From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 86679 invoked by alias); 19 Sep 2016 13:41:04 -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 86637 invoked by uid 89); 19 Sep 2016 13:41:01 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-2.1 required=5.0 tests=AWL,BAYES_00,FREEMAIL_FROM,RCVD_IN_DNSWL_LOW,RCVD_IN_SORBS_SPAM,SPF_PASS autolearn=ham version=3.3.2 spammy=Take X-HELO: mail-wm0-f52.google.com Received: from mail-wm0-f52.google.com (HELO mail-wm0-f52.google.com) (74.125.82.52) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with ESMTP; Mon, 19 Sep 2016 13:40:51 +0000 Received: by mail-wm0-f52.google.com with SMTP id l132so152487319wmf.0 for ; Mon, 19 Sep 2016 06:40:50 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:in-reply-to:references:from:date :message-id:subject:to:cc; bh=zQeG6T0VYCYp5LO2Fuyb+kyOMknHaXVRezDucCjt4HQ=; b=mgXGiA66tMxAF4ZrCkvLT6oU8vRbPke8ilRCBI36ZqQTMuBGXmSi0zXcQjplHZSMcH jeKOBnFn2418hvQbFBIUmqoveixgVdWxsTZ0rkQ+agXCwdbPx/PXbYiRelzRvgWKdgnl xDIrpYL6+v49dGm+r62FJlP6KjGOrbv15Nxj3XZcT0IEyh8ZGpLXp8+VX8H58HAexi3z gd/FosnExyzC2jr8s8hm19YATFUSVDfVxPjAEJcR3z541AJ8Kqfb6SPTm/f7mgFn5Kf3 4sXYVvovG0nsgLLWbsBGIibloKR7JANxyca+LJTS9IwmCDOoTpmErV2XnpPXPp5w73ZG wr3Q== X-Gm-Message-State: AE9vXwOs8OKjjO4RN250fNEaaIx2Te9SAoVcDsHZF4dPfuLAJvJd12KJyoxOndhQCMh7+cfjwB6zwDq/xkzWAA== X-Received: by 10.28.138.140 with SMTP id m134mr8958916wmd.92.1474292449036; Mon, 19 Sep 2016 06:40:49 -0700 (PDT) MIME-Version: 1.0 Received: by 10.28.137.129 with HTTP; Mon, 19 Sep 2016 06:40:47 -0700 (PDT) In-Reply-To: <0f3b4359-f5ff-d14c-1b15-2ae647e6fd3a@linaro.org> References: <0a1eaaf8-3ede-cd56-ffb5-40b25f94e46e@linaro.org> <98613cff-7c48-1a56-0014-6d87c35a8f26@linaro.org> <20160809214617.GB14857@tucnak.redhat.com> <7210cceb-be3b-44b1-13b7-4152e89d2a4f@linaro.org> <20160809215527.GC14857@tucnak.redhat.com> <0c53b0f3-4af6-387c-9350-95b1ae85850d@linaro.org> <20160810085703.GH14857@tucnak.redhat.com> <0f3b4359-f5ff-d14c-1b15-2ae647e6fd3a@linaro.org> From: Richard Biener Date: Mon, 19 Sep 2016 13:49:00 -0000 Message-ID: Subject: Re: [PR72835] Incorrect arithmetic optimization involving bitfield arguments To: kugan Cc: Jakub Jelinek , "gcc-patches@gcc.gnu.org" Content-Type: text/plain; charset=UTF-8 X-IsSubscribed: yes X-SW-Source: 2016-09/txt/msg01170.txt.bz2 On Sun, Sep 18, 2016 at 10:21 PM, kugan wrote: > Hi Richard, > > > On 14/09/16 21:31, Richard Biener wrote: >> >> On Fri, Sep 2, 2016 at 10:09 AM, Kugan Vivekanandarajah >> wrote: >>> >>> Hi Richard, >>> >>> On 25 August 2016 at 22:24, Richard Biener >>> wrote: >>>> >>>> On Thu, Aug 11, 2016 at 1:09 AM, kugan >>>> wrote: >>>>> >>>>> Hi, >>>>> >>>>> >>>>> On 10/08/16 20:28, Richard Biener wrote: >>>>>> >>>>>> >>>>>> On Wed, Aug 10, 2016 at 10:57 AM, Jakub Jelinek >>>>>> wrote: >>>>>>> >>>>>>> >>>>>>> On Wed, Aug 10, 2016 at 08:51:32AM +1000, kugan wrote: >>>>>>>> >>>>>>>> >>>>>>>> I see it now. The problem is we are just looking at (-1) being in >>>>>>>> the >>>>>>>> ops >>>>>>>> list for passing changed to rewrite_expr_tree in the case of >>>>>>>> multiplication >>>>>>>> by negate. If we have combined (-1), as in the testcase, we will >>>>>>>> not >>>>>>>> have >>>>>>>> the (-1) and will pass changed=false to rewrite_expr_tree. >>>>>>>> >>>>>>>> We should set changed based on what happens in >>>>>>>> try_special_add_to_ops. >>>>>>>> Attached patch does this. Bootstrap and regression testing are >>>>>>>> ongoing. >>>>>>>> Is >>>>>>>> this OK for trunk if there is no regression. >>>>>>> >>>>>>> >>>>>>> >>>>>>> I think the bug is elsewhere. In particular in >>>>>>> undistribute_ops_list/zero_one_operation/decrement_power. >>>>>>> All those look problematic in this regard, they change RHS of >>>>>>> statements >>>>>>> to something that holds a different value, while keeping the LHS. >>>>>>> So, generally you should instead just add a new stmt next to the old >>>>>>> one, >>>>>>> and adjust data structures (replace the old SSA_NAME in some ->op >>>>>>> with >>>>>>> the new one). decrement_power might be a problem here, dunno if all >>>>>>> the >>>>>>> builtins are const in all cases that DSE would kill the old one, >>>>>>> Richard, any preferences for that? reset flow sensitive info + reset >>>>>>> debug >>>>>>> stmt uses, or something different? Though, replacing the LHS with a >>>>>>> new >>>>>>> anonymous SSA_NAME might be needed too, in case it is before SSA_NAME >>>>>>> of >>>>>>> a >>>>>>> user var that doesn't yet have any debug stmts. >>>>>> >>>>>> >>>>>> >>>>>> I'd say