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src/hotspot/share/opto/loopTransform.cpp
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@@ -284,10 +284,13 @@
if (n1->is_Add() && n1->in(2)->is_Con()) return NULL;
Node* inv1 = n1->in(inv1_idx);
Node* n2 = n1->in(3 - inv1_idx);
int inv2_idx = is_invariant_addition(n2, phase);
if (!inv2_idx) return NULL;
+
+ if (!phase->may_require_nodes(10, 10)) return NULL;
+
Node* x = n2->in(3 - inv2_idx);
Node* inv2 = n2->in(inv2_idx);
bool neg_x = n2->is_Sub() && inv2_idx == 1;
bool neg_inv2 = n2->is_Sub() && inv2_idx == 2;
@@ -335,65 +338,76 @@
Node *n = _body.at(i);
for (int j = 0; j < 5; j++) {
Node* nn = reassociate_add_sub(n, phase);
if (nn == NULL) break;
n = nn; // again
- };
+ }
}
}
//------------------------------policy_peeling---------------------------------
-// Return TRUE or FALSE if the loop should be peeled or not. Peel if we can
-// make some loop-invariant test (usually a null-check) happen before the loop.
-bool IdealLoopTree::policy_peeling(PhaseIdealLoop *phase) const {
- IdealLoopTree *loop = (IdealLoopTree*)this;
+// Return TRUE if the loop should be peeled, otherwise return FALSE. Peeling
+// is applicable if we can make a loop-invariant test (usually a null-check)
+// execute before we enter the loop. When TRUE, the estimated node budget is
+// also requested.
+bool IdealLoopTree::policy_peeling(PhaseIdealLoop *phase) {
+ uint estimate = estimate_peeling(phase);
+
+ return estimate == 0 ? false : phase->may_require_nodes(estimate);
+}
+
+// Perform actual policy and size estimate for the loop peeling transform, and
+// return the estimated loop size if peeling is applicable, otherwise return
+// zero. No node budget is allocated.
+uint IdealLoopTree::estimate_peeling(PhaseIdealLoop *phase) {
// If nodes are depleted, some transform has miscalculated its needs.
assert(!phase->exceeding_node_budget(), "sanity");
- uint body_size = loop->_body.size();
- // Peeling does loop cloning which can result in O(N^2) node construction
- if (body_size > 255) {
- return false; // Prevent overflow for large body size
- }
- uint estimate = body_size * body_size;
+ // Peeling does loop cloning which can result in O(N^2) node construction.
+ if (_body.size() > 255) {
+ return 0; // Suppress too large body size.
+ }
+ // Optimistic estimate that approximates loop body complexity via data and
+ // control flow fan-out (instead of using the more pessimistic: BodySize^2).
+ uint estimate = est_loop_clone_sz(2);
+
if (phase->exceeding_node_budget(estimate)) {
- return false; // Too large to safely clone
+ return 0; // Too large to safely clone.
}
- // check for vectorized loops, any peeling done was already applied
+ // Check for vectorized loops, any peeling done was already applied.
if (_head->is_CountedLoop()) {
CountedLoopNode* cl = _head->as_CountedLoop();
if (cl->is_unroll_only() || cl->trip_count() == 1) {
- return false;
+ return 0;
}
}
- Node* test = loop->tail();
+ Node* test = tail();
while (test != _head) { // Scan till run off top of loop
if (test->is_If()) { // Test?
Node *ctrl = phase->get_ctrl(test->in(1));
if (ctrl->is_top()) {
- return false; // Found dead test on live IF? No peeling!
+ return 0; // Found dead test on live IF? No peeling!
}
- // Standard IF only has one input value to check for loop invariance
+ // Standard IF only has one input value to check for loop invariance.
assert(test->Opcode() == Op_If ||
test->Opcode() == Op_CountedLoopEnd ||
test->Opcode() == Op_RangeCheck,
"Check this code when new subtype is added");
// Condition is not a member of this loop?
if (!is_member(phase->get_loop(ctrl)) && is_loop_exit(test)) {
- // Found reason to peel!
- return phase->may_require_nodes(estimate);
+ return estimate; // Found reason to peel!
}
}
- // Walk up dominators to loop _head looking for test which is
- // executed on every path thru loop.
+ // Walk up dominators to loop _head looking for test which is executed on
+ // every path through the loop.
test = phase->idom(test);
}
- return false;
+ return 0;
}
//------------------------------peeled_dom_test_elim---------------------------
// If we got the effect of peeling, either by actually peeling or by making
// a pre-loop which must execute at least once, we can remove all
@@ -636,12 +650,12 @@
_igvn.hash_delete(use);
use->set_req(LoopNode::LoopBackControl, C->top());
}
}
-
// Step 4: Correct dom-depth info. Set to loop-head depth.
