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From: "qrzhang at gatech dot edu" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/101025] New: wrong code at -O3 on
 x86_64-linux-gnu
Date: Fri, 11 Jun 2021 04:51:28 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D101025

            Bug ID: 101025
           Summary: wrong code at -O3 on x86_64-linux-gnu
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: qrzhang at gatech dot edu
  Target Milestone: ---

It appears to be a recent regression.

Bisection points to g:128f43cf679e51564202b41f23fae4146347f93d



$ gcc-trunk -v
Supported LTO compression algorithms: zlib
gcc version 12.0.0 20210610 (experimental) [master revision
5ad76ad7f5b:c64ab1c4fe0:cce1697e6fe0134616ebc8f7040d99e66c12241a] (GCC)


$ gcc-trunk abc.c ; ./a.out
0

$ gcc-trunk -O3 abc.c ; ./a.out
4

$ cat abc.c
int a[10];
int b, d, g;
volatile char c;
short e;
volatile int f;
int main() {
  for (; d <=3D 9; d++) {
    b =3D e =3D 0;
    for (; e < 10; e++)
      a[e] =3D 4;
    for (; b <=3D 9; b++)
      if (g)
        f =3D 0;
      else
        a[b] =3D c;
  }
  printf("%d\n", a[1]);
}=