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From: "jiangning.liu at amperecomputing dot com" <gcc-bugzilla@gcc.gnu.org> 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 [thread overview] Message-ID: <bug-99946-4@http.gcc.gnu.org/bugzilla/> (raw) https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99946 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 #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
next reply other threads:[~2021-04-07 2:01 UTC|newest] Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-04-07 2:01 jiangning.liu at amperecomputing dot com [this message] 2021-04-07 2:03 ` [Bug tree-optimization/99946] " jiangning.liu at amperecomputing dot com 2021-04-07 7:33 ` rguenth at gcc dot gnu.org
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