+
int dd = dom_depth(head);
set_idom(head, head->in(1), dd);
for (uint j3 = 0; j3 < loop->_body.size(); j3++) {
Node *old = loop->_body.at(j3);
Node *nnn = old_new[old->_idx];
@@ -655,15 +669,34 @@
peeled_dom_test_elim(loop,old_new);
loop->record_for_igvn();
}
-#define EMPTY_LOOP_SIZE 7 // number of nodes in an empty loop
+// The Estimated Loop Unroll Size: UnrollFactor * (106% * BodySize + BC) + CC,
+// where BC and CC are (totally) ad-hoc/magic "body" and "clone" constants,
+// respectively, used to ensure that node usage estimates made are on the safe
+// side, for the most part. This is a simplified version of the loop clone
+// size calculation in est_loop_clone_sz(), defined for unroll factors larger
+// than one (>1), performing an overflow check and returning 'UINT_MAX' in
+// case of an overflow.
+static uint est_loop_unroll_sz(uint factor, uint size) {
+ precond(0 < factor);
+
+ uint const bc = 5;
+ uint const cc = 7;
+ uint const sz = size + (size + 15) / 16;
+ uint estimate = factor * (sz + bc) + cc;
+
+ return (estimate - cc) / factor == sz + bc ? estimate : UINT_MAX;
+}
+
+#define EMPTY_LOOP_SIZE 7 // Number of nodes in an empty loop.
//------------------------------policy_maximally_unroll------------------------
-// Calculate exact loop trip count and return true if loop can be maximally
-// unrolled.
+// Calculate the exact loop trip-count and return TRUE if loop can be fully,
+// i.e. maximally, unrolled, otherwise return FALSE. When TRUE, the estimated
+// node budget is also requested.
bool IdealLoopTree::policy_maximally_unroll(PhaseIdealLoop *phase) const {
CountedLoopNode *cl = _head->as_CountedLoop();
assert(cl->is_normal_loop(), "");
if (!cl->is_valid_counted_loop()) {
return false; // Malformed counted loop
@@ -691,11 +724,11 @@
return false;
}
// Take into account that after unroll conjoined heads and tails will fold,
// otherwise policy_unroll() may allow more unrolling than max unrolling.
- uint new_body_size = est_loop_clone_sz(trip_count, body_size - EMPTY_LOOP_SIZE);
+ uint new_body_size = est_loop_unroll_sz(trip_count, body_size - EMPTY_LOOP_SIZE);
if (new_body_size == UINT_MAX) { // Check for bad estimate (overflow).
return false;
}
@@ -740,12 +773,13 @@
return phase->may_require_nodes(new_body_size);
}
//------------------------------policy_unroll----------------------------------
-// Return TRUE or FALSE if the loop should be unrolled or not. Unroll if the
-// loop is a CountedLoop and the body is small enough.
+// Return TRUE or FALSE if the loop should be unrolled or not. Apply unroll if
+// the loop is a counted loop and the loop body is small enough. When TRUE,
+// the estimated node budget is also requested.
bool IdealLoopTree::policy_unroll(PhaseIdealLoop *phase) {
CountedLoopNode *cl = _head->as_CountedLoop();
assert(cl->is_normal_loop() || cl->is_main_loop(), "");
@@ -885,11 +919,11 @@
int slp_max_unroll_factor = cl->slp_max_unroll();
if ((LoopMaxUnroll < slp_max_unroll_factor) && FLAG_IS_DEFAULT(LoopMaxUnroll) && UseSubwordForMaxVector) {
LoopMaxUnroll = slp_max_unroll_factor;
}
- uint estimate = est_loop_clone_sz(2, body_size);
+ uint estimate = est_loop_clone_sz(2);
if (cl->has_passed_slp()) {
if (slp_max_unroll_factor >= future_unroll_cnt) {
return phase->may_require_nodes(estimate);
}
@@ -956,22 +990,24 @@
bool IdealLoopTree::policy_align(PhaseIdealLoop *phase) const {
return false;
}
//------------------------------policy_range_check-----------------------------
-// Return TRUE or FALSE if the loop should be range-check-eliminated.
-// Actually we do iteration-splitting, a more powerful form of RCE.
+// Return TRUE or FALSE if the loop should be range-check-eliminated or not.
+// When TRUE, the estimated node budget is also requested.
+//
+// We will actually perform iteration-splitting, a more powerful form of RCE.
bool IdealLoopTree::policy_range_check(PhaseIdealLoop *phase) const {
if (!RangeCheckElimination) return false;
// If nodes are depleted, some transform has miscalculated its needs.
assert(!phase->exceeding_node_budget(), "sanity");
CountedLoopNode *cl = _head->as_CountedLoop();
- // If we unrolled with no intention of doing RCE and we later
- // changed our minds, we got no pre-loop. Either we need to
- // make a new pre-loop, or we gotta disallow RCE.
+ // If we unrolled with no intention of doing RCE and we later changed our
+ // minds, we got no pre-loop. Either we need to make a new pre-loop, or we
+ // have to disallow RCE.
if (cl->is_main_no_pre_loop()) return false; // Disallowed for now.
Node *trip_counter = cl->phi();
// check for vectorized loops, some opts are no longer needed
if (cl->is_unroll_only()) return false;
@@ -1014,17 +1050,17 @@
}
if (!phase->is_scaled_iv_plus_offset(rc_exp, trip_counter, NULL, NULL)) {
continue;
}
- // Found a test like 'trip+off vs limit'. Test is an IfNode, has two
- // (2) projections. If BOTH are in the loop we need loop unswitching
- // instead of iteration splitting.
