/* * Copyright (c) 2000, 2011, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. * */ #include "precompiled.hpp" #include "compiler/compileLog.hpp" #include "memory/allocation.inline.hpp" #include "opto/addnode.hpp" #include "opto/callnode.hpp" #include "opto/connode.hpp" #include "opto/divnode.hpp" #include "opto/loopnode.hpp" #include "opto/mulnode.hpp" #include "opto/rootnode.hpp" #include "opto/runtime.hpp" #include "opto/subnode.hpp" //------------------------------is_loop_exit----------------------------------- // Given an IfNode, return the loop-exiting projection or NULL if both // arms remain in the loop. Node *IdealLoopTree::is_loop_exit(Node *iff) const { if( iff->outcnt() != 2 ) return NULL; // Ignore partially dead tests PhaseIdealLoop *phase = _phase; // Test is an IfNode, has 2 projections. If BOTH are in the loop // we need loop unswitching instead of peeling. if( !is_member(phase->get_loop( iff->raw_out(0) )) ) return iff->raw_out(0); if( !is_member(phase->get_loop( iff->raw_out(1) )) ) return iff->raw_out(1); return NULL; } //============================================================================= //------------------------------record_for_igvn---------------------------- // Put loop body on igvn work list void IdealLoopTree::record_for_igvn() { for( uint i = 0; i < _body.size(); i++ ) { Node *n = _body.at(i); _phase->_igvn._worklist.push(n); } } //------------------------------compute_exact_trip_count----------------------- // Compute loop exact trip count if possible. Do not recalculate trip count for // split loops (pre-main-post) which have their limits and inits behind Opaque node. void IdealLoopTree::compute_exact_trip_count( PhaseIdealLoop *phase ) { if (!_head->as_Loop()->is_valid_counted_loop()) { return; } CountedLoopNode* cl = _head->as_CountedLoop(); // Trip count may become nonexact for iteration split loops since // RCE modifies limits. Note, _trip_count value is not reset since // it is used to limit unrolling of main loop. cl->set_nonexact_trip_count(); // Loop's test should be part of loop. if (!phase->is_member(this, phase->get_ctrl(cl->loopexit()->in(CountedLoopEndNode::TestValue)))) return; // Infinite loop #ifdef ASSERT BoolTest::mask bt = cl->loopexit()->test_trip(); assert(bt == BoolTest::lt || bt == BoolTest::gt || bt == BoolTest::ne, "canonical test is expected"); #endif Node* init_n = cl->init_trip(); Node* limit_n = cl->limit(); if (init_n != NULL && init_n->is_Con() && limit_n != NULL && limit_n->is_Con()) { // Use longs to avoid integer overflow. int stride_con = cl->stride_con(); jlong init_con = cl->init_trip()->get_int(); jlong limit_con = cl->limit()->get_int(); int stride_m = stride_con - (stride_con > 0 ? 1 : -1); jlong trip_count = (limit_con - init_con + stride_m)/stride_con; if (trip_count > 0 && (julong)trip_count < (julong)max_juint) { // Set exact trip count. cl->set_exact_trip_count((uint)trip_count); } } } //------------------------------compute_profile_trip_cnt---------------------------- // Compute loop trip count from profile data as // (backedge_count + loop_exit_count) / loop_exit_count void IdealLoopTree::compute_profile_trip_cnt( PhaseIdealLoop *phase ) { if (!_head->is_CountedLoop()) { return; } CountedLoopNode* head = _head->as_CountedLoop(); if (head->profile_trip_cnt() != COUNT_UNKNOWN) { return; // Already computed } float trip_cnt = (float)max_jint; // default is big Node* back = head->in(LoopNode::LoopBackControl); while (back != head) { if ((back->Opcode() == Op_IfTrue || back->Opcode() == Op_IfFalse) && back->in(0) && back->in(0)->is_If() && back->in(0)->as_If()->_fcnt != COUNT_UNKNOWN && back->in(0)->as_If()->_prob != PROB_UNKNOWN) { break; } back = phase->idom(back); } if (back != head) { assert((back->Opcode() == Op_IfTrue || back->Opcode() == Op_IfFalse) && back->in(0), "if-projection exists"); IfNode* back_if = back->in(0)->as_If(); float loop_back_cnt = back_if->_fcnt * back_if->_prob; // Now compute a loop exit count float loop_exit_cnt = 0.0f; for( uint i = 0; i < _body.size(); i++ ) { Node *n = _body[i]; if( n->is_If() ) { IfNode *iff = n->as_If(); if( iff->_fcnt != COUNT_UNKNOWN && iff->_prob != PROB_UNKNOWN ) { Node *exit = is_loop_exit(iff); if( exit ) { float exit_prob = iff->_prob; if (exit->Opcode() == Op_IfFalse) exit_prob = 1.0 - exit_prob; if (exit_prob > PROB_MIN) { float exit_cnt = iff->_fcnt * exit_prob; loop_exit_cnt += exit_cnt; } } } } } if (loop_exit_cnt > 0.0f) { trip_cnt = (loop_back_cnt + loop_exit_cnt) / loop_exit_cnt; } else { // No exit count so use trip_cnt = loop_back_cnt; } } #ifndef PRODUCT if (TraceProfileTripCount) { tty->print_cr("compute_profile_trip_cnt lp: %d cnt: %f\n", head->_idx, trip_cnt); } #endif head->set_profile_trip_cnt(trip_cnt); } //---------------------is_invariant_addition----------------------------- // Return nonzero index of invariant operand for an Add or Sub // of (nonconstant) invariant and variant values. Helper for reassociate_invariants. int IdealLoopTree::is_invariant_addition(Node* n, PhaseIdealLoop *phase) { int op = n->Opcode(); if (op == Op_AddI || op == Op_SubI) { bool in1_invar = this->is_invariant(n->in(1)); bool in2_invar = this->is_invariant(n->in(2)); if (in1_invar && !in2_invar) return 1; if (!in1_invar && in2_invar) return 2; } return 0; } //---------------------reassociate_add_sub----------------------------- // Reassociate invariant add and subtract expressions: // // inv1 + (x + inv2) => ( inv1 + inv2) + x // (x + inv2) + inv1 => ( inv1 + inv2) + x // inv1 + (x - inv2) => ( inv1 - inv2) + x // inv1 - (inv2 - x) => ( inv1 - inv2) + x // (x + inv2) - inv1 => (-inv1 + inv2) + x // (x - inv2) + inv1 => ( inv1 - inv2) + x // (x - inv2) - inv1 => (-inv1 - inv2) + x // inv1 + (inv2 - x) => ( inv1 + inv2) - x // inv1 - (x - inv2) => ( inv1 + inv2) - x // (inv2 - x) + inv1 => ( inv1 + inv2) - x // (inv2 - x) - inv1 => (-inv1 + inv2) - x // inv1 - (x + inv2) => ( inv1 - inv2) - x // Node* IdealLoopTree::reassociate_add_sub(Node* n1, PhaseIdealLoop *phase) { if (!n1->is_Add() && !n1->is_Sub() || n1->outcnt() == 0) return NULL; if (is_invariant(n1)) return NULL; int inv1_idx = is_invariant_addition(n1, phase); if (!inv1_idx) return NULL; // Don't mess with add of constant (igvn moves them to expression tree root.) 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; 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; bool neg_inv1 = n1->is_Sub() && inv1_idx == 2; if (n1->is_Sub() && inv1_idx == 1) { neg_x = !neg_x; neg_inv2 = !neg_inv2; } Node* inv1_c = phase->get_ctrl(inv1); Node* inv2_c = phase->get_ctrl(inv2); Node* n_inv1; if (neg_inv1) { Node *zero = phase->_igvn.intcon(0); phase->set_ctrl(zero, phase->C->root()); n_inv1 = new (phase->C) SubINode(zero, inv1); phase->register_new_node(n_inv1, inv1_c); } else { n_inv1 = inv1; } Node* inv; if (neg_inv2) { inv = new (phase->C) SubINode(n_inv1, inv2); } else { inv = new (phase->C) AddINode(n_inv1, inv2); } phase->register_new_node(inv, phase->get_early_ctrl(inv)); Node* addx; if (neg_x) { addx = new (phase->C) SubINode(inv, x); } else { addx = new (phase->C) AddINode(x, inv); } phase->register_new_node(addx, phase->get_ctrl(x)); phase->_igvn.replace_node(n1, addx); assert(phase->get_loop(phase->get_ctrl(n1)) == this, ""); _body.yank(n1); return addx; } //---------------------reassociate_invariants----------------------------- // Reassociate invariant expressions: void IdealLoopTree::reassociate_invariants(PhaseIdealLoop *phase) { for (int i = _body.size() - 1; i >= 0; i--) { 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 { Node *test = ((IdealLoopTree*)this)->tail(); int body_size = ((IdealLoopTree*)this)->_body.size(); int uniq = phase->C->unique(); // Peeling does loop cloning which can result in O(N^2) node construction if( body_size > 255 /* Prevent overflow for large body_size */ || (body_size * body_size + uniq > MaxNodeLimit) ) { return false; // too large to safely clone } 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! // Standard IF only has one input value to check for loop invariance assert( test->Opcode() == Op_If || test->Opcode() == Op_CountedLoopEnd, "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) ) return true; // Found reason to peel! } // Walk up dominators to loop _head looking for test which is // executed on every path thru loop. test = phase->idom(test); } return false; } //------------------------------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 // loop-invariant dominated tests in the main body. void PhaseIdealLoop::peeled_dom_test_elim( IdealLoopTree *loop, Node_List &old_new ) { bool progress = true; while( progress ) { progress = false; // Reset for next iteration Node *prev = loop->_head->in(LoopNode::LoopBackControl);//loop->tail(); Node *test = prev->in(0); while( test != loop->_head ) { // Scan till run off top of loop int p_op = prev->Opcode(); if( (p_op == Op_IfFalse || p_op == Op_IfTrue) && test->is_If() && // Test? !test->in(1)->is_Con() && // And not already obvious? // Condition is not a member of this loop? !loop->is_member(get_loop(get_ctrl(test->in(1))))){ // Walk loop body looking for instances of this test for( uint i = 0; i < loop->_body.size(); i++ ) { Node *n = loop->_body.at(i); if( n->is_If() && n->in(1) == test->in(1) /*&& n != loop->tail()->in(0)*/ ) { // IfNode was dominated by version in peeled loop body progress = true; dominated_by( old_new[prev->_idx], n ); } } } prev = test; test = idom(test); } // End of scan tests in loop } // End of while( progress ) } //------------------------------do_peeling------------------------------------- // Peel the first iteration of the given loop. // Step 1: Clone the loop body. The clone becomes the peeled iteration. // The pre-loop illegally has 2 control users (old & new loops). // Step 2: Make the old-loop fall-in edges point to the peeled iteration. // Do this by making the old-loop fall-in edges act as if they came // around the loopback from the prior iteration (follow the old-loop // backedges) and then map to the new peeled iteration. This leaves // the pre-loop with only 1 user (the new peeled iteration), but the // peeled-loop backedge has 2 users. // Step 3: Cut the backedge on the clone (so its not a loop) and remove the // extra backedge user. // // orig // // stmt1 // | // v // loop predicate // | // v // loop<----+ // | | // stmt2 | // | | // v | // if ^ // / \ | // / \ | // v v | // false true | // / \ | // / ----+ // | // v // exit // // // after clone loop // // stmt1 // | // v // loop predicate // / \ // clone / \ orig // / \ // / \ // v v // +---->loop clone loop<----+ // | | | | // | stmt2 clone stmt2 | // | | | | // | v v | // ^ if clone If ^ // | / \ / \ | // | / \ / \ | // | v v v v | // | true false false true | // | / \ / \ | // +---- \ / ----+ // \ / // 1v v2 // region // | // v // exit // // // after peel and predicate move // // stmt1 // / // / // clone / orig // / // / +----------+ // / | | // / loop predicate | // / | | // v v | // TOP-->loop clone loop<----+ | // | | | | // stmt2 clone stmt2 | | // | | | ^ // v v | | // if clone If ^ | // / \ / \ | | // / \ / \ | | // v v v v | | // true false false true | | // | \ / \ | | // | \ / ----+ ^ // | \ / | // | 1v v2 | // v region | // | | | // | v | // | exit | // | | // +--------------->-----------------+ // // // final graph // // stmt1 // | // v // stmt2 clone // | // v // if clone // / | // / | // v v // false true // | | // | v // | loop predicate // | | // | v // | loop<----+ // | | | // | stmt2 | // | | | // | v | // v if ^ // | / \ | // | / \ | // | v v | // | false true | // | | \ | // v v --+ // region // | // v // exit // void PhaseIdealLoop::do_peeling( IdealLoopTree *loop, Node_List &old_new ) { C->set_major_progress(); // Peeling a 'main' loop in a pre/main/post situation obfuscates the // 'pre' loop from the main and the 'pre' can no longer have it's // iterations adjusted. Therefore, we need to declare this loop as // no longer a 'main' loop; it will need new pre and post loops before // we can do further RCE. #ifndef PRODUCT if (TraceLoopOpts) { tty->print("Peel "); loop->dump_head(); } #endif Node* head = loop->_head; bool counted_loop = head->is_CountedLoop(); if (counted_loop) { CountedLoopNode *cl = head->as_CountedLoop(); assert(cl->trip_count() > 0, "peeling a fully unrolled loop"); cl->set_trip_count(cl->trip_count() - 1); if (cl->is_main_loop()) { cl->set_normal_loop(); #ifndef PRODUCT if (PrintOpto && VerifyLoopOptimizations) { tty->print("Peeling a 'main' loop; resetting to 'normal' "); loop->dump_head(); } #endif } } Node* entry = head->in(LoopNode::EntryControl); // Step 1: Clone the loop body. The clone becomes the peeled iteration. // The pre-loop illegally has 2 control users (old & new loops). clone_loop( loop, old_new, dom_depth(head) ); // Step 2: Make the old-loop fall-in edges point to the peeled iteration. // Do this by making the old-loop fall-in edges act as if they came // around the loopback from the prior iteration (follow the old-loop // backedges) and then map to the new peeled iteration. This leaves // the pre-loop with only 1 user (the new peeled iteration), but the // peeled-loop backedge has 2 users. Node* new_entry = old_new[head->in(LoopNode::LoopBackControl)->_idx]; _igvn.hash_delete(head); head->set_req(LoopNode::EntryControl, new_entry); for (DUIterator_Fast jmax, j = head->fast_outs(jmax); j < jmax; j++) { Node* old = head->fast_out(j); if (old->in(0) == loop->_head && old->req() == 3 && old->is_Phi()) { Node* new_exit_value = old_new[old->in(LoopNode::LoopBackControl)->_idx]; if (!new_exit_value ) // Backedge value is ALSO loop invariant? // Then loop body backedge value remains the same. new_exit_value = old->in(LoopNode::LoopBackControl); _igvn.hash_delete(old); old->set_req(LoopNode::EntryControl, new_exit_value); } } // Step 3: Cut the backedge on the clone (so its not a loop) and remove the // extra backedge user. Node* new_head = old_new[head->_idx]; _igvn.hash_delete(new_head); new_head->set_req(LoopNode::LoopBackControl, C->top()); for (DUIterator_Fast j2max, j2 = new_head->fast_outs(j2max); j2 < j2max; j2++) { Node* use = new_head->fast_out(j2); if (use->in(0) == new_head && use->req() == 3 && use->is_Phi()) { _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]; if (!has_ctrl(nnn)) set_idom(nnn, idom(nnn), dd-1); } // Now force out all loop-invariant dominating tests. The optimizer // finds some, but we _know_ they are all useless. peeled_dom_test_elim(loop,old_new); loop->record_for_igvn(); } #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. 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 if (!cl->has_exact_trip_count()) { // Trip count is not exact. return false; } uint trip_count = cl->trip_count(); // Note, max_juint is used to indicate unknown trip count. assert(trip_count > 1, "one iteration loop should be optimized out already"); assert(trip_count < max_juint, "exact trip_count should be less than max_uint."); // Real policy: if we maximally unroll, does it get too big? // Allow the unrolled mess to get larger than standard loop // size. After all, it will no longer be a loop. uint body_size = _body.size(); uint unroll_limit = (uint)LoopUnrollLimit * 4; assert( (intx)unroll_limit == LoopUnrollLimit * 4, "LoopUnrollLimit must fit in 32bits"); if (trip_count > unroll_limit || body_size > unroll_limit) { return false; } // Fully unroll a loop with few iterations regardless next // conditions since following loop optimizations will split // such loop anyway (pre-main-post). if (trip_count <= 3) return true; // 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 = EMPTY_LOOP_SIZE + (body_size - EMPTY_LOOP_SIZE) * trip_count; uint tst_body_size = (new_body_size - EMPTY_LOOP_SIZE) / trip_count + EMPTY_LOOP_SIZE; if (body_size != tst_body_size) // Check for int overflow return false; if (new_body_size > unroll_limit || // Unrolling can result in a large amount of node construction new_body_size >= MaxNodeLimit - phase->C->unique()) { return false; } // Do not unroll a loop with String intrinsics code. // String intrinsics are large and have loops. for (uint k = 0; k < _body.size(); k++) { Node* n = _body.at(k); switch (n->Opcode()) { case Op_StrComp: case Op_StrEquals: case Op_StrIndexOf: case Op_AryEq: { return false; } } // switch } return true; // Do maximally unroll } #define MAX_UNROLL 16 // maximum number of unrolls for main loop //------------------------------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. bool IdealLoopTree::policy_unroll( PhaseIdealLoop *phase ) const { CountedLoopNode *cl = _head->as_CountedLoop(); assert(cl->is_normal_loop() || cl->is_main_loop(), ""); if (!cl->is_valid_counted_loop()) return false; // Malformed counted loop // Protect against over-unrolling. // After split at least one iteration will be executed in pre-loop. if (cl->trip_count() <= (uint)(cl->is_normal_loop() ? 