From: Igor Munkin via Tarantool-patches <tarantool-patches@dev.tarantool.org> To: Sergey Kaplun <skaplun@tarantool.org> Cc: tarantool-patches@dev.tarantool.org Subject: Re: [Tarantool-patches] [PATCH luajit] Prevent CSE of a REF_BASE operand across IR_RETF. Date: Wed, 10 Jan 2024 08:51:51 +0000 [thread overview] Message-ID: <ZZ5apz1VdykXePtv@tarantool.org> (raw) In-Reply-To: <20231128122112.16229-1-skaplun@tarantool.org> Sergey, I've checked the patchset into all long-term branches in tarantool/luajit and bumped a new version in master, release/2.11 and release/2.10. On 28.11.23, Sergey Kaplun via Tarantool-patches wrote: > From: Mike Pall <mike> > > Reported by XmiliaH. > > (cherry-picked from commit e73916d811710ab02a4dfe447d621c99f4e7186c) > > The RETF IR has a side effect: it shifts base when returning to a lower > frame, i.e., it affects `REF_BASE` IR (0000) (thus, we can say that this > IR is violating SSA form). So any optimization of IRs with `REF_BASE` as > an operand across RETF IR may lead to incorrect optimizations (see > details in the test file). > > This patch adds rules to the folding engine to prevent CSE across `IR_RETF` > for all possible IRs containing REF_BASE. > > 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-784-cse-ref-base-over-retf > Tarantool PR: https://github.com/tarantool/tarantool/pull/9421 > Related issues: > * https://github.com/LuaJIT/LuaJIT/issues/784 > * https://github.com/tarantool/tarantool/issues/9145 > > Interested reviewers can mention that only the `SUB any BASE` case is > tested. > The reason is that other cases are impossible to record in LuaJIT: > * EQ any BASE: EQ pgc REF_BASE IR for upvalues is emitted when > the open upvalue aliases a SSA slot, i.e., it belongs to the frame of > the currently executed function. In that case, if we want to emit RETF > IR, we need to leave this function. So we need to record the UCLO > bytecode, which is NIY in JIT. So, such a type of trace is impossible. > * SUB BASE any: SUB BASE fr is emitted for the recording of VARG > bytecode, in case varargs are undefined on trace. We need a vararg > function to call to create an additional frame. But returning to lower > frames from a vararg function isn't implemented in LuaJIT -- either > the trace recording is stopped or the error is rased and the trace > isn't compiled. Also, IINM, fr operands will always be different for > different frames, so there is no possible CSE here. > > So, these cases are needed to prevent any regressions in the future. > > Please correct me if I've missed something. > > src/lj_opt_fold.c | 11 +++ > .../lj-784-cse-ref-base-over-retf.test.lua | 86 +++++++++++++++++++ > 2 files changed, 97 insertions(+) > create mode 100644 test/tarantool-tests/lj-784-cse-ref-base-over-retf.test.lua > <snipped> > -- > 2.42.1 > -- Best regards, IM
prev parent reply other threads:[~2024-01-10 8:58 UTC|newest] Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top 2023-11-28 12:21 Sergey Kaplun via Tarantool-patches 2023-11-29 14:26 ` Sergey Bronnikov via Tarantool-patches 2023-11-30 7:34 ` Sergey Kaplun via Tarantool-patches 2023-11-30 8:53 ` Sergey Bronnikov via Tarantool-patches 2023-11-30 17:59 ` Maxim Kokryashkin via Tarantool-patches 2024-01-10 8:51 ` Igor Munkin via Tarantool-patches [this message]
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