nir: Add a nir_deref_foreach_leaf helper

Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Cc: "12.0" <mesa-stable@lists.freedesktop.org>

src/compiler/nir/nir.c

@@ -659,6 +659,122 @@ nir_copy_deref(void *mem_ctx, nir_deref *deref)
    return NULL;
 }
 
+/* This is the second step in the recursion.  We've found the tail and made a
+ * copy.  Now we need to iterate over all possible leaves and call the
+ * callback on each one.
+ */
+static bool
+deref_foreach_leaf_build_recur(nir_deref_var *deref, nir_deref *tail,
+                               nir_deref_foreach_leaf_cb cb, void *state)
+{
+   unsigned length;
+   union {
+      nir_deref_array arr;
+      nir_deref_struct str;
+   } tmp;
+
+   assert(tail->child == NULL);
+   switch (glsl_get_base_type(tail->type)) {
+   case GLSL_TYPE_UINT:
+   case GLSL_TYPE_INT:
+   case GLSL_TYPE_FLOAT:
+   case GLSL_TYPE_DOUBLE:
+   case GLSL_TYPE_BOOL:
+      if (glsl_type_is_vector_or_scalar(tail->type))
+         return cb(deref, state);
+      /* Fall Through */
+
+   case GLSL_TYPE_ARRAY:
+      tmp.arr.deref.deref_type = nir_deref_type_array;
+      tmp.arr.deref.type = glsl_get_array_element(tail->type);
+      tmp.arr.deref_array_type = nir_deref_array_type_direct;
+      tmp.arr.indirect = NIR_SRC_INIT;
+      tail->child = &tmp.arr.deref;
+
+      length = glsl_get_length(tail->type);
+      for (unsigned i = 0; i < length; i++) {
+         tmp.arr.deref.child = NULL;
+         tmp.arr.base_offset = i;
+         if (!deref_foreach_leaf_build_recur(deref, &tmp.arr.deref, cb, state))
+            return false;
+      }
+      return true;
+
+   case GLSL_TYPE_STRUCT:
+      tmp.str.deref.deref_type = nir_deref_type_struct;
+      tail->child = &tmp.str.deref;
+
+      length = glsl_get_length(tail->type);
+      for (unsigned i = 0; i < length; i++) {
+         tmp.arr.deref.child = NULL;
+         tmp.str.deref.type = glsl_get_struct_field(tail->type, i);
+         tmp.str.index = i;
+         if (!deref_foreach_leaf_build_recur(deref, &tmp.arr.deref, cb, state))
+            return false;
+      }
+      return true;
+
+   default:
+      unreachable("Invalid type for dereference");
+   }
+}
+
+/* This is the first step of the foreach_leaf recursion.  In this step we are
+ * walking to the end of the deref chain and making a copy in the stack as we
+ * go.  This is because we don't want to mutate the deref chain that was
+ * passed in by the caller.  The downside is that this deref chain is on the
+ * stack and , if the caller wants to do anything with it, they will have to
+ * make their own copy because this one will go away.
+ */
+static bool
+deref_foreach_leaf_copy_recur(nir_deref_var *deref, nir_deref *tail,
+                              nir_deref_foreach_leaf_cb cb, void *state)
+{
+   union {
+      nir_deref_array arr;
+      nir_deref_struct str;
+   } c;
+
+   if (tail->child) {
+      switch (tail->child->deref_type) {
+      case nir_deref_type_array:
+         c.arr = *nir_deref_as_array(tail->child);
+         tail->child = &c.arr.deref;
+         return deref_foreach_leaf_copy_recur(deref, &c.arr.deref, cb, state);
+
+      case nir_deref_type_struct:
+         c.str = *nir_deref_as_struct(tail->child);
+         tail->child = &c.str.deref;
+         return deref_foreach_leaf_copy_recur(deref, &c.str.deref, cb, state);
+
+      case nir_deref_type_var:
+      default:
+         unreachable("Invalid deref type for a child");
+      }
+   } else {
+      /* We've gotten to the end of the original deref.  Time to start
+       * building our own derefs.
+       */
+      return deref_foreach_leaf_build_recur(deref, tail, cb, state);
+   }
+}
+
+/**
+ * This function iterates over all of the possible derefs that can be created
+ * with the given deref as the head.  It then calls the provided callback with
+ * a full deref for each one.
+ *
+ * The deref passed to the callback will be allocated on the stack.  You will
+ * need to make a copy if you want it to hang around.
+ */
+bool
+nir_deref_foreach_leaf(nir_deref_var *deref,
+                       nir_deref_foreach_leaf_cb cb, void *state)
+{
+   nir_deref_var copy = *deref;
+   return deref_foreach_leaf_copy_recur(&copy, &copy.deref, cb, state);
+}
+
 /* Returns a load_const instruction that represents the constant
  * initializer for the given deref chain.  The caller is responsible for
  * ensuring that there actually is a constant initializer.

src/compiler/nir/nir.h

@@ -1943,6 +1943,10 @@ nir_deref_struct *nir_deref_struct_create(void *mem_ctx, unsigned field_index);
 
 nir_deref *nir_copy_deref(void *mem_ctx, nir_deref *deref);
 
+typedef bool (*nir_deref_foreach_leaf_cb)(nir_deref_var *deref, void *state);
+bool nir_deref_foreach_leaf(nir_deref_var *deref,
+                            nir_deref_foreach_leaf_cb cb, void *state);
+
 nir_load_const_instr *
 nir_deref_get_const_initializer_load(nir_shader *shader, nir_deref_var *deref);