On 8/17/22 03:42, Richard Biener wrote:
On Tue, 16 Aug 2022, Andrew MacLeod wrote:
On 8/16/22 05:18, Richard Biener wrote:
On Mon, 15 Aug 2022, Aldy Hernandez wrote:
On Mon, Aug 15, 2022 at 9:24 PM Andrew MacLeod <amacl...@redhat.com> wrote:
heh. or just
+ int_range<2> r;
+ if (!fold_range (r, const_cast <gcond *> (cond_stmt))
+ || !r.singleton_p (&val))
if you do not provide a range_query to any of the fold_using_range code,
it defaults to:
fur_source::fur_source (range_query *q)
{
if (q)
m_query = q;
else if (cfun)
m_query = get_range_query (cfun);
else
m_query = get_global_range_query ();
m_gori = NULL;
}
Sweet. Even better!
So when I do the following incremental change ontop of the posted
patch then I see that the path query is able to simplify more
"single BB paths" than the global range folding.
diff --git a/gcc/tree-ssa-threadbackward.cc
b/gcc/tree-ssa-threadbackward.cc
index 669098e4ec3..777e778037f 100644
--- a/gcc/tree-ssa-threadbackward.cc
+++ b/gcc/tree-ssa-threadbackward.cc
@@ -314,6 +314,12 @@ back_threader::find_taken_edge_cond (const
vec<basic_block> &path,
{
int_range_max r;
+ int_range<2> rf;
+ if (path.length () == 1)
+ {
+ fold_range (rf, cond);
+ }
+
m_solver->compute_ranges (path, m_imports);
m_solver->range_of_stmt (r, cond);
@@ -325,6 +331,8 @@ back_threader::find_taken_edge_cond (const
vec<basic_block> &path,
if (r == true_range || r == false_range)
{
+ if (path.length () == 1)
+ gcc_assert (r == rf);
edge e_true, e_false;
basic_block bb = gimple_bb (cond);
extract_true_false_edges_from_block (bb, &e_true, &e_false);
Even doing the following (not sure what's the difference and in
particular expense over the path range query) results in missed
simplifications (checking my set of cc1files).
diff --git a/gcc/tree-ssa-threadbackward.cc
b/gcc/tree-ssa-threadbackward.cc
index 669098e4ec3..1d43a179d08 100644
--- a/gcc/tree-ssa-threadbackward.cc
+++ b/gcc/tree-ssa-threadbackward.cc
@@ -99,6 +99,7 @@ private:
back_threader_registry m_registry;
back_threader_profitability m_profit;
+ gimple_ranger *m_ranger;
path_range_query *m_solver;
// Current path being analyzed.
@@ -146,12 +147,14 @@ back_threader::back_threader (function *fun,
unsigned flags, bool first)
// The path solver needs EDGE_DFS_BACK in resolving mode.
if (flags & BT_RESOLVE)
mark_dfs_back_edges ();
- m_solver = new path_range_query (flags & BT_RESOLVE);
+ m_ranger = new gimple_ranger;
+ m_solver = new path_range_query (flags & BT_RESOLVE, m_ranger);
}
back_threader::~back_threader ()
{
delete m_solver;
+ delete m_ranger;
loop_optimizer_finalize ();
}
@@ -314,6 +317,12 @@ back_threader::find_taken_edge_cond (const
vec<basic_block> &path,
{
int_range_max r;
+ int_range<2> rf;
+ if (path.length () == 1)
+ {
+ fold_range (rf, cond, m_ranger);
+ }
+
m_solver->compute_ranges (path, m_imports);
m_solver->range_of_stmt (r, cond);
@@ -325,6 +334,8 @@ back_threader::find_taken_edge_cond (const
vec<basic_block> &path,
if (r == true_range || r == false_range)
{
+ if (path.length () == 1)
+ gcc_assert (r == rf);
edge e_true, e_false;
basic_block bb = gimple_bb (cond);
extract_true_false_edges_from_block (bb, &e_true, &e_false);
one example is
<bb 176> [local count: 14414059]:
_128 = node_177(D)->typed.type;
pretmp_413 = MEM[(const union tree_node *)_128].base.code;
_431 = pretmp_413 + 65519;
if (_128 == 0B)
goto <bb 199>; [18.09%]
else
goto <bb 177>; [81.91%]
where m_imports for the path is just _128 and the range computed is
false while the ranger query returns VARYING. But
path_range_query::range_defined_in_block does
if (bb && POINTER_TYPE_P (TREE_TYPE (name)))
m_ranger->m_cache.m_exit.maybe_adjust_range (r, name, bb);
This is the coarse grained "side effect applies somewhere in the block"
mechanism. There is no understanding of where in the block it happens.
which adjusts the range to ~[0, 0], probably because of the
dereference in the following stmt.
