public inbox for gcc-bugs@sourceware.org help / color / mirror / Atom feed
From: "yann at droneaud dot fr" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug middle-end/107618] Incorrect diagnostics when using -Og, builtin_expect(), and function attribute "warning" or "error" Date: Thu, 10 Nov 2022 17:45:21 +0000 [thread overview] Message-ID: <bug-107618-4-RI9Yg3UWiI@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-107618-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107618 --- Comment #2 from Yann Droneaud <yann at droneaud dot fr> --- I was wondering what GCC expects __builtin_object_size(0, 0) to be, and used the following: void a_1 (void) __attribute__((__warning__("-1"))); void a0 (void) __attribute__((__warning__("0"))); void a1 (void) __attribute__((__warning__("1"))); void a2 (void) __attribute__((__warning__("2"))); void a3 (void) __attribute__((__warning__("3"))); void a4 (void) __attribute__((__warning__("4"))); int main(void) { unsigned long b = __builtin_object_size(0, 0); if (__builtin_expect(b == (unsigned long)-1, 0)) a_1(); if (__builtin_expect(b == 0, 0)) a0(); if (__builtin_expect(b == 1, 0)) a1(); if (__builtin_expect(b == 2, 0)) a2(); if (__builtin_expect(b == 3, 0)) a3(); if (__builtin_expect(b == 4, 0)) a4(); } It works as expected for any level above 0, except -Og: $ gcc -O1 -S warning.c warning.c: In function ‘main’: warning.c:11:5: warning: call to ‘a_1’ declared with attribute warning: -1 [-Wattribute-warning] 11 | a_1(); | ^~~~~ It's quite reassuring that __builtin_object_size(0, 0) returns -1, hence the emitted call to a_1(): $ cat warning.s .file "warning.c" .text .globl main .type main, @function main: endbr64 subq $8, %rsp call a_1@PLT movl $0, %eax addq $8, %rsp ret For -Og, there's a firework of warnings (shockingly they're the same than -O0 level): $ gcc -Og -S warning.c warning.c: In function ‘main’: warning.c:11:5: warning: call to ‘a_1’ declared with attribute warning: -1 [-Wattribute-warning] 11 | a_1(); | ^~~~~ warning.c:13:5: warning: call to ‘a0’ declared with attribute warning: 0 [-Wattribute-warning] 13 | a0(); | ^~~~ warning.c:15:5: warning: call to ‘a1’ declared with attribute warning: 1 [-Wattribute-warning] 15 | a1(); | ^~~~ warning.c:17:5: warning: call to ‘a2’ declared with attribute warning: 2 [-Wattribute-warning] 17 | a2(); | ^~~~ warning.c:19:5: warning: call to ‘a3’ declared with attribute warning: 3 [-Wattribute-warning] 19 | a3(); | ^~~~ warning.c:21:5: warning: call to ‘a4’ declared with attribute warning: 4 [-Wattribute-warning] 21 | a4(); | ^~~~ Generated assembly for -Og is the same than for levels above 0: a call to a_1() function is emitted, which mean GCC, at some point, knows __builtin_object_size(0, 0) is -1 here. Thus most of the warnings are not very useful. $ cat warning.s .file "warning.c" .text .globl main .type main, @function main: endbr64 subq $8, %rsp call a_1@PLT movl $0, %eax addq $8, %rsp ret
next prev parent reply other threads:[~2022-11-10 17:45 UTC|newest] Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-11-10 15:42 [Bug other/107618] New: " yann at droneaud dot fr 2022-11-10 17:21 ` [Bug middle-end/107618] " yann at droneaud dot fr 2022-11-10 17:45 ` yann at droneaud dot fr [this message] 2022-11-11 7:47 ` [Bug tree-optimization/107618] " rguenth at gcc dot gnu.org 2022-11-11 13:32 ` cvs-commit at gcc dot gnu.org 2022-11-11 13:33 ` rguenth at gcc dot gnu.org 2022-11-11 14:37 ` yann at droneaud dot fr 2022-11-28 22:19 ` pinskia at gcc dot gnu.org
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=bug-107618-4-RI9Yg3UWiI@http.gcc.gnu.org/bugzilla/ \ --to=gcc-bugzilla@gcc.gnu.org \ --cc=gcc-bugs@gcc.gnu.org \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: linkBe sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions for how to clone and mirror all data and code used for this inbox; as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).