[pbsd]

This theory is cool, but I don't think it works, all things considered. PDEP and PEXT should have the same unfused behavior as SHLX, since they also do not change any flags, but they _do_ fuse. BEXTR should (or could) fuse, but doesn't. So I don't know.

[BeeOnRope]

You are right, so yeah I can't explain really why certain ops fuse and some don't. There doesn't seem to be a strong pattern.