[ZweZeya]

First of a stack of seven. Each PR targets the one below it, so each diff is only its own change.

What this changes

Lowering and lifting no longer crash on input they did not expect.

• Lowering dereferenced fallback_impl and the source type unconditionally, though both are optional and every ownership-analysis test builds ops without them. It now names the op and the missing attribute.
• Lifting read operands by fixed index and called getResult() on try_pop, which segfaults where the result comes back through a hidden llvm.sret argument. wtc.queue_pop gains an optional result_slot operand (its result becomes optional; exactly one of the two is present), and lowering puts the slot back where the callee marks it, with the callee's argument attributes, sret included.
• A pop's element type is recovered from std::shared_ptr<T>'s layout as the first pointer reached through its leading members: libc++ puts T* first, libstdc++ puts it first in the std::__shared_ptr base. CI on Linux found the second case (separate commit, LiftCIRToWTC/libstdcxx-shared-ptr.mlir).
• Measured at the pin: the hidden argument depends on the target. On AArch64 macOS, try_pop and spawn return their records directly and the old indices happen to work; the same file emitted for x86-64 puts the slot first. docs/audit.md records this.

How it was checked

16 of 16 pass, no warnings. The five new tests (LiftCIRToWTC/libstdcxx-shared-ptr, LowerWTCToCIR/missing-attributes, LowerWTCToCIR/push-callee-returns-value, LiftCIRToWTC/sret-try-pop, LiftCIRToWTC/arity-mismatch) fail against main: three crash, one refuses the libstdc++ shape, one builds a call whose result disagrees with its callee. The prototype's example lifts and lowers back for both targets.

Checklist

• CI is green
• New behaviour has a test; a fixed bug has a test that failed before
• No file moves or renames mixed in with substantive changes
• The pinned LLVM revision is untouched, or this PR does nothing else

🤖 Generated with Claude Code

[apaznikov]

Closing this as superseded by #10, which carries a second line of work on the same slice that had been developed alongside this stack and goes further in the same direction.

What this PR fixes is covered there: lifting reads operands through the calling convention, so the hidden return slot of try_pop is handled on every target (mlir: Prove queue ownership and specialise on it), and lowering an operation without a fallback reports an error instead of crashing. The element type no longer needs recovering from shared_ptr's layout, because on that branch !wtc.queue<T> carries the queue object's type, not the element's. Thank you for finding the x86-64 shape by hand; it is why the sret handling there is exercised from real compiler output.