From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 5830 invoked by alias); 21 Jun 2005 12:49:09 -0000 Mailing-List: contact gcc-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Archive: List-Post: List-Help: Sender: gcc-owner@gcc.gnu.org Received: (qmail 5768 invoked by uid 22791); 21 Jun 2005 12:48:59 -0000 Received: from topconrd.ru (HELO TopconRD.RU) (62.105.138.7) by sourceware.org (qpsmtpd/0.30-dev) with ESMTP; Tue, 21 Jun 2005 12:48:59 +0000 Received: from osv.topcon.com (ttc.topconrd.ru [62.105.138.5]) by TopconRD.RU (8.12.3/8.12.3/Debian-6.6) with ESMTP id j5LCmtL0006496; Tue, 21 Jun 2005 16:48:55 +0400 To: Michael Meissner Cc: gcc@gcc.gnu.org, Andrew Pinski Subject: Re: How to replace -O1 with corresponding -f's? References: <878y159mhr.fsf@osv.topcon.com> <17078.52477.408454.106678@zapata.pink> <44a7432710d6ca83042f60c9fbab58d9@physics.uc.edu> <87zmtl84eo.fsf@osv.topcon.com> <87r7ex82ur.fsf@osv.topcon.com> <87mzpl81ia.fsf@osv.topcon.com> <20050621095059.GA24035@tiktok.the-meissners.org> X-attribution: osv From: Sergei Organov Date: Tue, 21 Jun 2005 12:49:00 -0000 In-Reply-To: <20050621095059.GA24035@tiktok.the-meissners.org> Message-ID: <87u0jr7u4t.fsf@osv.topcon.com> User-Agent: Gnus/5.0808 (Gnus v5.8.8) XEmacs/21.4 (Common Lisp) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-SW-Source: 2005-06/txt/msg00932.txt.bz2 Michael Meissner writes: > On Mon, Jun 20, 2005 at 07:57:17PM +0400, Sergei Organov wrote: > > Andrew Pinski writes: > > > > > On Jun 20, 2005, at 11:28 AM, Sergei Organov wrote: > > > > > > > Andrew Pinski writes: > > > > > > > >> On Jun 20, 2005, at 10:54 AM, Sergei Organov wrote: > > > >> > > > >>> so SYMBOL_FLAG_SMALL (flags 0x6 vs 0x2) is somehow being missed when -O1 > > > > > > >> > > > >>> is turned on. Seems to be something at tree-to-RTX conversion time. > > > >>> Constant folding? > > > >> > > > >> No, it would mean that the target says that this is not a small data. > > > >> Also try it with the following code and you will see there is no > > > >> difference: > > > > > > >> > > > >> double osvf() { return 314314314; } > > > > > > > > There is no difference in the sense that here both -O0 and -O1 behave > > > > roughly the same. So the problem is with detecting "smallness" for true > > > > constants by the target, right? > > > > > > I think the bug is in rs6000_elf_in_small_data_p but since I have not > > > debuged it yet I don't know for sure. > > > > > > Could you file a bug? This is a target bug. > > > > Yeah, and I've reported it rather long ago against gcc-3.3 (PR 9571). > > That time there were 3 problems reported in the PR of which only the > > first one seems to be fixed (or are the rest just re-appeared in 4.0?). > > > > I think PR 9571 is in fact regression with respect to 2.95.x despite the > > [wrong] comments: > > > > ------- Additional Comment #5 From Franz Sirl 2003-06-17 15:31 [reply] ------- > > > > r0 is used as a pointer to sdata2, this is a bug, it should be r2. And > > since only r2 is initialized in the ecrt*.o files, how can this work? > > Besides that, even if you initialize r0 manually, it is practically > > clobbered in about every function. > > It's been a long time since I've hacked the PowerPC, but IIRC the instruction > set, a base register of '0' does not mean r0, but instead it means use 0 as the > base address. Every place that uses a base register should use the register > class 'b' (BASE_REGS) instead of 'r' (GENERAL_REGS), which excludes r0 from > being considered. > > Under the 32-bit eABI calling sequence, you have three small data areas: > > The small data area that r2 points to (.sdata/.sbss). > > The small data area that r13 points to (.sdata2/.sbss2). > > The small data area centered around location 0 (ie, small positive > addresses, and the most negative addresses). I don't recall that we > had special sections for this, since for many embedded apps, they > couldn't allocate to those addresses. > > For these relocations, you should use R_PPC_EMB_SDA21, which the > linker will fill in both the offset and the appropriate base register > into the instruction. Exactly, and that's what gcc actually and correctly does. My comment in the PR exactly matches what you've said above: ------- Additional Comment #7 From Sergei Organov 2003-10-14 14:42 [reply] ------- > r0 is used as a pointer to sdata2, this is a bug, it should be r2. No, the %r0 you see is fake. In the object file it's a special relocatable symbol that is resolved to either 2 (r2) or 13 (r13) by the linker depending on actual output section the symbol refers to, so there is no bug here. IMHO, the assembly output is just somewhat misleading mentioning %r0 in the place in question, -- it better should be just 0 I think as SYM@sda21(0) would create less confusion than SYM@sda21(%r0). On the other hand, I must admit the PR with item 1 (wrong section attribute) fixed is not a regression anymore. I apologize, but I've compared gcc-3.x/4.x with *patched* version of gcc-2.95.x that I've hacked to force it to put double/float constants into .sdata2 section. Now I've applied my hack to gcc-4.1.0 and get similar results, though the patch is indeed a hack and is not satisfactory. I think there is a fundamental problem that compiler-generated symbols referring to constants are generated too late, at RTL level, and thus aren't handled by the small section logic working on the tree level. Any thoughts? -- Sergei.