From 6f55a689644fa85a6f650e6d33bcb882b1f507cd Mon Sep 17 00:00:00 2001
From: Robin Voetter <robin@voetter.nl>
Date: Sun, 17 Sep 2023 17:29:38 +0200
Subject: [PATCH] spirv: air struct_field_ptr for unions

---
 src/codegen/spirv.zig   | 22 ++++++++++++++++++++--
 test/behavior/union.zig |  1 -
 2 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/src/codegen/spirv.zig b/src/codegen/spirv.zig
index 7ac7672cdd..8a77899bc0 100644
--- a/src/codegen/spirv.zig
+++ b/src/codegen/spirv.zig
@@ -2651,17 +2651,35 @@ pub const DeclGen = struct {
         object_ptr: IdRef,
         field_index: u32,
     ) !?IdRef {
+        const result_ty_ref = try self.resolveType(result_ptr_ty, .direct);
+
         const mod = self.module;
         const object_ty = object_ptr_ty.childType(mod);
         switch (object_ty.zigTypeTag(mod)) {
             .Struct => switch (object_ty.containerLayout(mod)) {
                 .Packed => unreachable, // TODO
                 else => {
-                    const result_ty_ref = try self.resolveType(result_ptr_ty, .direct);
                     return try self.accessChain(result_ty_ref, object_ptr, &.{field_index});
                 },
             },
-            else => unreachable, // TODO
+            .Union => switch (object_ty.containerLayout(mod)) {
+                .Packed => unreachable, // TODO
+                else => {
+                    const storage_class = spvStorageClass(object_ptr_ty.ptrAddressSpace(mod));
+                    const un_active_ty_ref = try self.resolveUnionType(object_ty, field_index);
+                    const un_active_ptr_ty_ref = try self.spv.ptrType(un_active_ty_ref, storage_class);
+
+                    const casted_id = self.spv.allocId();
+                    try self.func.body.emit(self.spv.gpa, .OpBitcast, .{
+                        .id_result_type = self.typeId(un_active_ptr_ty_ref),
+                        .id_result = casted_id,
+                        .operand = object_ptr,
+                    });
+                    const layout = self.unionLayout(object_ty, field_index);
+                    return try self.accessChain(result_ty_ref, casted_id, &.{layout.active_field_index});
+                },
+            },
+            else => unreachable,
         }
     }
 
diff --git a/test/behavior/union.zig b/test/behavior/union.zig
index aa4ba3bc44..003b6d3f8f 100644
--- a/test/behavior/union.zig
+++ b/test/behavior/union.zig
@@ -496,7 +496,6 @@ test "union initializer generates padding only if needed" {
     if (builtin.zig_backend == .stage2_arm) return error.SkipZigTest;
     if (builtin.zig_backend == .stage2_aarch64) return error.SkipZigTest;
     if (builtin.zig_backend == .stage2_sparc64) return error.SkipZigTest; // TODO
-    if (builtin.zig_backend == .stage2_spirv64) return error.SkipZigTest;
 
     const U = union(enum) {
         A: u24,