[clang] [CIR] Upstream support for accessing structure members (PR #136383)

[Erich Keane via cfe-commits]

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@@ -309,6 +309,37 @@ RecordType::computeStructAlignment(const mlir::DataLayout &dataLayout) const {
   return recordAlignment;
 }
 
+uint64_t RecordType::getElementOffset(const ::mlir::DataLayout &dataLayout,
+                                      unsigned idx) const {
+  assert(idx < getMembers().size() && "access not valid");
+
+  // All union elements are at offset zero.
+  if (isUnion() || idx == 0)
+    return 0;
+
+  assert(isComplete() && "Cannot get layout of incomplete records");
+  assert(idx < getNumElements());
+  llvm::ArrayRef<mlir::Type> members = getMembers();
+
+  unsigned offset = 0;
+
+  for (unsigned i = 0, e = idx; i != e; ++i) {
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erichkeane wrote:

Typically clang prefers range-for for readability and avoiding the 'error-prone-ness' of an index.  Readability is because it assures that we are only visiting anything 'once', and the index is unchanged between iterations.  Typically when I see one of these types of loops, it means "funny-business is happening in the body, so look closely".

https://github.com/llvm/llvm-project/pull/136383