> On September 26, 2020 12:04:24 AM GMT+02:00, Jan Hubicka <hubi...@ucw.cz>
> wrote:
> >Hi,
> >while adding check for gimple_clobber I reversed the return value
> >so instead of ignoring the statement ipa-modref gives up. Fixed thus.
> >This explains the drop between originally reported disambinguations
> >stats and ones I got later.
>
> I don't think you can ignore clobbers. They are barriers for code motion.
modref is (before and after patch) about 1.4% of the WPA time (2s). This
is pretty the much cost of a single pass over the symbol table (other
non-busy IPA passes takes about the same, ipa-comdat is fater with 0.7%).
The iteration of dataflow happens only on non-trivial strongly connected
components and at least for GCC alway terminates in 3 iterations (to
trigger more one needs to function with many params with operation like
shifting every param right.
>
> Richard.
>
>
> >Bootstrapped/regtested x86_64-linux.
> >
> >gcc/ChangeLog:
> >
> >2020-09-25 Jan Hubicka <hubi...@ucw.cz>
> >
> > * ipa-modref.c (analyze_stmt): Fix return value for gimple_clobber.
> >
> >diff --git a/gcc/ipa-modref.c b/gcc/ipa-modref.c
> >index aa6929ff010..44b844b90db 100644
> >--- a/gcc/ipa-modref.c
> >+++ b/gcc/ipa-modref.c
> >@@ -658,7 +658,7 @@ analyze_stmt (modref_summary *summary, gimple
> >*stmt, bool ipa)
> > {
> > /* There is no need to record clobbers. */
> > if (gimple_clobber_p (stmt))
> >- return false;
> >+ return true;
> > /* Analyze all loads and stores in STMT. */
> > walk_stmt_load_store_ops (stmt, summary,
> > analyze_load, analyze_store);
>
