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

[Yaxun Liu via llvm-commits]

================
@@ -5267,6 +5273,57 @@ AllocaInst *SROA::rewritePartition(AllocaInst &AI, AllocaSlices &AS,
   if (VecTy)
     SliceTy = VecTy;
 
+  // Canonicalize homogeneous, tightly-packed 2- or 4-field structs to
+  // a fixed-width vector type when the DataLayout proves bitwise identity.
+  // Do this BEFORE the alloca reuse fast-path so that we don't miss
+  // opportunities to vectorize memcpy on allocas whose SliceTy initially
+  // equals the allocated type.
+  if (SROAMaxStructToVectorBytes) {
----------------
yxsamliu wrote:

Done. Extracted the logic into a helper function `tryCanonicalizeStructToVector()`
with early returns. The call site is now just:
```
  if (auto *STy = dyn_cast<StructType>(PartitionTy))
    if (auto *VTy = tryCanonicalizeStructToVector(STy, DL, MaxStructToVectorSize))
      PartitionTy = VTy;
```

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