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From: "hubicka at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/115277] New: ICF needs to match loop bound estimates
Date: Wed, 29 May 2024 14:11:29 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D115277

            Bug ID: 115277
           Summary: ICF needs to match loop bound estimates
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hubicka at gcc dot gnu.org
  Target Milestone: ---

jan@localhost:/tmp> cat tt.c
int array[1000];
void
test (int a)
{
        if (__builtin_expect (a > 3, 1))
                return;
        for (int i =3D 0; i < a; i++)
                array[i]=3Di;
}
void
test2 (int a)
{
        if (__builtin_expect (a > 10, 1))
                return;
        for (int i =3D 0; i < a; i++)
                array[i]=3Di;
}
int
main()
{
        test(1);
        test(2);
        test(3);
        test2(10);
        if (array[9] !=3D 9)
                __builtin_abort ();
        return 0;
}
jan@localhost:/tmp> gcc -O2 tt.c ; ./a.out
jan@localhost:/tmp> gcc -O3 tt.c ; ./a.out
Aborted (core dumped)


The problem here is that we do not match value ranges and thus we can end up
with different estimates on number of iterations.=