c++: suppress -Waddress warnings with *_cast [PR105569]
Commit Message
dynamic_cast can legally return nullptr, so I don't think it's helpful
for -Waddress to warn for
if (dynamic_cast<A*>(&ref))
// ...
More generally, it's likely not useful to warn for the artificial
POINTER_PLUS_EXPRs created by build_base_path.
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
PR c++/105569
gcc/cp/ChangeLog:
* class.cc (build_base_path): Suppress -Waddress warning.
gcc/testsuite/ChangeLog:
* g++.dg/warn/Waddress-9.C: New test.
---
gcc/cp/class.cc | 2 ++
gcc/testsuite/g++.dg/warn/Waddress-9.C | 34 ++++++++++++++++++++++++++
2 files changed, 36 insertions(+)
create mode 100644 gcc/testsuite/g++.dg/warn/Waddress-9.C
base-commit: 682e587f1021241758f7dfe0b22651008622a312
Comments
On 5/16/22 13:06, Marek Polacek wrote:
> dynamic_cast can legally return nullptr, so I don't think it's helpful
> for -Waddress to warn for
>
> if (dynamic_cast<A*>(&ref))
> // ...
>
> More generally, it's likely not useful to warn for the artificial
> POINTER_PLUS_EXPRs created by build_base_path.
Normally the POINTER_PLUS_EXPR is guarded by if (nonnull). But
build_base_path isn't adding that guard in this case because the operand
is known to be a reference, which cannot be null
(http://eel.is/c++draft/dcl.ref#5). So a warning is indicated for this
testcase, though it would be good to give a more informative one
("comparing address of reference to null").
> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
>
> PR c++/105569
>
> gcc/cp/ChangeLog:
>
> * class.cc (build_base_path): Suppress -Waddress warning.
>
> gcc/testsuite/ChangeLog:
>
> * g++.dg/warn/Waddress-9.C: New test.
> ---
> gcc/cp/class.cc | 2 ++
> gcc/testsuite/g++.dg/warn/Waddress-9.C | 34 ++++++++++++++++++++++++++
> 2 files changed, 36 insertions(+)
> create mode 100644 gcc/testsuite/g++.dg/warn/Waddress-9.C
>
> diff --git a/gcc/cp/class.cc b/gcc/cp/class.cc
> index 3c195b35396..06167380423 100644
> --- a/gcc/cp/class.cc
> +++ b/gcc/cp/class.cc
> @@ -518,6 +518,8 @@ build_base_path (enum tree_code code,
>
> expr = build1 (NOP_EXPR, ptr_target_type, expr);
>
> + suppress_warning (expr, OPT_Waddress);
> +
> indout:
> if (!want_pointer)
> {
> diff --git a/gcc/testsuite/g++.dg/warn/Waddress-9.C b/gcc/testsuite/g++.dg/warn/Waddress-9.C
> new file mode 100644
> index 00000000000..2ec41949ccf
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/warn/Waddress-9.C
> @@ -0,0 +1,34 @@
> +// PR c++/105569
> +// { dg-do compile { target c++11 } }
> +// { dg-options -Waddress }
> +
> +class A {};
> +
> +class B : public virtual A {};
> +
> +class C : public A {};
> +
> +int main() {
> + B* object = new B();
> + B &ref = *object;
> +
> + // -Waddress warns here
> + bool b = nullptr == dynamic_cast<A*>(&ref); // { dg-bogus "-Waddress" }
> + bool b4 = nullptr == static_cast<A*>(&ref); // { dg-bogus "-Waddress" }
> + if (dynamic_cast<A*>(&ref)) // { dg-bogus "-Waddress" }
> + {
> + }
> + if (static_cast<A*>(&ref)) // { dg-bogus "-Waddress" }
> + {
> + }
> +
> + // -Waddress doesn't warn anymore
> + auto ptr = dynamic_cast<A*>(&ref);
> + bool b2 = ptr == nullptr;
> +
> + C* cobject = new C();
> + C &cref = *cobject;
> +
> + // -Waddress also doesn't warn anymore
> + bool b3 = nullptr == dynamic_cast<A*>(&cref);
> +}
>
> base-commit: 682e587f1021241758f7dfe0b22651008622a312
@@ -518,6 +518,8 @@ build_base_path (enum tree_code code,
expr = build1 (NOP_EXPR, ptr_target_type, expr);
+ suppress_warning (expr, OPT_Waddress);
+
indout:
if (!want_pointer)
{
new file mode 100644
@@ -0,0 +1,34 @@
+// PR c++/105569
+// { dg-do compile { target c++11 } }
+// { dg-options -Waddress }
+
+class A {};
+
+class B : public virtual A {};
+
+class C : public A {};
+
+int main() {
+ B* object = new B();
+ B &ref = *object;
+
+ // -Waddress warns here
+ bool b = nullptr == dynamic_cast<A*>(&ref); // { dg-bogus "-Waddress" }
+ bool b4 = nullptr == static_cast<A*>(&ref); // { dg-bogus "-Waddress" }
+ if (dynamic_cast<A*>(&ref)) // { dg-bogus "-Waddress" }
+ {
+ }
+ if (static_cast<A*>(&ref)) // { dg-bogus "-Waddress" }
+ {
+ }
+
+ // -Waddress doesn't warn anymore
+ auto ptr = dynamic_cast<A*>(&ref);
+ bool b2 = ptr == nullptr;
+
+ C* cobject = new C();
+ C &cref = *cobject;
+
+ // -Waddress also doesn't warn anymore
+ bool b3 = nullptr == dynamic_cast<A*>(&cref);
+}