2 : 1)) return false; int future_unroll_ct = cl->unrolled_count() * 2; if (future_unroll_ct > MAX_UNROLL) return false; // Check for initial stride being a small enough constant if (abs(cl->stride_con()) > (1<<2)*future_unroll_ct) return false; // Don't unroll if the next round of unrolling would push us // over the expected trip count of the loop. One is subtracted // from the expected trip count because the pre-loop normally // executes 1 iteration. if (UnrollLimitForProfileCheck > 0 && cl->profile_trip_cnt() != COUNT_UNKNOWN && future_unroll_ct > UnrollLimitForProfileCheck && (float)future_unroll_ct > cl->profile_trip_cnt() - 1.0) { return false; } // When unroll count is greater than LoopUnrollMin, don't unroll if: // the residual iterations are more than 10% of the trip count // and rounds of "unroll,optimize" are not making significant progress // Progress defined as current size less than 20% larger than previous size. if (UseSuperWord && cl->node_count_before_unroll() > 0 && future_unroll_ct > LoopUnrollMin && (future_unroll_ct - 1) * 10.0 > cl->profile_trip_cnt() && 1.2 * cl->node_count_before_unroll() < (double)_body.size()) { return false; } Node *init_n = cl->init_trip(); Node *limit_n = cl->limit(); int stride_con = cl->stride_con(); // Non-constant bounds. // Protect against over-unrolling when init or/and limit are not constant // (so that trip_count's init value is maxint) but iv range is known. if (init_n == NULL || !init_n->is_Con() || limit_n == NULL || !limit_n->is_Con()) { Node* phi = cl->phi(); if (phi != NULL) { assert(phi->is_Phi() && phi->in(0) == _head, "Counted loop should have iv phi."); const TypeInt* iv_type = phase->_igvn.type(phi)->is_int(); int next_stride = stride_con * 2; // stride after this unroll if (next_stride > 0) { if (iv_type->_lo + next_stride <= iv_type->_lo || // overflow iv_type->_lo + next_stride > iv_type->_hi) { return false; // over-unrolling } } else if (next_stride < 0) { if (iv_type->_hi + next_stride >= iv_type->_hi || // overflow iv_type->_hi + next_stride < iv_type->_lo) { return false; // over-unrolling } } } } // After unroll limit will be adjusted: new_limit = limit-stride. // Bailout if adjustment overflow. const TypeInt* limit_type = phase->_igvn.type(limit_n)->is_int(); if (stride_con > 0 && ((limit_type->_hi - stride_con) >= limit_type->_hi) || stride_con < 0 && ((limit_type->_lo - stride_con) <= limit_type->_lo)) return false; // overflow // Adjust body_size to determine if we unroll or not uint body_size = _body.size(); // Key test to unroll loop in CRC32 java code int xors_in_loop = 0; // Also count ModL, DivL and MulL which expand mightly for (uint k = 0; k < _body.size(); k++) { Node* n = _body.at(k); switch (n->Opcode()) { case Op_XorI: xors_in_loop++; break; // CRC32 java code case Op_ModL: body_size += 30; break; case Op_DivL: body_size += 30; break; case Op_MulL: body_size += 10; break; case Op_StrComp: case Op_StrEquals: case Op_StrIndexOf: case Op_AryEq: { // Do not unroll a loop with String intrinsics code. // String intrinsics are large and have loops. return false; } } // switch } // Check for being too big if (body_size > (uint)LoopUnrollLimit) { if (xors_in_loop >= 4 && body_size < (uint)LoopUnrollLimit*4) return true; // Normal case: loop too big return false; } // Unroll once! (Each trip will soon do double iterations) return true; } //------------------------------policy_align----------------------------------- // Return TRUE or FALSE if the loop should be cache-line aligned. Gather the // expression that does the alignment. Note that only one array base can be // aligned in a loop (unless the VM guarantees mutual alignment). Note that // if we vectorize short memory ops into longer memory ops, we may want to // increase alignment. 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. bool IdealLoopTree::policy_range_check( PhaseIdealLoop *phase ) const { if (!RangeCheckElimination) return false; 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 (cl->is_main_no_pre_loop()) return false; // Disallowed for now. Node *trip_counter = cl->phi(); // Check loop body for tests of trip-counter plus loop-invariant vs // loop-invariant. for (uint i = 0; i < _body.size(); i++) { Node *iff = _body[i]; if (iff->Opcode() == Op_If) { // Test? // Comparing trip+off vs limit Node *bol = iff->in(1); if (bol->req() != 2) continue; // dead constant test if (!bol->is_Bool()) { assert(UseLoopPredicate && bol->Opcode() == Op_Conv2B, "predicate check only"); continue; } if (bol->as_Bool()->_test._test == BoolTest::ne) continue; // not RC Node *cmp = bol->in(1); Node *rc_exp = cmp->in(1); Node *limit = cmp->in(2); Node *limit_c = phase->get_ctrl(limit); if( limit_c == phase->C->top() ) return false; // Found dead test on live IF? No RCE! if( is_member(phase->get_loop(limit_c) ) ) { // Compare might have operands swapped; commute them rc_exp = cmp->in(2); limit = cmp->in(1); limit_c = phase->get_ctrl(limit); if( is_member(phase->get_loop(limit_c) ) ) continue; // Both inputs are loop varying; cannot RCE } if (!phase->is_scaled_iv_plus_offset(rc_exp, trip_counter, NULL, NULL)) { continue; } // Yeah! Found a test like 'trip+off vs limit' // Test is an IfNode, has 2 projections. If BOTH are in the loop // we need loop unswitching instead of iteration splitting. if( is_loop_exit(iff) ) return true; // Found reason to split iterations } // End of is IF } return false; } //------------------------------policy_peel_only------------------------------- // Return TRUE or FALSE if the loop should NEVER be RCE'd or aligned. Useful // for unrolling loops with NO array accesses. bool IdealLoopTree::policy_peel_only( PhaseIdealLoop *phase ) const { for( uint i = 0; i < _body.size(); i++ ) if( _body[i]->is_Mem() ) return false; // No memory accesses at all! return true; } //------------------------------clone_up_backedge_goo-------------------------- // If Node n lives in the back_ctrl block and cannot float, we clone a private // version of n in preheader_ctrl block and return that, otherwise return n. Node *PhaseIdealLoop::clone_up_backedge_goo( Node *back_ctrl, Node *preheader_ctrl, Node *n, VectorSet &visited, Node_Stack &clones ) { if( get_ctrl(n) != back_ctrl ) return n; // Only visit once if (visited.test_set(n->_idx)) { Node *x = clones.find(n->_idx); if (x != NULL) return x; return n; } Node *x = NULL; // If required, a clone of 'n' // Check for 'n' being pinned in the backedge. if( n->in(0) && n->in(0) == back_ctrl ) { assert(clones.find(n->_idx) == NULL, "dead loop"); x = n->clone(); // Clone a copy of 'n' to preheader clones.push(x, n->_idx); x->set_req( 0, preheader_ctrl ); // Fix x's control input to preheader } // Recursive fixup any other input edges into x. // If there are no changes we can just return 'n', otherwise // we need to clone a private copy and change it. for( uint i = 1; i < n->req(); i++ ) { Node *g = clone_up_backedge_goo( back_ctrl, preheader_ctrl, n->in(i), visited, clones ); if( g != n->in(i) ) { if( !x ) { assert(clones.find(n->_idx) == NULL, "dead loop"); x = n->clone(); clones.push(x, n->_idx); } x->set_req(i, g); } } if( x ) { // x can legally float to pre-header location register_new_node( x, preheader_ctrl ); return x; } else { // raise n to cover LCA of uses set_ctrl( n, find_non_split_ctrl(back_ctrl->in(0)) ); } return n; } //------------------------------insert_pre_post_loops-------------------------- // Insert pre and post loops. If peel_only is set, the pre-loop can not have // more iterations added. It acts as a 'peel' only, no lower-bound RCE, no // alignment. Useful to unroll loops that do no array accesses. void PhaseIdealLoop::insert_pre_post_loops( IdealLoopTree *loop, Node_List &old_new, bool peel_only ) { #ifndef PRODUCT if (TraceLoopOpts) { if (peel_only) tty->print("PeelMainPost "); else tty->print("PreMainPost "); loop->dump_head(); } #endif C->set_major_progress(); // Find common pieces of the loop being guarded with pre & post loops CountedLoopNode *main_head = loop->_head->as_CountedLoop(); assert( main_head->is_normal_loop(), "" ); CountedLoopEndNode *main_end = main_head->loopexit(); assert( main_end->outcnt() == 2, "1 true, 1 false path only" ); uint dd_main_head = dom_depth(main_head); uint max = main_head->outcnt(); Node *pre_header= main_head->in(LoopNode::EntryControl); Node *init = main_head->init_trip(); Node *incr = main_end ->incr(); Node *limit = main_end ->limit(); Node *stride = main_end ->stride(); Node *cmp = main_end ->cmp_node(); BoolTest::mask b_test = main_end->test_trip(); // Need only 1 user of 'bol' because I will be hacking the loop bounds. Node *bol = main_end->in(CountedLoopEndNode::TestValue); if( bol->outcnt() != 1 ) { bol = bol->clone(); register_new_node(bol,main_end->in(CountedLoopEndNode::TestControl)); _igvn.hash_delete(main_end); main_end->set_req(CountedLoopEndNode::TestValue, bol); } // Need only 1 user of 'cmp' because I will be hacking the loop bounds. if( cmp->outcnt() != 1 ) { cmp = cmp->clone(); register_new_node(cmp,main_end->in(CountedLoopEndNode::TestControl)); _igvn.hash_delete(bol); bol->set_req(1, cmp); } //------------------------------ // Step A: Create Post-Loop. Node* main_exit = main_end->proj_out(false); assert( main_exit->Opcode() == Op_IfFalse, "" ); int dd_main_exit = dom_depth(main_exit); // Step A1: Clone the loop body. The clone becomes the post-loop. The main // loop pre-header illegally has 2 control users (old & new loops). clone_loop( loop, old_new, dd_main_exit ); assert( old_new[main_end ->_idx]->Opcode() == Op_CountedLoopEnd, "" ); CountedLoopNode *post_head = old_new[main_head->_idx]->as_CountedLoop(); post_head->set_post_loop(main_head); // Reduce the post-loop trip count. CountedLoopEndNode* post_end = old_new[main_end ->_idx]->as_CountedLoopEnd(); post_end->_prob = PROB_FAIR; // Build the main-loop normal exit. IfFalseNode *new_main_exit = new (C) IfFalseNode(main_end); _igvn.register_new_node_with_optimizer( new_main_exit ); set_idom(new_main_exit, main_end, dd_main_exit ); set_loop(new_main_exit, loop->_parent); // Step A2: Build a zero-trip guard for the post-loop. After leaving the // main-loop, the post-loop may not execute at all. We 'opaque' the incr // (the main-loop trip-counter exit value) because we will be changing // the exit value (via unrolling) so we cannot