Verification failure for recursive struct

[gitoleg]

The following code

struct ListNode {
  struct ListNode *next;
};

struct List {
  struct ListNode head;
};

void foo(struct List *lst) {
  lst->head.next = &lst->head;
}

currently fails verification due to

$ clang -fclangir-enable -S tmp.c
...
loc(fused["tmp.c":10:3, "tmp.c":10:26]): error: 'cir.store' op failed to verify that type of 'value' matches pointee type of 'addr'
fatal error: error in backend: CIR codegen: module verification error before running CIR passes

The problem is in the assignment operation which expands to

cir.store %2, %5 : !cir.ptr<!cir.struct<"struct.ListNode", !cir.ptr<!cir.struct<"struct.ListNode", incomplete, #cir.recdecl.ast>>, #cir.recdecl.ast>>, cir.ptr <!cir.ptr<!cir.struct<"struct.ListNode", incomplete, #cir.recdecl.ast>>>

As we can see type of the stored value is complete:

!cir.ptr<!cir.struct<"struct.ListNode", !cir.ptr<!cir.struct<"struct.ListNode", incomplete, #cir.recdecl.ast>>, #cir.recdecl.ast>>

but type of the address is not:

!cir.ptr<!cir.ptr<!cir.struct<"struct.ListNode", incomplete, #cir.recdecl.ast>>>

This cause verification failure due to StoreOp's TypesMatchWith constraint.

What would be the best way to fix this? My understanding is that MLIR does not allow recursive types...

[bcardosolopes]

@gitoleg thanks for creating an issue for it, it's something we are aware but haven't tackled just yet.

I have a few ideas on how to workaround this limitation but hard to expose them without double checking whether it will JustWork™. I'll link a given PR to this issue when we get there, ideas/patches are welcome if you wanna work on this.

[bcardosolopes]

Should this be closed?

[sitio-couto]

Fixed in #303.