[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 #13 from law at redhat dot com  2006-03-28 19:13 -------
Subject: Re:  [4.1/4.2 Regression] missed jump
        threading after unroller

On Wed, 2006-03-22 at 16:06 +0100, Richard Guenther wrote:
> On 3/22/06, Jeffrey A Law <law@redhat.com> wrote:
> > 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.
> 
> struct tree_opt_pass pass_phi_only_cprop =
> {
>   "phicprop",                           /* name */
>   gate_dominator,                       /* gate */
>   eliminate_degenerate_phis,            /* execute */
>   NULL,                                 /* sub */
>   NULL,                                 /* next */
>   0,                                    /* static_pass_number */
>   TV_TREE_CCP,                          /* tv_id */
>   PROP_cfg | PROP_ssa | PROP_alias,     /* properties_required */
>   0,                                    /* properties_provided */
>   PROP_smt_usage,                       /* properties_destroyed */
>   0,                                    /* todo_flags_start */
>   TODO_cleanup_cfg | TODO_dump_func
>     | TODO_ggc_collect | TODO_verify_ssa
>     | TODO_verify_stmts | TODO_update_smt_usage
>     | TODO_update_ssa, /* todo_flags_finish */
>   0                                     /* letter */
> };
> 
> see tv_id - so I guess increased CCP times are expected.
I've created a separate timevar for the phi-only cprop code so
at least we can see how much time's taking.  Note that while we
should be seeing a small amount of time in phi-cprop, we should
be seeing a reduction in TV_TREE_CCP and TV_TREE_COPY_PROP.

Can you send me a recent tramp3d.ii file so that I can poke
around and see if there's anything we can do about the compile
time regression?

Thanks,
jeff


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