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* [Bug c/64639] New: false negative of -Wunused-value
@ 2015-01-17 7:48 chengniansun at gmail dot com
2015-01-17 8:15 ` [Bug c/64639] " chengniansun at gmail dot com
` (4 more replies)
0 siblings, 5 replies; 6+ messages in thread
From: chengniansun at gmail dot com @ 2015-01-17 7:48 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64639
Bug ID: 64639
Summary: false negative of -Wunused-value
Product: gcc
Version: 5.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: chengniansun at gmail dot com
I think GCC should also warn that the value of the expression "(a = 0) != 0" is
not used.
$: cat s.c
int *a;
int b;
void f() {
b = (0, (a = 0) != 0, 0);
}
$:
$: gcc-trunk -c -Wunused-value s.c
s.c: In function ‘f’:
s.c:4:9: warning: left-hand operand of comma expression has no effect
[-Wunused-value]
b = (0, (a = 0) != 0, 0);
^
$:
$: clang-trunk -c -Wunused-value s.c
s.c:4:8: warning: expression result unused [-Wunused-value]
b = (0, (a = 0) != 0, 0);
^
s.c:4:19: warning: expression result unused [-Wunused-value]
b = (0, (a = 0) != 0, 0);
~~~~~~~ ^ ~
2 warnings generated.
$:
$:
>From gcc-bugs-return-473635-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Sat Jan 17 07:51:49 2015
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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/64639] false negative of -Wunused-value
Date: Sat, 17 Jan 2015 07:51:00 -0000
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--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
"(a = 0) != 0" has a side effect of setting a to 0.
I think in this case, clang is incorrectly warning about it.
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug c/64639] false negative of -Wunused-value
2015-01-17 7:48 [Bug c/64639] New: false negative of -Wunused-value chengniansun at gmail dot com
@ 2015-01-17 8:15 ` chengniansun at gmail dot com
2015-01-17 18:53 ` chengniansun at gmail dot com
` (3 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: chengniansun at gmail dot com @ 2015-01-17 8:15 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64639
Chengnian Sun <chengniansun at gmail dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |chengniansun at gmail dot com
--- Comment #2 from Chengnian Sun <chengniansun at gmail dot com> ---
(In reply to Andrew Pinski from comment #1)
> "(a = 0) != 0" has a side effect of setting a to 0.
>
> I think in this case, clang is incorrectly warning about it.
I agree that (a = 0) has a side effect, but the comparison "!=" is not used.
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug c/64639] false negative of -Wunused-value
2015-01-17 7:48 [Bug c/64639] New: false negative of -Wunused-value chengniansun at gmail dot com
2015-01-17 8:15 ` [Bug c/64639] " chengniansun at gmail dot com
@ 2015-01-17 18:53 ` chengniansun at gmail dot com
2015-01-18 13:29 ` manu at gcc dot gnu.org
` (2 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: chengniansun at gmail dot com @ 2015-01-17 18:53 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64639
--- Comment #3 from Chengnian Sun <chengniansun at gmail dot com> ---
(In reply to Chengnian Sun from comment #2)
> (In reply to Andrew Pinski from comment #1)
> > "(a = 0) != 0" has a side effect of setting a to 0.
> >
> > I think in this case, clang is incorrectly warning about it.
>
> I agree that (a = 0) has a side effect, but the comparison "!=" is not used.
Please refer to the following test program. GCC emits a warning for the
expression "(a = 0) != 0".
$: cat t.c
int a;
void f() {
(a = 0) != 0;
}
$: gcc-trunk -c -Wunused-value t.c
t.c: In function ¡®f¡¯:
t.c:3:11: warning: value computed is not used [-Wunused-value]
(a = 0) != 0;
^
>From gcc-bugs-return-473670-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Sat Jan 17 18:59:14 2015
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From: "chengniansun at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/64648] New: Incorrect message description of -Wunused-value
Date: Sat, 17 Jan 2015 18:59:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64648
Bug ID: 64648
Summary: Incorrect message description of -Wunused-value
Product: gcc
Version: 5.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: chengniansun at gmail dot com
GCC emits a -Wunused-value warning with a wrong description for the expression
"(a = 0) >= 0". There is no comma expression, but the message is
right-hand operand of comma expression has no effect
If I change the operator from ">=" to "!=", then the message is correct.
