From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gabriele@rzerosystems.com>
Received: from mail-vs1-xe34.google.com (mail-vs1-xe34.google.com
 [IPv6:2607:f8b0:4864:20::e34])
 by sourceware.org (Postfix) with ESMTPS id 086CF385782D
 for <gcc-help@gcc.gnu.org>; Fri, 11 Mar 2022 09:57:26 +0000 (GMT)
DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 086CF385782D
Received: by mail-vs1-xe34.google.com with SMTP id u124so8902774vsb.10
 for <gcc-help@gcc.gnu.org>; Fri, 11 Mar 2022 01:57:26 -0800 (PST)
X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;
 d=1e100.net; s=20210112;
 h=x-gm-message-state:mime-version:from:date:message-id:subject:to;
 bh=mneRf1NCwbadU4UpLyRS3kT8KwUPX0y+bIWlKsfaF6s=;
 b=GtSve9KHjkJU+M8hzCsaIDC/Bl2fZwCCzQaPZHs69WczOS1L9Tq4/esWhj097fQf+O
 BXD6UbvxnXVA190kSHK/K39juezdQXn99wsxsPRRQmd17mcgaZBggRr1WVBooiYfquyz
 DLNVdZEAxmPTAKSnFwIeTTsl0hIGrjBQnIfJ/C2q2MFJS01weUk6Cq5eYsPr83YQUWGp
 CEkBQmLHXlQ2VWjDI2zzhxOwsw6FZ3AxNIvatPEJjpPyQMoD9am+Fj1teR0SX6u1nHH7
 Y059QjZ+Mt2A2OZRztzITOepwT1LJjUuLzyLW/m4rIOym4sYIC1i61jwtFKWCuIALuJ/
 PQ5w==
X-Gm-Message-State: AOAM531sSZhoYv/qH6ylVPWkYkd14VoBa1GYvMiNQhYC5IrkO7dP4oFD
 L2D9j/CtkP0zll1IyQiZwRnnHpSi6pkeYPIqy+wqQsH2kUA8KjaGnrU2LbCrywDrRJj4jbR9Nun
 KowvvLv8M3iO1g6OgFrfl8GiSsGmG5VuFk125yxPDD++yrahH25PK/6+wN9RA9orQQwbPu4T+uZ
 9nPGkdgSP1wEwCEh3YREQrV3pof9vBADmjEkpbA5ZNPEo=
X-Google-Smtp-Source: ABdhPJxMHu8537zfjP8oxMQLsR0qSmLhNuQ5cIEccwSVWpF3dQntHdgnp18Q9+K2P2uy13zRO0c3Ws7zjT8c+jfMMYk=
X-Received: by 2002:a05:6102:944:b0:322:92db:cef5 with SMTP id
 a4-20020a056102094400b0032292dbcef5mr4628925vsi.36.1646992644973; Fri, 11 Mar
 2022 01:57:24 -0800 (PST)
MIME-Version: 1.0
From: Gabriele Favalessa <gabriele@rzerosystems.com>
Date: Fri, 11 Mar 2022 10:57:14 +0100
Message-ID: <CAGRyuqx8Y=KsqGGOEG6OtdQo_U68Wx-=OHe6yJqMNDqiZ-dUXw@mail.gmail.com>
Subject: ARM: code size increase starting from gcc 10
To: gcc-help@gcc.gnu.org
X-CLOUD-SEC-AV-Sent: true
X-CLOUD-SEC-AV-Info: rzerosystems,google_mail,monitor
X-Gm-Spam: 0
X-Gm-Phishy: 0
X-Spam-Status: No, score=-1.2 required=5.0 tests=BAYES_00, DKIM_SIGNED,
 DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, HTML_MESSAGE, KAM_NUMSUBJECT,
 RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_PASS, TXREP,
 T_SCC_BODY_TEXT_LINE autolearn=no autolearn_force=no version=3.4.4
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on
 server2.sourceware.org
Content-Type: text/plain; charset="UTF-8"
X-Content-Filtered-By: Mailman/MimeDel 2.1.29
X-BeenThere: gcc-help@gcc.gnu.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: Gcc-help mailing list <gcc-help.gcc.gnu.org>
List-Unsubscribe: <https://gcc.gnu.org/mailman/options/gcc-help>,
 <mailto:gcc-help-request@gcc.gnu.org?subject=unsubscribe>
List-Archive: <https://gcc.gnu.org/pipermail/gcc-help/>
List-Post: <mailto:gcc-help@gcc.gnu.org>
List-Help: <mailto:gcc-help-request@gcc.gnu.org?subject=help>
List-Subscribe: <https://gcc.gnu.org/mailman/listinfo/gcc-help>,
 <mailto:gcc-help-request@gcc.gnu.org?subject=subscribe>
X-List-Received-Date: Fri, 11 Mar 2022 09:57:28 -0000

Hi,

up to gcc 9 this function

#include <stdint.h>
#include <stdbool.h>

bool f() {
    return *(volatile uint32_t*)0x42143fa8 == 0;
}

compiles (arm-none-eabi-gcc -mcpu=cortex-m4 -Os) to:

   0: 4b02       ldr r3, [pc, #8] ; (c <f+0xc>)
   2: 6818       ldr r0, [r3, #0]
   4: fab0 f080 clz r0, r0
   8: 0940       lsrs r0, r0, #5
   a: 4770       bx lr
   c: 42143fa8 .word 0x42143fa8

Starting with gcc 10 it compiles to:

   0: 4b03       ldr r3, [pc, #12] ; (10 <f+0x10>)
   2: f8d3 0fa8 ldr.w r0, [r3, #4008] ; 0xfa8
   6: fab0 f080 clz r0, r0
   a: 0940       lsrs r0, r0, #5
   c: 4770       bx lr
   e: bf00       nop
  10: 42143000 .word 0x42143000

Questions:

1) why newer gcc versions don't generate the smallest possible size in
spite of -Os?
2) is there a way to get the smaller code with newer gcc versions?

Thanks

Gabriele