From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 7993 invoked by alias); 2 Feb 2011 16:06:05 -0000 Received: (qmail 7983 invoked by uid 22791); 2 Feb 2011 16:06:04 -0000 X-SWARE-Spam-Status: No, hits=-2.6 required=5.0 tests=ALL_TRUSTED,AWL,BAYES_00 X-Spam-Check-By: sourceware.org Received: from localhost (HELO gcc.gnu.org) (127.0.0.1) by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Wed, 02 Feb 2011 16:06:00 +0000 From: "hariharans at picochip dot com" To: gcc-bugs@gcc.gnu.org Subject: [Bug debug/47590] New: var tracking produces wrong debug in code where optimization is turned off using pragma X-Bugzilla-Reason: CC X-Bugzilla-Type: new X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: gcc X-Bugzilla-Component: debug X-Bugzilla-Keywords: X-Bugzilla-Severity: normal X-Bugzilla-Who: hariharans at picochip dot com X-Bugzilla-Status: UNCONFIRMED X-Bugzilla-Priority: P3 X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org X-Bugzilla-Target-Milestone: --- X-Bugzilla-Changed-Fields: Message-ID: X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/ Auto-Submitted: auto-generated Content-Type: text/plain; charset="UTF-8" MIME-Version: 1.0 Date: Wed, 02 Feb 2011 16:06:00 -0000 Mailing-List: contact gcc-bugs-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Id: List-Archive: List-Post: List-Help: Sender: gcc-bugs-owner@gcc.gnu.org X-SW-Source: 2011-02/txt/msg00300.txt.bz2 http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47590 Summary: var tracking produces wrong debug in code where optimization is turned off using pragma Product: gcc Version: 4.6.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: debug AssignedTo: unassigned@gcc.gnu.org ReportedBy: hariharans@picochip.com Created attachment 23216 --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=23216 The source code In the attached testcase #pragma has been used to turn optimization off (The file is otherwise compiled at -Os). By turning off optimization, we expected to be able to get better debug experience. We noticed that the variable n in the function "fn" takes the following values, if you step through the function. 4 3 0 2 1 5 0 10 -1 which is obviously wrong. I reckon the problem lies in var-tracking. Our dwarf reader tells me that the value of "n" could be found in the following places. Name: n Location: [29, 48) : DW_OP_reg1 [48, 66) : DW_OP_reg4 [66, 102) : DW_OP_fbreg[-6] [102, 112) : DW_OP_reg4 I will attach the address encoded assembly so you can see that var-tracking gets it wrong. If i compile the whole file at -O0, the dwarf information the dwarf gets it right. Name: n Location: DW_OP_fbreg[-6] In this particular case, adding -fno-var-tracking has the same effect in correcting the debug information. I guess there are 2 things that could be done. 1. Find out the problem in var-tracking in this case and fix it. 2. Turn off var-tracking for functions where optimization is turned off using attributes/pragmas. Please let me know if you need any other information on this. I tried all my experiments with master (as of 2-feb-2011). The experiments were conducted on picochip (picochip-unknown-none target triplet). Thanks Hari