[Bug tree-optimization/21829] [4.1/4.2 Regression] missed jump threading after unroller

["law at redhat dot com" <gcc-bugzilla@gcc.gnu.org>]

------- Comment #10 from law at redhat dot com  2006-03-22 14:01 -------
Subject: Re:  [4.1/4.2 Regression] missed jump
        threading after unroller

On Wed, 2006-03-22 at 12:14 +0100, Richard Guenther wrote:
> On 3/21/06, Jeffrey A Law <law@redhat.com> wrote:
> > It turns out this specialized PHI optimization pass is as effective
> > as running copy-prop and CCP on PHI nodes after DOM.  Better yet, it
> > is a teeny tiny slowdown compared to just running the stripped down
> > copyprop.  ie, for an almost unmeasurable slowdown we can do both
> > constant and copy propagation instead of just copy propagation.
> 
> This patch caused a compile-time regression from 139s to 143s, resp.
> 192s to 197s (leafify) accounted by increases of operand scan / SSA incremental
> and tree CCP times for compiling tramp3d.  Also memory usage during compiling
> went up from 655494 kB to 660626kB (this may be due to the VRP patch, though).
> 
> Runtime of tramp3d did not improve but regress slightly (but that
> might be in the
> noise - we'll see).
> 
> For this simple cleanup pass can you try updating SSA form manually please?
I'm more than happy to look at it; however, be aware that if you're
seeing increased time in CCP then either you're seeing some truly
bizzarre secondary effect or your testing methodology is suspect.
The patch did not affect CCP.  In fact, the changes only affect
passes which run *after* CCP in the optimization pipeline.

Jeff


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21829