On Tue, Aug 16, 2022 at 4:12 PM Richard Biener
<richard.guent...@gmail.com> wrote:
>
> On Tue, Aug 16, 2022 at 3:59 PM Aldy Hernandez <al...@redhat.com> wrote:
> >
> > [Richi, I'm trying to make things more obvious for others working for the
> > cose base. What do you think?]
> >
> > This makes a few things explicit to avoid misuse. First, we add a
> > flag to differentiate between a path whose depdenency ranges are being
> > computed, and a path that is finalized and no further calculations
> > should be done. I've also enhanced the comments to document what
> > queries are supported. Finally, I added some asserts to make sure
> > range_of_expr is only used on the final conditional once the path has
> > been finalized.
> >
> > Unfortunately, the forward threader builds dummy statements it passes
> > to the path solver. Most of these don't have a BB associated with
> > them. I've cleared the BB field for the one that still had one, to
> > make the asserts above work.
> >
> > No difference in thread counts over my cc1 .ii files.
> >
> > gcc/ChangeLog:
> >
> > * gimple-range-path.cc (path_range_query::path_range_query):
> > Initialized m_path_finalized.
> > (path_range_query::internal_range_of_expr): Avoid further
> > recomputations once path is finalized.
> > Take basic_block instead of stmt as argument.
> > (path_range_query::range_of_expr): Document. Add asserts.
> > (path_range_query::compute_ranges): Set m_path_finalized.
> > * gimple-range-path.h (path_range_query::internal_range_of_expr):
> > Replace statement argument with basic block.
> > (class path_range_query): Add m_path_finalized.
> > * tree-ssa-threadedge.cc
> > (jump_threader::simplify_control_stmt_condition): Clear BB field
> > in dummy_switch.
> > ---
> > gcc/gimple-range-path.cc | 50 ++++++++++++++++++++++++++++++++++----
> > gcc/gimple-range-path.h | 7 +++++-
> > gcc/tree-ssa-threadedge.cc | 1 +
> > 3 files changed, 52 insertions(+), 6 deletions(-)
> >
> > diff --git a/gcc/gimple-range-path.cc b/gcc/gimple-range-path.cc
> > index c99d77dd340..a8412dd090b 100644
> > --- a/gcc/gimple-range-path.cc
> > +++ b/gcc/gimple-range-path.cc
> > @@ -40,7 +40,8 @@ path_range_query::path_range_query (bool resolve,
> > gimple_ranger *ranger)
> > : m_cache (new ssa_global_cache),
> > m_has_cache_entry (BITMAP_ALLOC (NULL)),
> > m_resolve (resolve),
> > - m_alloced_ranger (!ranger)
> > + m_alloced_ranger (!ranger),
> > + m_path_finalized (false)
> > {
> > if (m_alloced_ranger)
> > m_ranger = new gimple_ranger;
> > @@ -159,7 +160,7 @@ path_range_query::range_on_path_entry (vrange &r, tree
> > name)
> > // Return the range of NAME at the end of the path being analyzed.
> >
> > bool
> > -path_range_query::internal_range_of_expr (vrange &r, tree name, gimple
> > *stmt)
> > +path_range_query::internal_range_of_expr (vrange &r, tree name,
> > basic_block bb)
> > {
> > if (!r.supports_type_p (TREE_TYPE (name)))
> > return false;
> > @@ -174,8 +175,16 @@ path_range_query::internal_range_of_expr (vrange &r,
> > tree name, gimple *stmt)
> > return true;
> > }
> >
> > - if (stmt
> > - && range_defined_in_block (r, name, gimple_bb (stmt)))
> > + // Avoid further recomputations once the path has been finalized.
> > + if (m_path_finalized)
> > + {
> > + gimple_range_global (r, name);
>
> I suppose we can't assert here instead?
>
> > + return true;
> > + }
> > +
> > + // We're being called as part of the calculation of ranges for exit
> > + // dependencies. Set the cache as we traverse the path top-down.
> > + if (bb && range_defined_in_block (r, name, bb))
> > {
> > if (TREE_CODE (name) == SSA_NAME)
> > {
> > @@ -192,10 +201,37 @@ path_range_query::internal_range_of_expr (vrange &r,
> > tree name, gimple *stmt)
> > return true;
> > }
> >
> > +// This, as well as range_of_stmt, are the main entry points for
> > +// making queries about a path.
> > +//
> > +// Once the ranges for the exit dependencies have been pre-calculated,
> > +// the path is considered finalized, and the only valid query is
> > +// asking the range of a NAME at the end of the path.
> > +//
> > +// Note that this method can also be called internally before the path
> > +// is finalized, as part of the path traversal pre-calculating the
> > +// ranges for exit dependencies. In this case, it may be called on
> > +// statements that are not the final conditional as described above.
