[PATCH 06/10] tree-object-size: Support dynamic sizes in conditions

Jakub Jelinek jakub@redhat.com
Tue Nov 23 16:19:53 GMT 2021

On Tue, Nov 23, 2021 at 09:30:30PM +0530, Siddhesh Poyarekar wrote:
> On 11/23/21 21:22, Jakub Jelinek wrote:
> > Evaluating __bdos in both passes is undesirable, certainly for the same
> > SSA_NAME, but even for different SSA_NAMEs, if everything is done in a
> > single pass it can easily share temporaries (object sizes for SSA_NAMEs it
> > uses), while if some __bdos is evaluated early and other late, we'll need to
> > hope further optimizations CSE those.
> OK, then treat __bdos like __bos in objsz1, adding MIN?MAX for subobjects
> and full evaluation in objsz2?

Yes.  It is not perfect, but unfortunately it is hard to get perfect
results.  The subobject stuff for __bos has been designed when GCC wasn't
doing such optimizations, later MEM_REF has been introduced and we really
can't prevent all those optimizations just because there could be a
subobject __bos somewhere that cares about that.


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