From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0b-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com [148.163.158.5]) by sourceware.org (Postfix) with ESMTPS id BE5CC3833011 for ; Mon, 28 Jun 2021 07:00:34 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org BE5CC3833011 Received: from pps.filterd (m0098417.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.43/8.16.0.43) with SMTP id 15S6Xncs090676; Mon, 28 Jun 2021 03:00:34 -0400 Received: from ppma01fra.de.ibm.com (46.49.7a9f.ip4.static.sl-reverse.com [159.122.73.70]) by mx0a-001b2d01.pphosted.com with ESMTP id 39f77mu4hc-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Mon, 28 Jun 2021 03:00:34 -0400 Received: from pps.filterd (ppma01fra.de.ibm.com [127.0.0.1]) by ppma01fra.de.ibm.com (8.16.1.2/8.16.1.2) with SMTP id 15S6pwu7019856; Mon, 28 Jun 2021 07:00:32 GMT Received: from b06cxnps4076.portsmouth.uk.ibm.com (d06relay13.portsmouth.uk.ibm.com [9.149.109.198]) by ppma01fra.de.ibm.com with ESMTP id 39duv88atk-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Mon, 28 Jun 2021 07:00:32 +0000 Received: from d06av23.portsmouth.uk.ibm.com (d06av23.portsmouth.uk.ibm.com [9.149.105.59]) by b06cxnps4076.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 15S70TWm31260974 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 28 Jun 2021 07:00:29 GMT Received: from d06av23.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 2D135A4127; Mon, 28 Jun 2021 07:00:28 +0000 (GMT) Received: from d06av23.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 0E0EEA40E8; Mon, 28 Jun 2021 07:00:27 +0000 (GMT) Received: from kewenlins-mbp.cn.ibm.com (unknown [9.200.147.143]) by d06av23.portsmouth.uk.ibm.com (Postfix) with ESMTP; Mon, 28 Jun 2021 07:00:26 +0000 (GMT) Subject: PING^1 [PATCH v2] combine: Tweak the condition of last_set invalidation To: GCC Patches Cc: Bill Schmidt , Segher Boessenkool References: <6bcd32fa-d0ef-b136-ddd9-92a1d21f60af@linux.ibm.com> <20210609201735.GJ18427@gate.crashing.org> From: "Kewen.Lin" Message-ID: <78d62c14-5731-17e3-e6a1-0deb4780ce37@linux.ibm.com> Date: Mon, 28 Jun 2021 15:00:25 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.10.0 In-Reply-To: Content-Type: text/plain; charset=gbk Content-Language: en-US X-TM-AS-GCONF: 00 X-Proofpoint-GUID: _DPHP0kNiBRF0sGt31SNLSoWL7nbFFu2 X-Proofpoint-ORIG-GUID: _DPHP0kNiBRF0sGt31SNLSoWL7nbFFu2 Content-Transfer-Encoding: 8bit X-Proofpoint-UnRewURL: 0 URL was un-rewritten MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.391, 18.0.790 definitions=2021-06-28_03:2021-06-25, 2021-06-28 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 lowpriorityscore=0 phishscore=0 mlxscore=0 mlxlogscore=999 impostorscore=0 spamscore=0 priorityscore=1501 adultscore=0 bulkscore=0 suspectscore=0 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2104190000 definitions=main-2106280045 X-Spam-Status: No, score=-2.4 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_EF, KAM_SHORT, MIME_CHARSET_FARAWAY, RCVD_IN_MSPIKE_H2, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.2 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on server2.sourceware.org X-BeenThere: gcc-patches@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 28 Jun 2021 07:00:36 -0000 Hi! I'd like to gentle ping this: https://gcc.gnu.org/pipermail/gcc-patches/2021-June/572555.html BR, Kewen on 2021/6/11 ÏÂÎç9:16, Kewen.Lin via Gcc-patches wrote: > Hi Segher, > > Thanks for the review! > > on 2021/6/10 ÉÏÎç4:17, Segher Boessenkool wrote: >> Hi! >> >> On Wed, Dec 16, 2020 at 04:49:49PM +0800, Kewen.Lin wrote: >>> Currently we have the check: >>> >>> if (!insn >>> || (value && rsp->last_set_table_tick >= label_tick_ebb_start)) >>> rsp->last_set_invalid = 1; >>> >>> which means if we want to record some value for some reg and >>> this reg got refered before in a valid scope, >> >> If we already know it is *set* in this same extended basic block. >> Possibly by the same instruction btw. >> >>> we invalidate the >>> set of reg (last_set_invalid to 1). It avoids to find the wrong >>> set for one reg reference, such as the case like: >>> >>> ... op regX // this regX could find wrong last_set below >>> regX = ... // if we think this set is valid >>> ... op regX >> >> Yup, exactly. >> >>> But because of retry's existence, the last_set_table_tick could >>> be set by some later reference insns, but we see it's set due >>> to retry on the set (for that reg) insn again, such as: >>> >>> insn 1 >>> insn 2 >>> >>> regX = ... --> (a) >>> ... op regX --> (b) >>> >>> insn 3 >>> >>> // assume all in the same BB. >>> >>> Assuming we combine 1, 2 -> 3 sucessfully and replace them as two >>> (3 insns -> 2 insns), >> >> This will delete insn 1 and write the combined