https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105539
--- Comment #9 from Qing Zhao <qing.zhao at oracle dot com> ---
> It's a conditional uninit use which we do not warn on early by design
> (for the fear of too many false positives, that is).
Okay.
>
>> 2. the ccp optimization deletes the if (z) statement completely:
>>
>> [opc@qinzhao-aarch64-ol8 105539]$ cat t.c.034t.ccp1
>>
>> ;; Function x (x, funcdef_no=0, decl_uid=3591, cgraph_uid=1, symbol_order=0)
>>
>> Removing basic block 3
>> Merging blocks 2 and 4
>> int x (int z)
>> {
>> int y;
>>
>> <bb 2> :
>> return 10;
>>
>> }
>
> That's expected from optimistic lattice propagation which merges TOP with
> the constant.
If y is initialized to 0 at declaration site, the “if z” statement is NOT
deleted by CCP.
However, per design of -ftrivial-auto-var-init, we intent to not treat
y = .DEFERRED_INIT (4, 2, &"y"[0]);
Same as
y= 0
In order to keep -Wuninitialized warning analysis working as expected.
So, yes, I agree that this issue is unavoided based on the current design.
>
>> are the above two bugs?
>
> Well, it works as designed. But sure, that we fail to diagnose the uninit
> use is unfortunate and there exist bugs for this specific issue already.
