[llvm] [SLP]Improve minbitwidth analysis. (PR #84536)

[Alexey Bataev via llvm-commits]

alexey-bataev wrote:

> > AS I said, I'll revert it, better to commit fixed versions. Will revert ASAP.
> 
> Thanks, much appreciated!
> 
> > Think this also is causing a failure when building `llvm-test-suite` (which might be easier to reproduce):
> > ```
> > FAILED: MultiSource/Benchmarks/MiBench/consumer-jpeg/CMakeFiles/consumer-jpeg.dir/jdsample.c.o 
> > ```
> 
> I think this is the same issue as I had reduced above; building libjpeg (in some form) triggers failed asserts in `jdsample.c` and `jcsample.c`, the one above that I had reduced was from `jcsample.c`.
> 
> But the cases that trigger no asserts but produce wrong results at runtime are probably harder to sort out.

Thanks, I fixed one small bug and currently investigating the last one.

https://github.com/llvm/llvm-project/pull/84536