[clang] [llvm] [SROA] Canonicalize homogeneous structs into fixed vectors (PR #165159)

[Yaxun Liu via cfe-commits]

yxsamliu wrote:

> > > I'll look at the changes tomorrow, at first glance it looks good though. Could you confirm this is the latest benchmark run? [dtcxzyw/llvm-opt-benchmark#3520](https://github.com/dtcxzyw/llvm-opt-benchmark/pull/3520). Looks like really good improvements!
> > 
> > 
> > That one is pretty close but I made some minor changes after that but forgot to trigger a new run. I just triggered a new run and let's see how it goes: [dtcxzyw/llvm-opt-benchmark#3547](https://github.com/dtcxzyw/llvm-opt-benchmark/pull/3547)
> 
> Hmm unfortunately looks like there's one regression that doesn't look good. We're vectorizing when the alloca gets promoted as a scalar anyway, but then this requires a bunch of inserts and extracts.
> 
> Sorry to be such a stickler, again I haven't reviewed much so IDK exactly what LLVM policy is, but I assume there should be a pretty high bar for transforms like SROA because it's such an important pass.

I am OK. I think we should try fixing any regressions caused by changes in llvm passes since that could be a tip of an iceberg. I will look into this. Thanks. 

https://github.com/llvm/llvm-project/pull/165159