[llvm] Update the base and index value for masked gather (PR #130920)

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

Here is my experiment: https://github.com/llvm/llvm-project/compare/main...RKSimon:llvm-project:x86-gather-scatter-addr-scale

It still needs work: it stupidly moves 1 bit of shift left per combine instead of doing something smarter, plus we should probably only bother trying to do this if we think it will eventually allow truncation.

Anyway, take a look and see if there's anything you can use that will help.

https://github.com/llvm/llvm-project/pull/130920