[llvm] [SLP]Improved reduction cost/codegen (PR #118293)

[Alexey Bataev via llvm-commits]

alexey-bataev wrote:

> This change miscompiles one file in ffmpeg, for x86 and x86_64.
> 
> To reproduce, clone https://github.com/ffmpeg/ffmpeg, compile and run tests like this:
> 
> ```
> $ git clone https://github.com/ffmpeg/ffmpeg
> $ mkdir ffmpeg-build
> $ cd ffmpeg-build
> $ ../ffmpeg/configure --cc=clang --samples=$(pwd)/../ffmpeg-samples
> $ make fate-rsync
> $ make -j$(nproc) fate-msnsiren
> ```
> 
> The miscompiled object file is `libavcodec/siren.o`.

Fixed

https://github.com/llvm/llvm-project/pull/118293