$: cat t.c
int a;
void f() {
(a = 0) != 0;
(a = 0) >= 0;
}
$:
$: gcc-trunk -c -Wunused-value t.c
t.c: In function ‘f’:
t.c:3:11: warning: value computed is not used [-Wunused-value]
(a = 0) != 0;
^
t.c:4:11: warning: right-hand operand of comma expression has no effect
[-Wunused-value]
(a = 0) >= 0;
^
$:
$: clang-trunk -c -Wunused-value t.c
t.c:3:11: warning: inequality comparison result unused [-Wunused-comparison]
(a = 0) != 0;
~~~~~~~~^~~~
t.c:4:11: warning: relational comparison result unused [-Wunused-comparison]
(a = 0) >= 0;
~~~~~~~~^~~~
2 warnings generated.
$:
>From gcc-bugs-return-473671-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Sat Jan 17 19:09:21 2015
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From: "janus at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug fortran/60922] [4.9/5 regression] Memory leak with allocatable CLASS components
Date: Sat, 17 Jan 2015 19:09:00 -0000
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janus at gcc dot gnu.org changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |ASSIGNED
Assignee|unassigned at gcc dot gnu.org |janus at gcc dot gnu.org
--- Comment #10 from janus at gcc dot gnu.org ---
The following patchlet seems to fix it. Might just be a copy'n'paste error?
Index: gcc/fortran/class.c
==================================================================--- gcc/fortran/class.c (Revision 219801)
+++ gcc/fortran/class.c (Arbeitskopie)
@@ -875,7 +875,7 @@ finalize_component (gfc_expr *expr, gfc_symbol *de
/* Add IF (fini_coarray). */
if (comp->attr.codimension
|| (comp->ts.type == BT_CLASS && CLASS_DATA (comp)
- && CLASS_DATA (comp)->attr.allocatable))
+ && CLASS_DATA (comp)->attr.codimension))
{
block = gfc_get_code (EXEC_IF);
if (*code)
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug c/64639] false negative of -Wunused-value
2015-01-17 7:48 [Bug c/64639] New: false negative of -Wunused-value chengniansun at gmail dot com
2015-01-17 8:15 ` [Bug c/64639] " chengniansun at gmail dot com
2015-01-17 18:53 ` chengniansun at gmail dot com
@ 2015-01-18 13:29 ` manu at gcc dot gnu.org
2015-01-20 9:32 ` maltsevm at gmail dot com
2020-05-19 17:19 ` [Bug c/64639] missing warning by -Wunused-value in compound expressions msebor at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: manu at gcc dot gnu.org @ 2015-01-18 13:29 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64639
Manuel López-Ibáñez <manu at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Last reconfirmed| |2015-01-18
CC| |manu at gcc dot gnu.org
Ever confirmed|0 |1
--- Comment #4 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
b = (0, (a = 0) != 0, 0);
gets somehow transformed into
b = (a = 0B) != 0B;, 0;
(or the pretty-printer in tree-original cannot actually represent the internal
AST).
The warning is bizarre anyway.
>From gcc-bugs-return-473706-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Sun Jan 18 13:36:10 2015
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From: "manu at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/64644] "warning: anonymous union with no members" should be an error with -pedantic-errors
Date: Sun, 18 Jan 2015 13:36:00 -0000
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Manuel López-Ibáñez <manu at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |manu at gcc dot gnu.org
--- Comment #1 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
A untested patch, feel free to test it and submit it.
Index: decl2.c
===================================================================
--- decl2.c (revision 218749)
+++ decl2.c (working copy)
@@ -1604,11 +1604,11 @@ finish_anon_union (tree anon_union_decl)
main_decl = build_anon_union_vars (type, anon_union_decl);
if (main_decl == error_mark_node)
return;
if (main_decl == NULL_TREE)
{
- warning (0, "anonymous union with no members");
+ pedwarn (input_location, 0, "anonymous union with no members");
return;
}
if (!processing_template_decl)
{
>From gcc-bugs-return-473707-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Sun Jan 18 13:47:05 2015
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Subject: [Bug c++/64643] bad location for multiple fields in union initialized
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Manuel López-Ibáñez <manu at gcc dot gnu.org> changed:
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----------------------------------------------------------------------------
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--- Comment #1 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
You can find the code in gcc/cp/class.c. You'll need to replace:
error ("multiple fields in union %qT initialized", t);
with something like:
error_at (loc2, "multiple fields in union %qT initialized", t);
inform (loc1, "a field is already initialized here");
where the tricky part is to set loc1 and loc2 appropriately.