constant-fold away the zero // trip guard until all unrolling is done. Node *zer_opaq = new (C) Opaque1Node(C, incr); Node *zer_cmp = new (C) CmpINode( zer_opaq, limit ); Node *zer_bol = new (C) BoolNode( zer_cmp, b_test ); register_new_node( zer_opaq, new_main_exit ); register_new_node( zer_cmp , new_main_exit ); register_new_node( zer_bol , new_main_exit ); // Build the IfNode IfNode *zer_iff = new (C) IfNode( new_main_exit, zer_bol, PROB_FAIR, COUNT_UNKNOWN ); _igvn.register_new_node_with_optimizer( zer_iff ); set_idom(zer_iff, new_main_exit, dd_main_exit); set_loop(zer_iff, loop->_parent); // Plug in the false-path, taken if we need to skip post-loop _igvn.replace_input_of(main_exit, 0, zer_iff); set_idom(main_exit, zer_iff, dd_main_exit); set_idom(main_exit->unique_out(), zer_iff, dd_main_exit); // Make the true-path, must enter the post loop Node *zer_taken = new (C) IfTrueNode( zer_iff ); _igvn.register_new_node_with_optimizer( zer_taken ); set_idom(zer_taken, zer_iff, dd_main_exit); set_loop(zer_taken, loop->_parent); // Plug in the true path _igvn.hash_delete( post_head ); post_head->set_req(LoopNode::EntryControl, zer_taken); set_idom(post_head, zer_taken, dd_main_exit); Arena *a = Thread::current()->resource_area(); VectorSet visited(a); Node_Stack clones(a, main_head->back_control()->outcnt()); // Step A3: Make the fall-in values to the post-loop come from the // fall-out values of the main-loop. for (DUIterator_Fast imax, i = main_head->fast_outs(imax); i < imax; i++) { Node* main_phi = main_head->fast_out(i); if( main_phi->is_Phi() && main_phi->in(0) == main_head && main_phi->outcnt() >0 ) { Node *post_phi = old_new[main_phi->_idx]; Node *fallmain = clone_up_backedge_goo(main_head->back_control(), post_head->init_control(), main_phi->in(LoopNode::LoopBackControl), visited, clones); _igvn.hash_delete(post_phi); post_phi->set_req( LoopNode::EntryControl, fallmain ); } } // Update local caches for next stanza main_exit = new_main_exit; //------------------------------ // Step B: Create Pre-Loop. // Step B1: Clone the loop body. The clone becomes the pre-loop. The main // loop pre-header illegally has 2 control users (old & new loops). clone_loop( loop, old_new, dd_main_head ); CountedLoopNode* pre_head = old_new[main_head->_idx]->as_CountedLoop(); CountedLoopEndNode* pre_end = old_new[main_end ->_idx]->as_CountedLoopEnd(); pre_head->set_pre_loop(main_head); Node *pre_incr = old_new[incr->_idx]; // Reduce the pre-loop trip count. pre_end->_prob = PROB_FAIR; // Find the pre-loop normal exit. Node* pre_exit = pre_end->proj_out(false); assert( pre_exit->Opcode() == Op_IfFalse, "" ); IfFalseNode *new_pre_exit = new (C) IfFalseNode(pre_end); _igvn.register_new_node_with_optimizer( new_pre_exit ); set_idom(new_pre_exit, pre_end, dd_main_head); set_loop(new_pre_exit, loop->_parent); // Step B2: Build a zero-trip guard for the main-loop. After leaving the // pre-loop, the main-loop may not execute at all. Later in life this // zero-trip guard will become the minimum-trip guard when we unroll // the main-loop. Node *min_opaq = new (C) Opaque1Node(C, limit); Node *min_cmp = new (C) CmpINode( pre_incr, min_opaq ); Node *min_bol = new (C) BoolNode( min_cmp, b_test ); register_new_node( min_opaq, new_pre_exit ); register_new_node( min_cmp , new_pre_exit ); register_new_node( min_bol , new_pre_exit ); // Build the IfNode (assume the main-loop is executed always). IfNode *min_iff = new (C) IfNode( new_pre_exit, min_bol, PROB_ALWAYS, COUNT_UNKNOWN ); _igvn.register_new_node_with_optimizer( min_iff ); set_idom(min_iff, new_pre_exit, dd_main_head); set_loop(min_iff, loop->_parent); // Plug in the false-path, taken if we need to skip main-loop _igvn.hash_delete( pre_exit ); pre_exit->set_req(0, min_iff); set_idom(pre_exit, min_iff, dd_main_head); set_idom(pre_exit->unique_out(), min_iff, dd_main_head); // Make the true-path, must enter the main loop Node *min_taken = new (C) IfTrueNode( min_iff ); _igvn.register_new_node_with_optimizer( min_taken ); set_idom(min_taken, min_iff, dd_main_head); set_loop(min_taken, loop->_parent); // Plug in the true path _igvn.hash_delete( main_head ); main_head->set_req(LoopNode::EntryControl, min_taken); set_idom(main_head, min_taken, dd_main_head); visited.Clear(); clones.clear(); // Step B3: Make the fall-in values to the main-loop come from the // fall-out values of the pre-loop. for (DUIterator_Fast i2max, i2 = main_head->fast_outs(i2max); i2 < i2max; i2++) { Node* main_phi = main_head->fast_out(i2); if( main_phi->is_Phi() && main_phi->in(0) == main_head && main_phi->outcnt() > 0 ) { Node *pre_phi = old_new[main_phi->_idx]; Node *fallpre = clone_up_backedge_goo(pre_head->back_control(), main_head->init_control(), pre_phi->in(LoopNode::LoopBackControl), visited, clones); _igvn.hash_delete(main_phi); main_phi->set_req( LoopNode::EntryControl, fallpre ); } } // Step B4: Shorten the pre-loop to run only 1 iteration (for now). // RCE and alignment may change this later. Node *cmp_end = pre_end->cmp_node(); assert( cmp_end->in(2) == limit, "" ); Node *pre_limit = new (C) AddINode( init, stride ); // Save the original loop limit in this Opaque1 node for // use by range check elimination. Node *pre_opaq = new (C) Opaque1Node(C, pre_limit, limit); register_new_node( pre_limit, pre_head->in(0) ); register_new_node( pre_opaq , pre_head->in(0) ); // Since no other users of pre-loop compare, I can hack limit directly assert( cmp_end->outcnt() == 1, "no other users" ); _igvn.hash_delete(cmp_end); cmp_end->set_req(2, peel_only ? pre_limit : pre_opaq); // Special case for not-equal loop bounds: // Change pre loop test, main loop test, and the // main loop guard test to use lt or gt depending on stride // direction: // positive stride use < // negative stride use > // // not-equal test is kept for post loop to handle case // when init > limit when stride > 0 (and reverse). if (pre_end->in(CountedLoopEndNode::TestValue)->as_Bool()->_test._test == BoolTest::ne) { BoolTest::mask new_test = (main_end->stride_con() > 0) ? BoolTest::lt : BoolTest::gt; // Modify pre loop end condition Node* pre_bol = pre_end->in(CountedLoopEndNode::TestValue)->as_Bool(); BoolNode* new_bol0 = new (C) BoolNode(pre_bol->in(1), new_test); register_new_node( new_bol0, pre_head->in(0) ); _igvn.hash_delete(pre_end); pre_end->set_req(CountedLoopEndNode::TestValue, new_bol0); // Modify main loop guard condition assert(min_iff->in(CountedLoopEndNode::TestValue) == min_bol, "guard okay"); BoolNode* new_bol1 = new (C) BoolNode(min_bol->in(1), new_test); register_new_node( new_bol1, new_pre_exit ); _igvn.hash_delete(min_iff); min_iff->set_req(CountedLoopEndNode::TestValue, new_bol1); // Modify main loop end condition BoolNode* main_bol = main_end->in(CountedLoopEndNode::TestValue)->as_Bool(); BoolNode* new_bol2 = new (C) BoolNode(main_bol->in(1), new_test); register_new_node( new_bol2, main_end->in(CountedLoopEndNode::TestControl) ); _igvn.hash_delete(main_end); main_end->set_req(CountedLoopEndNode::TestValue, new_bol2); } // Flag main loop main_head->set_main_loop(); if( peel_only ) main_head->set_main_no_pre_loop(); // Subtract a trip count for the pre-loop. main_head->set_trip_count(main_head->trip_count() - 1); // It's difficult to be precise about the trip-counts // for the pre/post loops. They are usually very short, // so guess that 4 trips is a reasonable value. post_head->set_profile_trip_cnt(4.0); pre_head->set_profile_trip_cnt(4.0); // Now force out all loop-invariant dominating tests. The optimizer // finds some, but we _know_ they are all useless. peeled_dom_test_elim(loop,old_new); } //------------------------------is_invariant----------------------------- // Return true if n is invariant bool IdealLoopTree::is_invariant(Node* n) const { Node *n_c = _phase->has_ctrl(n) ? _phase->get_ctrl(n) : n; if (n_c->is_top()) return false; return !is_member(_phase->get_loop(n_c)); } //------------------------------do_unroll-------------------------------------- // Unroll the loop body one step - make each trip do 2 iterations. void PhaseIdealLoop::do_unroll( IdealLoopTree *loop, Node_List &old_new, bool adjust_min_trip ) { assert(LoopUnrollLimit, ""); CountedLoopNode *loop_head = loop->_head->as_CountedLoop(); CountedLoopEndNode *loop_end = loop_head->loopexit(); assert(loop_end, ""); #ifndef PRODUCT if (PrintOpto && VerifyLoopOptimizations) { tty->print("Unrolling "); loop->dump_head(); } else if (TraceLoopOpts) { if (loop_head->trip_count() < (uint)LoopUnrollLimit) { tty->print("Unroll %d(%2d) ", loop_head->unrolled_count()*2, loop_head->trip_count()); } else { tty->print("Unroll %d ", loop_head->unrolled_count()*2); } loop->dump_head(); } #endif // Remember loop node count before unrolling to detect // if rounds of unroll,optimize are making progress loop_head->set_node_count_before_unroll(loop->_body.size()); Node *ctrl = loop_head->in(LoopNode::EntryControl); Node *limit = loop_head->limit(); Node *init = loop_head->init_trip(); Node *stride = loop_head->stride(); Node *opaq = NULL; if (adjust_min_trip) { // If not maximally unrolling, need