On 2/24/21 5:25 PM, Martin Sebor wrote:
In r11-6900 (PR 98646 - static_cast confuses -Wnonnull) we decided
that issuing -Wnonnull for dereferencing the result of dynamic_cast
was helpful despite the false positives it causes when the pointer
is guaranteed not to be null because of a prior test.
The test case in PR 99251 along with the feedback I got from Martin
Liska have convinced me it was not the right decision.
The attached patch arranges for dynamic_cast to also suppress -Wnonnull
analogously to static_cast. Since there already is a helper function
that builds the if-not-null test (ifnonnull) and sets TREE_NO_WARNING,
I factored out the corresponding code from build_base_path that sets
the additional TREE_NO_WARNING bit for static_cast into the function
and called it from both places. I also renamed the function to make
its purpose clearer and for consistency with other build_xxx APIs.
Let's call it build_if_nonnull, as it builds the COND_EXPR as well as
the test.
+ /* The dynamic_cast might fail but so a warning might be justified
+ but not when the operand is guarded. See pr99251. */
+ if (B *q = p->bptr ())
+ dynamic_cast<C*>(q)->g (); // { dg-bogus "\\\[-Wnonnull" }
This guard is no more necessary than it is for static_cast; both cases
deal with null arguments. Let's not add these checks to the testcases.
This guard doesn't check for the mentioned case of dynamic_cast failing
because the B* does not in fact point to a C.
I think we can just change the dg-warning to dg-bogus. Sure,
dynamic_cast might fail, but AFAICT -Wnonnull isn't supposed to warn
about arguments that *might* be null, only arguments that are *known* to
be null.
Jason
