Commit `49fddbf4c1`

Luuk de Gram <luuk@degram.dev>

2023-05-22 19:06:38

wasm: `union_init` correctly store the tag

Previously we would only store the payload, but not the actual tag that was set. This meant miscompilations where it would incorrectly return the tag value. This also adds a tiny optimization for payloads which are not `byRef` by directly storing them based on offset, rather than first calculating a pointer to an offset.

master

1 parent 00dedab

Changed files (1)

src

arch

wasm

CodeGen.zig

@@ -4982,26 +4982,52 @@ fn airUnionInit(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const result = result: {
         const union_ty = func.air.typeOfIndex(inst);
         const layout = union_ty.unionGetLayout(func.target);
+        const union_obj = union_ty.cast(Type.Payload.Union).?.data;
+        const field = union_obj.fields.values()[extra.field_index];
+        const field_name = union_obj.fields.keys()[extra.field_index];
+
+        const tag_int = blk: {
+            const tag_ty = union_ty.unionTagTypeHypothetical();
+            const enum_field_index = tag_ty.enumFieldIndex(field_name).?;
+            var tag_val_payload: Value.Payload.U32 = .{
+                .base = .{ .tag = .enum_field_index },
+                .data = @intCast(u32, enum_field_index),
+            };
+            const tag_val = Value.initPayload(&tag_val_payload.base);
+            break :blk try func.lowerConstant(tag_val, tag_ty);
+        };
         if (layout.payload_size == 0) {
             if (layout.tag_size == 0) {
                 break :result WValue{ .none = {} };
             }
             assert(!isByRef(union_ty, func.target));
-            break :result WValue{ .imm32 = extra.field_index };
+            break :result tag_int;
         }
         assert(isByRef(union_ty, func.target));
 
         const result_ptr = try func.allocStack(union_ty);
         const payload = try func.resolveInst(extra.init);
-        const union_obj = union_ty.cast(Type.Payload.Union).?.data;
-        assert(union_obj.haveFieldTypes());
-        const field = union_obj.fields.values()[extra.field_index];
-
         if (layout.tag_align >= layout.payload_align) {
-            const payload_ptr = try func.buildPointerOffset(result_ptr, layout.tag_size, .new);
-            try func.store(payload_ptr, payload, field.ty, 0);
+            if (isByRef(field.ty, func.target)) {
+                const payload_ptr = try func.buildPointerOffset(result_ptr, layout.tag_size, .new);
+                try func.store(payload_ptr, payload, field.ty, 0);
+            } else {
+                try func.store(result_ptr, payload, field.ty, @intCast(u32, layout.tag_size));
+            }
+
+            if (layout.tag_size > 0) {
+                try func.store(result_ptr, tag_int, union_obj.tag_ty, 0);
+            }
         } else {
             try func.store(result_ptr, payload, field.ty, 0);
+            if (layout.tag_size > 0) {
+                try func.store(
+                    result_ptr,
+                    tag_int,
+                    union_obj.tag_ty,
+                    @intCast(u32, layout.payload_size),
+                );
+            }
         }
         break :result result_ptr;
     };

Commit 49fddbf4c1

Commit `49fddbf4c1`