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From: "zfigura at codeweavers dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/111669] New: bogus -Wnonnull in conditionally
 executed code
Date: Tue, 03 Oct 2023 04:34:03 +0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: middle-end
X-Bugzilla-Version: 13.2.0
X-Bugzilla-Keywords: diagnostic
X-Bugzilla-Severity: normal
X-Bugzilla-Who: zfigura at codeweavers dot com
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D111669

            Bug ID: 111669
           Summary: bogus -Wnonnull in conditionally executed code
           Product: gcc
           Version: 13.2.0
            Status: UNCONFIRMED
          Keywords: diagnostic
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: zfigura at codeweavers dot com
  Target Milestone: ---

Created attachment 56032
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D56032&action=3Dedit
reduced testcase, compile with -O2 -Werror=3Dnonnull

Sorry about the rather useless title, but I can't really figure out what
actually triggers this error. It seems to depend on some arcane combination=
 of
optimizations.

I was able to reduce this down to a pretty minimal test case, attached here=
. It
may be possible to reduce it further but I couldn't easily find a way.

The actual code that triggers this is here [1]. lstrcpyA() and lstrcatA() a=
re
trivial wrappers around strcpy/strcat. The NULL comes from get_search_path(=
) at
line 192. The offending strcpy/strcat will never be reached if
GetWindowsDirectoryA() returns nonzero, which it always should. However, gcc
triggers a -Wnonnull warning anyway.

Interestingly, the original Wine code only triggers the warning with
-march=3Dbdver2 (or other values of -march), but the reduced testcase trigg=
ers it
with no -march flags.

[1]
https://source.winehq.org/git/wine.git/blob/HEAD:/dlls/krnl386.exe16/file.c=
#l639=