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From: Marek Polacek <mpolacek@gcc.gnu.org> To: gcc-cvs@gcc.gnu.org Subject: [gcc r13-784] c++: improve -Waddress warnings with *_cast [PR105569] Date: Thu, 26 May 2022 21:11:44 +0000 (GMT) [thread overview] Message-ID: <20220526211144.B479C38344E5@sourceware.org> (raw) https://gcc.gnu.org/g:6f56efa94e845db0d5c934ca202295019bf334c1 commit r13-784-g6f56efa94e845db0d5c934ca202295019bf334c1 Author: Marek Polacek <polacek@redhat.com> Date: Wed May 11 14:38:49 2022 -0400 c++: improve -Waddress warnings with *_cast [PR105569] 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. Diff: --- gcc/cp/typeck.cc | 12 ++++++++++-- gcc/testsuite/g++.dg/warn/Waddress-9.C | 31 +++++++++++++++++++++++++++++++ 2 files changed, 41 insertions(+), 2 deletions(-) diff --git a/gcc/cp/typeck.cc b/gcc/cp/typeck.cc index 385cdf4d733..190d710cd27 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, "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; } 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..d3e469734b8 --- /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 "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); +}
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