* [PATCH] c++: Quash bogus -Wunused-value with new [PR107797]
@ 2023-01-20 2:03 Marek Polacek
2023-01-20 19:37 ` Jason Merrill
0 siblings, 1 reply; 4+ messages in thread
From: Marek Polacek @ 2023-01-20 2:03 UTC (permalink / raw)
To: Jason Merrill, GCC Patches
We shouldn't emit "right operand of comma operator has no effect"
when that comma operator was created by the compiler for "new int{}".
convert_to_void/COMPOUND_EXPR already checks warning_suppressed_p so
we can just suppress -Wunused-value.
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
PR c++/107797
gcc/cp/ChangeLog:
* cvt.cc (ocp_convert): copy_warning when creating a new
COMPOUND_EXPR.
* init.cc (build_new_1): Suppress -Wunused-value on
compiler-generated COMPOUND_EXPRs.
gcc/testsuite/ChangeLog:
* g++.dg/warn/Wunused-value-1.C: New test.
---
gcc/cp/cvt.cc | 6 ++++--
gcc/cp/init.cc | 2 ++
gcc/testsuite/g++.dg/warn/Wunused-value-1.C | 12 ++++++++++++
3 files changed, 18 insertions(+), 2 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/warn/Wunused-value-1.C
diff --git a/gcc/cp/cvt.cc b/gcc/cp/cvt.cc
index 0cbfd8060cb..17827d06a4a 100644
--- a/gcc/cp/cvt.cc
+++ b/gcc/cp/cvt.cc
@@ -711,8 +711,10 @@ ocp_convert (tree type, tree expr, int convtype, int flags,
return error_mark_node;
if (e == TREE_OPERAND (expr, 1))
return expr;
- return build2_loc (EXPR_LOCATION (expr), COMPOUND_EXPR, TREE_TYPE (e),
- TREE_OPERAND (expr, 0), e);
+ e = build2_loc (EXPR_LOCATION (expr), COMPOUND_EXPR, TREE_TYPE (e),
+ TREE_OPERAND (expr, 0), e);
+ copy_warning (e, expr);
+ return e;
}
complete_type (type);
diff --git a/gcc/cp/init.cc b/gcc/cp/init.cc
index f816c474cef..52e96fbe590 100644
--- a/gcc/cp/init.cc
+++ b/gcc/cp/init.cc
@@ -3800,6 +3800,8 @@ build_new_1 (vec<tree, va_gc> **placement, tree type, tree nelts,
if (cookie_expr)
rval = build2 (COMPOUND_EXPR, TREE_TYPE (rval), cookie_expr, rval);
+ suppress_warning (rval, OPT_Wunused_value);
+
if (rval == data_addr && TREE_CODE (alloc_expr) == TARGET_EXPR)
/* If we don't have an initializer or a cookie, strip the TARGET_EXPR
and return the call (which doesn't need to be adjusted). */
diff --git a/gcc/testsuite/g++.dg/warn/Wunused-value-1.C b/gcc/testsuite/g++.dg/warn/Wunused-value-1.C
new file mode 100644
index 00000000000..2ba5587fce0
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wunused-value-1.C
@@ -0,0 +1,12 @@
+// PR c++/107797
+// { dg-do compile { target c++11 } }
+// { dg-options "-Wunused" }
+
+void
+g ()
+{
+ (long) new int{};
+ long(new int{});
+ (long) new int();
+ long(new int());
+}
base-commit: 86caab6c5d1e26e1c54c3dceacc873d6e27bfc09
--
2.39.0
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH] c++: Quash bogus -Wunused-value with new [PR107797]
2023-01-20 2:03 [PATCH] c++: Quash bogus -Wunused-value with new [PR107797] Marek Polacek
@ 2023-01-20 19:37 ` Jason Merrill
2023-01-23 21:28 ` Marek Polacek
0 siblings, 1 reply; 4+ messages in thread
From: Jason Merrill @ 2023-01-20 19:37 UTC (permalink / raw)
To: Marek Polacek, GCC Patches
On 1/19/23 21:03, Marek Polacek wrote:
> We shouldn't emit "right operand of comma operator has no effect"
> when that comma operator was created by the compiler for "new int{}".
