[llvm] [LSROA] Support arrays, vectors, and nested structs (PR #218846)

[Deric C. via llvm-commits]

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@@ -1809,23 +1809,20 @@ class StructuredGEPInst : public IntrinsicInst {
     return make_range(op_begin() + 1, op_begin() + 1 + getNumIndices());
   }
 
+  static Type *getTypeAtIndex(Type *Ty, const Value *Index) {
+    if (ArrayType *AT = dyn_cast<ArrayType>(Ty))
+      return AT->getElementType();
+    if (VectorType *VT = dyn_cast<VectorType>(Ty))
+      return VT->getElementType();
+    if (StructType *ST = dyn_cast<StructType>(Ty))
+      return ST->getElementType(cast<ConstantInt>(Index)->getZExtValue());
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Icohedron wrote:

[QUESTION] Should we align with the GEP's `getTypeAtIndex` implementation and check that the struct element index is valid? 
https://github.com/llvm/llvm-project/blob/2e718be51d78bec269a883e9606f621539fe567a/llvm/lib/IR/Instructions.cpp#L1592-L1593

GEP's `getTypeAtIndex` also returns `nullptr` instead of using `llvm_unreachable`, so the caller is at least guaranteed a known value (`nullptr`) instead of undefined behavior in a release build.

https://github.com/llvm/llvm-project/pull/218846