From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.220.29]) by sourceware.org (Postfix) with ESMTPS id 4A3413858C54 for ; Fri, 10 Mar 2023 07:41:43 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org 4A3413858C54 Authentication-Results: sourceware.org; dmarc=pass (p=none dis=none) header.from=suse.de Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=suse.de Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out2.suse.de (Postfix) with ESMTP id 5ACA72060E; Fri, 10 Mar 2023 07:41:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1678434101; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=6IGi1silQdLnS4ysj11lKsBDgBYB5aN/Ge33Fvu1jG4=; b=IvU9PNBawcanC2H3xrq8AWvCoX5/HNwyxuz6mFNIbDe43ecCfigT6bHB/8L8zTH2WRpNCM 1fgzj3ptFwhjohtrfsuOx7gjlA8mbiEkYCYydrRebDtgfIPrb6W0MRzBmW2bPz0jrW5QvQ /6FBcv/MQD7raVWs5FzNgOEFbg0w6II= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1678434101; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=6IGi1silQdLnS4ysj11lKsBDgBYB5aN/Ge33Fvu1jG4=; b=ILuPyEI7O4v2ay7qkF+kjgbhVLo11FJjCNZf5V+DFS7QdGVf7dMo8zjX0mC5MCYIQvcaOa 1mYr01YzRVBnhqDw== Received: from wotan.suse.de (wotan.suse.de [10.160.0.1]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay2.suse.de (Postfix) with ESMTPS id 431ED2C142; Fri, 10 Mar 2023 07:41:41 +0000 (UTC) Date: Fri, 10 Mar 2023 07:41:41 +0000 (UTC) From: Richard Biener To: Tamar Christina cc: gcc-patches@gcc.gnu.org, nd@arm.com, jlaw@ventanamicro.com, richard.sandiford@arm.com Subject: Re: [PATCH]middle-end: don't form FMAs when multiplication is not single use. [PR108583] In-Reply-To: Message-ID: References: User-Agent: Alpine 2.22 (LSU 394 2020-01-19) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Spam-Status: No, score=-11.0 required=5.0 tests=BAYES_00,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,GIT_PATCH_0,SPF_HELO_NONE,SPF_PASS,TXREP 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 Thu, 9 Mar 2023, Tamar Christina wrote: > Hi All, > > The testcase > > typedef unsigned int vec __attribute__((vector_size(32))); > vec > f3 (vec a, vec b, vec c) > { > vec d = a * b; > return d + ((c + d) >> 1); > } > > shows a case where we don't want to form an FMA due to the MUL not being single > use. In this case to form an FMA we have to redo the MUL as well as we no > longer have it to share. > > As such making an FMA here would be a de-optimization. > > Bootstrapped Regtested on aarch64-none-linux-gnu and no issues. > > Ok for master? OK. Thanks, Richard. > Thanks, > Tamar > > gcc/ChangeLog: > > PR target/108583 > * tree-ssa-math-opts.cc (convert_mult_to_fma): Inhibit FMA in case not > single use. > > gcc/testsuite/ChangeLog: > > PR target/108583 > * gcc.dg/mla_1.c: New test. > > Co-Authored-By: Richard Sandiford > > --- inline copy of patch -- > diff --git a/gcc/testsuite/gcc.dg/mla_1.c b/gcc/testsuite/gcc.dg/mla_1.c > new file mode 100644 > index 0000000000000000000000000000000000000000..a92ecf248116d89b1bc4207a907ea5ed95728a28 > --- /dev/null > +++ b/gcc/testsuite/gcc.dg/mla_1.c > @@ -0,0 +1,40 @@ > +/* { dg-do compile } */ > +/* { dg-require-effective-target vect_int } */ > +/* { dg-options "-O2 -msve-vector-bits=256 -march=armv8.2-a+sve -fdump-tree-optimized" } */ > + > +unsigned int > +f1 (unsigned int a, unsigned int b, unsigned int c) { > + unsigned int d = a * b; > + return d + ((c + d) >> 1); > +} > + > +unsigned int > +g1 (unsigned int a, unsigned int b, unsigned int c) { > + return a * b + c; > +} > + > +__Uint32x4_t > +f2 (__Uint32x4_t a, __Uint32x4_t b, __Uint32x4_t c) { > + __Uint32x4_t d = a * b; > + return d + ((c + d) >> 1); > +} > + > +__Uint32x4_t > +g2 (__Uint32x4_t a, __Uint32x4_t b, __Uint32x4_t c) { > + return a * b + c; > +} > + > +typedef unsigned int vec __attribute__((vector_size(32))); vec > +f3 (vec a, vec b, vec c) > +{ > + vec d = a * b; > + return d + ((c + d) >> 1); > +} > + > +vec > +g3 (vec a, vec b, vec c) > +{ > + return a * b + c; > +} > + > +/* { dg-final { scan-tree-dump-times {\.FMA } 1 "optimized" { target aarch64*-*-* } } } */ > diff --git a/gcc/tree-ssa-math-opts.cc b/gcc/tree-ssa-math-opts.cc > index 5ab5b944a573ad24ce8427aff24fc5215bf05dac..26ed91d58fa4709a67c903ad446d267a3113c172 100644 > --- a/gcc/tree-ssa-math-opts.cc > +++ b/gcc/tree-ssa-math-opts.cc > @@ -3346,6 +3346,20 @@ convert_mult_to_fma (gimple *mul_stmt, tree op1, tree op2, > param_avoid_fma_max_bits)); > bool defer = check_defer; > bool seen_negate_p = false; > + > + /* There is no numerical difference between fused and unfused integer FMAs, > + and the assumption below that FMA is as cheap as addition is unlikely > + to be true, especially if the multiplication occurs multiple times on > + the same chain. E.g., for something like: > + > + (((a * b) + c) >> 1) + (a * b) > + > + we do not want to duplicate the a * b into two additions, not least > + because the result is not a natural FMA chain. */ > + if (ANY_INTEGRAL_TYPE_P (type) > + && !has_single_use (mul_result)) > + return false; > + > /* Make sure that the multiplication statement becomes dead after > the transformation, thus that all uses are transformed to FMAs. > This means we assume that an FMA operation has the same cost > > > > > -- Richard Biener SUSE Software Solutions Germany GmbH, Frankenstrasse 146, 90461 Nuernberg, Germany; GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman; HRB 36809 (AG Nuernberg)