From c2e6731032b72c20b5caf2182883aaede9c1a5ea Mon Sep 17 00:00:00 2001
From: Mick Sayson <mick@sayson.com>
Date: Wed, 8 Jul 2026 16:05:43 -0700
Subject: [PATCH] Implement spirv optional_payload_ptr_set

This fixes functions that return non-primitive optional values. E.g.

    fn someFnWithOptional(x: f32) ?[2]f32 {
        if (x > 5) return null;
        return .{ x, x };
    }

Pieced together referencing airIsNull, and airUnwrapOptionalPtr. Tested
that shaders in an external project are outputting the expected values
---
 src/codegen/spirv/CodeGen.zig | 34 ++++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/src/codegen/spirv/CodeGen.zig b/src/codegen/spirv/CodeGen.zig
index 0ea7567b5eed6859069b031835c57d1b539afbed..9d86ae254d51dfe4cdc201ce68b956eeb56da28e 100644
--- a/src/codegen/spirv/CodeGen.zig
+++ b/src/codegen/spirv/CodeGen.zig
@@ -4459,6 +4459,7 @@ fn genInst(cg: *CodeGen, inst: Air.Inst.Index) Error!void {
 
             .optional_payload     => try cg.airUnwrapOptional(inst),
             .optional_payload_ptr => try cg.airUnwrapOptionalPtr(inst),
+            .optional_payload_ptr_set => try cg.airSetOptionalPtr(inst),
             .wrap_optional        => try cg.airWrapOptional(inst),
 
             .assembly => try cg.airAssembly(inst),
@@ -8017,6 +8018,39 @@ fn airUnwrapOptionalPtr(cg: *CodeGen, inst: Air.Inst.Index) !?Id {
     return try cg.accessChain(result_ty_id, operand_id, &.{0});
 }
 
+fn airSetOptionalPtr(cg: *CodeGen, inst: Air.Inst.Index) !?Id {
+    const zcu = cg.zcu;
+    const ty_op = cg.air.instructions.items(.data)[@intFromEnum(inst)].ty_op;
+
+    const ptr_ty = cg.typeOf(ty_op.operand);
+    const ptr_id = try cg.resolve(ty_op.operand);
+
+    const optional_ty = ptr_ty.childType(zcu);
+    const payload_ty = optional_ty.optionalChild(zcu);
+    const result_ty = cg.typeOfIndex(inst);
+
+    if (optional_ty.optionalReprIsPayload(zcu)) {
+        return try cg.bitCast(result_ty, ptr_ty, ptr_id);
+    }
+
+    const storage_class = cg.storageClass(ptr_ty.ptrAddressSpace(zcu));
+    const bool_indirect_ty_id = try cg.resolveType(.bool, .indirect);
+    const bool_ptr_ty_id = try cg.ptrType(bool_indirect_ty_id, storage_class);
+    const result_ty_id = try cg.resolveType(result_ty, .direct);
+
+    const bool_ptr_id, const ret = switch (payload_ty.hasRuntimeBits(zcu)) {
+        true => .{
+            try cg.accessChain(bool_ptr_ty_id, ptr_id, &.{1}),
+            try cg.accessChain(result_ty_id, ptr_id, &.{0}),
+        },
+        false => .{ ptr_id, try cg.bitCast(result_ty, ptr_ty, ptr_id) },
+    };
+
+    try cg.store(.bool, bool_ptr_id, try cg.constBool(true, .direct), .{});
+
+    return ret;
+}
+
 fn airWrapOptional(cg: *CodeGen, inst: Air.Inst.Index) !?Id {
     const zcu = cg.zcu;
     const ty_op = cg.air.instructions.items(.data)[@intFromEnum(inst)].ty_op;
-- 
2.54.0