kraid: Add a very dumb message slot assignment pass

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/41841>

src/panfrost/compiler/kraid/compile.rs

@@ -81,6 +81,10 @@ pub extern "C" fn kraid_compile_nir(
     dump_shader(&s, "after register assignment");
     s.validate();
 
+    s.assign_message_slots();
+    dump_shader(&s, "after message slot assignment");
+    s.validate();
+
     let bin = model.encode_shader(&s);
     dynarray_append_vec(binary, bin);
 }

src/panfrost/compiler/kraid/lib.rs

@@ -9,6 +9,7 @@ mod encode_v9;
 mod flow;
 mod ir;
 mod isa;
+mod message_slots;
 mod model;
 mod nir;
 mod ops;

src/panfrost/compiler/kraid/message_slots.rs

@@ -0,0 +1,26 @@
+// Copyright © 2026 Collabora, Ltd.
+// SPDX-License-Identifier: MIT
+
+use crate::flow::FlowWaitBit;
+use crate::ir::*;
+
+fn op_is_message(op: &Op) -> bool {
+    // TODO: Make this real
+    matches!(
+        op,
+        Op::LdPka(_) | Op::LeaPka(_) | Op::Load(_) | Op::Store(_)
+    )
+}
+
+impl Shader<'_> {
+    pub fn assign_message_slots(&mut self) {
+        for b in self.blocks.iter_mut() {
+            for i in b.instrs.iter_mut() {
+                if op_is_message(&i.op) {
+                    i.flow.set_msg_slot_idx(0);
+                    i.flow.set_wait_bit(FlowWaitBit::Slot0);
+                }
+            }
+        }
+    }
+}