From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-x533.google.com (mail-ed1-x533.google.com [IPv6:2a00:1450:4864:20::533]) by sourceware.org (Postfix) with ESMTPS id 08FE13858D3C for ; Mon, 27 Sep 2021 14:11:59 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 08FE13858D3C Received: by mail-ed1-x533.google.com with SMTP id ba1so11894086edb.4 for ; Mon, 27 Sep 2021 07:11:58 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=4MplTIbwIYC1PrfWWhR0ix/Kjm59sCap+A/ZCn7FEp0=; b=Yc5N0H85+ktu+OVfEevdxyUV0pCH39OntniGCQHIMqMbDH4IhV6wGVq9XHFa0fSvlf /HTvUK6qbivc/0evePB1BLS1Dnr9m9QFAZH7MF3h5z57xfqudPOzsUVf1mnARkCRN9gZ HR7+LEPEXYEDMly2s0T8EoSbAeOZCnHWpITZTx9dFtoZ6/L+nbF89zQ9/6KnFn+1QgBS CYlEUwifwD+wRogTVwK4UFJtvbJZdTmals4j6BbIS4fnMRyvJV7N+HSyKbG+4P5I/W3p WsNeJlGmt6FVPXrpb1gHbjqoWvOkyX9JehLRGUvKGhkdrJnq6DdG2rY20tftpIrhj4F7 VRDg== X-Gm-Message-State: AOAM530oZk3HXftfMMEA54xVTeQSNXZckk+FlfWD1pKRKByYXzxKlkWw lOx9HWZjfctISnSTL9SiaM2nHsBS/3DUyulqGFhNzvD+KRg= X-Google-Smtp-Source: ABdhPJxKJiHrufz2M6A/1yey0iWueRZW3mhDUeS0zuzSLbh4aMbPqUopYyRqREuwpEe1Rw5gonuBeEgnaWaZyTk68LI= X-Received: by 2002:a17:906:ccca:: with SMTP id ot10mr214064ejb.429.1632751917801; Mon, 27 Sep 2021 07:11:57 -0700 (PDT) MIME-Version: 1.0 References: In-Reply-To: From: Richard Biener Date: Mon, 27 Sep 2021 16:11:47 +0200 Message-ID: Subject: Re: [PATCH] tree-optimization/100112 - VN last_vuse and redundant store elimination To: Richard Biener Cc: GCC Patches Content-Type: text/plain; charset="UTF-8" X-Spam-Status: No, score=-8.5 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, FREEMAIL_FROM, GIT_PATCH_0, RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) 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, 27 Sep 2021 14:12:02 -0000 On Mon, Sep 27, 2021 at 3:08 PM Richard Biener via Gcc-patches wrote: > > This avoids the last_vuse optimization hindering redundant store > elimination by always also recording the original VUSE that was > in effect on the load. > > Bootstrapped and tested on x86_64-unknown-linux-gnu. > > I'm still pondering on how to avoid the wastage of adding the ref > twice and will at least record some statistics for this. In stage3 gcc/*.o we have 3182752 times recorded a single entry and 903409 times two entries (that's ~20% overhead). With just recording a single entry the number of hashtable lookups done when walking the vuse->vdef links to find an earlier access is 28961618. When recording the second entry this makes us find that earlier for donwnstream redundant accesses, reducing the number of hashtable lookups to 25401052 (that's a ~10% reduction). Overall I think it's a reasonable trade-off but as said, I'm pondering a bit on how to reduce the overhead without too ugly hacks. Richard. > 2021-09-27 Richard Biener > > PR tree-optimization/100112 > * tree-ssa-sccvn.c (visit_reference_op_load): Record the > referece into the hashtable twice in case last_vuse is > different from the original vuse on the stmt. > > * gcc.dg/tree-ssa/ssa-fre-95.c: New testcase. > --- > gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-95.c | 25 ++++++++++++++++++++++ > gcc/tree-ssa-sccvn.c | 17 +++++++++++---- > 2 files changed, 38 insertions(+), 4 deletions(-) > create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-95.c > > diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-95.c b/gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-95.c > new file mode 100644 > index 00000000000..b0936be5e77 > --- /dev/null > +++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-95.c > @@ -0,0 +1,25 @@ > +/* PR100112 and dups. */ > +/* { dg-do compile } */ > +/* { dg-options "-O2 -fdump-tree-fre1-details -fdump-tree-optimized" } */ > + > +int *c, *b; > +void foo() > +{ > + int *tem = b; > + *tem = 0; > + int *footem = c; > + c = footem; > +} > + > +void bar() > +{ > + int *tem = b; > + int *bartem = c; > + *tem = 0; > + c = bartem; > +} > + > +/* We should elide the redundant store in foo, in bar it is not redundant since > + the *tem = 0 store might alias. */ > +/* { dg-final { scan-tree-dump "Deleted redundant store c = footem" "fre1" } } */ > +/* { dg-final { scan-tree-dump "c = bartem" "optimized" } } */ > diff --git a/gcc/tree-ssa-sccvn.c b/gcc/tree-ssa-sccvn.c > index e8b1c39184d..416a5252144 100644 > --- a/gcc/tree-ssa-sccvn.c > +++ b/gcc/tree-ssa-sccvn.c > @@ -5125,13 +5125,12 @@ static bool > visit_reference_op_load (tree lhs, tree op, gimple *stmt) > { > bool changed = false; > - tree last_vuse; > tree result; > vn_reference_t res; > > - last_vuse = gimple_vuse (stmt); > - result = vn_reference_lookup (op, gimple_vuse (stmt), > - default_vn_walk_kind, &res, true, &last_vuse); > + tree vuse = gimple_vuse (stmt); > + tree last_vuse = vuse; > + result = vn_reference_lookup (op, vuse, default_vn_walk_kind, &res, true, &last_vuse); > > /* We handle type-punning through unions by value-numbering based > on offset and size of the access. Be prepared to handle a > @@ -5174,6 +5173,16 @@ visit_reference_op_load (tree lhs, tree op, gimple *stmt) > { > changed = set_ssa_val_to (lhs, lhs); > vn_reference_insert (op, lhs, last_vuse, NULL_TREE); > + if (vuse && SSA_VAL (last_vuse) != SSA_VAL (vuse)) > + { > + if (dump_file && (dump_flags & TDF_DETAILS)) > + { > + fprintf (dump_file, "Using extra use virtual operand "); > + print_generic_expr (dump_file, last_vuse); > + fprintf (dump_file, "\n"); > + } > + vn_reference_insert (op, lhs, vuse, NULL_TREE); > + } > } > > return changed; > -- > 2.31.1