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From: "abbeyj+gcc at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/111750] New: Spurious -Warray-bounds warning
 when using member function pointers
Date: Mon, 09 Oct 2023 23:53:18 +0000
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X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 14.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D111750

            Bug ID: 111750
           Summary: Spurious -Warray-bounds warning when using member
                    function pointers
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: abbeyj+gcc at gmail dot com
  Target Milestone: ---

Created attachment 56086
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D56086&action=3Dedit
Reproducer

The source code below generates a -Warray-bounds warning which I believe is
incorrect.  Compile with `g++ -c -Wall -O2`.

```
struct MyClass {
    void my_method();
};

MyClass g;

void pre();

inline void FetchValue(MyClass& c, void(MyClass::*func)()) {
    pre();
    (c.*func)();
}

int get_int();

inline int Check() {
    static const int ret =3D get_int();
    return ret;
}

inline void ReadValue(MyClass& c, void(MyClass::*func)()) {
    Check();
    FetchValue(c, func);
}

void Main() {
    ReadValue(g, &MyClass::my_method);
}
```

This produces:
```
In function 'void FetchValue(MyClass&, void (MyClass::*)())',
    inlined from 'void ReadValue(MyClass&, void (MyClass::*)())' at
<source>:23:15,
    inlined from 'void Main()' at <source>:27:14:
<source>:11:14: warning: array subscript 'int (**)(...)[0]' is partly outsi=
de
array bounds of 'MyClass [1]' [-Warray-bounds=3D]
   11 |     (c.*func)();
      |     ~~~~~~~~~^~
<source>: In function 'void Main()':
<source>:5:9: note: object 'g' of size 1
    5 | MyClass g;
      |         ^
```

Godbolt link: https://godbolt.org/z/6YsWd9xhr

That this source produces a -Warray-bounds warning is somewhat surprising s=
ince
it contains no arrays, no array indexing, and no pointer arithmetic.  Small
changes such as removing the static variable or manually inlining a function
into its caller make the warning go away.=20=20

The earliest version that I've been able to reproduce this with is GCC 11.1=
 and
it still reproduces on the trunk version that's currently available on
godbolt.org.=