[Tarantool-patches] [PATCH luajit v2] x64: Fix 64 bit shift code generation.

[Igor Munkin]

Max,

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 13.06.23, Maxim Kokryashkin via Tarantool-patches wrote:
> From: Mike Pall <mike>
> 
> Reported by Philipp Kutin.
> Fix contributed by Peter Cawley.
> 
> (cherry-picked from commit 03a7ebca4f6819658cdaa12ba3af54a17b8035e9)
> 
> In a situation where a variable shift left bitwise rotation that
> has a 64-bit result is recorded on an x86 64-bit processor and
> the result is supposed to end up in the `rcx` register, that value
> could be written into the `ecx` instead, thus being truncated into
> 32 bits. This patch fixes the described behavior, so now that
> value is written into the `rcx`.
> 
> Resulting assembly changes from the following before the patch:
> | rol rsi, cl
> | mov ecx, esi
> 
> to the following after the patch:
> | rol rsi, cl
> | mov rcx, rsi
> 
> Importantly, the same behavior is impossible with the right
> rotation on machines with BMI2 support because there is a
> BMI2 instruction for it, so it is handled differently.
> 
> Maxim Kokryashkin:
> * added the description and the test for the problem
> 
> Part of tarantool/tarantool#8516
> ---
> Changes in v2:
> - Fixed comments as per review by Sergey
> 
> Branch: https://github.com/tarantool/luajit/tree/fckxorg/fix-bit-shift-generation
> PR: https://github.com/tarantool/tarantool/pull/8727
> 
>  src/lj_asm_x86.h                              |  2 +-
>  test/tarantool-tests/CMakeLists.txt           |  1 +
>  .../fix-bit-shift-generation.test.lua         | 48 +++++++++++++++++++
>  .../fix-bit-shift-generation/CMakeLists.txt   |  1 +
>  .../libtestbitshift.c                         |  8 ++++
>  5 files changed, 59 insertions(+), 1 deletion(-)
>  create mode 100644 test/tarantool-tests/fix-bit-shift-generation.test.lua
>  create mode 100644 test/tarantool-tests/fix-bit-shift-generation/CMakeLists.txt
>  create mode 100644 test/tarantool-tests/fix-bit-shift-generation/libtestbitshift.c
> 

<snipped>

> -- 
> 2.40.1
> 

-- 
Best regards,
IM