[Tarantool-patches] [PATCH luajit] Fix TNEW load forwarding with instable types.
Igor Munkin
imun at tarantool.org
Tue Jul 4 20:09:26 MSK 2023
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 11.05.23, Sergey Kaplun via Tarantool-patches wrote:
> From: Mike Pall <mike>
>
> (cherry picked from commit d4c0c6e17ef7edf1f2893bc807746b80612e63e9)
>
> During loop unrolling IR instructions are coped, substituted and
> re-emitted for the FOLD/CSE/etc. pipeline. Assume, we have the following
> loop-carried dependency: we create a new table or load some stored one
> depends on iteration number. In case when we copy the emitted ALOAD IR
> instruction (from from the stored table), we copy it as is, including
> loading type. But the ALOAD from the new table created (on the previous
> iteration) should have nil type, so the assertion in `fwd_ahload()` is
> failed.
>
> This patch replaces the assertion to `return 0` to avoid the assertion
> failure and stop forwarding in such situations.
>
> But the emitted type-guarded ALOAD will lead to the persistent failure
> of the assertion guard on the trace. Hence, another one fix should be
> added. Also, TDUP IR is affected, too.
> See also the issue mentioned in the test.
>
> Sergey Kaplun:
> * added the description and the test for the problem
>
> Part of tarantool/tarantool#8516
> ---
>
> Branch: https://github.com/tarantool/luajit/tree/skaplun/lj-994-instable-types-during-loop-unroll
> PR: https://github.com/tarantool/tarantool/pull/8642
> Related issues:
> * https://github.com/tarantool/tarantool/issues/8516
> * https://github.com/LuaJIT/LuaJIT/issues/994
>
> I don't mention the 994 intentionally to avoid Mike bothering. Also, it
> isn't the origin of this commit. Quite the opposite: as a result of this
> backporting the following issue was created.
>
> I prefer to backport the patches (this one and the prospective for 994)
> separately. So, after this patch is backported, it doesn't add any
> critical bugs (always failing guard just creates a new side trace), but
> helps to avoid conflicts for future backporting (sadly remembered
> "Improve assertions.").
>
> src/lj_opt_mem.c | 3 +-
> ...instable-types-during-loop-unroll.test.lua | 53 +++++++++++++++++++
> 2 files changed, 55 insertions(+), 1 deletion(-)
> create mode 100644 test/tarantool-tests/lj-994-instable-types-during-loop-unroll.test.lua
>
<snipped>
> --
> 2.34.1
>
--
Best regards,
IM
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