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Re: [tree-ssa][PATCH]: Alias stats



On Dec 19, 2003, at 7:24 PM, Dan Nicolaescu wrote:


Jason Merrill <jason@redhat.com> writes:

On Fri, 19 Dec 2003 14:51:53 -0800, Richard Henderson <rth@redhat.com> wrote:

On Fri, Dec 19, 2003 at 12:49:50AM -0500, Daniel Berlin wrote:
That's 99.2% of the PTA queries returning no alias, where TBAA only got
23.2% of it's queries resolved to no alias.

IIRC, tbaa is crippled on c++ due to some MI wierdness.

For some mysterious reason, the C++ frontend says that a class with virtual
bases can alias anything. Dan, you seem to have been involved with that
code; can you explain why?

I am the other Dan :-), but I can explain.


That patch as a consequence of the long thread that started at:
http://gcc.gnu.org/ml/gcc/2002-01/msg01478.html

Somewhere in that thread Mark Mitchell said that virtual base classes
are not safe for aliasing, so the patch was written that way. That is
the only reason.


Right. It was better than what we had at the time (which was nothing).



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