From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 48) id CD9C83894C25; Wed, 7 Apr 2021 02:01:51 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org CD9C83894C25 From: "jiangning.liu at amperecomputing dot com" To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/99946] New: fail to exchange if conditions in terms of likely/unlikely probability Date: Wed, 07 Apr 2021 02:01:51 +0000 X-Bugzilla-Reason: CC X-Bugzilla-Type: new X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: gcc X-Bugzilla-Component: tree-optimization X-Bugzilla-Version: 11.0 X-Bugzilla-Keywords: X-Bugzilla-Severity: normal X-Bugzilla-Who: jiangning.liu at amperecomputing dot com X-Bugzilla-Status: UNCONFIRMED X-Bugzilla-Resolution: X-Bugzilla-Priority: P3 X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org X-Bugzilla-Target-Milestone: --- X-Bugzilla-Flags: X-Bugzilla-Changed-Fields: bug_id short_desc product version bug_status bug_severity priority component assigned_to reporter target_milestone Message-ID: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/ Auto-Submitted: auto-generated MIME-Version: 1.0 X-BeenThere: gcc-bugs@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc-bugs mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 07 Apr 2021 02:01:51 -0000 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99946 Bug ID: 99946 Summary: fail to exchange if conditions in terms of likely/unlikely probability Product: gcc Version: 11.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: tree-optimization Assignee: unassigned at gcc dot gnu.org Reporter: jiangning.liu at amperecomputing dot com Target Milestone: --- For this simple case, $ cat test_cond.c=20 #define likely(x) __builtin_expect((x),1) #define unlikely(x) __builtin_expect((x),0) extern void g(void); int a, b; void f(void) { if (likely(a>0)) if (unlikely(b>0)) g(); } We expect gcc compiler can exchange the if conditions to be like below, if (unlikely(b>0)) if (likely(a>0)) g(); This way, performance can be improved due to saving the comparison for a>0. At the moment, gcc generate code as below, .LFB0: .cfi_startproc movl a(%rip), %edx testl %edx, %edx jle .L1 movl b(%rip), %eax testl %eax, %eax jg .L4 .L1: ret=