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Re: [tree-ssa] RFC: Making control flow more explicit
- From: Zdenek Dvorak <rakdver at atrey dot karlin dot mff dot cuni dot cz>
- To: law at redhat dot com
- Cc: Michael Matz <matz at suse dot de>,Andrew MacLeod <amacleod at redhat dot com>,Steven Bosscher <s dot bosscher at student dot tudelft dot nl>,Daniel Berlin <dberlin at dberlin dot org>,Diego Novillo <dnovillo at redhat dot com>,gcc mailing list <gcc at gcc dot gnu dot org>
- Date: Tue, 12 Aug 2003 19:22:08 +0200
- Subject: Re: [tree-ssa] RFC: Making control flow more explicit
- References: <Pine.LNX.firstname.lastname@example.org> <200308112238.h7BMbdAU004089@speedy.slc.redhat.com>
> >> >because parent obviously is not what you want here. IIRC in the ssa dce
> >> >algorithm marking of the neccesary control statements is somehow
> >> >done using dominator information.
> >> The RTL version does use dominator information, the tree version does not
> >> use dominator information to find necessary control statements.
> >> The tree version uses the nested control structure and goto following to
> >> deduce control dependency.
> >The question is, do we eventually somewhen will need postdoms anyway?
> Very very rarely within the DCE optimizer.
if I understand the code correctly, only when some control statement is
actually removed. This together with your claim that it occurs rarely
implies that the optimization is almost useless in practice. Would not
it then make sense to perform it only with -O3, then the extra time
for computing postdominators would be more acceptable?