nak/nir: Add a few more NIR helpers

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/30402>

src/nouveau/compiler/nak/nir.rs

@@ -570,6 +570,7 @@ pub trait NirBlock {
     fn successors(&self) -> [Option<&nir_block>; 2];
     fn following_if(&self) -> Option<&nir_if>;
     fn following_loop(&self) -> Option<&nir_loop>;
+    fn parent(&self) -> &nir_cf_node;
 }
 
 impl NirBlock for nir_block {
@@ -593,6 +594,10 @@ impl NirBlock for nir_block {
         let self_ptr = self as *const _ as *mut _;
         unsafe { nir_block_get_following_loop(self_ptr).as_ref() }
     }
+
+    fn parent(&self) -> &nir_cf_node {
+        self.cf_node.parent().unwrap()
+    }
 }
 
 pub trait NirIf {
@@ -623,6 +628,7 @@ impl NirIf for nir_if {
 
 pub trait NirLoop {
     fn iter_body(&self) -> ExecListIter<nir_cf_node>;
+    fn first_block(&self) -> &nir_block;
     fn following_block(&self) -> &nir_block;
 }
 
@@ -631,6 +637,10 @@ impl NirLoop for nir_loop {
         ExecListIter::new(&self.body, offset_of!(nir_cf_node, node))
     }
 
+    fn first_block(&self) -> &nir_block {
+        self.iter_body().next().unwrap().as_block().unwrap()
+    }
+
     fn following_block(&self) -> &nir_block {
         self.cf_node.next().unwrap().as_block().unwrap()
     }
@@ -642,6 +652,7 @@ pub trait NirCfNode {
     fn as_loop(&self) -> Option<&nir_loop>;
     fn next(&self) -> Option<&nir_cf_node>;
     fn prev(&self) -> Option<&nir_cf_node>;
+    fn parent(&self) -> Option<&nir_cf_node>;
 }
 
 impl NirCfNode for nir_cf_node {
@@ -680,6 +691,10 @@ impl NirCfNode for nir_cf_node {
             ExecListIter::at(&self.node, offset_of!(nir_cf_node, node), true);
         iter.next()
     }
+
+    fn parent(&self) -> Option<&nir_cf_node> {
+        NonNull::new(self.parent).map(|b| unsafe { b.as_ref() })
+    }
 }
 
 pub trait NirFunctionImpl {