[Bug libstdc++/86516] Spurious warning __builtin_memset at O3 when protected by a conditional involving empty()

[paulg at chiark dot greenend.org.uk]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86516

--- Comment #2 from Paul Gotch <paulg at chiark dot greenend.org.uk> ---
I can reproduce this at will with GCC 7.3 it does not reproduce with GCC 8

// Compile with g++ -c -Wextra -Wall -Werror -O3 test.cpp

#include <vector>

class Foo
{
public:

    Foo() {}

    virtual ~Foo()
    {
    }

    // warning only reproduces if this calls inner and is virtual
    virtual void outer()
    {
        inner();
    }

    void inner()
    {
        while ( ! vInt.empty() )
        {
            vInt.resize( vInt.size() - 1 );
        }
    }

    std::vector<int*> vInt;
};

// An instantiation of Foo is required for warning to reproduce
void* makeFoo()
{
    return new Foo();
}