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

[Yaxun Liu via cfe-commits]

yxsamliu wrote:

@YonahGoldberg 

I updated the heuristic to try to keep the useful performance wins from vectorizing alloca partitions, while avoiding the cases that looked like they were causing regressions, and I triggered a new llvm-opt-benchmark run for that latest change here: 

https://github.com/dtcxzyw/llvm-opt-benchmark-nightly/pull/152

The IR report there still shows a few apparent regressions, so I followed up locally by checking the corresponding assembly for those changed files, and I could not find a clear asm-level performance regression signal. Most of the changed cases looked neutral to better in asm, and the one remaining small positive asm delta in `cpython/compile` still looked more like control-flow / register-allocation noise than a real slowdown. So my current reading is that the updated heuristic is keeping the vectorization benefit we want, and that the apparent regressions in the IR diff do not look like real performance regressions from the assembly side.


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