> convert_to_void/COMPOUND_EXPR already checks warning_suppressed_p so
> we can just suppress -Wunused-value.
>
> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
>
> PR c++/107797
>
> gcc/cp/ChangeLog:
>
> * cvt.cc (ocp_convert): copy_warning when creating a new
> COMPOUND_EXPR.
> * init.cc (build_new_1): Suppress -Wunused-value on
> compiler-generated COMPOUND_EXPRs.
>
> gcc/testsuite/ChangeLog:
>
> * g++.dg/warn/Wunused-value-1.C: New test.
> ---
> gcc/cp/cvt.cc | 6 ++++--
> gcc/cp/init.cc | 2 ++
> gcc/testsuite/g++.dg/warn/Wunused-value-1.C | 12 ++++++++++++
> 3 files changed, 18 insertions(+), 2 deletions(-)
> create mode 100644 gcc/testsuite/g++.dg/warn/Wunused-value-1.C
>
> diff --git a/gcc/cp/init.cc b/gcc/cp/init.cc
> index f816c474cef..52e96fbe590 100644
> --- a/gcc/cp/init.cc
> +++ b/gcc/cp/init.cc
> @@ -3800,6 +3800,8 @@ build_new_1 (vec<tree, va_gc> **placement, tree type, tree nelts,
> if (cookie_expr)
> rval = build2 (COMPOUND_EXPR, TREE_TYPE (rval), cookie_expr, rval);
>
> + suppress_warning (rval, OPT_Wunused_value);
This makes sense, but IIUC since rval is built with no location, this
just sets nowarning_flag?
> if (rval == data_addr && TREE_CODE (alloc_expr) == TARGET_EXPR)
> /* If we don't have an initializer or a cookie, strip the TARGET_EXPR
> and return the call (which doesn't need to be adjusted). */
> diff --git a/gcc/cp/cvt.cc b/gcc/cp/cvt.cc
> index 0cbfd8060cb..17827d06a4a 100644
> --- a/gcc/cp/cvt.cc
> +++ b/gcc/cp/cvt.cc
> @@ -711,8 +711,10 @@ ocp_convert (tree type, tree expr, int convtype, int flags,
> return error_mark_node;
> if (e == TREE_OPERAND (expr, 1))
> return expr;
> - return build2_loc (EXPR_LOCATION (expr), COMPOUND_EXPR, TREE_TYPE (e),
> - TREE_OPERAND (expr, 0), e);
> + e = build2_loc (EXPR_LOCATION (expr), COMPOUND_EXPR, TREE_TYPE (e),
> + TREE_OPERAND (expr, 0), e);
> + copy_warning (e, expr);
And so I don't know what effect this would have; copy_warning doesn't
seem to propagate nowarning_flag, which seems like a bug.
> + return e;
> }
>
> complete_type (type);
> diff --git a/gcc/testsuite/g++.dg/warn/Wunused-value-1.C b/gcc/testsuite/g++.dg/warn/Wunused-value-1.C
> new file mode 100644
> index 00000000000..2ba5587fce0
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/warn/Wunused-value-1.C
> @@ -0,0 +1,12 @@
> +// PR c++/107797
> +// { dg-do compile { target c++11 } }
> +// { dg-options "-Wunused" }
> +
> +void
> +g ()
> +{
> + (long) new int{};
> + long(new int{});
> + (long) new int();
> + long(new int());
> +}
>
> base-commit: 86caab6c5d1e26e1c54c3dceacc873d6e27bfc09
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH] c++: Quash bogus -Wunused-value with new [PR107797]
2023-01-20 19:37 ` Jason Merrill
@ 2023-01-23 21:28 ` Marek Polacek
2023-01-23 21:34 ` Jason Merrill
0 siblings, 1 reply; 4+ messages in thread
From: Marek Polacek @ 2023-01-23 21:28 UTC (permalink / raw)
To: Jason Merrill; +Cc: GCC Patches
On Fri, Jan 20, 2023 at 02:37:19PM -0500, Jason Merrill wrote:
> On 1/19/23 21:03, Marek Polacek wrote:
> > We shouldn't emit "right operand of comma operator has no effect"
> > when that comma operator was created by the compiler for "new int{}".
