Method begin

crates/rustc_codegen_spirv/src/abi.rs:190–223

(&self, cx: &CodegenCx<'tcx>, span: Span, pointee: PointeeTy<'tcx>)

impl<'tcx> RecursivePointeeCache<'tcx> {
    fn begin(&self, cx: &CodegenCx<'tcx>, span: Span, pointee: PointeeTy<'tcx>) -> Option<Word> {
        match self.map.borrow_mut().entry(pointee) {
            // State: This is the first time we've seen this type. Record that we're beginning to translate this type,
            // and start doing the translation.
            Entry::Vacant(entry) => {
                entry.insert(PointeeDefState::Defining);
                None
            }
            Entry::Occupied(mut entry) => match *entry.get() {
                // State: This is the second time we've seen this type, and we're already translating this type. If we
                // were to try to translate the type now, we'd get a stack overflow, due to continually recursing. So,
                // emit an OpTypeForwardPointer, and use that ID. (This is the juicy part of this algorithm)
                PointeeDefState::Defining => {
                    let new_id = cx.emit_global().id();
                    // NOTE(eddyb) we emit `StorageClass::Generic` here, but later
                    // the linker will specialize the entire SPIR-V module to use
                    // storage classes inferred from `OpVariable`s.
                    cx.emit_global()
                        .type_forward_pointer(new_id, StorageClass::Generic);
                    entry.insert(PointeeDefState::DefiningWithForward(new_id));
                    cx.zombie_with_span(
                        new_id,
                        span,
                        "cannot create self-referential types, even through pointers",
                    );
                    Some(new_id)
                }
                // State: This is the third or more time we've seen this type, and we've already emitted an
                // OpTypeForwardPointer. Just use the ID we've already emitted. (Alternatively, we already defined this
                // type, so just use that.)
                PointeeDefState::DefiningWithForward(id) | PointeeDefState::Defined(id) => Some(id),
            },
        }
    }

    fn end(
        &self,