+ // Found a test like 'trip+off vs limit'. Test is an IfNode, has two (2)
+ // projections. If BOTH are in the loop we need loop unswitching instead
+ // of iteration splitting.
if (is_loop_exit(iff)) {
// Found valid reason to split iterations (if there is room).
// NOTE: Usually a gross overestimate.
- return phase->may_require_nodes(est_loop_clone_sz(2, _body.size()));
+ return phase->may_require_nodes(est_loop_clone_sz(2));
}
} // End of is IF
}
return false;
@@ -1519,13 +1555,10 @@
CountedLoopNode *cl = loop->_head->as_CountedLoop();
// only process vectorized main loops
if (!cl->is_vectorized_loop() || !cl->is_main_loop()) return;
- if (!may_require_nodes(est_loop_clone_sz(2, loop->_body.size()))) {
- return;
- }
int slp_max_unroll_factor = cl->slp_max_unroll();
int cur_unroll = cl->unrolled_count();
if (slp_max_unroll_factor == 0) return;
@@ -1533,10 +1566,14 @@
if (cur_unroll != slp_max_unroll_factor) return;
// we only ever process this one time
if (cl->has_atomic_post_loop()) return;
+ if (!may_require_nodes(loop->est_loop_clone_sz(2))) {
+ return;
+ }
+
#ifndef PRODUCT
if (TraceLoopOpts) {
tty->print("PostVector ");
loop->dump_head();
}
@@ -3176,24 +3213,21 @@
return true; // Here we removed an empty loop
}
AutoNodeBudget node_budget(phase);
- bool should_peel = policy_peeling(phase);
- bool should_unswitch = policy_unswitching(phase);
-
// Non-counted loops may be peeled; exactly 1 iteration is peeled.
// This removes loop-invariant tests (usually null checks).
if (!_head->is_CountedLoop()) { // Non-counted loop
if (PartialPeelLoop && phase->partial_peel(this, old_new)) {
// Partial peel succeeded so terminate this round of loop opts
return false;
}
- if (should_peel) { // Should we peel?
+ if (policy_peeling(phase)) { // Should we peel?
if (PrintOpto) { tty->print_cr("should_peel"); }
- phase->do_peeling(this,old_new);
- } else if (should_unswitch) {
+ phase->do_peeling(this, old_new);
+ } else if (policy_unswitching(phase)) {
phase->do_unswitching(this, old_new);
}
return true;
}
CountedLoopNode *cl = _head->as_CountedLoop();
@@ -3207,23 +3241,25 @@
compute_profile_trip_cnt(phase);
// Before attempting fancy unrolling, RCE or alignment, see if we want
// to completely unroll this loop or do loop unswitching.
if (cl->is_normal_loop()) {
- if (should_unswitch) {
+ if (policy_unswitching(phase)) {
phase->do_unswitching(this, old_new);
return true;
}
- bool should_maximally_unroll = policy_maximally_unroll(phase);
- if (should_maximally_unroll) {
+ if (policy_maximally_unroll(phase)) {
// Here we did some unrolling and peeling. Eventually we will
// completely unroll this loop and it will no longer be a loop.
phase->do_maximally_unroll(this, old_new);
return true;
}
}
+ uint est_peeling = estimate_peeling(phase);
+ bool should_peel = 0 < est_peeling;
+
// Counted loops may be peeled, may need some iterations run up
// front for RCE, and may want to align loop refs to a cache
// line. Thus we clone a full loop up front whose trip count is
// at least 1 (if peeling), but may be several more.
@@ -3250,18 +3286,19 @@
// If we have any of these conditions (RCE, alignment, unrolling) met, then
// we switch to the pre-/main-/post-loop model. This model also covers
// peeling.
if (should_rce || should_align || should_unroll) {
if (cl->is_normal_loop()) { // Convert to 'pre/main/post' loops
- if (!phase->may_require_nodes(est_loop_clone_sz(3, _body.size()))) {
+ uint estimate = est_loop_clone_sz(3);
+ if (!phase->may_require_nodes(estimate)) {
return false;
}
- phase->insert_pre_post_loops(this,old_new, !may_rce_align);
+ phase->insert_pre_post_loops(this, old_new, !may_rce_align);
}
// Adjust the pre- and main-loop limits to let the pre and post loops run
- // with full checks, but the main-loop with no checks. Remove said
- // checks from the main body.
+ // with full checks, but the main-loop with no checks. Remove said checks
+ // from the main body.
if (should_rce) {
if (phase->do_range_check(this, old_new) != 0) {
cl->mark_has_range_checks();
}
} else if (PostLoopMultiversioning) {
@@ -3291,11 +3328,13 @@
if (should_align) {
Unimplemented();
}
} else { // Else we have an unchanged counted loop
if (should_peel) { // Might want to peel but do nothing else
- phase->do_peeling(this,old_new);
+ if (phase->may_require_nodes(est_peeling)) {
+ phase->do_peeling(this, old_new);
+ }
}
}
return true;
}
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