Why does fold_range not do this when folding the exit test? Is there
a way to make it do so? It looks like the only routine using this
in gimple-range.cc is range_on_edge and there it's used for e->src
after calling range_on_exit for e->src (why's it not done in
range_on_exit?). A testcase for this is
Fold_range doesnt do this because it is simply another statement. It makes no
attempt to understand the context in which you are folding something. you
could be folding that stmt from a different location (ie recomputing) If
your context is that you are looking for the range after the last statement
has been executed, then one needs to check to see if there are any side
effects.
Hmm, but I'm asking it to fold a specific statement - how can that ever
be folded "from a different context"? In fact it traces as
" at stmt " with the stmt I pass it. But yes, the issue is of course
that to compute the range of q != 0 it needs to compute the range
of 'q' but it simply does
// If no name, simply call the base routine.
if (!name)
{
res = fold_range_internal (r, s, NULL_TREE);
if (res && is_a <gcond *> (s))
{
// Update any exports in the cache if this is a gimple cond
statement.
tree exp;
basic_block bb = gimple_bb (s);
FOR_EACH_GORI_EXPORT_NAME (m_cache.m_gori, bb, exp)
m_cache.propagate_updated_value (exp, bb);
and fur_depend seems to get the context so it could adjust ranges
in its get_operand which seems to just call range_of_expr with
the stmt as third arg. Unfortunately gimple_ranger::range_of_expr
is undocumented, but again 'stmt' is dumped as " at stmt " thus
seems to be the "context" here?
Oh, so you are looking at gimple_ranger::range_of_stmt(), not fold_range.
// If name is defined in this block, try to get an range from S.
what is 'S'? def_stmt or stmt?
if (def_stmt && gimple_bb (def_stmt) == bb)
{
// Declared in this block, if it has a global set, check for an
// override from a block walk, otherwise calculate it.
if (m_cache.get_global_range (r, expr))
m_cache.block_range (r, bb, expr, false);
else
range_of_stmt (r, def_stmt, expr);
so, add
if (is_ctrl_stmt (stmt))
m_cache.m_exit.maybe_adjust_range (r, expr, bb);
at the end (also covering the range_on_entry case). I suppose
range_on_entry does not evaluate all possible paths from definition
to BB, using maybe_adjust_range on blocks inbetween and unioning
ranges at path merges? That would likely be prohibitly expensive.
in fact it does. The cache takes care of filling in the blanks and
requesting ranges that have not been satisfied yet in a reasonably
efficient way. Maybe_adjust_range() will deal only with inferred ranges
that are marked as having occurred in this block.
The problem I ran into with trying to doing it in range_on_exit(), is
that if there is an abnornal edge out of the block, it is unsafe to
assume that anything is true at block exit.. when processing the
abnormal destination, we ask for range_on_exit of anything it uses from
the src block.
That said, I suppose is should be safe for range_of_stmt to assume the
statement successfully executed (or there wouldnt be a defintion
produced), and therefore if it is the last stmt in the block, we should
in theory be able to do as you suggest there.
Im trying to think if its safe to also do it in range_of_expr. if
is_ctrl_stmt() is true, can I assume that the stmt cannot throw an
exception under any circumstance? in which case, its proabbly safe to
put that in range_of_expr. Ive attached a patch which does that if you
want to try it.
The caveat is that it is only a partial solution... it will only work
for names on that stmt. if you have anything more complex, ie
if (a == 0 || b == 0) we have a seqeunce feeding the ctrl stmt..
c_1 = a == 0
c_2 = b == 0
c_3 = c_1 && c_2
if (c_3 == 0)
only the evaluation of c_3 will have the ctrl stmt as its context.. the
others will be evaluted on their own statement, and thus neither a nor b
would pick up anything from the block as they are evalauted and cached
as they are seen. unless of course we are doing a walk :-P
ranger uses it for range_on_edge (), because it knows all the statements in
the block have been executed, and its safe to apply anything seen in the
block. It does it right after range_on_exit() is called internally.
