[PATCH] Make any_cast compare typeinfo as well as function pointers

[Jonathan Wakely]

On 24/05/19 11:26 +0100, Jonathan Wakely wrote:
>On 24/05/19 10:57 +0200, Christophe Lyon wrote:
>>Hi Jonathan,
>>
>>On Thu, 23 May 2019 at 16:13, Jonathan Wakely <jwakely@redhat.com> wrote:
>>>
>>>It's possible for the function pointer comparison to fail even though
>>>the type is correct, because the function could be defined multiple
>>>times with different addresses when shared libraries are in use.
>>>
>>>Retain the function pointer check for the common case where the check
>>>succeeds, but compare typeinfo (if RTTI is enabled) if the first check
>>>fails.
>>>
>>>        * include/experimental/any (__any_caster): Use RTTI if comparing
>>>        addresses fails, to support non-unique addresses in shared libraries.
>>>        * include/std/any (__any_caster): Likewise.
>>>
>>>Tested powerpc64le-linux, committed to trunk, backports to follow.
>>>
>>>
>>
>>It seems OK on trunk, but on gcc-7/gcc-8 branches I see:
>>/libstdc++-v3/testsuite/experimental/any/misc/any_cast_neg.cc:20:
>>/aci-gcc-fsf/builds/gcc-fsf-gccsrc/obj-aarch64-none-linux-gnu/gcc3/aarch64-none-linux-gnu/libstdc++-v3/include/experimental/any:
>>In instantiation of '_ValueType
>>std::experimental::fundamentals_v1::any_cast(const
>>std::experimental::fundamentals_v1::any&) [with _ValueType = int&]':
>>/libstdc++-v3/testsuite/experimental/any/misc/any_cast_neg.cc:28:
>>required from here
>>/aci-gcc-fsf/builds/gcc-fsf-gccsrc/obj-aarch64-none-linux-gnu/gcc3/aarch64-none-linux-gnu/libstdc++-v3/include/experimental/any:358:
>>error: binding reference of type 'int&' to 'const int' discards
>>qualifiers
>>compiler exited with status 1
>>FAIL: experimental/any/misc/any_cast_neg.cc  (test for errors, line 357)
>>FAIL: experimental/any/misc/any_cast_neg.cc (test for excess errors)
>>
>>on arm/aarch64
>
>I don't see how you can have that error when the test was changed to
>match on any line:
>
>https://gcc.gnu.org/viewcvs/gcc/branches/gcc-7-branch/libstdc%2B%2B-v3/testsuite/experimental/any/misc/any_cast_neg.cc?r1=271566&r2=271565&pathrev=271566
>https://gcc.gnu.org/viewcvs/gcc/branches/gcc-8-branch/libstdc%2B%2B-v3/testsuite/experimental/any/misc/any_cast_neg.cc?r1=271562&r2=271561&pathrev=271562


As discussed on IRC, the failure was seen at r271565 and fixed at
r271566.