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* [Bug middle-end/97931] New: missing -Wuninitialized initializing an aggregate member with itself
@ 2020-11-20 23:11 msebor at gcc dot gnu.org
2020-11-23 7:31 ` [Bug middle-end/97931] " rguenth at gcc dot gnu.org
` (3 more replies)
0 siblings, 4 replies; 5+ messages in thread
From: msebor at gcc dot gnu.org @ 2020-11-20 23:11 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97931
Bug ID: 97931
Summary: missing -Wuninitialized initializing an aggregate
member with itself
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: msebor at gcc dot gnu.org
Target Milestone: ---
Quoting from my reply to
https://gcc.gnu.org/pipermail/gcc-patches/2020-November/559626.html:
> Martin, I notice that the middle-end warning doesn't currently catch this:
>
> struct B { int i,j; };
>
> struct A
> {
> B b;
> A(): b({b.i}) { }
> };
>
> A a;
>
> It does warn if B only has one member; adding the second wrongly
> silences the warning.
The GIMPLE for A's ctor looks like this:
A::A (struct A * const this)
{
*this = {CLOBBER};
{
this->b = {};
_1 = this->b.i;
this->b.i = _1;
}
}
so the b member is cleared first before it's read from and there's
nothing to warn about. This happens for C structs too:
void f (void*);
struct A { int i, j; };
void g (void)
{
struct A a = { a.i };
f (&a);
}
The uninitialized read is in the original dump (below) so the zero
initialization happens in the gimplifier and could be diagnosed
there.
;; enabled by -tree-original
{
struct A a = {.i=a.i};
struct A a = {.i=a.i};
f ((void *) &a);
}
Martin
PS I think the C++ original dump (below) shows the same problem
despite the Unknown trees that obscure it:
;; Function A::A() (null)
;; enabled by -tree-original
<<cleanup_point <<< Unknown tree: expr_stmt
*(struct A *) this = {CLOBBER} >>>>>;
{
<<cleanup_point <<< Unknown tree: expr_stmt
(void) (((struct A *) this)->b = TARGET_EXPR <D.2389, {.i=((struct A
*) this)->b.i}>) >>>>>;
}
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug middle-end/97931] missing -Wuninitialized initializing an aggregate member with itself
2020-11-20 23:11 [Bug middle-end/97931] New: missing -Wuninitialized initializing an aggregate member with itself msebor at gcc dot gnu.org
@ 2020-11-23 7:31 ` rguenth at gcc dot gnu.org
2020-11-24 0:09 ` egallager at gcc dot gnu.org
` (2 subsequent siblings)
3 siblings, 0 replies; 5+ messages in thread
From: rguenth at gcc dot gnu.org @ 2020-11-23 7:31 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97931
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Version|unknown |11.0
--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Probably because the FE emits a CONSTRUCTOR node were missing elements are
implicitely zero in GENERIC semantics, unless CONSTRUCTOR_NO_CLEARING is set.
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug middle-end/97931] missing -Wuninitialized initializing an aggregate member with itself
2020-11-20 23:11 [Bug middle-end/97931] New: missing -Wuninitialized initializing an aggregate member with itself msebor at gcc dot gnu.org
2020-11-23 7:31 ` [Bug middle-end/97931] " rguenth at gcc dot gnu.org
@ 2020-11-24 0:09 ` egallager at gcc dot gnu.org
2020-11-24 23:11 ` msebor at gcc dot gnu.org
2021-08-25 22:05 ` [Bug c++/97931] " msebor at gcc dot gnu.org
3 siblings, 0 replies; 5+ messages in thread
From: egallager at gcc dot gnu.org @ 2020-11-24 0:09 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97931
Eric Gallager <egallager at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |egallager at gcc dot gnu.org
--- Comment #2 from Eric Gallager <egallager at gcc dot gnu.org> ---
Shouldn't this go under -Winit-self?
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug middle-end/97931] missing -Wuninitialized initializing an aggregate member with itself
2020-11-20 23:11 [Bug middle-end/97931] New: missing -Wuninitialized initializing an aggregate member with itself msebor at gcc dot gnu.org
2020-11-23 7:31 ` [Bug middle-end/97931] " rguenth at gcc dot gnu.org
2020-11-24 0:09 ` egallager at gcc dot gnu.org
@ 2020-11-24 23:11 ` msebor at gcc dot gnu.org
2021-08-25 22:05 ` [Bug c++/97931] " msebor at gcc dot gnu.org
3 siblings, 0 replies; 5+ messages in thread
From: msebor at gcc dot gnu.org @ 2020-11-24 23:11 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97931
--- Comment #3 from Martin Sebor <msebor at gcc dot gnu.org> ---
-Winit-self isn't enabled by -Wall in C (to accommodate the 'int i = i;' hack)
so unless that changes I'd rather see it in -Wuninitialized (which is in -Wall
in all C languages).
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c++/97931] missing -Wuninitialized initializing an aggregate member with itself
2020-11-20 23:11 [Bug middle-end/97931] New: missing -Wuninitialized initializing an aggregate member with itself msebor at gcc dot gnu.org
` (2 preceding siblings ...)
2020-11-24 23:11 ` msebor at gcc dot gnu.org
@ 2021-08-25 22:05 ` msebor at gcc dot gnu.org
3 siblings, 0 replies; 5+ messages in thread
From: msebor at gcc dot gnu.org @ 2021-08-25 22:05 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97931
Martin Sebor <msebor at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Component|middle-end |c++
Last reconfirmed| |2021-08-25
Status|UNCONFIRMED |NEW
Ever confirmed|0 |1
--- Comment #4 from Martin Sebor <msebor at gcc dot gnu.org> ---
There's nothing the middle end can do to warn because the front end emits code
to zero-initialize the struct/class first and only then to use the value of the
zero-initialized member to [re]initialize it. The detection needs to happen in
the front ends (both C and C++).
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2021-08-25 22:05 UTC | newest]
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2020-11-20 23:11 [Bug middle-end/97931] New: missing -Wuninitialized initializing an aggregate member with itself msebor at gcc dot gnu.org
2020-11-23 7:31 ` [Bug middle-end/97931] " rguenth at gcc dot gnu.org
2020-11-24 0:09 ` egallager at gcc dot gnu.org
2020-11-24 23:11 ` msebor at gcc dot gnu.org
2021-08-25 22:05 ` [Bug c++/97931] " msebor at gcc dot gnu.org
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