Re: [Tarantool-patches] [PATCH luajit] Fix FOLD rule for strength reduction of widening.

[Igor Munkin via Tarantool-patches <tarantool-patches@dev.tarantool.org>]

Sergey,

I've checked the patch into all long-term branches in tarantool/luajit
and bumped a new version in master, 2.10 and 1.10.

On 18.10.21, Sergey Kaplun wrote:
> From: Mike Pall <mike>
> 
> Reported by Matthew Burk.
> 
> (cherry picked from commit 9f0caad0e43f97a4613850b3874b851cb1bc301d)
> 
> The simplify_conv_sext optimization is used for reduction of widening.
> cdata indexing narrow optimization uses it for narrowing of a C array
> index. The optimization eliminates sign extension for corresponding
> integer value. However, this conversion cannot be omitted for non
> constant values (for example loading stack slots) as far as their sign
> extension may change. The emitted machine code may be incorrect without
> aforementioned conversion (for example mov instruction instead movsxd is
> used on x86 architecture). As a result the value in a destination
> register during trace execution is invalid.
> 
> This patch allows this optimization only for constant integer values.
> 
> Sergey Kaplun:
> * added the description and the test for the problem
> ---
> 
> Tarantool branch: https://github.com/tarantool/tarantool/tree/skaplun/gh-noticket-fix-fold-simplify-conv-sext
> Branch: https://github.com/tarantool/luajit/tree/skaplun/gh-noticket-fix-fold-simplify-conv-sext
> 
>  src/lj_opt_fold.c                             |  2 +-
>  .../lj-fix-fold-simplify-conv-sext.test.lua   | 35 +++++++++++++++++++
>  2 files changed, 36 insertions(+), 1 deletion(-)
>  create mode 100644 test/tarantool-tests/lj-fix-fold-simplify-conv-sext.test.lua
> 

<snipped>

> -- 
> 2.31.0
> 

-- 
Best regards,
IM