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] Fix FOLD rule for x-0. Date: Tue, 31 Oct 2023 15:44:46 +0300 [thread overview] Message-ID: <20231031124446.17478-1-skaplun@tarantool.org> (raw) From: Mike Pall <mike> Reported by XmiliaH. (cherry-picked from commit 7b994e0ee0399caf6319865bbac88ddf62129a36) Fold optimization x - (-0) ==> x is INVALID for x = -0 in FP arithmetic. Its result is -0 instead of +0. This patch allows only x - (+0) ==> x optimization. Sergey Kaplun: * added the description and the test for the problem Part of tarantool/tarantool#9145 --- Branch: https://github.com/tarantool/luajit/tree/skaplun/lj-783-fix-fold-x-0 Tarantool PR: https://github.com/tarantool/tarantool/pull/9320 Related Issues: * https://github.com/tarantool/tarantool/issues/9145 * https://github.com/LuaJIT/LuaJIT/pull/783 src/lj_opt_fold.c | 3 +-- test/tarantool-tests/lj-783-fold--0.test.lua | 28 ++++++++++++++++++++ 2 files changed, 29 insertions(+), 2 deletions(-) create mode 100644 test/tarantool-tests/lj-783-fold--0.test.lua diff --git a/src/lj_opt_fold.c b/src/lj_opt_fold.c index 09e6c87b..944a9ecc 100644 --- a/src/lj_opt_fold.c +++ b/src/lj_opt_fold.c @@ -1005,8 +1005,7 @@ LJFOLDF(simplify_numadd_xneg) LJFOLD(SUB any KNUM) LJFOLDF(simplify_numsub_k) { - lua_Number n = knumright; - if (n == 0.0) /* x - (+-0) ==> x */ + if (ir_knum(fright)->u64 == 0) /* x - (+0) ==> x */ return LEFTFOLD; return NEXTFOLD; } diff --git a/test/tarantool-tests/lj-783-fold--0.test.lua b/test/tarantool-tests/lj-783-fold--0.test.lua new file mode 100644 index 00000000..d6b4b493 --- /dev/null +++ b/test/tarantool-tests/lj-783-fold--0.test.lua @@ -0,0 +1,28 @@ +local tap = require('tap') + +-- Test file to demonstrate LuaJIT's incorrect fold optimization +-- x - (-0) ==> x. +-- See also https://github.com/LuaJIT/LuaJIT/issues/783. +local test = tap.test('lj-783-fold--0'):skipcond({ + ['Test requires JIT enabled'] = not jit.status(), +}) + +test:plan(2) + +-- XXX: Use the variable to avoid folding during parsing. +local minus_zero = -0 +local results = {} + +jit.opt.start('hotloop=1') + +for i = 1, 4 do + results[i] = tostring(minus_zero - (-0)) +end + +-- Fold optimization x - (-0) ==> x is INVALID for x = -0 in FP +-- arithmetic. Its result is -0 instead of +0. + +test:is(results[1], '0', 'correct VM value for -0 - (-0)') +test:samevalues(results, '-0 folding in simplify_numsub_k') + +test:done(true) -- 2.42.0
next reply other threads:[~2023-10-31 12:49 UTC|newest] Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top 2023-10-31 12:44 Sergey Kaplun via Tarantool-patches [this message] 2023-10-31 15:17 ` Maxim Kokryashkin via Tarantool-patches 2023-11-08 19:36 ` Sergey Bronnikov via Tarantool-patches 2023-11-23 6:29 ` Igor Munkin via Tarantool-patches
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