nir/spirv: Rework the way pointers get dereferenced

This has the advantage of moving all of the "extend an access chain"
code into one place.

Reviewed-by: Connor Abbott <cwabbott0@gmail.com>

src/compiler/spirv/vtn_private.h

@@ -255,8 +255,12 @@ struct vtn_access_link {
 struct vtn_access_chain {
    uint32_t length;
 
-   /* Struct elements and array offsets */
+   /** Struct elements and array offsets.
-   struct vtn_access_link link[0];
+    *
+    * This is an array of 1 so that it can conveniently be created on the
+    * stack but the real length is given by the length field.
+    */
+   struct vtn_access_link link[1];
 };
 
 enum vtn_variable_mode {

src/compiler/spirv/vtn_variables.c

@@ -28,6 +28,20 @@
 #include "vtn_private.h"
 #include "spirv_info.h"
 
+static struct vtn_access_chain *
+vtn_access_chain_create(struct vtn_builder *b, unsigned length)
+{
+   struct vtn_access_chain *chain;
+
+   /* Subtract 1 from the length since there's already one built in */
+   size_t size = sizeof(*chain) +
+                 (MAX2(length, 1) - 1) * sizeof(chain->link[0]);
+   chain = rzalloc_size(b, size);
+   chain->length = length;
+
+   return chain;
+}
+
 static struct vtn_access_chain *
 vtn_access_chain_extend(struct vtn_builder *b, struct vtn_access_chain *old,
                         unsigned new_ids)
@@ -35,11 +49,7 @@ vtn_access_chain_extend(struct vtn_builder *b, struct vtn_access_chain *old,
    struct vtn_access_chain *chain;
 
    unsigned old_len = old ? old->length : 0;
-   unsigned new_len = old_len + new_ids;
+   chain = vtn_access_chain_create(b, old_len + new_ids);
-   /* TODO: don't use rzalloc */
-   chain = rzalloc_size(b, sizeof(*chain) + new_len * sizeof(chain->link[0]));
-
-   chain->length = new_len;
 
    for (unsigned i = 0; i < old_len; i++)
       chain->link[i] = old->link[i];
@@ -47,6 +57,37 @@ vtn_access_chain_extend(struct vtn_builder *b, struct vtn_access_chain *old,
    return chain;
 }
 
+/* Dereference the given base pointer by the access chain */
+static struct vtn_pointer *
+vtn_pointer_dereference(struct vtn_builder *b,
+                        struct vtn_pointer *base,
+                        struct vtn_access_chain *deref_chain)
+{
+   struct vtn_access_chain *chain =
+      vtn_access_chain_extend(b, base->chain, deref_chain->length);
+   struct vtn_type *type = base->type;
+
+   unsigned start = base->chain ? base->chain->length : 0;
+   for (unsigned i = 0; i < deref_chain->length; i++) {
+      chain->link[start + i] = deref_chain->link[i];
+
+      if (glsl_type_is_struct(type->type)) {
+         assert(deref_chain->link[i].mode == vtn_access_mode_literal);
+         type = type->members[deref_chain->link[i].id];
+      } else {
+         type = type->array_element;
+      }
+   }
+
+   struct vtn_pointer *ptr = rzalloc(b, struct vtn_pointer);
+   ptr->mode = base->mode;
+   ptr->type = type;
+   ptr->var = base->var;
+   ptr->chain = chain;
+
+   return ptr;
+}
+
 static nir_ssa_def *
 vtn_access_link_as_ssa(struct vtn_builder *b, struct vtn_access_link link,
                        unsigned stride)
@@ -730,15 +771,16 @@ _vtn_variable_load_store(struct vtn_builder *b, bool load,
          (*inout)->elems = rzalloc_array(b, struct vtn_ssa_value *, elems);
       }
 
-      struct vtn_pointer elem = *ptr;
+      struct vtn_access_chain chain = {
-      elem.chain = vtn_access_chain_extend(b, ptr->chain, 1);
+         .length = 1,
-      unsigned link_idx = ptr->chain ? ptr->chain->length : 0;
+         .link = {
-      elem.chain->link[link_idx].mode = vtn_access_mode_literal;
+            { .mode = vtn_access_mode_literal, },
+         }
+      };
       for (unsigned i = 0; i < elems; i++) {
-         elem.chain->link[link_idx].id = i;
+         chain.link[0].id = i;
-         elem.type = (base_type == GLSL_TYPE_ARRAY) ? ptr->type->array_element :
+         struct vtn_pointer *elem = vtn_pointer_dereference(b, ptr, &chain);
-                                                      ptr->type->members[i];
+         _vtn_variable_load_store(b, load, elem, &(*inout)->elems[i]);
-         _vtn_variable_load_store(b, load, &elem, &(*inout)->elems[i]);
       }
       return;
    }
@@ -797,24 +839,21 @@ _vtn_variable_copy(struct vtn_builder *b, struct vtn_pointer *dest,
 
