } #else diff --git a/test/tarantool-tests/lj-1079-fix-64-bitshift-folds.test.lua b/test/tarantool-tests/lj-1079-fix-64-bitshift-folds.test.lua new file mode 100644 index 00000000..6cc0b319 --- /dev/null +++ b/test/tarantool-tests/lj-1079-fix-64-bitshift-folds.test.lua @@ -0,0 +1,74 @@ +local tap = require('tap') + +-- Test file to demonstrate LuaJIT misbehaviour on folding +-- for bitshift operations. +-- See also, https://github.com/LuaJIT/LuaJIT/issues/1079. + +local test = tap.test('lj-1079-fix-64-bitshift-folds'):skipcond({ + ['Test requires JIT enabled'] = not jit.status(), +}) + +local bit = require('bit') + +test:plan(4) + +-- Generic function for `bit.ror()`, `bit.rol()`. +local function bitop_rotation(bitop) + local r = {} + for i = 1, 4 do + -- (i & k1) o k2 ==> (i o k2) & (k1 o k2) + local int64 = bit.band(i, 7LL) + r[i] = tonumber(bitop(int64, 32)) + end + return r +end + +-- Similar function for `bit.rshift()`. +local function bitop_rshift_signed() + local r = {} + for i = 1, 4 do + -- (i & k1) o k2 ==> (i o k2) & (k1 o k2) + -- XXX: Use `-i` instead of `i` to prevent other folding due + -- to IR difference so the IRs don't match fold rule mask. + -- (-i & 7LL) < 1 << 32 => result == 0. + local int64 = bit.band(-i, 7LL) + r[i] = tonumber(bit.rshift(int64, 32)) + end + return r +end + +-- A little bit different example, which leads to the assertion +-- failure due to the incorrect recording. +local function bitop_rshift_huge() + local r = {} + for i = 1, 4 do + -- (i & k1) o k2 ==> (i o k2) & (k1 o k2) + -- XXX: Need to use cast to the int64_t via `+ 0LL`, see the + -- documentation [1] for the details. + -- [1]: https://bitop.luajit.org/semantics.html + local int64 = bit.band(2 ^ 33 + i, 2 ^ 33 + 0LL) + r[i] = tonumber(bit.rshift(int64, 32)) + end + return r +end + +local function test_64bitness(subtest, payload_func, bitop) + subtest:plan(1) + + jit.off() + jit.flush() + local results_joff = payload_func(bitop) + jit.on() + -- Reset hotcounters. + jit.opt.start('hotloop=1') + local results_jon = payload_func(bitop) + subtest:is_deeply(results_jon, results_joff, + 'same results for VM and JIT for ' .. subtest.name) +end + +test:test('rol', test_64bitness, bitop_rotation, bit.rol) +test:test('ror', test_64bitness, bitop_rotation, bit.ror) +test:test('rshift signed', test_64bitness, bitop_rshift_signed) +test:test('rshift huge', test_64bitness, bitop_rshift_huge) + +test:done(true) -- 2.46.2
next prev parent reply other threads:[~2024-10-02 8:10 UTC|newest] Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top 2024-10-02 8:09 [Tarantool-patches] [PATCH luajit 0/2] Fixes for 64 bit operands of the bit library Sergey Kaplun via Tarantool-patches 2024-10-02 8:09 ` [Tarantool-patches] [PATCH luajit 1/2] Fix bit op coercion in DUALNUM builds Sergey Kaplun via Tarantool-patches 2024-10-08 10:12 ` Sergey Bronnikov via Tarantool-patches 2024-10-11 19:08 ` Maxim Kokryashkin via Tarantool-patches 2024-10-02 8:09 ` Sergey Kaplun via Tarantool-patches [this message] 2024-10-08 12:07 ` [Tarantool-patches] [PATCH luajit 2/2] FFI: Fix 64 bit shift fold rules Sergey Bronnikov via Tarantool-patches 2024-10-08 14:24 ` Sergey Kaplun via Tarantool-patches 2024-10-09 14:29 ` Sergey Bronnikov via Tarantool-patches 2024-10-11 19:12 ` Maxim Kokryashkin via Tarantool-patches 2024-10-18 15:17 ` [Tarantool-patches] [PATCH luajit 0/2] Fixes for 64 bit operands of the bit library Sergey Kaplun via Tarantool-patches
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