================
@@ -797,14 +806,44 @@ void insertArgCoercion(
if (destAlloca)
pendingParamSlots.emplace_back(destAlloca, blockArg);
} else {
- // byval: load the incoming pointer so the body sees a T value (and
- // any CIRGen param-slot store becomes a local copy of that value).
+ // With byval the callee works on its own copy. A record's padding
+ // bytes can hold another union member's live data, so its spill slot
+ // is filled by a byte copy of the incoming object. A _BitInt keeps
+ // its load and spill store, which are its conversion between value
+ // and in-memory form.
+ cir::StoreOp paramStore;
+ if (mlir::isa<cir::RecordType>(blockArg.getType()))
+ paramStore = maybeFindParamSpill(blockArg);
+
+ // Erasing the spill before the block argument is retyped keeps the
----------------
adams381 wrote:
Four shapes reach the byval arm on x86_64: a record classified MEMORY, a
`_BitInt` wider than 128 bits, an oversized vector, and `_Complex long double`.
The `_BitInt` and the vector store their whole slot, and the complex skips
only x87 padding that nothing can alias. Only in a record can the bytes a
store skips be another union member's value.
https://github.com/llvm/llvm-project/pull/224672
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