> > convert_to_void/COMPOUND_EXPR already checks warning_suppressed_p so
> > we can just suppress -Wunused-value.
> >
> > Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
> >
> > PR c++/107797
> >
> > gcc/cp/ChangeLog:
> >
> > * cvt.cc (ocp_convert): copy_warning when creating a new
> > COMPOUND_EXPR.
> > * init.cc (build_new_1): Suppress -Wunused-value on
> > compiler-generated COMPOUND_EXPRs.
> >
> > gcc/testsuite/ChangeLog:
> >
> > * g++.dg/warn/Wunused-value-1.C: New test.
> > ---
> > gcc/cp/cvt.cc | 6 ++++--
> > gcc/cp/init.cc | 2 ++
> > gcc/testsuite/g++.dg/warn/Wunused-value-1.C | 12 ++++++++++++
> > 3 files changed, 18 insertions(+), 2 deletions(-)
> > create mode 100644 gcc/testsuite/g++.dg/warn/Wunused-value-1.C
> >
> > diff --git a/gcc/cp/init.cc b/gcc/cp/init.cc
> > index f816c474cef..52e96fbe590 100644
> > --- a/gcc/cp/init.cc
> > +++ b/gcc/cp/init.cc
> > @@ -3800,6 +3800,8 @@ build_new_1 (vec<tree, va_gc> **placement, tree type, tree nelts,
> > if (cookie_expr)
> > rval = build2 (COMPOUND_EXPR, TREE_TYPE (rval), cookie_expr, rval);
> > + suppress_warning (rval, OPT_Wunused_value);
>
> This makes sense, but IIUC since rval is built with no location, this just
> sets nowarning_flag?
Correct (I didn't realize this when writing the patch). There's another
suppress_warning on a location-less expr just a few lines above.
> > if (rval == data_addr && TREE_CODE (alloc_expr) == TARGET_EXPR)
> > /* If we don't have an initializer or a cookie, strip the TARGET_EXPR
> > and return the call (which doesn't need to be adjusted). */
> > diff --git a/gcc/cp/cvt.cc b/gcc/cp/cvt.cc
> > index 0cbfd8060cb..17827d06a4a 100644
> > --- a/gcc/cp/cvt.cc
> > +++ b/gcc/cp/cvt.cc
> > @@ -711,8 +711,10 @@ ocp_convert (tree type, tree expr, int convtype, int flags,
> > return error_mark_node;
> > if (e == TREE_OPERAND (expr, 1))
> > return expr;
> > - return build2_loc (EXPR_LOCATION (expr), COMPOUND_EXPR, TREE_TYPE (e),
> > - TREE_OPERAND (expr, 0), e);
> > + e = build2_loc (EXPR_LOCATION (expr), COMPOUND_EXPR, TREE_TYPE (e),
> > + TREE_OPERAND (expr, 0), e);
> > + copy_warning (e, expr);
>
> And so I don't know what effect this would have; copy_warning doesn't seem
> to propagate nowarning_flag, which seems like a bug.
It actually does propagate nowarning_flag: in copy_warning we have
219 /* The no-warning bit might be set even if the map has not been consulted, or
220 otherwise if there's no entry in the map. */
221 set_no_warning_bit (to, supp);
so 'e' ends up with TREE_NO_WARNING set.
I would not think we want to build 'rval' in build_new_1 with a location
or use TREE_NO_WARNING directly instead of suppress_warning so I'm leaving
the patch as-is, but please let me know if you disagree.
Marek
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH] c++: Quash bogus -Wunused-value with new [PR107797]
2023-01-23 21:28 ` Marek Polacek
@ 2023-01-23 21:34 ` Jason Merrill
0 siblings, 0 replies; 4+ messages in thread
From: Jason Merrill @ 2023-01-23 21:34 UTC (permalink / raw)
To: Marek Polacek; +Cc: GCC Patches
On 1/23/23 16:28, Marek Polacek wrote:
> On Fri, Jan 20, 2023 at 02:37:19PM -0500, Jason Merrill wrote:
>> On 1/19/23 21:03, Marek Polacek wrote:
>>> We shouldn't emit "right operand of comma operator has no effect"
>>> when that comma operator was created by the compiler for "new int{}".