adjustment // Search for zero-trip guard. assert( loop_head->is_main_loop(), "" ); assert( ctrl->Opcode() == Op_IfTrue || ctrl->Opcode() == Op_IfFalse, "" ); Node *iff = ctrl->in(0); assert( iff->Opcode() == Op_If, "" ); Node *bol = iff->in(1); assert( bol->Opcode() == Op_Bool, "" ); Node *cmp = bol->in(1); assert( cmp->Opcode() == Op_CmpI, "" ); opaq = cmp->in(2); // Occasionally it's possible for a zero-trip guard Opaque1 node to be // optimized away and then another round of loop opts attempted. // We can not optimize this particular loop in that case. if (opaq->Opcode() != Op_Opaque1) return; // Cannot find zero-trip guard! Bail out! // Zero-trip test uses an 'opaque' node which is not shared. assert(opaq->outcnt() == 1 && opaq->in(1) == limit, ""); } C->set_major_progress(); Node* new_limit = NULL; if (UnrollLimitCheck) { int stride_con = stride->get_int(); int stride_p = (stride_con > 0) ? stride_con : -stride_con; uint old_trip_count = loop_head->trip_count(); // Verify that unroll policy result is still valid. assert(old_trip_count > 1 && (!adjust_min_trip || stride_p <= (1<<3)*loop_head->unrolled_count()), "sanity"); // Adjust loop limit to keep valid iterations number after unroll. // Use (limit - stride) instead of (((limit - init)/stride) & (-2))*stride // which may overflow. if (!adjust_min_trip) { assert(old_trip_count > 1 && (old_trip_count & 1) == 0, "odd trip count for maximally unroll"); // Don't need to adjust limit for maximally unroll since trip count is even. } else if (loop_head->has_exact_trip_count() && init->is_Con()) { // Loop's limit is constant. Loop's init could be constant when pre-loop // become peeled iteration. jlong init_con = init->get_int(); // We can keep old loop limit if iterations count stays the same: // old_trip_count == new_trip_count * 2 // Note: since old_trip_count >= 2 then new_trip_count >= 1 // so we also don't need to adjust zero trip test. jlong limit_con = limit->get_int(); // (stride_con*2) not overflow since stride_con <= 8. int new_stride_con = stride_con * 2; int stride_m = new_stride_con - (stride_con > 0 ? 1 : -1); jlong trip_count = (limit_con - init_con + stride_m)/new_stride_con; // New trip count should satisfy next conditions. assert(trip_count > 0 && (julong)trip_count < (julong)max_juint/2, "sanity"); uint new_trip_count = (uint)trip_count; adjust_min_trip = (old_trip_count != new_trip_count*2); } if (adjust_min_trip) { // Step 2: Adjust the trip limit if it is called for. // The adjustment amount is -stride. Need to make sure if the // adjustment underflows or overflows, then the main loop is skipped. Node* cmp = loop_end->cmp_node(); assert(cmp->in(2) == limit, "sanity"); assert(opaq != NULL && opaq->in(1) == limit, "sanity"); // Verify that policy_unroll result is still valid. const TypeInt* limit_type = _igvn.type(limit)->is_int(); assert(stride_con > 0 && ((limit_type->_hi - stride_con) < limit_type->_hi) || stride_con < 0 && ((limit_type->_lo - stride_con) > limit_type->_lo), "sanity"); if (limit->is_Con()) { // The check in policy_unroll and the assert above guarantee // no underflow if limit is constant. new_limit = _igvn.intcon(limit->get_int() - stride_con); set_ctrl(new_limit, C->root()); } else { // Limit is not constant. if (loop_head->unrolled_count() == 1) { // only for first unroll // Separate limit by Opaque node in case it is an incremented // variable from previous loop to avoid using pre-incremented // value which could increase register pressure. // Otherwise reorg_offsets() optimization will create a separate // Opaque node for each use of trip-counter and as result // zero trip guard limit will be different from loop limit. assert(has_ctrl(opaq), "should have it"); Node* opaq_ctrl = get_ctrl(opaq); limit = new (C) Opaque2Node( C, limit ); register_new_node( limit, opaq_ctrl ); } if (stride_con > 0 && ((limit_type->_lo - stride_con) < limit_type->_lo) || stride_con < 0 && ((limit_type->_hi - stride_con) > limit_type->_hi)) { // No underflow. new_limit = new (C) SubINode(limit, stride); } else { // (limit - stride) may underflow. // Clamp the adjustment value with MININT or MAXINT: // // new_limit = limit-stride // if (stride > 0) // new_limit = (limit < new_limit) ? MININT : new_limit; // else // new_limit = (limit > new_limit) ? MAXINT : new_limit; // BoolTest::mask bt = loop_end->test_trip(); assert(bt == BoolTest::lt || bt == BoolTest::gt, "canonical test is expected"); Node* adj_max = _igvn.intcon((stride_con > 0) ? min_jint : max_jint); set_ctrl(adj_max, C->root()); Node* old_limit = NULL; Node* adj_limit = NULL; Node* bol = limit->is_CMove() ? limit->in(CMoveNode::Condition) : NULL; if (loop_head->unrolled_count() > 1 && limit->is_CMove() && limit->Opcode() == Op_CMoveI && limit->in(CMoveNode::IfTrue) == adj_max && bol->as_Bool()->_test._test == bt && bol->in(1)->Opcode() == Op_CmpI && bol->in(1)->in(2) == limit->in(CMoveNode::IfFalse)) { // Loop was unrolled before. // Optimize the limit to avoid nested CMove: // use original limit as old limit. old_limit = bol->in(1)->in(1); // Adjust previous adjusted limit. adj_limit = limit->in(CMoveNode::IfFalse); adj_limit = new (C) SubINode(adj_limit, stride); } else { old_limit = limit; adj_limit = new (C) SubINode(limit, stride); } assert(old_limit != NULL && adj_limit != NULL, ""); register_new_node( adj_limit, ctrl ); // adjust amount Node* adj_cmp = new (C) CmpINode(old_limit, adj_limit); register_new_node( adj_cmp, ctrl ); Node* adj_bool = new (C) BoolNode(adj_cmp, bt); register_new_node( adj_bool, ctrl ); new_limit = new (C) CMoveINode(adj_bool, adj_limit, adj_max, TypeInt::INT); } register_new_node(new_limit, ctrl); } assert(new_limit != NULL, ""); // Replace in loop test. assert(loop_end->in(1)->in(1) == cmp, "sanity"); if (cmp->outcnt() == 1 && loop_end->in(1)->outcnt() == 1) { // Don't need to create new test since only one user. _igvn.hash_delete(cmp); cmp->set_req(2, new_limit); } else { // Create new test since it is shared. Node* ctrl2 = loop_end->in(0); Node* cmp2 = cmp->clone(); cmp2->set_req(2, new_limit); register_new_node(cmp2, ctrl2); Node* bol2 = loop_end->in(1)->clone(); bol2->set_req(1, cmp2); register_new_node(bol2, ctrl2); _igvn.hash_delete(loop_end); loop_end->set_req(1, bol2); } // Step 3: Find the min-trip test guaranteed before a 'main' loop. // Make it a 1-trip test (means at least 2 trips). // Guard test uses an 'opaque' node which is not shared. Hence I // can edit it's inputs directly. Hammer in the new limit for the // minimum-trip guard. assert(opaq->outcnt() == 1, ""); _igvn.hash_delete(opaq); opaq->set_req(1, new_limit); } // Adjust max trip count. The trip count is intentionally rounded // down here (e.g. 15-> 7-> 3-> 1) because if we unwittingly over-unroll, // the main, unrolled, part of the loop will never execute as it is protected // by the min-trip test. See bug 4834191 for a case where we over-unrolled // and later determined that part of the unrolled loop was dead. loop_head->set_trip_count(old_trip_count / 2); // Double the count of original iterations in the unrolled loop body. loop_head->double_unrolled_count(); } else { // LoopLimitCheck // Adjust max trip count. The trip count is intentionally rounded // down here (e.g. 15-> 7-> 3-> 1) because if we unwittingly over-unroll, // the main, unrolled, part of the loop will never execute as it is protected // by the min-trip test. See bug 4834191 for a case where we over-unrolled // and later determined that part of the unrolled loop was dead. loop_head->set_trip_count(loop_head->trip_count() / 2); // Double the count of original iterations in the unrolled loop body. loop_head->double_unrolled_count(); // ----------- // Step 2: Cut back the trip counter for an unroll amount of 2. // Loop will normally trip (limit - init)/stride_con. Since it's a // CountedLoop this is exact (stride divides limit-init exactly). // We are going to double the loop body, so we want to knock off any // odd iteration: (trip_cnt & ~1). Then back compute a new limit. Node *span = new (C) SubINode( limit, init ); register_new_node( span, ctrl ); Node *trip = new (C) DivINode( 0, span, stride ); register_new_node( trip, ctrl ); Node *mtwo = _igvn.intcon(-2); set_ctrl(mtwo, C->root()); Node *rond = new (C) AndINode( trip, mtwo ); register_new_node( rond, ctrl ); Node *spn2 = new (C) MulINode( rond, stride ); register_new_node( spn2, ctrl ); new_limit = new (C) AddINode( spn2, init ); register_new_node( new_limit, ctrl ); // Hammer in the new limit Node *ctrl2 = loop_end->in(0); Node *cmp2 = new (C) CmpINode( loop_head->incr(), new_limit ); register_new_node( cmp2, ctrl2 ); Node *bol2 = new (C) BoolNode( cmp2, loop_end->test_trip() ); register_new_node( bol2, ctrl2 ); _igvn.hash_delete(loop_end); loop_end->set_req(CountedLoopEndNode::TestValue, bol2); // Step 3: Find the min-trip test guaranteed before a 'main' loop. // Make it a 1-trip test (means at least 2 trips). if( adjust_min_trip ) { assert( new_limit != NULL, "" ); // Guard test uses an 'opaque' node which is not shared. Hence I // can edit it's inputs