> > +
> > bool
> > path_range_query::range_of_expr (vrange &r, tree name, gimple *stmt)
> > {
> > - if (internal_range_of_expr (r, name, stmt))
> > + basic_block bb = stmt ? gimple_bb (stmt) : NULL;
> > +
> > + // Once a path is finalized, the only valid queries are of the final
> > + // statement in the exit block.
>
> why? shouldn't we support queries for all dependent ranges (what
> the user specified as imports argument to compute_ranges)?
Yes, we allow queries of all dependent ranges, but as viewed from the
exit from the path.
>
> If we want to restrict things this way shouldn't we simply not expose
> this function but instead just path_range_query::range_of_exit,
> or even what the threader uses as find_taken_edge?
Hmm, that's a very good point. For that matter, the original
implementation just had a range_of_exit public method. It evolved to
the current version, because having it behave like a range_query has
other benefits. For example, I thought that you could pass the path
query to things like simplify_using_ranges, to simplify a statement
given a path. In reality, that hasn't happened.
So lemme put this aside for now, while I think and experiment a little.
Thanks for the feedback.
Aldy
>
> The loop header copying case would also work with this,
> it's interested in the known outgoing edge of the path.
>
> > + if (flag_checking && m_path_finalized && stmt)
> > + {
> > + // The forward threader may query dummy statements without a
> > + // basic block.
> > + if (bb)
> > + {
> > + gcc_assert (stmt == last_stmt (bb));
> > + gcc_assert (bb == exit_bb ());
> > + }
> > + }
> > +
> > + if (internal_range_of_expr (r, name, bb))
> > {
> > if (r.undefined_p ())
> > m_undefined_path = true;
> > @@ -608,6 +644,7 @@ path_range_query::compute_ranges (const
> > vec<basic_block> &path,
> >
> > set_path (path);
> > m_undefined_path = false;
> > + m_path_finalized = false;
> >
> > if (dependencies)
> > bitmap_copy (m_exit_dependencies, dependencies);
> > @@ -642,6 +679,7 @@ path_range_query::compute_ranges (const
> > vec<basic_block> &path,
> >
> > move_next ();
> > }
> > + m_path_finalized = true;
> >
> > if (DEBUG_SOLVER)
> > {
> > @@ -730,6 +768,8 @@ jt_fur_source::query_relation (tree op1, tree op2)
> > }
> >
> > // Return the range of STMT at the end of the path being analyzed.
> > +//
> > +// See notes in range_of_expr as to what are considered valid queries.
> >
> > bool
> > path_range_query::range_of_stmt (vrange &r, gimple *stmt, tree)
> > diff --git a/gcc/gimple-range-path.h b/gcc/gimple-range-path.h
> > index 3cb794e34a9..61a7d0f656e 100644
> > --- a/gcc/gimple-range-path.h
> > +++ b/gcc/gimple-range-path.h
> > @@ -46,7 +46,7 @@ public:
> > void debug ();
> >
> > private:
> > - bool internal_range_of_expr (vrange &r, tree name, gimple *);
> > + bool internal_range_of_expr (vrange &r, tree name, basic_block);
> > bool defined_outside_path (tree name);
> > void range_on_path_entry (vrange &r, tree name);
> > path_oracle *get_path_oracle () { return (path_oracle *)m_oracle; }
> > @@ -113,6 +113,11 @@ private:
> > // True if m_ranger was allocated in this class and must be freed at
> > // destruction.
> > bool m_alloced_ranger;
> > +
> > +// Once the ranges for the exit dependencies have been pre-calculated,
> > +// the path is considered finalized and this is set to TRUE.
> > +// Otherwise, the path is being analyzed.
> > + bool m_path_finalized;
> > };
> >
> > #endif // GCC_TREE_SSA_THREADSOLVER_H
> > diff --git a/gcc/tree-ssa-threadedge.cc b/gcc/tree-ssa-threadedge.cc
> > index e64e4f209f7..213796c10cc 100644
> > --- a/gcc/tree-ssa-threadedge.cc
> > +++ b/gcc/tree-ssa-threadedge.cc
> > @@ -451,6 +451,7 @@ jump_threader::simplify_control_stmt_condition (edge e,
> > gimple *stmt)
> > possible, the simplified value will be a CASE_LABEL_EXPR of
> > the label that is proven to be taken. */
> > gswitch *dummy_switch = as_a<gswitch *> (gimple_copy (stmt));
> > + gimple_set_bb (dummy_switch, NULL);
>
> I think it's not wrong to say the stmt is in the block though
>
> > gimple_switch_set_index (dummy_switch, cached_lhs);
> > cached_lhs = m_simplifier->simplify (dummy_switch, stmt,
> > e->src,
> > m_state);
> > --
> > 2.37.1
> >
>
