[llvm] [SLP]Vectorize gathered loads (PR #107461)

[Alexey Bataev via llvm-commits]

alexey-bataev wrote:

> I've reverted this due to very large compile-time impact, esp. on lencod, see: http://llvm-compile-time-tracker.com/compare.php?from=b1339abb713063363e7804124b8fb3d84143a003&to=de1f5b96adcea52bf7c9670c46123fe1197050d2&stat=instructions:u
> 
> For non-LTO cases, me_distortion.c is one of the files with largest impact (~80%).

Reduced the time for lencode. There is just one significant regression in bullet (btSolve2LinearConstraint.cpp, +4%) remains, but there is no way to reduce it without affecting the vectorization result

https://github.com/llvm/llvm-project/pull/107461