replacing the LHS is the way to go, with calling the >>>>>> appropriate >>>>>> helper >>>>>> on the old stmt to generate a debug stmt for it / its uses (would need >>>>>> to look it >>>>>> up here). >>>>>> >>>>> >>>>> Here is an attempt to fix it. The problem arises when in >>>>> undistribute_ops_list, we linearize_expr_tree such that NEGATE_EXPR is >>>>> added >>>>> (-1) MULT_EXPR (OP). Real problem starts when we handle this in >>>>> zero_one_operation. Unlike what was done earlier, we now change the >>>>> stmt >>>>> (with propagate_op_to_signle use or by directly) such that the value >>>>> computed by stmt is no longer what it used to be. Because of this, what >>>>> is >>>>> computed in undistribute_ops_list and rewrite_expr_tree are also >>>>> changed. >>>>> >>>>> undistribute_ops_list already expects this but rewrite_expr_tree will >>>>> not if >>>>> we dont pass the changed as an argument. >>>>> >>>>> The way I am fixing this now is, in linearize_expr_tree, I set >>>>> ops_changed >>>>> to true if we change NEGATE_EXPR to (-1) MULT_EXPR (OP). Then when we >>>>> call >>>>> zero_one_operation with ops_changed = true, I replace all the LHS in >>>>> zero_one_operation with the new SSA and replace all the uses. I also >>>>> call >>>>> the rewrite_expr_tree with changed = false in this case. >>>>> >>>>> Does this make sense? Bootstrapped and regression tested for >>>>> x86_64-linux-gnu without any new regressions. >>>> >>>> >>>> I don't think this solves the issue. zero_one_operation associates the >>>> chain starting at the first *def and it will change the intermediate >>>> values >>>> of _all_ of the stmts visited until the operation to be removed is >>>> found. >>>> Note that this is independent of whether try_special_add_to_ops did >>>> anything. >>>> >>>> Even for the regular undistribution cases we get this wrong. >>>> >>>> So we need to back-track in zero_one_operation, replacing each LHS >>>> and in the end the op in the opvector of the main chain. That's >>>> basically >>>> the same as if we'd do a regular re-assoc operation on the sub-chains. >>>> Take their subops, simulate zero_one_operation by >>>> appending the cancelling operation and optimizing the oplist, and then >>>> materializing the associated ops via rewrite_expr_tree. >>>> >>> Here is a draft patch which records the stmt chain when in >>> zero_one_operation and then fixes it when OP is removed. when we >>> update *def, that will update the ops vector. Does this looks sane? >> >> >> Yes. A few comments below >> >> + /* PR72835 - Record the stmt chain that has to be updated such that >> + we dont use the same LHS when the values computed are different. */ >> + auto_vec stmts_to_fix; >> >> use auto_vec here so we get stack allocation only most >> of the times > > Done. > >> if (stmt_is_power_of_op (stmt, op)) >> { >> + make_new_ssa_for_all_defs (def, op, stmts_to_fix); >> if (decrement_power (stmt) == 1) >> propagate_op_to_single_use (op, stmt, def); >> >> for the cases you end up with propagate_op_to_single_use its argument >> stmt is handled superfluosly in the new SSA making, I suggest to pop it >> from the stmts_to_fix vector in that case. I suggest to break; instead >> of return in all cases and do the make_new_ssa_for_all_defs call at >> the function end instead. >> > Done. > >> @@ -1253,14 +1305,18 @@ zero_one_operation (tree *def, enum tree_code >> opcode, tree op) >> if (gimple_assign_rhs1 (stmt2) == op) >> { >> tree cst = build_minus_one_cst (TREE_TYPE (op)); >> + stmts_to_fix.safe_push (stmt2); >> + make_new_ssa_for_all_defs (def, op, stmts_to_fix); >> propagate_op_to_single_use (cst, stmt2, def); >> return; >> >> this safe_push should be unnecessary for the above reason (others are >> conditionally unnecessary). >> > Done. > > Bootstrapped and regression tested on X86_64-linux-gnu with no new > regression. Is this OK? +static void +make_new_ssa_for_all_defs (tree *def, tree op, + auto_vec &stmts_to_fix) I think you need to use vec &stmts_to_fix here AFAIK. Ok with that change. Richard. > Thanks, > Kugan > > >> I thought about simplifying the whole thing by instead of clearing an >> op from the chain pre-pend >> one that does the job by means of visiting the chain from reassoc >> itself but that doesn't work out >> for RDIV_EXPR nor does it play well with undistribute handling >> mutliple opportunities on the same >> chain. >> >> Thanks, >> Richard. >> >> >>> >>> Bootstrapped and regression tested on x86_64-linux-gnu with no new >>> regressions. >>> >>> Thanks, >>> Kugan