[Tarantool-patches] [PATCH luajit] IR_MIN/IR_MAX is non-commutative due to underlying FPU ops.

[Igor Munkin]

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 24.10.23, Sergey Kaplun via Tarantool-patches wrote:
> From: Mike Pall <mike>
> 
> Thanks to Peter Cawley.
> 
> (cherry-picked from commit 7a2b83a0c5d980bf3db0aeda33c79e7bb4b3da01)
> 
> Even after the commit c05d103305da0626e025dbf81370ca9f4f788c83 ("Fix
> math.min()/math.max() inconsistencies."), some of the corner cases (see
> tests in the commit for details) for `math.min()`/`math.max()` still
> inconsistent in the JIT and the VM. This happens because `IR_MIN` and
> `IR_MAX` are marked as commutative, so their operands were swapped by
> `asm_swapops()`. As a result, because `minsd`[1]/`maxsd`[2] instructions
> don't change the sign byte of the destination register, its sign is
> preserved if we compare 0 with -0. When we compare something with NaN,
> the second source operand (either a NaN or a valid floating-point value)
> is written to the result. Hence, swapping the operands changed the
> resulting value.
> 
> This patch removes the commutative flag from the aforementioned IRs to
> prevent swapping of their operands.
> 
> [1]: https://c9x.me/x86/html/file_module_x86_id_173.html
> [2]: https://c9x.me/x86/html/file_module_x86_id_168.html
> 
> 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-1082-min-max-0-commutative
> Tarantool PR: https://github.com/tarantool/tarantool/pull/9294
> Related Issues:
> * https://github.com/tarantool/tarantool/issues/9145
> * https://github.com/LuaJIT/LuaJIT/issues/1082
> * https://github.com/LuaJIT/LuaJIT/issues/957
> 
>  src/lj_ir.h                                   |  4 +-
>  test/tarantool-tests/gh-6163-min-max.test.lua | 23 ++++-------
>  .../lj-1082-min-max-0-commutative.test.lua    | 41 +++++++++++++++++++
>  3 files changed, 51 insertions(+), 17 deletions(-)
>  create mode 100644 test/tarantool-tests/lj-1082-min-max-0-commutative.test.lua
> 

<snipped>

> -- 
> 2.42.0
> 

-- 
Best regards,
IM