Once upon a time, it was integrated with range-on-exit, but it turned out
there were certain times that it was causing problems. There have been some
cleanups since then, it probably safe now to return that call to
range_on_exit.. but doesnt buy us a whole lot by itself.. except of course I
have now OKd using range_on-entry/exit generally :-)
the cache also uses it when walking blocks to pick up inferred values during
an on-entry cache fill.
int foo (int **p, int i)
{
int *q = *p;
int res = *q + i;
if (q)
return res;
return -1;
}
which we "thread" with the path and with the above ICEs because
fold_range doesn't get that if (q) is always true. Without the
Its a known limitation that, unless you are doing a walk, on-demand requests
will "miss" some inferred ranges, because they are only maintained at the
basic block level. (ie, we will know that q is non-null in BB2, but we don't
know where, so we can make no assumptions at the exit condition about q in
this case. the path_query is invoked in on-demand mode because it wont walk
the entire IL,. so the first time you ask for the range of an ssa-name, it
will quickly zip over the immediate use list and "fill" the on-exit structure
for any blocks which a non-null reference is seen. This allows the threader
to pick up non-null from blocks outside the path that havent been examined.
VRP does a walk, and while during the walk, adjusts ranges on the fly for the
current block via the gimple_ranger::register_inferred_ranges () routine.
which is really just a wrapper around ranger_cache::apply_inferred_ranges ()
(in gimple-range-cache.cc)
This is called after every statement and is where we take care of bookkeeping
for adjusting values, and adding them to the blocks list.
if the path query is walking those statement, it could also "adjust" the range
of q on the fly... but it has to have walked those statements. from that
routine, the relevant bits use the gimple-infer class to find any inferred
ranges from the statement, and would look something like:
gimple_infer_range infer(s);
for (unsigned x = 0; x < infer.num (); x++)
{
tree name = infer.name (x);
if (!interesting_p (name))
continue;
get_current_path_range (r, name);
if (r.intersect (infer.range (x)))
set_current_path_range (name, r);
}
That would adjust the value of q to be non-zero after "int res = *q + i;"
but you need to have walked the statement before you get to the condition.
as long as they are all in your list of interesting statement to look at, then
you'd be golden.
Ah, so while the above might work it would go against the spirit of this
being only fully useful if applied during a walk, adjusting the
cached ranges? It's still a bit unfortunate that one needs to walk all
stmts for this - the usecase wants to just walk the CFG and control stmts,
and with the path query it would only cover the single BB of each
control stmt (thus the above hack would probably work out).
I wouldn't say its against the spirit, merely against trying to catch
all cases in a practical way :-). If we add that, it should work for
this case. for the threader, we will have visited all the uses of q to
fill the inferred block cache q will have a non-null refererence in
bb2. and when calculating the final value, if we are indeed assuming
anything in the block can be applied to the final stmt, then it should
be ok. but we'll still mis anything but the simpliest cases. maybe
thats OK. better to catch a few cases than none.
let me think about how, especially for paths, we might be able to take
care of calculating an entire complex condition/expression in the
context of the original call.
So, a longer term goal was to perhaps have some sort of persistent
ranger across compatible passes.. turn it into a pass property, and only
dispose of it when a pass makes enough IL changes to invalidate it...
In the meantime, it should be possible to take a ranger that just
completed a VRP pass, and use that as the root ranger for a threading
pass immediately after.. I think there may be some lingering issues with
abnormal edges if we "re-visit" blocks which we claim to have walked due
to the way I store inferred ranges in those block.. (the expectation
being we never go back up into the block, so the on-entry cache works
like the "current def" vector in the original EVRP. I'd have to think
about that too.
Meanwhile I'm leaning towards calling this a phase ordering issue
of threading + VRP, but that also means we shouldn't deliberately
try to preserve "threadings" of this kind - in fact we might want
to explicitely reject them?
we are probably going to want to visit some pass ordering.
Richard.
diff --git a/gcc/gimple-range.cc b/gcc/gimple-range.cc
index eb347eee45b..188acb2c308 100644
--- a/gcc/gimple-range.cc
+++ b/gcc/gimple-range.cc
@@ -128,6 +128,10 @@ gimple_ranger::range_of_expr (vrange &r, tree expr, gimple *stmt)
// Otherwise OP comes from outside this block, use range on entry.
else
range_on_entry (r, bb, expr);
+ // If the context is the final statement, it is safe to apply any
+ // known inferred ranges for the block.
+ if (is_ctrl_stmt (stmt))
+ m_cache.m_exit.maybe_adjust_range (r, expr, bb);
}
if (idx)
tracer.trailer (idx, "range_of_expr", true, expr, r);
