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Date: Tue, 10 Apr 2012 12:26:00 -0000
From: Michael Matz <matz@suse.de>
To: Jakub Jelinek <jakub@redhat.com>
Cc: Xinliang David Li <davidxl@google.com>,	Richard Guenther <richard.guenther@gmail.com>,	Bernd Schmidt <bernds@codesourcery.com>,	Gabriel Dos Reis <gdr@integrable-solutions.net>,	David Edelsohn <dje.gcc@gmail.com>,	Diego Novillo <dnovillo@google.com>, gcc <gcc@gcc.gnu.org>
Subject: Re: Switching to C++ by default in 4.8
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Hi,

On Tue, 10 Apr 2012, Jakub Jelinek wrote:

> >    *) gcc implementation has lots of hard coded TREE_OPERAND (exp, nn)
> > 
> >      e.g.
> >             exp->as_component_ref().get_field() ..
> >             exp->as_mem_access().get_base() ...
> >             exp->as_mem_acesss().get_address() --> produces the
> > address expression for memory access
> >             exp->as_mem_access().get_alias_handle ()
> > 
> >             gimple_inst->serialize (&fixup_list) --> a virtual
> > function overriden by actual instruction types that knows its byte
> > code format.
> 
> That silently assumes we want to change basic GIMPLE/tree data structures
> to virtual classes, which is a significant change that has a significant
> cost as well.  E.g. all such changed data structures grow by a virtual
> pointer field.  Those data structures are heavily optimized for memory
> footprint.
> Not to mention it is very questionable if the above stuff is more readable
> than what we currently have.

Actually it's not questionable.  The above stuff is _horrible_.


Ciao,
Michael.