[ast-optimizer-branch] Bootstrap fixes [patch]

[Daniel Berlin]

On Tue, 7 May 2002, Diego Novillo wrote:

> With this patch we can bootstrap the C front end (botstrapping
> C++ dies when building libstdc++ with the bootstrapped compiler).  
> 
> The patch doesn't fix much, it disables the simplification of
> MODIFY_EXPR, INIT_EXPR, SAVE_EXPR and binary expressions.
> Enabling any of these 4 produces a bootstrap failure.

Really?

Let me do some diffs.
I only need to disable simplify_self_mod_expr and simplify_save_expr to be 
able to bootstrap before.

This includes simplifying statement expressions.

Not copying nodes also ends up making optimizations harder.  For things 
like copy-prop, i now have to make sure we don't screw over shared 
expressions when replacing.

It's not that easy, either, since it may be shared at a level or two above 
the expression in the reference.

--Dan