>>> convert_to_void/COMPOUND_EXPR already checks warning_suppressed_p so
>>> we can just suppress -Wunused-value.
>>>
>>> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
>>>
>>> PR c++/107797
>>>
>>> gcc/cp/ChangeLog:
>>>
>>> * cvt.cc (ocp_convert): copy_warning when creating a new
>>> COMPOUND_EXPR.
>>> * init.cc (build_new_1): Suppress -Wunused-value on
>>> compiler-generated COMPOUND_EXPRs.
>>>
>>> gcc/testsuite/ChangeLog:
>>>
>>> * g++.dg/warn/Wunused-value-1.C: New test.
>>> ---
>>> gcc/cp/cvt.cc | 6 ++++--
>>> gcc/cp/init.cc | 2 ++
>>> gcc/testsuite/g++.dg/warn/Wunused-value-1.C | 12 ++++++++++++
>>> 3 files changed, 18 insertions(+), 2 deletions(-)
>>> create mode 100644 gcc/testsuite/g++.dg/warn/Wunused-value-1.C
>>>
>>> diff --git a/gcc/cp/init.cc b/gcc/cp/init.cc
>>> index f816c474cef..52e96fbe590 100644
>>> --- a/gcc/cp/init.cc
>>> +++ b/gcc/cp/init.cc
>>> @@ -3800,6 +3800,8 @@ build_new_1 (vec<tree, va_gc> **placement, tree type, tree nelts,
>>> if (cookie_expr)
>>> rval = build2 (COMPOUND_EXPR, TREE_TYPE (rval), cookie_expr, rval);
>>> + suppress_warning (rval, OPT_Wunused_value);
>>
>> This makes sense, but IIUC since rval is built with no location, this just
>> sets nowarning_flag?
>
> Correct (I didn't realize this when writing the patch). There's another
> suppress_warning on a location-less expr just a few lines above.
>
>>> if (rval == data_addr && TREE_CODE (alloc_expr) == TARGET_EXPR)
>>> /* If we don't have an initializer or a cookie, strip the TARGET_EXPR
>>> and return the call (which doesn't need to be adjusted). */
>>> diff --git a/gcc/cp/cvt.cc b/gcc/cp/cvt.cc
>>> index 0cbfd8060cb..17827d06a4a 100644
>>> --- a/gcc/cp/cvt.cc
>>> +++ b/gcc/cp/cvt.cc
>>> @@ -711,8 +711,10 @@ ocp_convert (tree type, tree expr, int convtype, int flags,
>>> return error_mark_node;
>>> if (e == TREE_OPERAND (expr, 1))
>>> return expr;
>>> - return build2_loc (EXPR_LOCATION (expr), COMPOUND_EXPR, TREE_TYPE (e),
>>> - TREE_OPERAND (expr, 0), e);
>>> + e = build2_loc (EXPR_LOCATION (expr), COMPOUND_EXPR, TREE_TYPE (e),
>>> + TREE_OPERAND (expr, 0), e);
>>> + copy_warning (e, expr);
>>
>> And so I don't know what effect this would have; copy_warning doesn't seem
>> to propagate nowarning_flag, which seems like a bug.
>
> It actually does propagate nowarning_flag: in copy_warning we have
>
> 219 /* The no-warning bit might be set even if the map has not been consulted, or
> 220 otherwise if there's no entry in the map. */
> 221 set_no_warning_bit (to, supp);
>
> so 'e' ends up with TREE_NO_WARNING set.
Ah, yes. Pesky overloaded functions.
> I would not think we want to build 'rval' in build_new_1 with a location
> or use TREE_NO_WARNING directly instead of suppress_warning so I'm leaving
> the patch as-is, but please let me know if you disagree.
Agreed, the patch is OK.
Jason
^ permalink raw reply [flat|nested] 4+ messages in thread
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2023-01-20 2:03 [PATCH] c++: Quash bogus -Wunused-value with new [PR107797] Marek Polacek
2023-01-20 19:37 ` Jason Merrill
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