    case GLSL_TYPE_ARRAY:
    case GLSL_TYPE_STRUCT: {
-      struct vtn_pointer src_elem = *src, dest_elem = *dest;
+      struct vtn_access_chain chain = {
-      src_elem.chain = vtn_access_chain_extend(b, src->chain, 1);
+         .length = 1,
-      dest_elem.chain = vtn_access_chain_extend(b, dest->chain, 1);
+         .link = {
-      src_elem.chain->link[src_elem.chain->length - 1].mode = vtn_access_mode_literal;
+            { .mode = vtn_access_mode_literal, },
-      dest_elem.chain->link[dest_elem.chain->length - 1].mode = vtn_access_mode_literal;
+         }
-
+      };
       unsigned elems = glsl_get_length(src->type->type);
       for (unsigned i = 0; i < elems; i++) {
-         src_elem.chain->link[src_elem.chain->length - 1].id = i;
+         chain.link[0].id = i;
-         dest_elem.chain->link[dest_elem.chain->length - 1].id = i;
+         struct vtn_pointer *src_elem =
-         if (base_type == GLSL_TYPE_STRUCT) {
+            vtn_pointer_dereference(b, src, &chain);
-            src_elem.type = src->type->members[i];
+         struct vtn_pointer *dest_elem =
-            dest_elem.type = dest->type->members[i];
+            vtn_pointer_dereference(b, dest, &chain);
-         } else {
+
-            src_elem.type = src->type->array_element;
+         _vtn_variable_copy(b, dest_elem, src_elem);
-            dest_elem.type = dest->type->array_element;
-         }
-         _vtn_variable_copy(b, &dest_elem, &src_elem);
       }
       return;
    }
@@ -1548,7 +1587,22 @@ vtn_handle_variables(struct vtn_builder *b, SpvOp opcode,
 
    case SpvOpAccessChain:
    case SpvOpInBoundsAccessChain: {
-      struct vtn_pointer *base, *ptr;
+      struct vtn_access_chain *chain = vtn_access_chain_create(b, count - 4);
+
+      unsigned idx = 0;
+      for (int i = 4; i < count; i++) {
+         struct vtn_value *link_val = vtn_untyped_value(b, w[i]);
+         if (link_val->value_type == vtn_value_type_constant) {
+            chain->link[idx].mode = vtn_access_mode_literal;
+            chain->link[idx].id = link_val->constant->values[0].u32[0];
+         } else {
+            chain->link[idx].mode = vtn_access_mode_id;
+            chain->link[idx].id = w[i];
+
+         }
+         idx++;
+      }
+
       struct vtn_value *base_val = vtn_untyped_value(b, w[3]);
       if (base_val->value_type == vtn_value_type_sampled_image) {
          /* This is rather insane.  SPIR-V allows you to use OpSampledImage
@@ -1558,51 +1612,17 @@ vtn_handle_variables(struct vtn_builder *b, SpvOp opcode,
           * sampler when crawling the access chain, but it does leave us
           * with this rather awkward little special-case.
           */
-         base = base_val->sampled_image->image;
-      } else {
-         assert(base_val->value_type == vtn_value_type_pointer);
-         base = base_val->pointer;
-      }
-
-      struct vtn_access_chain *chain =
-         vtn_access_chain_extend(b, base->chain, count - 4);
-      struct vtn_type *type = base->type;
-
-      unsigned idx = base->chain ? base->chain->length : 0;
-      for (int i = 4; i < count; i++) {
-         struct vtn_value *link_val = vtn_untyped_value(b, w[i]);
-         if (link_val->value_type == vtn_value_type_constant) {
-            chain->link[idx].mode = vtn_access_mode_literal;
-            chain->link[idx].id = link_val->constant->values[0].u32[0];
-         } else {
-            chain->link[idx].mode = vtn_access_mode_id;
-            chain->link[idx].id = w[i];
-         }
-
-         if (glsl_type_is_struct(type->type)) {
-            assert(chain->link[idx].mode == vtn_access_mode_literal);
-            type = type->members[chain->link[idx].id];
-         } else {
-            type = type->array_element;
-         }
-         idx++;
-      }
-
-      ptr = ralloc(b, struct vtn_pointer);
-      *ptr = *base;
-      ptr->chain = chain;
-      ptr->type = type;
-
-      if (base_val->value_type == vtn_value_type_sampled_image) {
          struct vtn_value *val =
             vtn_push_value(b, w[2], vtn_value_type_sampled_image);
          val->sampled_image = ralloc(b, struct vtn_sampled_image);
-         val->sampled_image->image = ptr;
+         val->sampled_image->image =
+            vtn_pointer_dereference(b, base_val->sampled_image->image, chain);
          val->sampled_image->sampler = base_val->sampled_image->sampler;
       } else {
+         assert(base_val->value_type == vtn_value_type_pointer);
          struct vtn_value *val =
             vtn_push_value(b, w[2], vtn_value_type_pointer);
-         val->pointer = ptr;
+         val->pointer = vtn_pointer_dereference(b, base_val->pointer, chain);
       }
       break;
    }