On Fri, 12 Aug 2022, Andrew MacLeod wrote:
>
> On 8/12/22 07:31, Aldy Hernandez wrote:
> > On Fri, Aug 12, 2022 at 12:59 PM Richard Biener <rguent...@suse.de> wrote:
> >> With the last re-org I failed to make sure to not add SSA names
> >> nor supported by ranger into m_imports which then triggers an
> >> ICE in range_on_path_entry because range_of_expr returns false. I've
> >> noticed that range_on_path_entry does mightly complicated things
> >> that don't make sense to me and the commentary might just be
> >> out of date. For the sake of it I replaced it with range_on_entry
> >> and statistics show we thread _more_ jumps with that, so better
> >> not do magic there.
> > Hang on, hang on. range_on_path_entry was written that way for a
> > reason. Andrew and I had numerous discussions about this. For that
> > matter, my first implementation did exactly what you're proposing, but
> > he had reservations about using range_on_entry, which IIRC he thought
> > should be removed from the (public) API because it had a tendency to
> > blow up lookups.
> >
> > Let's wait for Andrew to chime in on this. If indeed the commentary
> > is out of date, I would much rather use range_on_entry like you
> > propose, but he and I have fought many times about this... over
> > various versions of the path solver :).
>
> The original issue with range-on-entry is one needed to be very careful with
> it. If you ask for range-on-entry of something which is not dominated by the
> definition, then the cache filling walk was getting filled all the way back to
> the top of the IL, and that was both a waste of time and memory., and in some
> pathological cases was outrageous.
I think this won't happen with the backthreader sanitizing of m_imports.
I have pushed the change given the comments made later.
Thanks,
Richard.
> And it was happening more frequently than
> one imagines... even if accidentally. I think the most frequent accidental
> misuse we saw was calling range on entry for a def within the block, or a PHI
> for the block.
>
> Its a legitimate issue for used before defined cases, but there isnt much we
> can do about those anyway,
>
> range_of_expr on any stmt within a block, when the definition comes from
> outside he block causes ranger to trigger its internal range-on-entry "more
> safely", which is why it didn't need to be part of the API... but i admit it
> does cause some conniptions when for instance there is no stmt in the block.
>
> That said, the improvements since then to the cache to be able to always use
> dominators, and selectively update the cache at strategic locations probably
> removes most issues with it. That plus we're more careful about timing things
> these days to make sure something horrid isn't introduced. I also notice all
> my internal range_on_entry and _exit routines have evolved and are much
> cleaner than they once were.
>
> So. now that we are sufficiently mature in this space... I think we can
> promote range_on_entry and range_on_exit to full public API.. It does seem
> that there is some use practical use for them.
>
> Andrew
>
> PS. It might even be worthwhile to add an assert to make sure it isnt being
> called on the def block.. just to avoid that particular stupidty :-) I'll
> take care of doing this.
>
>
>
>
>
> > For now I would return VARYING in range_on_path_entry if range_of_expr
> > returns false. We shouldn't be ICEing when we can gracefully handle
> > things. This gcc_unreachable was there to catch implementation issues
> > during development.
> >
> > I would keep your gimple_range_ssa_p check regardless. No sense doing
> > extra work if we're absolutely sure we won't handle it.
> >
> > Aldy
> >
> >> Bootstrapped on x86_64-unknown-linux-gnu, testing in progress.
> >>
> >> Will push if that succeeds.
> >>
> >> PR tree-optimization/106593
> >> * tree-ssa-threadbackward.cc (back_threader::find_paths):
> >> If the imports from the conditional do not satisfy
> >> gimple_range_ssa_p don't try to thread anything.
> >> * gimple-range-path.cc (range_on_path_entry): Just
> >> call range_on_entry.
> >> ---
> >> gcc/gimple-range-path.cc | 33 +--------------------------------
> >> gcc/tree-ssa-threadbackward.cc | 6 +++++-
> >> 2 files changed, 6 insertions(+), 33 deletions(-)
> >>
> >> diff --git a/gcc/gimple-range-path.cc b/gcc/gimple-range-path.cc
> >> index b6148eb5bd7..a7d277c31b8 100644
> >> --- a/gcc/gimple-range-path.cc
> >> +++ b/gcc/gimple-range-path.cc
> >> @@ -153,38 +153,7 @@ path_range_query::range_on_path_entry (vrange &r, tree
> >> name)
> >> {
> >> gcc_checking_assert (defined_outside_path (name));
> >> basic_block entry = entry_bb ();
> >> -
> >> - // Prefer to use range_of_expr if we have a statement to look at,
> >> - // since it has better caching than range_on_edge.
> >> - gimple *last = last_stmt (entry);
> >> - if (last)
> >> - {
> >> - if (m_ranger->range_of_expr (r, name, last))
> >> - return;
> >> - gcc_unreachable ();
> >> - }
> > I
> >> -
> >> - // If we have no statement, look at all the incoming ranges to the
> >> - // block. This can happen when we're querying a block with only an
> >> - // outgoing edge (no statement but the fall through edge), but for
> >> - // which we can determine a range on entry to the block.
> >> - Value_Range tmp (TREE_TYPE (name));
> >> - bool changed = false;
> >> - r.set_undefined ();
> >> - for (unsigned i = 0; i < EDGE_COUNT (entry->preds); ++i)
> >> - {
> >> - edge e = EDGE_PRED (entry, i);
> >> - if (e->src != ENTRY_BLOCK_PTR_FOR_FN (cfun)
> >> - && m_ranger->range_on_edge (tmp, e, name))
> >> - {
> >> - r.union_ (tmp);
> >> - changed = true;
> >> - }
> >> - }
> >> -
> >> - // Make sure we don't return UNDEFINED by mistake.
> >> - if (!changed)
> >> - r.set_varying (TREE_TYPE (name));
> >> + m_ranger->range_on_entry (r, entry, name);
> >> }
> >>
> >> // Return the range of NAME at the end of the path being analyzed.
> >> diff --git a/gcc/tree-ssa-threadbackward.cc
> >> b/gcc/tree-ssa-threadbackward.cc
> >> index 0a992213dad..669098e4ec3 100644
> >> --- a/gcc/tree-ssa-threadbackward.cc
> >> +++ b/gcc/tree-ssa-threadbackward.cc
> >> @@ -525,7 +525,11 @@ back_threader::find_paths (basic_block bb, tree name)
> >> bitmap_clear (m_imports);
> >> ssa_op_iter iter;
> >> FOR_EACH_SSA_TREE_OPERAND (name, stmt, iter, SSA_OP_USE)
> >> - bitmap_set_bit (m_imports, SSA_NAME_VERSION (name));
> >> + {
> >> + if (!gimple_range_ssa_p (name))
> >> + return;
> >> + bitmap_set_bit (m_imports, SSA_NAME_VERSION (name));
> >> + }
> >>
> >> // Interesting is the set of imports we still not have see
> >> // the definition of. So while imports only grow, the
> >> --
> >> 2.35.3
> >>
>
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH, Frankenstrasse 146, 90461 Nuernberg,
Germany; GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman;
HRB 36809 (AG Nuernberg)