result to insns 2 and 3. >> >>> retrying from insn1 or insn2 again: >> >> Always 2, but your point remains valid. >> >>> it will scan insn (a) again, the below condition holds for regX: >>> >>> (value && rsp->last_set_table_tick >= label_tick_ebb_start) >>> >>> it will mark this set as invalid set. But actually the >>> last_set_table_tick here is set by insn (b) before retrying, so it >>> should be safe to be taken as valid set. >> >> Yup. >> >>> This proposal is to check whether the last_set_table safely happens >>> after the current set, make the set still valid if so. >> >>> Full SPEC2017 building shows this patch gets more sucessful combines >>> from 1902208 to 1902243 (trivial though). >> >> Do you have some example, or maybe even a testcase? :-) >> > > Sorry for the late reply, it took some time to get one reduced case. > > typedef struct SA *pa_t; > > struct SC { > int h; > pa_t elem[]; > }; > > struct SD { > struct SC *e; > }; > > struct SA { > struct { > struct SD f[1]; > } g; > }; > > void foo(pa_t *k, char **m) { > int l, i; > pa_t a; > l = (int)a->g.f[5].e; > i = 0; > for (; i < l; i++) { > k[i] = a->g.f[5].e->elem[i]; > m[i] = ""; > } > } > > Baseline is r12-0 and the option is "-O3 -mcpu=power9 -fno-strict-aliasing", > with this patch, the generated assembly can save two rlwinm s. > >>> + /* Record the luid of the insn whose expression involving register n. */ >>> + >>> + int last_set_table_luid; >> >> "Record the luid of the insn for which last_set_table_tick was set", >> right? >> > > But it can be updated later to one smaller luid, how about the wording like: > > > + /* Record the luid of the insn which uses register n, the insn should > + be the first one using register n in that block of the insn which > + last_set_table_tick was set for. */ > > >>> -static void update_table_tick (rtx); >>> +static void update_table_tick (rtx, int); >> >> Please remove this declaration instead, the function is not used until >> after its actual definition :-) >> > > Done. > >>> @@ -13243,7 +13247,21 @@ update_table_tick (rtx x) >>> for (r = regno; r < endregno; r++) >>> { >>> reg_stat_type *rsp = ®_stat[r]; >>> - rsp->last_set_table_tick = label_tick; >>> + if (rsp->last_set_table_tick >= label_tick_ebb_start) >>> + { >>> + /* Later references should not have lower ticks. */ >>> + gcc_assert (label_tick >= rsp->last_set_table_tick); >> >> This should be obvious, but checking it won't hurt, okay. >> >>> + /* Should pick up the lowest luid if the references >>> + are in the same block. */ >>> + if (label_tick == rsp->last_set_table_tick >>> + && rsp->last_set_table_luid > insn_luid) >>> + rsp->last_set_table_luid = insn_luid; >> >> Why? Is it conservative for the check you will do later? Please spell >> this out, it is crucial! >> > > Since later the combinations involving this insn probably make the > register be used in one insn sitting ahead (which has smaller luid than > the one which was recorded before). Yes, it's very conservative, this > ensure that we always use the luid of the insn which is the first insn > using this register in the block. The last_set invalidation is going > to catch the case like: > > ... regX // avoid the set used here ... > regX = ... > ... > > Once we have the smallest luid one of all insns which use register X, > any unsafe regX sets should be caught. > > I updated the comments to: > > + /* Since combination may generate some instructions > + to replace some foregoing instructions with the > + references to register r (using register r), we > + need to make sure we record the first instruction > + which is using register r, so always update with > + the lowest luid here. If the given set happens > + before this recorded earliest reference, the set > + value should be safe to be used. */ > >>> @@ -13359,7 +13378,10 @@ record_value_for_reg (rtx reg, rtx_insn *insn, rtx value) >>> >>> /* Mark registers that are being referenced in this value. */ >>> if (value) >>> - update_table_tick (value); >>> + { >>> + gcc_assert (insn); >>> + update_table_tick (value, DF_INSN_LUID (insn)); >>> + } >> >> Don't add that assert please. If you really want one it should come >> right at the start of the function, not 60 lines later :-) >> > > Exactly, fixed. > >> Looks good if I understood this correctly :-) >> >> > > Thanks again, I also updated the comments in func record_value_for_reg, > the new version is attached. > > BR, > Kewen > ----- > gcc/ChangeLog: > > * combine.c (struct reg_stat_type): New member > last_set_table_luid. > (update_table_tick): Add one argument for insn luid and > set last_set_table_luid with it, remove its declaration. > (record_value_for_reg): Adjust the condition to set > last_set_invalid nonzero. >