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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/104603] wrong detection of g++ -Warray-bounds about downcast
Date: Sat, 19 Feb 2022 05:46:19 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D104603

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
-DA just changes inlining.

This is just an inlining mess which you can see from the diagnostic on the
trunk:
In member function 'bool Base::isX() const',
    inlined from 'bool Base::operator=3D=3D(const Base&) const' at <source>=
:16:15,
    inlined from 'bool X::operator=3D=3D(const X&) const' at <source>:10:51,
    inlined from 'bool Base::operator=3D=3D(const Base&) const' at <source>=
:16:63,
    inlined from 'bool X::operator=3D=3D(const X&) const' at <source>:10:51,
    inlined from 'void f()' at <source>:24:11:
<source>:4:29: warning: array subscript 2 is outside array bounds of 'X [1]'
[-Warray-bounds]
    4 |   bool isX() const { return isX_; }
      |                             ^~~~


The warning happens before some other optimizations happen which allows GCC=
 to
prove the function will just always return false ...=