[clang] [CIR][AArch64] Upstream for vector vector shl (PR #191655)

[Andrzej Warzyński via cfe-commits]

banach-space wrote:

> the original codegen adds it to the map and creates new cases, similar to what I have done.
> Link to original code below
> https://github.com/llvm/clangir/blob/63412d47b3d573ba2d7d55920541269930d4a303/clang/lib/CIR/CodeGen/CIRGenBuiltinAArch64.cpp#L2709

That's the incubator implementation. By the "original" implementation we usually mean the path that does not involve ClangIR, i.e. what is implemented in https://github.com/llvm/llvm-project/blob/7b4c9bb2069536e0df18597795b858e18a1cbaaf/clang/lib/CodeGen/TargetBuiltins/ARM.cpp. 

The incubator implementation diverged from the "original" implementation. It is not clear to me _why_ - we should avoid that. Instead, I am suggesting to follow the "original" implementation from ARM.cpp. This means "re-implementing" this particular builtin, which is not uncommon when upstreaming code :-)

Let me know whether that helps. Thanks for working on this!

https://github.com/llvm/llvm-project/pull/191655