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

["richard dot guenther at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

------- Comment #11 from richard dot guenther at gmail dot com  2006-03-22 15:06 -------
Subject: Re:  [4.1/4.2 Regression] missed jump threading after unroller

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.

Richard.


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