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c++: improve -Waddress warnings with *_cast [PR105569]

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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: the compiler can assume that the address of 'ref' will never be 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.
This commit is contained in:
Marek Polacek 2022-05-11 14:38:49 -04:00
parent 3397563ad6
commit 6f56efa94e
2 changed files with 41 additions and 2 deletions
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12
gcc/cp/typeck.cc
View File

@ -4757,8 +4757,16 @@ warn_for_null_address (location_t location, tree op, tsubst_flags_t complain)
tree off = TREE_OPERAND (cop, 1); tree off = TREE_OPERAND (cop, 1);
if (!integer_zerop (off) if (!integer_zerop (off)
&& !warning_suppressed_p (cop, OPT_Waddress)) && !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, "the compiler can assume that "
"the address of %qE will never be NULL", base);
else
warning_at (location, OPT_Waddress, "comparing the result of "
"pointer addition %qE and NULL", cop);
}
return; return;
} }
else if (CONVERT_EXPR_P (op) else if (CONVERT_EXPR_P (op)

31
gcc/testsuite/g++.dg/warn/Waddress-9.C Normal file
View File

@ -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 "the address of 'ref' will never be NULL" }
bool b4 = nullptr == static_cast<A*>(&ref); // { dg-warning "the address of 'ref' will never be NULL" }
if (dynamic_cast<A*>(&ref)) // { dg-warning "the address of 'ref' will never be NULL" }
{
}
if (static_cast<A*>(&ref)) // { dg-warning "the address of 'ref' will never be 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);
}