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| author | Alexandre Oliva <oliva@adacore.com> | 2024-11-07 02:47:34 -0300 |
|---|---|---|
| committer | Alexandre Oliva <oliva@gnu.org> | 2024-11-07 02:47:34 -0300 |
| commit | 02dc5036ba8d816048b942e51f74a9e4b3fde173 (patch) | |
| tree | 4fef172f04a1d3a5d66745108cf95d08a98e4e03 /gcc/tree-ssa-ifcombine.cc | |
| parent | f9fb8f96cd7d849ca68da8839b2e8fe8eeb70411 (diff) | |
| download | gcc-02dc5036ba8d816048b942e51f74a9e4b3fde173.zip gcc-02dc5036ba8d816048b942e51f74a9e4b3fde173.tar.gz gcc-02dc5036ba8d816048b942e51f74a9e4b3fde173.tar.bz2 | |
adjust update_profile_after_ifcombine for noncontiguous ifcombine
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.
Diffstat (limited to 'gcc/tree-ssa-ifcombine.cc')
| -rw-r--r-- | gcc/tree-ssa-ifcombine.cc | 109 |
1 files changed, 85 insertions, 24 deletions
diff --git a/gcc/tree-ssa-ifcombine.cc b/gcc/tree-ssa-ifcombine.cc index 1f28cde..6431987 100644 --- a/gcc/tree-ssa-ifcombine.cc +++ b/gcc/tree-ssa-ifcombine.cc @@ -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)); - - /* 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; + 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. */ + + 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; - - outer_to_inner->probability = profile_probability::always (); - outer2->probability = profile_probability::never (); + { + /* 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. */ + + 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. |