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From: "652023330028 at smail dot nju.edu.cn" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/111718] New: Missed optimization of '(a+a)/a'
Date: Sat, 07 Oct 2023 11:05:10 +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: 14.0
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: 652023330028 at smail dot nju.edu.cn
X-Bugzilla-Status: UNCONFIRMED
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X-Bugzilla-Priority: P3
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D111718

            Bug ID: 111718
           Summary: Missed optimization of '(a+a)/a'
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: 652023330028 at smail dot nju.edu.cn
  Target Milestone: ---

Hello, we found some optimizations (regarding Arithmetic optimization) that=
 GCC
may have missed. We would greatly appreicate if you can take a look and let=
 us
know what you think.

Given the following code:=20
https://godbolt.org/z/5de17zvz9

unsigned n1,n2;
void func1(unsigned a){
    if(a>10&&a<20){
        n1=3Da+a;
        n2=3D(a+a)/a;
    }
}

We note that `(a+a)/a` should be optimized to `2`, but gcc-trunk -O3 does n=
ot:
func1(unsigned int):
        lea     eax, [rdi-11]
        cmp     eax, 8
        ja      .L1
        lea     eax, [rdi+rdi]
        xor     edx, edx
        mov     DWORD PTR n1[rip], eax
        div     edi
        mov     DWORD PTR n2[rip], eax
.L1:
        ret


Thank you very much for your time and effort! We look forward to hearing fr=
om
you.=