From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mo4-p00-ob.smtp.rzone.de (mo4-p00-ob.smtp.rzone.de [85.215.255.21]) by sourceware.org (Postfix) with ESMTPS id 1341A3858414 for ; Thu, 19 Oct 2023 15:36:51 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org 1341A3858414 Authentication-Results: sourceware.org; dmarc=none (p=none dis=none) header.from=gjlay.de Authentication-Results: sourceware.org; spf=none smtp.mailfrom=gjlay.de ARC-Filter: OpenARC Filter v1.0.0 sourceware.org 1341A3858414 Authentication-Results: server2.sourceware.org; arc=pass smtp.remote-ip=85.215.255.21 ARC-Seal: i=2; a=rsa-sha256; d=sourceware.org; s=key; t=1697729813; cv=pass; b=IZx5cfBpufwt2FRcSUphAVxojtM+aW09Ws3uVzMaf7UK1jCXMXWXiJMbyDt4TrOnDSBjTn9lQcdgKXMQYmHZJCB8PfjcAXNX65KOL729ol0AYTgLdTiovVN/MvsuADfu4gjMez3pekL1gFwqxVwjjCjXMVcRb9S6gcW209BFje8= ARC-Message-Signature: i=2; a=rsa-sha256; d=sourceware.org; s=key; t=1697729813; c=relaxed/simple; bh=Ud8El63gTw0oMB3kNU1NJo6oJHqLTdnXntp1vXYuewM=; h=DKIM-Signature:DKIM-Signature:Message-ID:Date:MIME-Version:To: From:Subject; b=nihc8x12jF83S1+0xsuXYD9FGGkHCyr8yGPvfpPPC6k36PN1/OC31vY2xnMhQzDLj6bZasAqaypUmEHBzjxsoG4fm9q3AVi5DILnaOLLVLbbPO0XvLBfk4DYOOQmgZ/l9CiQ2OrtjF+E/HHFrEHyjcPaYTk6rDneY2DZTVt5sf4= ARC-Authentication-Results: i=2; server2.sourceware.org ARC-Seal: i=1; a=rsa-sha256; t=1697729810; cv=none; d=strato.com; s=strato-dkim-0002; b=IbHxHsh6Ul09A9+3F3AGhApZdUet0hCC4G6gwulpNp/w8cvxjh6QHRPah+Kz7DcHii aYkVkbZC0OctZlgi2esBIaqA0gR14WxYieuI56i8gkPQgBwkGKXzve1oQHw8tKHhf0qI 8CpgRSWt0NCpWskwN9OfmXYjdWL7VrhQ8UJwHoJ02ORduuF06sWpsHeRtPlBNlfhlZ5N mCwlbaDjHOE/8qmob7YM4+8TfTU6wYHVkUnWGRMZGBSTOdjnyoUg+3HvQ7ngZed2x8q9 O7APC/dwuuhokD9Oe+ONQir7yFLlYUZ/7sSHjAa2Lz/ZptJ2JIcXUq0cMSh46V4w4ouQ GXGg== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; t=1697729810; s=strato-dkim-0002; d=strato.com; h=Subject:From:To:Date:Message-ID:Cc:Date:From:Subject:Sender; bh=7vSTKwY1EPaRYqV3Fe8sw1xt+grEvKNStuGY9Soj8Cw=; b=WLaxsOxa7pAEvabkxPxI9gVlRy7mJ+MlanaP9CahhvhDWsxu23il/jfP/nSxfAsoH5 5RkQvZk9Yfoasy7f/U37UDrjds2aFa5ZvRqyLaVEaRKUUEDQF+TAIS5AqDAQgdalm6ud UjTMPhXqecixQ2tzxEvAxWcb4V18MBzxM0PGbwxgOnWgZmgSepBK7Yv2JOEiJbWC1NA6 Kj+8PQo7Xf4MEXKlvfGrD89eH14RX1DnxVb4RKpLr91a2pTW2n3AunEQ1KEIztkbqyux aa8A8iiPDfEI5spc9VOzNvUyrVv3+lWFerJxlTDqNan0r8lFj6rMvlVEidyw9J88+wWL 5PIA== ARC-Authentication-Results: i=1; strato.com; arc=none; dkim=none X-RZG-CLASS-ID: mo00 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; t=1697729810; s=strato-dkim-0002; d=gjlay.de; h=Subject:From:To:Date:Message-ID:Cc:Date:From:Subject:Sender; bh=7vSTKwY1EPaRYqV3Fe8sw1xt+grEvKNStuGY9Soj8Cw=; b=hVpgxD/6XWWnTcyMrdqEOo8/zsiDDoxeQBSD79V10YwYBnopirWCACqMdHtWM7vZWq 4/GVxSEkjTTOqoFtxp7ZjsGlsvJfagTxwPeKXhrXlfZBWBPyu3KkTaQBvJl5cB3o7/xK 3lj1PkPzWdkJ53BlPFVrsCOg8t2W5kADMGMu8hF+Z+haPdRQrq/ouMusOn2PkrY4OXof Ic8dRytp4q/pKGz5yQKrccJnfCH7E3kLxi5ro7T1ZFy9XxIRZgqSt0ds7dweo7zetGhg 0LAsLsA8zUt5K6XeQ4sX7yeYIUNKviHq3ralOndxypZb7TCggQOpw+QigJiIZ4v0n4ns Sghw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; t=1697729810; s=strato-dkim-0003; d=gjlay.de; h=Subject:From:To:Date:Message-ID:Cc:Date:From:Subject:Sender; bh=7vSTKwY1EPaRYqV3Fe8sw1xt+grEvKNStuGY9Soj8Cw=; b=E7ycFZE/KZeZIE44CKvUsqgaxxOYmkzWvqZsOIap3FHIKg4wjpdpfYg82vkHHmVyW9 ua4EpwUJsR+iW9WabpCQ== X-RZG-AUTH: ":LXoWVUeid/7A29J/hMvvT3koxZnKT7Qq0xotTetVnKkSjsSjo3O/MHXSzlaR/rBp" Received: from [192.168.2.102] by smtp.strato.de (RZmta 49.9.0 DYNA|AUTH) with ESMTPSA id e316f3z9JFaoNFc (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256 bits)) (Client did not present a certificate) for ; Thu, 19 Oct 2023 17:36:50 +0200 (CEST) Message-ID: <2d7481fb-7fa3-11f9-8b34-50812336a9fe@gjlay.de> Date: Thu, 19 Oct 2023 17:36:50 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.15.1 Content-Language: en-US To: gcc-help@gcc.gnu.org From: Georg-Johann Lay Subject: Any changes in C23's aliasing rules (or a gcc problem?) Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-4.0 required=5.0 tests=BAYES_00,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE,RCVD_IN_MSPIKE_H5,RCVD_IN_MSPIKE_WL,SPF_HELO_PASS,SPF_NONE,TXREP autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: Just came across the following test case #include int main (void) { float a = -248.75; printf ("%f\n", a); unsigned char* ptr = (unsigned char*) &a; for (size_t i = 0; i < sizeof (a); i++) { printf ("%.2X ", ptr[i]); } } Compiled with gcc v13.2 (or master) and -O3 -std=c2x. The for loop prints "00 00 00 00" which is because "a" is not written to the frame, but read in the loop thus garbage. With -fno-strict-aliasing, output is "00 C0 78 C3" as expected. https://godbolt.org/z/GMcez7M95 What am I missing? Johann