From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 28089 invoked by alias); 6 Nov 2014 17:57:29 -0000 Mailing-List: contact gcc-patches-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Id: List-Archive: List-Post: List-Help: Sender: gcc-patches-owner@gcc.gnu.org Received: (qmail 27958 invoked by uid 89); 6 Nov 2014 17:57:28 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-3.2 required=5.0 tests=AWL,BAYES_00,RP_MATCHES_RCVD,SPF_HELO_PASS autolearn=ham version=3.3.2 X-Spam-User: qpsmtpd, 2 recipients X-HELO: mx1.redhat.com Received: from mx1.redhat.com (HELO mx1.redhat.com) (209.132.183.28) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with (AES256-GCM-SHA384 encrypted) ESMTPS; Thu, 06 Nov 2014 17:57:26 +0000 Received: from int-mx14.intmail.prod.int.phx2.redhat.com (int-mx14.intmail.prod.int.phx2.redhat.com [10.5.11.27]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id sA6HvN7p010302 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Thu, 6 Nov 2014 12:57:24 -0500 Received: from [10.10.60.106] (vpn-60-106.rdu2.redhat.com [10.10.60.106]) by int-mx14.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id sA6HvMsP017028; Thu, 6 Nov 2014 12:57:22 -0500 Message-ID: <545BB682.9000209@redhat.com> Date: Thu, 06 Nov 2014 17:57:00 -0000 From: Andrew MacLeod User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.2.0 MIME-Version: 1.0 To: Richard Biener , Richard Henderson , gcc-patches CC: Jeff Law , Andrew Haley , java@gcc.gnu.org Subject: Re: [patch] Provide a can_compare_and_swap_p target hook. References: <5458FE9C.2090409@redhat.com> <54590C19.40208@redhat.com> <54591348.1010904@redhat.com> <545913A4.5010400@redhat.com> <54591B3A.8030908@redhat.com> <70044BE8-9F38-4BDB-B73F-6E2FC9AC2629@gmail.com> <54593352.2000700@redhat.com> In-Reply-To: <54593352.2000700@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-IsSubscribed: yes X-SW-Source: 2014-11/txt/msg00527.txt.bz2 On 11/04/2014 03:13 PM, Andrew MacLeod wrote: > >from targhooks.c: >>> bool >>> default_builtin_support_vector_misalignment (machine_mode mode, >>> const_tree type, <...>) >>> { >>> if (optab_handler (movmisalign_optab, mode) != CODE_FOR_nothing) >>> return true; >>> return false; >>> } >>> >>> the idea is to move all the functionality that front ends need into >>> well >>> defined and controlled places so we can increase the separation. "can >>> perform a compare_and_swap operation" is clearly a target specific >>> question isn't it? >> I would rather question what is so special about java that it needs >> to ask that and other frontends not. Don't we have generic atomics >> support now? >> >> Richard. >> > True... I don't know if this is a thing that simply predates our > current level of support or if it is something else that is java > specific for its builtins. > Don't know enough about java to comment. > > aph? Looks like you wrote the originals in 2006... Can the java CAS > builtins simply use our current atomic calls rather than doing their > own thing and querying whether the target has a sync compare and swap > operation? > > Andrew It looks like java is deciding whether or not GCC can inline atomic operations or not, and if it can't, doesn't want the atomic operations... which presumably means there is no dependency on libatomic at runtime. A call to can_compare_and_swap_p(mode) is analogous to a compile time version of folding atomic_always_lock_free(mode) to a constant... Frankly that seems like a reasonable question for some front end to ask... and elect not to emit atomic calls if so desired. (which is what java is doing I think) whether it still needs to do that is a question for some java person. Andrew