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From: "qinzhao at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug rtl-optimization/108132] New: Wrong instruction scheduling
 around function call with longjmp on aarch64 at O2
Date: Thu, 15 Dec 2022 17:51:28 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: rtl-optimization
X-Bugzilla-Version: 13.0
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: major
X-Bugzilla-Who: qinzhao at gcc dot gnu.org
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=3D108132

            Bug ID: 108132
           Summary: Wrong instruction scheduling around function call with
                    longjmp on aarch64 at O2
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: qinzhao at gcc dot gnu.org
  Target Milestone: ---

The error only happens on aarch64 (fine on X86).=20

The following testing case:
[opc@qinzhao-aarch64-ol8]$ cat t.c
#include <stdio.h>=20
#include <setjmp.h>=20
#include <stdbool.h>=20

jmp_buf ex_buf__;=20

int f(int x)=20
{=20
  int arr[] =3D {1,2,6,8,9,10};=20
  int lo=3D0;=20
  int hi=3D5;=20

  while(lo<=3Dhi) {=20
        int mid=3D(lo+hi)/2;=20

        if(arr[mid]=3D=3Dx) {=20
          longjmp(ex_buf__, 1);=20
        } else if(arr[mid]<x) {=20
          lo=3Dmid+1;=20
        } else if(arr[mid]>x) {=20
          hi=3Dmid-1;=20
        }=20
  }=20

  return -1;=20
}=20

int=20
main(int argc, char** argv)=20
{=20
  int a=3D2;=20
  bool b=3Dfalse;=20

  do {
    if( !setjmp(ex_buf__) ){
        a=3Df(a);=20
        b=3Dtrue;=20
    } else {=20
      printf("a : %d\n",a);=20
      printf("Got Exception!\n");=20
    }=20
  } while(0);

  if(b) {=20
        printf("b is true!\n");=20
  }=20
  return 0;=20
}

when compiled with the latest upstream gcc13 on aarch64 with -O2, the varia=
ble
"b" was set to true, which is wrong.=20
when disable insn scheduling by adding -fno-schedule-insns, the issue gone:
[opc@qinzhao-aarch64-ol8]$ /home/opc/Install/latest/bin/gcc -v
Using built-in specs.
COLLECT_GCC=3D/home/opc/Install/latest/bin/gcc
COLLECT_LTO_WRAPPER=3D/home/opc/Install/latest/libexec/gcc/aarch64-unknown-=
linux-gnu/13.0.0/lto-wrapper
Target: aarch64-unknown-linux-gnu
Configured with: ../latest_gcc/configure --prefix=3D/home/opc/Install/latest
--enable-languages=3Dc,c++ --disable-bootstrap
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 13.0.0 20221215 (experimental) (GCC)=20
[opc@qinzhao-aarch64-ol8]$ /home/opc/Install/latest/bin/gcc -O2 t.c
[opc@qinzhao-aarch64-ol8]$ ./a.out
a : 2
Got Exception!
b is true!
[opc@qinzhao-aarch64-ol8]$ /home/opc/Install/latest/bin/gcc -O2
-fno-schedule-insns t.c
[opc@qinzhao-aarch64-ol8]$ ./a.out
a : 2
Got Exception!
[opc@qinzhao-aarch64-ol8]$=