[Issue 21013] dwarfeh: Comparing LSDA is too unreliable to determine if two exceptions can be merged

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=21013

--- Comment #2 from Iain Buclaw <ibuclaw at gdcproject.org> ---
(In reply to Iain Buclaw from comment #1)
> One stable input that could instead be used is the function FQN, or perhaps
> better, the hash of it.
> 

Though shortly after sending the last message, I now see that I was thinking
only about problem [2], and not what would also work for [1] as well.

What instead works for both would be if an internal state were to be updated
when entering each try/catch or try/finally region.

e.g:
---
void bug1513a()
{
     throw new Exception("d");
}

void bug1513()
{
    try
    {
        ///
        _d_eh_setContext("bug1513");
        ///
        try
        {
            ///
            _d_eh_setContext("bug1513");
            ///
            bug1513a();
        }
        finally
        {
           throw new Exception("f");
        }
    }
    catch(Exception e)
    {
        assert(e.msg == "d");
        assert(e.next.msg == "f");
        assert(!e.next.next);
    }
}
---

void test4()
{
    void throw_catch()
    {
        try
        {
            ///
            _d_eh_setContext("test4.throw_catch");
            ///
            throw new MyException;
        }
        catch (MyException)
        {
        }
        catch (Exception)
        {
            assert(false);
        }
    }
    try
    {
        ///
        _d_eh_setContext("test4");
        ///
        try
        {
            ///
            _d_eh_setContext("test4");
            ///
            throw new Exception("a");
        }
        finally
        {
            throw_catch();
        }
    }
    catch(Exception e)
    {
        assert(e.msg == "a");
        assert(!e.next);
    }
}
---

Which means there's unfortunately going to be a heavy performance penalty for
using EH.

--