Emit code with PHMINPOSUW on x86 to calculate min of values in array

[teaalltr]

https://www.youtube.com/watch?v=egG5Kraswhc

[llvmbot]

@llvm/issue-subscribers-backend-x86

Author: None (teaalltr)


https://www.youtube.com/watch?v=egG5Kraswhc

[dzaima]

As the comments on the video say, clang already does this optimization. https://godbolt.org/z/qY3PGozG5

[RKSimon]

Closing - we've had PHMINPOSUW lowering for signed/unsigned vXi8/vXi16 reductions for a long time - but it looks like the middle end improved min/max reduction pattern recognition more recently which allowed the lowering to trigger more often.