================
@@ -388,26 +378,18 @@ llvm::TypeSize
RecordType::getTypeSizeInBits(const mlir::DataLayout &dataLayout,
mlir::DataLayoutEntryListRef params) const {
if (isUnion()) {
- mlir::Type largest = getLargestMember(dataLayout);
- if (!largest)
- return llvm::TypeSize::getFixed(0);
- // `getLargestMember` returns the highest-aligned variant (which dictates
- // the union's alignment), not necessarily the largest by size. When the
- // union is `padded` -- i.e., its highest-aligned variant is strictly
- // smaller than its layout size, as happens for any union containing both
- // a small high-alignment scalar and a larger low-alignment array (e.g.,
- // `union { char[16]; size_t; }`) -- `lowerUnion` appended a trailing
- // byte-array member to extend the highest-aligned variant up to the
- // layout size, and `LowerToLLVM` mirrors this by emitting the union as
- // `{largest, padding}`. Include that padding here so `getTypeSize`
- // reports the same size `LowerToLLVM` produces; otherwise a parent
- // record containing the union gets a spurious tail-padding member added
- // by `insertPadding`, making `sizeof(parent)` and array GEPs off by the
- // missing bytes.
- llvm::TypeSize size = dataLayout.getTypeSizeInBits(largest);
- if (mlir::Type tailPad = getPadding())
- size += dataLayout.getTypeSizeInBits(tailPad);
- return size;
+ // The size of a union is the size of the largest member.
+ llvm::ArrayRef<Type> members = getMembers();
+ if (members.empty() || (getPadded() && members.size() == 1))
+ return llvm::TypeSize::getFixed(8);
+
+ mlir::Type largestType = *std::max_element(
+ members.begin(), std::prev(members.end(), getPadded()),
+ [&](Type lhs, Type rhs) {
+ return dataLayout.getTypeSize(lhs) < dataLayout.getTypeSize(rhs);
+ });
+
+ return dataLayout.getTypeSizeInBits(largestType);
----------------
andykaylor wrote:
I don't think this is right. If we have user-specified alignment, we could have
padding that forces us to increase the size of the union beyond the size of the
largest member, right?
```
union alignas(32) U {
int n[4];
long long ll;
};
```
Gives me:
`%union.U = type { i64, [24 x i8] }`
https://github.com/llvm/llvm-project/pull/199292
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