On 5/25/22 16:25, Marek Polacek wrote:
On Wed, May 18, 2022 at 09:43:47AM -0400, Jason Merrill wrote:
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").
Ah, got it. How about this patch instead? Thanks,
Do we also warn about plain &ref == nullptr?
-- >8 --
This patch improves the diagnostic for -Waddress when it warns for
if (dynamic_cast<A*>(&ref))
// ...
where 'ref' is a reference, which cannot be null. In particular, it
changes
warning: comparing the result of pointer addition '(((A*)ref) + ((sizetype)(*(long
int*)((& ref)->B::_vptr.B + -24))))' and NULL
to
warning: comparing address of reference 'ref' to null
PR c++/105569
gcc/cp/ChangeLog:
* typeck.cc (warn_for_null_address): Improve the warning when
the POINTER_PLUS_EXPR's base is of reference type.
gcc/testsuite/ChangeLog:
* g++.dg/warn/Waddress-9.C: New test.
---
gcc/cp/typeck.cc | 12 ++++++++--
gcc/testsuite/g++.dg/warn/Waddress-9.C | 31 ++++++++++++++++++++++++++
2 files changed, 41 insertions(+), 2 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/warn/Waddress-9.C
diff --git a/gcc/cp/typeck.cc b/gcc/cp/typeck.cc
index 385cdf4d733..0837f2484ba 100644
--- a/gcc/cp/typeck.cc
+++ b/gcc/cp/typeck.cc
@@ -4757,8 +4757,16 @@ warn_for_null_address (location_t location, tree op,
tsubst_flags_t complain)
tree off = TREE_OPERAND (cop, 1);
if (!integer_zerop (off)
&& !warning_suppressed_p (cop, OPT_Waddress))
- warning_at (location, OPT_Waddress, "comparing the result of pointer "
- "addition %qE and NULL", cop);
+ {
+ tree base = TREE_OPERAND (cop, 0);
+ STRIP_NOPS (base);
+ if (TYPE_REF_P (TREE_TYPE (base)))
+ warning_at (location, OPT_Waddress, "comparing address of "
+ "reference %qE and NULL", base);
+ else
+ warning_at (location, OPT_Waddress, "comparing the result of "
+ "pointer addition %qE and NULL", cop);
+ }
return;
}
else if (CONVERT_EXPR_P (op)
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..a3654ff1f91
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Waddress-9.C
@@ -0,0 +1,31 @@
+// 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;
+
+ bool b = nullptr == dynamic_cast<A*>(&ref); // { dg-warning "comparing address
of reference .ref. and NULL" }
+ bool b4 = nullptr == static_cast<A*>(&ref); // { dg-warning "comparing address
of reference .ref. and NULL" }
+ if (dynamic_cast<A*>(&ref)) // { dg-warning "comparing address of reference
.ref. and NULL" }
+ {
+ }
+ if (static_cast<A*>(&ref)) // { dg-warning "comparing address of reference
.ref. and NULL" }
+ {
+ }
+
+ auto ptr = dynamic_cast<A*>(&ref);
+ bool b2 = ptr == nullptr;
+
+ C* cobject = new C();
+ C &cref = *cobject;
+
+ bool b3 = nullptr == dynamic_cast<A*>(&cref);
+}
base-commit: 34970d08c6297e12f3f9117b6ac19fb2de522e24
