From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.220.28]) by sourceware.org (Postfix) with ESMTPS id 67B923858D32 for ; Mon, 26 Sep 2022 11:32:41 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 67B923858D32 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-out1.suse.de (Postfix) with ESMTP id 39F7D21DBD; Mon, 26 Sep 2022 11:32:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1664191960; 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=rEarNnkn623sqIL6WO8QqFhgNh6eh3HUAkUDPzyUav8=; b=jMlpUraQDpzHntr8yk+IoUj3l2e6m6bulJSByqhxHkgzQQer7hV/dFgRrUzMu2Ft5iCI1O qT/8jkuw+Ge/kaqB/EwoAevAFeDHvEgEat4OhO+lQsarwAvM4Jb10nNVe7CezQv94Jnf/X rumVbR3GBU0nBgc7JIJDHHuSbNYrXU0= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1664191960; 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=rEarNnkn623sqIL6WO8QqFhgNh6eh3HUAkUDPzyUav8=; b=8E6XLz4/FxG2DTPegr6cP1rBk/c7T5anDZbsY2pV/VxFFu2r/c5/1ApHIACUtVK55c3++z 9PUFIz+lgFdsTHAA== 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 1B9BB2C17E; Mon, 26 Sep 2022 11:32:39 +0000 (UTC) Date: Mon, 26 Sep 2022 11:32:39 +0000 (UTC) From: Richard Biener To: Tamar Christina cc: "gcc-patches@gcc.gnu.org" , nd , "jeffreyalaw@gmail.com" , Richard Sandiford Subject: Re: [PATCH 1/2]middle-end: RFC: On expansion of conditional branches, give hint if argument is a truth type to backend 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=-11.1 required=5.0 tests=BAYES_00,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,GIT_PATCH_0,KAM_SHORT,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 Mon, 26 Sep 2022, Tamar Christina wrote: > > > This pattern occurs more than 120,000 times in SPECCPU 2017 and so is quite common. > > > How does this help a target? > > So the idea is to communicate that only the bottom bit of the value is relevant and not the entire value itself. > > > Why does RTL nonzerop bits not recover thisinformation and the desired optimization done later during combinefor example? > > I'm not sure it works here. We (AArch64) don't have QImode integer registers, so our apcs says that the top bits of the 32-bit registers it's passed in are undefined. > > We have to zero extend the value first if we really want it as an 8-bit value. So the problem is if you e.g. Pass a boolean as an argument of a function I don't think nonzero bits will return anything useful. > > > Why's a SImode compare not OK if there's no QImode compare? > > The mode then becomes irrelevant because we're telling the backend that only a single bit matters. And we have instructions to test and branch on the value of a single bit. See https://gcc.gnu.org/pipermail/gcc-patches/2022-September/602090.html for the testcases Maybe the target could use (subreg:SI (reg:BI ...)) as argument. Heh. > > We have undocumented addcc, negcc, etc. patterns, should we have aandcc pattern for this indicating support for andcc + jump as opposedto cmpcc + jump? > > This could work yeah. I didn't know these existed. Ah, so they are conditional add, not add setting CC, so andcc wouldn't be appropriate. So I'm not sure how we'd handle such situation - maybe looking at REG_DECL and recognizing a _Bool PARM_DECL is OK? Richard. > > So - what's the target and what's a testcase? > > See https://gcc.gnu.org/pipermail/gcc-patches/2022-September/602090.html :) > > Thanks, > Tamar > > ________________________________ > From: Richard Biener > Sent: Monday, September 26, 2022 11:35 AM > To: Tamar Christina > Cc: gcc-patches@gcc.gnu.org ; nd ; jeffreyalaw@gmail.com ; Richard Sandiford > Subject: Re: [PATCH 1/2]middle-end: RFC: On expansion of conditional branches, give hint if argument is a truth type to backend > > On Fri, 23 Sep 2022, Tamar Christina wrote: > > > Hi All, > > > > This is an RFC to figure out how to deal with targets that don't have native > > comparisons against QImode values. > > > > Booleans, at least in C99 and higher are 0-1 valued. This means that we only > > really need to test a single bit. However in RTL we no longer have this > > information available and just have an SImode value (due to the promotion of > > QImode to SImode). > > > > This RFC fixes it by emitting an explicit & 1 during the expansion of the > > conditional branch. > > > > However it's unlikely that we want to do this unconditionally. Most targets > > I've tested seem to have harmless code changes, like x86 changes from testb to > > andl, $1. > > > > So I have two questions: > > > > 1. Should I limit this behind a target macro? Or should I just leave it for all > > targets and deal with the fallout. > > 2. How can I tell whether the C99 0-1 values bools are being used or the older > > 0, non-0 variant? > > > > Bootstrapped Regtested on aarch64-none-linux-gnu and no issues. > > However there are some benign codegen changes on x86, testb changed to andl $1. > > > > This pattern occurs more than 120,000 times in SPECCPU 2017 and so is quite common. > > How does this help a target? Why does RTL nonzerop bits not recover this > information and the desired optimization done later during combine > for example? Why's a SImode compare not OK if there's no QImode compare? > We have undocumented addcc, negcc, etc. patterns, should we have a > andcc pattern for this indicating support for andcc + jump as opposed > to cmpcc + jump? > > So - what's the target and what's a testcase? > > Thanks, > Richard. > > > Thanks, > > Tamar > > > > gcc/ChangeLog: > > > > * tree.h (tree_zero_one_valued_p): New. > > * dojump.cc (do_jump): Add & 1 if truth type. > > > > --- inline copy of patch -- > > diff --git a/gcc/dojump.cc b/gcc/dojump.cc > > index 2af0cd1aca3b6af13d5d8799094ee93f18022296..8eaf1be49cd12298e61c6946ae79ca9de6197864 100644 > > --- a/gcc/dojump.cc > > +++ b/gcc/dojump.cc > > @@ -605,7 +605,17 @@ do_jump (tree exp, rtx_code_label *if_false_label, > > /* Fall through and generate the normal code. */ > > default: > > normal: > > - temp = expand_normal (exp); > > + tree cmp = exp; > > + /* If the expression is a truth type then explicitly generate an & 1 > > + to indicate to the target that it's a zero-one values type. This > > + allows the target to further optimize the comparison should it > > + choose to. */ > > + if (tree_zero_one_valued_p (exp)) > > + { > > + type = TREE_TYPE (exp); > > + cmp = build2 (BIT_AND_EXPR, type, exp, build_int_cstu (type, 1)); > > + } > > + temp = expand_normal (cmp); > > do_pending_stack_adjust (); > > /* The RTL optimizers prefer comparisons against pseudos. */ > > if (GET_CODE (temp) == SUBREG) > > diff --git a/gcc/tree.h b/gcc/tree.h > > index 8f8a9660c9e0605eb516de194640b8c1b531b798..be3d2dee82f692e81082cf21c878c10f9fe9e1f1 100644 > > --- a/gcc/tree.h > > +++ b/gcc/tree.h > > @@ -4690,6 +4690,7 @@ extern tree signed_or_unsigned_type_for (int, tree); > > extern tree signed_type_for (tree); > > extern tree unsigned_type_for (tree); > > extern bool is_truth_type_for (tree, tree); > > +extern bool tree_zero_one_valued_p (tree); > > extern tree truth_type_for (tree); > > extern tree build_pointer_type_for_mode (tree, machine_mode, bool); > > extern tree build_pointer_type (tree); > > > > > > > > > > > > -- > 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) > -- 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)