>From gcc-bugs-return-473708-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Sun Jan 18 13:48:04 2015
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Subject: [Bug c/64637] Incorrect location for -Wunused-value warnings in for-loop
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Manuel López-Ibáñez <manu at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
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Last reconfirmed| |2015-01-18
CC| |manu at gcc dot gnu.org
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--- Comment #1 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
Confirmed, but I think we already have a duplicated PR for this somewhere.
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idd435
--- Comment #7 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
And the reason for that is that aarch64 again changed ABI, what a stable port
:(.
https://sourceware.org/git/?p=glibc.git;a=commit;h\40c3bab2fddaca8cfe12d75944d1fef8adf1a4
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug c/64639] false negative of -Wunused-value
2015-01-17 7:48 [Bug c/64639] New: false negative of -Wunused-value chengniansun at gmail dot com
` (2 preceding siblings ...)
2015-01-18 13:29 ` manu at gcc dot gnu.org
@ 2015-01-20 9:32 ` maltsevm at gmail dot com
2020-05-19 17:19 ` [Bug c/64639] missing warning by -Wunused-value in compound expressions msebor at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: maltsevm at gmail dot com @ 2015-01-20 9:32 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64639
Mikhail Maltsev <maltsevm at gmail dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |maltsevm at gmail dot com
--- Comment #5 from Mikhail Maltsev <maltsevm at gmail dot com> ---
> gets somehow transformed into
> b = (a = 0B) != 0B;, 0;
Probably folding works this way. Anyway, I think, I can explain how the warning
is [not] generated (I stepped through the code using GDB). So:
We start parsing RHS of assignment expression (the outermost one). After
parsing two operands of comma, we get into build_compound_expr function (in
c-typeck.c) and this function generates a warning because "left-hand operand of
comma expression" (i.e. 0) "has no effect" (that's true, but the wording is a
bit strange). Then we parse the next comma expression and get into the same
function. The code of build_compound_expr looks like this:
...
if (!TREE_SIDE_EFFECTS (expr1))
...
else if (TREE_CODE (expr1) == COMPOUND_EXPR && warn_unused_value)
...
/* With -Wunused, we should also warn if the left-hand operand does have
side-effects, but computes a value which is not used. For example, in
`foo() + bar(), baz()' the result of the `+' operator is not used,
so we should issue a warning. */
else if (warn_unused_value)
warn_if_unused_value (expr1, loc);
Unfortunately, we don't get into warn_if_unused_value because the condition of
previous branch is true. That's why there is no warning about the result of
comparison.
P.S. I know, that it all might be obvious for most of you, but I'm just trying
to get acquainted with GCC sources and (hopefully) do something useful for the
project, while waiting for next stage1 (bugs being fixed during stage 4 are
obviously not for newcomers).
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug c/64639] missing warning by -Wunused-value in compound expressions
2015-01-17 7:48 [Bug c/64639] New: false negative of -Wunused-value chengniansun at gmail dot com
` (3 preceding siblings ...)
2015-01-20 9:32 ` maltsevm at gmail dot com
@ 2020-05-19 17:19 ` msebor at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: msebor at gcc dot gnu.org @ 2020-05-19 17:19 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64639
Martin Sebor <msebor at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |msebor at gcc dot gnu.org
--- Comment #7 from Martin Sebor <msebor at gcc dot gnu.org> ---
*** Bug 95217 has been marked as a duplicate of this bug. ***
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2020-05-19 17:19 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2015-01-17 7:48 [Bug c/64639] New: false negative of -Wunused-value chengniansun at gmail dot com
2015-01-17 8:15 ` [Bug c/64639] " chengniansun at gmail dot com
2015-01-17 18:53 ` chengniansun at gmail dot com
2015-01-18 13:29 ` manu at gcc dot gnu.org
2015-01-20 9:32 ` maltsevm at gmail dot com
2020-05-19 17:19 ` [Bug c/64639] missing warning by -Wunused-value in compound expressions msebor at gcc dot gnu.org
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