Inclusion Criteria:  Histologically confirmed DLBCL based on the World Health Organization (WHO) 2008 classification of tumors of hematopoietic and lymphoid tissue. Positive CD79B mutation confirmed by the central laboratory. Previously received at least 1 line of adequate systemic anti-DLBCL therapy, defined as an anti-CD20 antibody-based chemoimmunotherapy for at least 2 consecutive cycles, unless patients had disease progression before Cycle 2  Relapsed or refractory (R/R) disease before study entry, defined as either  Recurrent disease after having achieved disease remission (CR or partial response [PR]) at the completion of the latest treatment regimen. Stable disease or PD at the completion of the latest treatment regimen  Ineligible for high dose therapy/stem cell transplantation, which is defined as meeting any of the following criteria:  Significant organ dysfunction (eg, left ventricular ejection fraction < 50% by echocardiogram or multiple gated acquisition scan [MUGA], diffuse lung capacity for carbon monoxide < 60% predicted by pulmonary function test, creatinine clearance < 70 mL/min shown by nuclear medicine scan or 24-hour urine collection) or comorbidities precluding the use of high dose therapy/stem cell transplantation on the basis of unacceptable risk of treatment-related morbidity Failure to achieve CR or PR with salvage therapy. Failure to collect stem cells or unable to perform stem cell collection as assessed by the investigator.  Exclusion Criteria:  Patients who have NHL other than classical histology DLBCL, eg, patients with DLBCL transformed from indolent lymphomas, primary mediastinal (thymic) large B-cell lymphoma, primary cutaneous DLBCL, primary effusion lymphoma, and central nervous system (CNS) lymphoma. History of allogeneic stem cell transplantation or chimeric antigen receptor (CAR) T-cell therapy. Prior exposure to a BTK inhibitor.  Receipt of the following treatment at the time indicated before the first dose of study drug:  Corticosteroids given with antineoplastic intent more than 7 days, unless it is for control of lymphoma-related symptoms provided it is tapered off within 5 days after initiation of study treatment. Chemotherapy or radiotherapy within 2 weeks. Monoclonal antibody within 2 weeks. Investigational therapy within 2 weeks. Chinese patent medicine with antineoplastic intent within 2 weeks. History of other active malignancies within 2 years before study entry, with the exception of (1) adequately treated in-situ carcinoma of the cervix; (2) localized basal cell or squamous cell carcinoma of the skin; (3) previous malignancy confined and treated locally (surgery or other modality) with curative intent. Note: Other protocol defined Inclusion/Exclusion criteria may apply.