restoreErrRetIndex

fn restoreErrRetIndex(
    gz: *GenZir,
    bt: GenZir.BranchTarget,
    ri: ResultInfo,
    node: Ast.Node.Index,
    result: Zir.Inst.Ref,
) !void {
    const op = switch (nodeMayEvalToError(gz.astgen.tree, node)) {
        .always => return, // never restore/pop
        .never => .none, // always restore/pop
        .maybe => switch (ri.ctx) {
            .error_handling_expr, .@"return", .fn_arg, .const_init => switch (ri.rl) {
                .ptr => |ptr_res| try gz.addUnNode(.load, ptr_res.inst, node),
                .inferred_ptr => blk: {
                    // This is a terrible workaround for Sema's inability to load from a .alloc_inferred ptr
                    // before its type has been resolved. There is no valid operand to use here, so error
                    // traces will be popped prematurely.
                    // TODO: Update this to do a proper load from the rl_ptr, once Sema can support it.
                    break :blk .none;
                },
                .destructure => return, // value must be a tuple or array, so never restore/pop
                else => result,
            },
            else => .none, // always restore/pop
        },
    };
    _ = try gz.addRestoreErrRetIndex(bt, .{ .if_non_error = op }, node);
}