Re: [PATCH] New code size estimate

[Richard Guenther <rguenth at tat dot physik dot uni-tuebingen dot de>]

On Mon, 28 Feb 2005, Steven Bosscher wrote:

> Ref: http://gcc.gnu.org/ml/gcc-patches/2005-02/msg01796.html
>
> > 	* tree-inline.c (estimate_num_insns_1): Ignore stores to decls with
> > 	ignored flag set.
>
> Someone still has to explain why this makes sense.  All large
> expressions will now suddenly look really small, if I understand
> this change correctly.  For example, say you have,
>
> x = a + b + c + d + e + .... + z;
>
> then the equivalent GIMPLE will look something like,
>
> t2 = a + b;
> t3 = t2 + c;
> ...
> ...
> x = t25 + z;
>
> and all the "t[0-9]+" temporaries would result in real code being
> generated, but their assignments would be ignored if this patch is
> applied, because all temporaries would have DECL_IGNORED set on
> them.  Ignoring them would be not quite sane IMHO. Am I missing
> something here?

Sorry to followup myself again, there are certainly ways to improve
estimate_num_insns - f.i. we assign the same cost (1) to EXPR nodes
with any number of arguments, while it may be better (if we are
no longer counting those virtual stores) to assign 1 to NEGATE_EXPR
and 2 to ADD_EXPR, f.i., it also doesn't make much sense in my
view to assign 10 to RDIV_EXPR (for a code size estimate).  But
changing too much at once is probably not a good idea.

Richard.