[Bug tree-optimization/109041] Bogus compile time check by __builtin_memset? error: ‘__builtin_memset’ writing 4 bytes into a region of size 0 overflows the destination [-Werror=stringop-overflow=]

["ishikawa at yk dot rim.or.jp" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109041

--- Comment #4 from ishikawa,chiaki <ishikawa at yk dot rim.or.jp> ---
Right, when I replaced gcc-11 with gcc-12 in my script, I got the following
warnings. One of them was there before, the other is new.

/tmp/sqlite3-preprocessed-2.c: In function ‘posixUnlock’:
/tmp/sqlite3-preprocessed-2.c:22632:42: error: self-comparison always evaluates
to true [-Werror=tautological-compare]
22632 |                      sqlite3PendingByte+1==(sqlite3PendingByte+1)
      |                                          ^~
/tmp/sqlite3-preprocessed-2.c: In function ‘vtabCallConstructor’:
/tmp/sqlite3-preprocessed-2.c:121095:4: error: the comparison will always
evaluate as ‘true’ for the address of ‘pVtabCtx’ will never be NULL
[-Werror=address]
121095 |  ) ? (void) (0) : __assert_fail (
       |    ^
/tmp/sqlite3-preprocessed-2.c:5226:12: note: ‘pVtabCtx’ declared here
 5226 |   VtabCtx *pVtabCtx;
      |            ^~~~~~~~
cc1: all warnings being treated as errors


The latter one is a new one. Not sure why it was not triggered with gcc-11.

Anyway, actually, I have found out that there is a runtime assertion triggered
by thunderbird mail client when it is compiled with gcc-12, and not with
gcc-10|gcc-11.
So, I wanted to check the source code as much as possible with -Werror before I
dive into runtime code generation issues.
"-Werror" signals so many dubious constructs, and it has been an uphill battle
to make the code compile.
I found a missing "break" statement (implicit fallthrough), and strange size
check (3rd argument to strncpy) already, but  I am close to being able to
compile mozilla source tree with more compile time check right now.

Thank you again for making advanced compiler available free of charge.