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Content-Language: en-US To: Jakub Jelinek Cc: Segher Boessenkool , Ajit Agarwal , gcc-patches , jeff Law , Richard Biener References: <236aab6b-537f-7fb6-125c-220fb63f7521@linux.ibm.com> <20230419200011.GG19790@gate.crashing.org> <809ed95b-686c-e515-584b-a1a1d40e6f68@linux.ibm.com> From: Peter Bergner In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: d1T-uPGD0RzTQJys0dyhH27pEgZfYdAO X-Proofpoint-ORIG-GUID: 4Xtu3lwnJQiVtWGh05Jfu0Lg9OS29sH6 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.254,Aquarius:18.0.942,Hydra:6.0.573,FMLib:17.11.170.22 definitions=2023-04-24_09,2023-04-21_01,2023-02-09_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 malwarescore=0 phishscore=0 clxscore=1015 impostorscore=0 adultscore=0 priorityscore=1501 mlxscore=0 lowpriorityscore=0 spamscore=0 mlxlogscore=647 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2303200000 definitions=main-2304240140 X-Spam-Status: No, score=-4.0 required=5.0 tests=BAYES_00,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_EF,NICE_REPLY_A,RCVD_IN_MSPIKE_H2,SPF_HELO_NONE,SPF_PASS,TXREP,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: On 4/24/23 10:28 AM, Jakub Jelinek wrote: > On Mon, Apr 24, 2023 at 10:23:06AM -0500, Peter Bergner wrote: >> On 4/19/23 3:00 PM, Segher Boessenkool wrote: >>> On Wed, Apr 19, 2023 at 11:23:07PM +0530, Ajit Agarwal wrote: >>>> * common/config/rs6000/rs6000-common.cc: Add REE pass as a >>>> default rs6000 target pass for O2 and above. >>> >>> Why only for -O2? Only when optimising at all makes sense, people use >>> -O0 only when they want to skip as many optimisations as possible, maybe >>> because of compilation time concerns, maybe to avoid an ICE or other >>> bug. Isn't REE *always* a good thing, it never degrades code quality? >>> Or are there situations where it results in worse code? >> >> I think this is a case of following what the other architectures are doing. >> Namely, x86, aarch64, riscv, sparc, alpha and h8300 all enable -free at >> -O2 and above, not -O1. Not to say that is the best answer, but I think >> that is why we did the same. I agree I don't think -free can produce >> worse code which makes using it with -O1 and above an option. Maybe someone >> was worried about compile time??? Doesn't seem like an optimization like >> this would be too expensive though. > > I thought that > df_chain_add_problem (DF_UD_CHAIN + DF_DU_CHAIN); > is quite expensive (only other pass which does that is SMS pass) and > df_mir_add_problem (); > as well (REE pass being the only user of that). As -O1 is meant to scale > well on huge compiler generated functions, perhaps REE isn't appropriate > for those by default. Ah, so it is an issue with compile time then. If so, then sure, being -O2 and above makes sense then. Thanks for pointing that out! Peter