Re: [tree-ssa] New regressions as of 2003-11-04

[Zdenek Dvorak <rakdver at atrey dot karlin dot mff dot cuni dot cz>]

Hello,

>  >remove_useless_stmts_and_vars_cond could keep the cfg updated if it
>  >wanted to. It didnt before becuase it was thrown away immediately
>  >aftewards, so what was the point. Now perhaps there is a point.
> Correct.  Nothing after remove_useless_stmts_and_vars cared about the CFG
> and by not doing silly work, remove_useless_stmts_and_vars actually improved
> compilation times and kept the code reasonably simple.
> 
> So one thing we need to look at before we go and make that code CFG aware
> is whether or not it's actually going to be a good thing from the various
> angles, including the ability to eliminate obviously useless statements
> created by the out-of-ssa translation, compile time concerns, the need to
> actually eliminate all the empty statements, etc etc.

if we want to keep it at all, we must make it cfg aware, since soon we
will be making a transition from trees to rtl without clobbering the cfg
(this is not only useful from performance pov, but also neccesary in
order to be able to do profiling on trees).

Concerning compile time -- there is nothing much to worry about, since
no transformation done by remove_useless_stmts_and_vars does anything
important with it.

And finally, I already have it done -- see
http://gcc.gnu.org/ml/gcc-patches/2003-11/msg00388.html.

Zdenek