[llvm] [VectorCombine] Fold chain of (scalar load)->ext->ext to load->ext. (PR #141109)

[Philip Reames via llvm-commits]

preames wrote:

Two high level comments:

1) Why does this need to be a single unified transform?  It really seems like the scalar-load+insert+bitcast --> vector load, and the ext+shuffle+ext are independent transforms.  Is there a reason these can't be separated?

2) All of your tests appear to use identity shuffles.  Those can just be removed.  Once that's done, we have two adjacent extends, which should already be handled?  Either your tests need updated, or there's something off here?

https://github.com/llvm/llvm-project/pull/141109