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adjust update_profile_after_ifcombine for noncontiguous ifcombine

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Prepare for ifcombining noncontiguous blocks, adding (still unused)
logic to the ifcombine profile updater to handle such cases.


for  gcc/ChangeLog

	* tree-ssa-ifcombine.cc (known_succ_p): New.
	(update_profile_after_ifcombine): Handle noncontiguous blocks.
This commit is contained in:
Alexandre Oliva 2024-11-07 02:47:34 -03:00 committed by Alexandre Oliva
parent f9fb8f96cd
commit 02dc5036ba
1 changed files with 82 additions and 21 deletions
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103
gcc/tree-ssa-ifcombine.cc
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@ -50,6 +50,21 @@ along with GCC; see the file COPYING3. If not see
false) >= 2)
#endif
/* Return FALSE iff the COND_BB ends with a conditional whose result is not a
known constant. */
static bool
known_succ_p (basic_block cond_bb)
{
gcond *cond = safe_dyn_cast <gcond *> (*gsi_last_bb (cond_bb));
if (!cond)
return true;
return (CONSTANT_CLASS_P (gimple_cond_lhs (cond))
&& CONSTANT_CLASS_P (gimple_cond_rhs (cond)));
}
/* This pass combines COND_EXPRs to simplify control flow. It
currently recognizes bit tests and comparisons in chains that
represent logical and or logical or of two COND_EXPRs.
@ -357,14 +372,28 @@ recognize_bits_test (gcond *cond, tree *name, tree *bits, bool inv)
}
/* Update profile after code in outer_cond_bb was adjusted so
outer_cond_bb has no condition. */
/* Update profile after code in either outer_cond_bb or inner_cond_bb was
adjusted so that it has no condition. */
static void
update_profile_after_ifcombine (basic_block inner_cond_bb,
basic_block outer_cond_bb)
{
edge outer_to_inner = find_edge (outer_cond_bb, inner_cond_bb);
/* In the following we assume that inner_cond_bb has single predecessor. */
gcc_assert (single_pred_p (inner_cond_bb));
basic_block outer_to_inner_bb = inner_cond_bb;
profile_probability prob = profile_probability::always ();
for (;;)
{
basic_block parent = single_pred (outer_to_inner_bb);
prob *= find_edge (parent, outer_to_inner_bb)->probability;
if (parent == outer_cond_bb)
break;
outer_to_inner_bb = parent;
}
edge outer_to_inner = find_edge (outer_cond_bb, outer_to_inner_bb);
edge outer2 = (EDGE_SUCC (outer_cond_bb, 0) == outer_to_inner
? EDGE_SUCC (outer_cond_bb, 1)
: EDGE_SUCC (outer_cond_bb, 0));
@ -375,29 +404,61 @@ update_profile_after_ifcombine (basic_block inner_cond_bb,
std::swap (inner_taken, inner_not_taken);
gcc_assert (inner_taken->dest == outer2->dest);
/* In the following we assume that inner_cond_bb has single predecessor. */
gcc_assert (single_pred_p (inner_cond_bb));
if (outer_to_inner_bb == inner_cond_bb
&& known_succ_p (outer_cond_bb))
{
/* Path outer_cond_bb->(outer2) needs to be merged into path
outer_cond_bb->(outer_to_inner)->inner_cond_bb->(inner_taken)
and probability of inner_not_taken updated. */
/* Path outer_cond_bb->(outer2) needs to be merged into path
outer_cond_bb->(outer_to_inner)->inner_cond_bb->(inner_taken)
and probability of inner_not_taken updated. */
inner_cond_bb->count = outer_cond_bb->count;
inner_cond_bb->count = outer_cond_bb->count;
/* Handle special case where inner_taken probability is always. In this
case we know that the overall outcome will be always as well, but
combining probabilities will be conservative because it does not know
that outer2->probability is inverse of
outer_to_inner->probability. */
if (inner_taken->probability == profile_probability::always ())
;
else
inner_taken->probability = outer2->probability
+ outer_to_inner->probability * inner_taken->probability;
inner_not_taken->probability = profile_probability::always ()
- inner_taken->probability;
/* Handle special case where inner_taken probability is always. In this case
we know that the overall outcome will be always as well, but combining
probabilities will be conservative because it does not know that
outer2->probability is inverse of outer_to_inner->probability. */
if (inner_taken->probability == profile_probability::always ())
;
outer_to_inner->probability = profile_probability::always ();
outer2->probability = profile_probability::never ();
}
else if (known_succ_p (inner_cond_bb))
{
/* Path inner_cond_bb->(inner_taken) needs to be merged into path
outer_cond_bb->(outer2). We've accumulated the probabilities from
outer_cond_bb->(outer)->...->inner_cond_bb in prob, so we have to
adjust that by inner_taken, and make inner unconditional. */
prob *= inner_taken->probability;
outer2->probability += prob;
outer_to_inner->probability = profile_probability::always ()
- outer2->probability;
inner_taken->probability = profile_probability::never ();
inner_not_taken->probability = profile_probability::always ();
}
else
inner_taken->probability = outer2->probability + outer_to_inner->probability
* inner_taken->probability;
inner_not_taken->probability = profile_probability::always ()
- inner_taken->probability;
{
/* We've moved part of the inner cond to outer, but we don't know the
probabilities for each part, so estimate the effects by moving half of
the odds of inner_taken to outer. */
outer_to_inner->probability = profile_probability::always ();
outer2->probability = profile_probability::never ();
inner_taken->probability *= profile_probability::even ();
inner_not_taken->probability = profile_probability::always ()
- inner_taken->probability;
prob *= inner_taken->probability;
outer2->probability += prob;
outer_to_inner->probability = profile_probability::always ()
- outer2->probability;
}
}
/* Replace the conditions in INNER_COND with COND.