directly. Hammer in the new limit for the // minimum-trip guard. assert( opaq->outcnt() == 1, "" ); _igvn.hash_delete(opaq); opaq->set_req(1, new_limit); } } // LoopLimitCheck // --------- // Step 4: Clone the loop body. Move it inside the loop. This loop body // represents the odd iterations; since the loop trips an even number of // times its backedge is never taken. Kill the backedge. uint dd = dom_depth(loop_head); clone_loop( loop, old_new, dd ); // Make backedges of the clone equal to backedges of the original. // Make the fall-in from the original come from the fall-out of the clone. for (DUIterator_Fast jmax, j = loop_head->fast_outs(jmax); j < jmax; j++) { Node* phi = loop_head->fast_out(j); if( phi->is_Phi() && phi->in(0) == loop_head && phi->outcnt() > 0 ) { Node *newphi = old_new[phi->_idx]; _igvn.hash_delete( phi ); _igvn.hash_delete( newphi ); phi ->set_req(LoopNode:: EntryControl, newphi->in(LoopNode::LoopBackControl)); newphi->set_req(LoopNode::LoopBackControl, phi ->in(LoopNode::LoopBackControl)); phi ->set_req(LoopNode::LoopBackControl, C->top()); } } Node *clone_head = old_new[loop_head->_idx]; _igvn.hash_delete( clone_head ); loop_head ->set_req(LoopNode:: EntryControl, clone_head->in(LoopNode::LoopBackControl)); clone_head->set_req(LoopNode::LoopBackControl, loop_head ->in(LoopNode::LoopBackControl)); loop_head ->set_req(LoopNode::LoopBackControl, C->top()); loop->_head = clone_head; // New loop header set_idom(loop_head, loop_head ->in(LoopNode::EntryControl), dd); set_idom(clone_head, clone_head->in(LoopNode::EntryControl), dd); // Kill the clone's backedge Node *newcle = old_new[loop_end->_idx]; _igvn.hash_delete( newcle ); Node *one = _igvn.intcon(1); set_ctrl(one, C->root()); newcle->set_req(1, one); // Force clone into same loop body uint max = loop->_body.size(); for( uint k = 0; k < max; k++ ) { Node *old = loop->_body.at(k); Node *nnn = old_new[old->_idx]; loop->_body.push(nnn); if (!has_ctrl(old)) set_loop(nnn, loop); } loop->record_for_igvn(); } //------------------------------do_maximally_unroll---------------------------- void PhaseIdealLoop::do_maximally_unroll( IdealLoopTree *loop, Node_List &old_new ) { CountedLoopNode *cl = loop->_head->as_CountedLoop(); assert(cl->has_exact_trip_count(), "trip count is not exact"); assert(cl->trip_count() > 0, ""); #ifndef PRODUCT if (TraceLoopOpts) { tty->print("MaxUnroll %d ", cl->trip_count()); loop->dump_head(); } #endif // If loop is tripping an odd number of times, peel odd iteration if ((cl->trip_count() & 1) == 1) { do_peeling(loop, old_new); } // Now its tripping an even number of times remaining. Double loop body. // Do not adjust pre-guards; they are not needed and do not exist. if (cl->trip_count() > 0) { assert((cl->trip_count() & 1) == 0, "missed peeling"); do_unroll(loop, old_new, false); } } //------------------------------dominates_backedge--------------------------------- // Returns true if ctrl is executed on every complete iteration bool IdealLoopTree::dominates_backedge(Node* ctrl) { assert(ctrl->is_CFG(), "must be control"); Node* backedge = _head->as_Loop()->in(LoopNode::LoopBackControl); return _phase->dom_lca_internal(ctrl, backedge) == ctrl; } //------------------------------adjust_limit----------------------------------- // Helper function for add_constraint(). Node* PhaseIdealLoop::adjust_limit(int stride_con, Node * scale, Node *offset, Node *rc_limit, Node *loop_limit, Node *pre_ctrl) { // Compute "I :: (limit-offset)/scale" Node *con = new (C) SubINode(rc_limit, offset); register_new_node(con, pre_ctrl); Node *X = new (C) DivINode(0, con, scale); register_new_node(X, pre_ctrl); // Adjust loop limit loop_limit = (stride_con > 0) ? (Node*)(new (C) MinINode(loop_limit, X)) : (Node*)(new (C) MaxINode(loop_limit, X)); register_new_node(loop_limit, pre_ctrl); return loop_limit; } //------------------------------add_constraint--------------------------------- // Constrain the main loop iterations so the conditions: // low_limit <= scale_con * I + offset < upper_limit // always holds true. That is, either increase the number of iterations in // the pre-loop or the post-loop until the condition holds true in the main // loop. Stride, scale, offset and limit are all loop invariant. Further, // stride and scale are constants (offset and limit often are). void PhaseIdealLoop::add_constraint( int stride_con, int scale_con, Node *offset, Node *low_limit, Node *upper_limit, Node *pre_ctrl, Node **pre_limit, Node **main_limit ) { // For positive stride, the pre-loop limit always uses a MAX function // and the main loop a MIN function. For negative stride these are // reversed. // Also for positive stride*scale the affine function is increasing, so the // pre-loop must check for underflow and the post-loop for overflow. // Negative stride*scale reverses this; pre-loop checks for overflow and // post-loop for underflow. Node *scale = _igvn.intcon(scale_con); set_ctrl(scale, C->root()); if ((stride_con^scale_con) >= 0) { // Use XOR to avoid overflow // The overflow limit: scale*I+offset < upper_limit // For main-loop compute // ( if (scale > 0) /* and stride > 0 */ // I < (upper_limit-offset)/scale // else /* scale < 0 and stride < 0 */ // I > (upper_limit-offset)/scale // ) // // (upper_limit-offset) may overflow or underflow. // But it is fine since main loop will either have // less iterations or will be skipped in such case. *main_limit = adjust_limit(stride_con, scale, offset, upper_limit, *main_limit, pre_ctrl); // The underflow limit: low_limit <= scale*I+offset. // For pre-loop compute // NOT(scale*I+offset >= low_limit) // scale*I+offset < low_limit // ( if (scale > 0) /* and stride > 0 */ // I < (low_limit-offset)/scale // else /* scale < 0 and stride < 0 */ // I > (low_limit-offset)/scale // ) if (low_limit->get_int() == -max_jint) { if (!RangeLimitCheck) return; // We need this guard when scale*pre_limit+offset >= limit // due to underflow. So we need execute pre-loop until // scale*I+offset >= min_int. But (min_int-offset) will // underflow when offset > 0 and X will be > original_limit // when stride > 0. To avoid it we replace positive offset with 0. // // Also (min_int+1 == -max_int) is used instead of min_int here // to avoid problem with scale == -1 (min_int/(-1) == min_int). Node* shift = _igvn.intcon(31); set_ctrl(shift, C->root()); Node* sign = new (C) RShiftINode(offset, shift); register_new_node(sign, pre_ctrl); offset = new (C) AndINode(offset, sign); register_new_node(offset, pre_ctrl); } else { assert(low_limit->get_int() == 0, "wrong low limit for range check"); // The only problem we have here when offset == min_int // since (0-min_int) == min_int. It may be fine for stride > 0 // but for stride < 0 X will be < original_limit. To avoid it // max(pre_limit, original_limit) is used in do_range_check(). } // Pass (-stride) to indicate pre_loop_cond = NOT(main_loop_cond); *pre_limit = adjust_limit((-stride_con), scale, offset, low_limit, *pre_limit, pre_ctrl); } else { // stride_con*scale_con < 0 // For negative stride*scale pre-loop checks for overflow and // post-loop for underflow. // // The overflow limit: scale*I+offset < upper_limit // For pre-loop compute // NOT(scale*I+offset < upper_limit) // scale*I+offset >= upper_limit // scale*I+offset+1 > upper_limit // ( if (scale < 0) /* and stride > 0 */ // I < (upper_limit-(offset+1))/scale // else /* scale > 0 and stride < 0 */ // I > (upper_limit-(offset+1))/scale // ) // // (upper_limit-offset-1) may underflow or overflow. // To avoid it min(pre_limit, original_limit) is used // in do_range_check() for stride > 0 and max() for < 0. Node *one = _igvn.intcon(1); set_ctrl(one, C->root()); Node *plus_one = new (C) AddINode(offset, one); register_new_node( plus_one, pre_ctrl ); // Pass (-stride) to indicate pre_loop_cond = NOT(main_loop_cond); *pre_limit = adjust_limit((-stride_con), scale, plus_one, upper_limit, *pre_limit, pre_ctrl); if (low_limit->get_int() == -max_jint) { if (!RangeLimitCheck) return; // We need this guard when scale*main_limit+offset >= limit // due to underflow. So we need execute main-loop while // scale*I+offset+1 > min_int. But (min_int-offset-1) will // underflow when (offset+1) > 0 and X will be < main_limit // when scale < 0 (and stride > 0). To avoid it we replace // positive (offset+1) with 0. // // Also (min_int+1 == -max_int) is used instead of min_int here // to avoid problem with scale == -1 (min_int/(-1) == min_int). Node* shift = _igvn.intcon(31); set_ctrl(shift, C->root()); Node* sign = new (C) RShiftINode(plus_one, shift); register_new_node(sign, pre_ctrl); plus_one = new (C) AndINode(plus_one, sign); register_new_node(plus_one, pre_ctrl); } else { assert(low_limit->get_int() == 0, "wrong low limit for range check"); // The only problem we have here when offset == max_int // since (max_int+1) == min_int and (0-min_int) == min_int. // But it is fine since main loop will either have // less iterations or will be skipped in such case. } // The underflow limit: low_limit <= scale*I+offset. // For main-loop compute // scale*I+offset+1 > low_limit // ( if (scale < 0) /* and stride > 0 */ // I < (low_limit-(offset+1))/scale // else /* scale > 0 and stride < 0 */ // I > (low_limit-(offset+1))/scale // ) *main_limit = adjust_limit(stride_con, scale, plus_one, low_limit, *main_limit, pre_ctrl); } } //------------------------------is_scaled_iv--------------------------------- // Return true if exp is a constant times an induction var bool PhaseIdealLoop::is_scaled_iv(Node* exp, Node* iv, int* p_scale) { if (exp == iv) { if (p_scale != NULL) { *p_scale = 1; } return true; } int opc = exp->Opcode(); if (opc == Op_MulI) { if (exp->in(1) == iv && exp->in(2)->is_Con()) { if (p_scale != NULL) { *p_scale = exp->in(2)->get_int(); } return true; } if (exp->in(2) == iv && exp->in(1)->is_Con()) { if (p_scale != NULL) { *p_scale = exp->in(1)->get_int(); } return true; } } else if (opc == Op_LShiftI) { if (exp->in(1) == iv && exp->in(2)->is_Con()) { if (p_scale != NULL) { *p_scale = 1 << exp->in(2)->get_int(); } return true; } } return false; } //-----------------------------is_scaled_iv_plus_offset------------------------------ // Return true if exp is a simple induction variable expression: k1*iv + (invar + k2) bool PhaseIdealLoop::is_scaled_iv_plus_offset(Node* exp, Node* iv, int* p_scale, Node** p_offset, int depth) { if (is_scaled_iv(exp, iv, p_scale)) { if (p_offset != NULL) { Node *zero = _igvn.intcon(0); set_ctrl(zero, C->root()); *p_offset = zero; } return true; } int opc = exp->Opcode(); if (opc == Op_AddI) { if (is_scaled_iv(exp->in(1), iv, p_scale)) { if (p_offset != NULL) { *p_offset = exp->in(2); } return true; } if (exp->in(2)->is_Con()) { Node* offset2 = NULL; if (depth < 2 && is_scaled_iv_plus_offset(exp->in(1), iv, p_scale, p_offset != NULL ? &offset2 : NULL, depth+1)) { if (p_offset != NULL) { Node *ctrl_off2 = get_ctrl(offset2); Node* offset = new (C) AddINode(offset2, exp->in(2)); register_new_node(offset, ctrl_off2); *p_offset = offset; } return true; } } } else if (opc == Op_SubI) { if (is_scaled_iv(exp->in(1), iv, p_scale)) { if (p_offset != NULL) { Node *zero = _igvn.intcon(0); set_ctrl(zero, C->root()); Node *ctrl_off = get_ctrl(exp->in(2)); Node* offset = new (C) SubINode(zero, exp->in(2)); register_new_node(offset, ctrl_off); *p_offset = offset; } return true; } if (is_scaled_iv(exp->in(2), iv, p_scale)) { if (p_offset != NULL) { *p_scale *= -1; *p_offset = exp->in(1); } return true; } } return false; } //------------------------------do_range_check--------------------------------- // Eliminate range-checks and other trip-counter vs loop-invariant tests. void PhaseIdealLoop::do_range_check( IdealLoopTree *loop, Node_List &old_new ) { #ifndef PRODUCT if (PrintOpto && VerifyLoopOptimizations) { tty->print("Range Check Elimination "); loop->dump_head(); } else if (TraceLoopOpts) { tty->print("RangeCheck "); loop->dump_head(); } #endif assert(RangeCheckElimination, ""); CountedLoopNode *cl = loop->_head->as_CountedLoop(); assert(cl->is_main_loop(), ""); // protect against stride not being a constant if (!cl->stride_is_con()) return; // Find the trip counter; we are iteration splitting based on it Node *trip_counter = cl->phi(); // Find the main loop limit; we will trim it's iterations // to not ever trip end tests Node *main_limit = cl->limit(); // Need to find the main-loop zero-trip guard Node *ctrl = cl->in(LoopNode::EntryControl); assert(ctrl->Opcode() == Op_IfTrue || ctrl->Opcode() == Op_IfFalse, ""); Node *iffm = ctrl->in(0); assert(iffm->Opcode() == Op_If, ""); Node *bolzm = iffm->in(1); assert(bolzm->Opcode() == Op_Bool, ""); Node *cmpzm = bolzm->in(1); assert(cmpzm->is_Cmp(), ""); Node *opqzm = cmpzm->in(2); // Can not optimize a loop if zero-trip Opaque1 node is optimized // away and then another round of loop opts attempted. if (opqzm->Opcode() != Op_Opaque1) return; assert(opqzm->in(1) == main_limit, "do not understand situation"); // Find the pre-loop limit; we will expand it's iterations to // not ever trip low tests. Node *p_f = iffm->in(0); assert(p_f->Opcode() == Op_IfFalse, ""); CountedLoopEndNode *pre_end = p_f->in(0)->as_CountedLoopEnd(); assert(pre_end->loopnode()->is_pre_loop(), ""); Node *pre_opaq1 = pre_end->limit(); // Occasionally it's possible for a pre-loop Opaque1 node to be // optimized away and then another round of loop opts attempted. // We can not optimize this particular loop in that case. if (pre_opaq1->Opcode() != Op_Opaque1) return; Opaque1Node *pre_opaq = (Opaque1Node*)pre_opaq1; Node *pre_limit = pre_opaq->in(1); // Where do we put new limit calculations Node *pre_ctrl = pre_end->loopnode()->in(LoopNode::EntryControl); // Ensure the original loop limit is available from the // pre-loop Opaque1 node. Node *orig_limit = pre_opaq->original_loop_limit(); if (orig_limit == NULL || _igvn.type(orig_limit) == Type::TOP) return; // Must know if its a count-up or count-down loop int stride_con = cl->stride_con(); Node *zero = _igvn.intcon(0); Node *one = _igvn.intcon(1); // Use symmetrical int range [-max_jint,max_jint] Node *mini = _igvn.intcon(-max_jint); set_ctrl(zero, C->root()); set_ctrl(one, C->root()); set_ctrl(mini, C->root()); // Range checks that do not dominate the loop backedge (ie. // conditionally executed) can lengthen the pre loop limit beyond // the original loop limit. To prevent this, the pre limit is // (for stride > 0) MINed with the original loop limit (MAXed // stride < 0) when some range_check (rc) is conditionally // executed. bool conditional_rc = false; // Check loop body for tests of trip-counter plus loop-invariant vs // loop-invariant. for( uint i = 0; i < loop->_body.size(); i++ ) { Node *iff = loop->_body[i]; if( iff->Opcode() == Op_If ) { // Test? // Test is an IfNode, has 2 projections. If BOTH are in the loop // we need loop unswitching instead of iteration splitting. Node *exit = loop->is_loop_exit(iff); if( !exit ) continue; int flip = (exit->Opcode() == Op_IfTrue) ? 1 : 0; // Get boolean condition to test Node *i1 = iff->in(1); if( !i1->is_Bool() ) continue; BoolNode *bol = i1->as_Bool(); BoolTest b_test = bol->_test; // Flip sense of test if exit condition is flipped if( flip ) b_test = b_test.negate(); // Get compare Node *cmp = bol->in(1); // Look for trip_counter + offset vs limit Node *rc_exp = cmp->in(1); Node *limit = cmp->in(2); jint scale_con= 1; // Assume trip counter not scaled Node *limit_c = get_ctrl(limit); if( loop->is_member(get_loop(limit_c) ) ) { // Compare might have operands swapped; commute them b_test = b_test.commute(); rc_exp = cmp->in(2); limit = cmp->in(1); limit_c = get_ctrl(limit); if( loop->is_member(get_loop(limit_c) ) ) continue; // Both inputs are loop varying; cannot RCE } // Here we know 'limit' is loop invariant // 'limit' maybe pinned below the zero trip test (probably from a // previous round of rce), in which case, it can't be used in the // zero trip test expression which must occur before the zero test's if. if( limit_c == ctrl ) { continue; // Don't rce this check but continue looking for other candidates. } // Check for scaled induction variable plus an offset Node *offset = NULL; if (!is_scaled_iv_plus_offset(rc_exp, trip_counter, &scale_con, &offset)) { continue; } Node *offset_c = get_ctrl(offset); if( loop->is_member( get_loop(offset_c) ) ) continue; // Offset is not really loop invariant // Here we know 'offset' is loop invariant. // As above for the 'limit', the 'offset' maybe pinned below the // zero trip test. if( offset_c == ctrl ) { continue; // Don't rce this check but continue looking for other candidates. } #ifdef ASSERT if (TraceRangeLimitCheck) { tty->print_cr("RC bool node%s", flip ? " flipped:" : ":"); bol->dump(2); } #endif // At this point we have the expression as: // scale_con * trip_counter + offset :: limit // where scale_con, offset and limit are loop invariant. Trip_counter // monotonically increases by stride_con, a constant. Both (or either) // stride_con and scale_con can be negative which will flip about the // sense of the test. // Adjust pre and main loop limits to guard the correct iteration set if( cmp->Opcode() == Op_CmpU ) {// Unsigned compare is really 2 tests if( b_test._test == BoolTest::lt ) { // Range checks always use lt // The underflow and overflow limits: 0 <= scale*I+offset < limit add_constraint( stride_con, scale_con, offset, zero, limit, pre_ctrl, &pre_limit, &main_limit ); if (!conditional_rc) { // (0-offset)/scale could be outside of loop iterations range. conditional_rc = !loop->dominates_backedge(iff) || RangeLimitCheck; } } else { #ifndef PRODUCT if( PrintOpto ) tty->print_cr("missed RCE opportunity"); #endif continue; // In release mode, ignore it } } else { // Otherwise work on normal compares switch( b_test._test ) { case BoolTest::gt: // Fall into GE case case BoolTest::ge: // Convert (I*scale+offset) >= Limit to (I*(-scale)+(-offset)) <= -Limit scale_con = -scale_con; offset = new (C) SubINode( zero, offset ); register_new_node( offset, pre_ctrl ); limit = new (C) SubINode( zero, limit ); register_new_node( limit, pre_ctrl ); // Fall into LE case case BoolTest::le: if (b_test._test != BoolTest::gt) { // Convert X <= Y to X < Y+1 limit = new (C) AddINode( limit, one ); register_new_node( limit, pre_ctrl ); } // Fall into LT case case BoolTest::lt: // The underflow and overflow limits: MIN_INT <= scale*I+offset < limit // Note: (MIN_INT+1 == -MAX_INT) is used instead of MIN_INT here // to avoid problem with scale == -1: MIN_INT/(-1) == MIN_INT. add_constraint( stride_con, scale_con, offset, mini, limit, pre_ctrl, &pre_limit, &main_limit ); if (!conditional_rc) { // ((MIN_INT+1)-offset)/scale could be outside of loop iterations range. // Note: negative offset is replaced with 0 but (MIN_INT+1)/scale could // still be outside of loop range. conditional_rc = !loop->dominates_backedge(iff) || RangeLimitCheck; } break; default: #ifndef PRODUCT if( PrintOpto ) tty->print_cr("missed RCE opportunity"); #endif continue; // Unhandled case } } // Kill the eliminated test C->set_major_progress(); Node *kill_con = _igvn.intcon( 1-flip ); set_ctrl(kill_con, C->root()); _igvn.replace_input_of(iff, 1, kill_con); // Find surviving projection assert(iff->is_If(), ""); ProjNode* dp = ((IfNode*)iff)->proj_out(1-flip); // Find loads off the surviving projection; remove their control edge for (DUIterator_Fast imax, i = dp->fast_outs(imax); i < imax; i++) { Node* cd = dp->fast_out(i); // Control-dependent node if( cd->is_Load() ) { // Loads can now float around in the loop // Allow the load to float around in the loop, or before it // but NOT before the pre-loop. _igvn.replace_input_of(cd, 0, ctrl); // ctrl, not NULL --i; --imax; } } } // End of is IF } // Update loop limits if (conditional_rc) { pre_limit = (stride_con > 0) ? (Node*)new (C) MinINode(pre_limit, orig_limit) : (Node*)new (C) MaxINode(pre_limit, orig_limit); register_new_node(pre_limit, pre_ctrl); } _igvn.hash_delete(pre_opaq); pre_opaq->set_req(1, pre_limit); // Note:: we are making the main loop limit no longer precise; // need to round up based on stride. cl->set_nonexact_trip_count(); if (!LoopLimitCheck && stride_con != 1 && stride_con != -1) { // Cutout for common case // "Standard" round-up logic: ([main_limit-init+(y-1)]/y)*y+init // Hopefully, compiler will optimize for powers of 2. Node *ctrl = get_ctrl(main_limit); Node *stride = cl->stride(); Node *init = cl->init_trip(); Node *span = new (C) SubINode(main_limit,init); register_new_node(span,ctrl); Node *rndup = _igvn.intcon(stride_con + ((stride_con>0)?-1:1)); Node *add = new (C) AddINode(span,rndup); register_new_node(add,ctrl); Node *div = new (C) DivINode(0,add,stride); register_new_node(div,ctrl); Node *mul = new (C) MulINode(div,stride); register_new_node(mul,ctrl); Node *newlim = new (C) AddINode(mul,init); register_new_node(newlim,ctrl); main_limit = newlim; } Node *main_cle = cl->loopexit(); Node *main_bol = main_cle->in(1); // Hacking loop bounds; need private copies of exit test if( main_bol->outcnt() > 1 ) {// BoolNode shared? _igvn.hash_delete(main_cle); main_bol = main_bol->clone();// Clone a private BoolNode register_new_node( main_bol, main_cle->in(0) ); main_cle->set_req(1,main_bol); } Node *main_cmp = main_bol->in(1); if( main_cmp->outcnt() > 1 ) { // CmpNode shared? _igvn.hash_delete(main_bol); main_cmp = main_cmp->clone();// Clone a private CmpNode register_new_node( main_cmp, main_cle->in(0) ); main_bol->set_req(1,main_cmp); } // Hack the now-private loop bounds _igvn.replace_input_of(main_cmp, 2, main_limit); // The OpaqueNode is unshared by design assert( opqzm->outcnt() == 1, "cannot hack shared node" ); _igvn.replace_input_of(opqzm, 1, main_limit); } //------------------------------DCE_loop_body---------------------------------- // Remove simplistic dead code from loop body void IdealLoopTree::DCE_loop_body() { for( uint i = 0; i < _body.size(); i++ ) if( _body.at(i)->outcnt() == 0 ) _body.map( i--, _body.pop() ); } //------------------------------adjust_loop_exit_prob-------------------------- // Look for loop-exit tests with the 50/50 (or worse) guesses from the parsing stage. // Replace with a 1-in-10 exit guess. void IdealLoopTree::adjust_loop_exit_prob( PhaseIdealLoop *phase ) { Node *test = tail(); while( test != _head ) { uint top = test->Opcode(); if( top == Op_IfTrue || top == Op_IfFalse ) { int test_con = ((ProjNode*)test)->_con; assert(top == (uint)(test_con? Op_IfTrue: Op_IfFalse), "sanity"); IfNode *iff = test->in(0)->as_If(); if( iff->outcnt() == 2 ) { // Ignore dead tests Node *bol = iff->in(1); if( bol && bol->req() > 1 && bol->in(1) && ((bol->in(1)->Opcode() == Op_StorePConditional ) || (bol->in(1)->Opcode() == Op_StoreIConditional ) || (bol->in(1)->Opcode() == Op_StoreLConditional ) || (bol->in(1)->Opcode() == Op_CompareAndSwapI ) || (bol->in(1)->Opcode() == Op_CompareAndSwapL ) || (bol->in(1)->Opcode() == Op_CompareAndSwapP ) || (bol->in(1)->Opcode() == Op_CompareAndSwapN ))) return; // Allocation loops RARELY take backedge // Find the OTHER exit path from the IF Node* ex = iff->proj_out(1-test_con); float p = iff->_prob; if( !phase->is_member( this, ex ) && iff->_fcnt == COUNT_UNKNOWN ) { if( top == Op_IfTrue ) { if( p < (PROB_FAIR + PROB_UNLIKELY_MAG(3))) { iff->_prob = PROB_STATIC_FREQUENT; } } else { if( p > (PROB_FAIR - PROB_UNLIKELY_MAG(3))) { iff->_prob = PROB_STATIC_INFREQUENT; } } } } } test = phase->idom(test); } } //------------------------------policy_do_remove_empty_loop-------------------- // Micro-benchmark spamming. Policy is to always remove empty loops. // The 'DO' part is to replace the trip counter with the value it will // have on the last iteration. This will break the loop. bool IdealLoopTree::policy_do_remove_empty_loop( PhaseIdealLoop *phase ) { // Minimum size must be empty loop if (_body.size() > EMPTY_LOOP_SIZE) return false; if (!_head->is_CountedLoop()) return false; // Dead loop CountedLoopNode *cl = _head->as_CountedLoop(); if (!cl->is_valid_counted_loop()) return false; // Malformed loop if (!phase->is_member(this, phase->get_ctrl(cl->loopexit()->in(CountedLoopEndNode::TestValue)))) return false; // Infinite loop #ifdef ASSERT // Ensure only one phi which is the iv. Node* iv = NULL; for (DUIterator_Fast imax, i = cl->fast_outs(imax); i < imax; i++) { Node* n = cl->fast_out(i); if (n->Opcode() == Op_Phi) { assert(iv == NULL, "Too many phis" ); iv = n; } } assert(iv == cl->phi(), "Wrong phi" ); #endif // main and post loops have explicitly created zero trip guard bool needs_guard = !cl->is_main_loop() && !cl->is_post_loop(); if (needs_guard) { // Skip guard if values not overlap. const TypeInt* init_t = phase->_igvn.type(cl->init_trip())->is_int(); const TypeInt* limit_t = phase->_igvn.type(cl->limit())->is_int(); int stride_con = cl->stride_con(); if (stride_con > 0) { needs_guard = (init_t->_hi >= limit_t->_lo); } else { needs_guard = (init_t->_lo <= limit_t->_hi); } } if (needs_guard) { // Check for an obvious zero trip guard. Node* inctrl = PhaseIdealLoop::skip_loop_predicates(cl->in(LoopNode::EntryControl)); if (inctrl->Opcode() == Op_IfTrue) { // The test should look like just the backedge of a CountedLoop Node* iff = inctrl->in(0); if (iff->is_If()) { Node* bol = iff->in(1); if (bol->is_Bool() && bol->as_Bool()->_test._test == cl->loopexit()->test_trip()) { Node* cmp = bol->in(1); if (cmp->is_Cmp() && cmp->in(1) == cl->init_trip() && cmp->in(2) == cl->limit()) { needs_guard = false; } } } } } #ifndef PRODUCT if (PrintOpto) { tty->print("Removing empty loop with%s zero trip guard", needs_guard ? "out" : ""); this->dump_head(); } else if (TraceLoopOpts) { tty->print("Empty with%s zero trip guard ", needs_guard ? "out" : ""); this->dump_head(); } #endif if (needs_guard) { // Peel the loop to ensure there's a zero trip guard Node_List old_new; phase->do_peeling(this, old_new); } // Replace the phi at loop head with the final value of the last // iteration. Then the CountedLoopEnd will collapse (backedge never // taken) and all loop-invariant uses of the exit values will be correct. Node *phi = cl->phi(); Node *exact_limit = phase->exact_limit(this); if (exact_limit != cl->limit()) { // We also need to replace the original limit to collapse loop exit. Node* cmp = cl->loopexit()->cmp_node(); assert(cl->limit() == cmp->in(2), "sanity"); phase->_igvn._worklist.push(cmp->in(2)); // put limit on worklist phase->_igvn.replace_input_of(cmp, 2, exact_limit); // put cmp on worklist } // Note: the final value after increment should not overflow since // counted loop has limit check predicate. Node *final = new (phase->C) SubINode( exact_limit, cl->stride() ); phase->register_new_node(final,cl->in(LoopNode::EntryControl)); phase->_igvn.replace_node(phi,final); phase->C->set_major_progress(); return true; } //------------------------------policy_do_one_iteration_loop------------------- // Convert one iteration loop into normal code. bool IdealLoopTree::policy_do_one_iteration_loop( PhaseIdealLoop *phase ) { if (!_head->as_Loop()->is_valid_counted_loop()) return false; // Only for counted loop CountedLoopNode *cl = _head->as_CountedLoop(); if (!cl->has_exact_trip_count() || cl->trip_count() != 1) { return false; } #ifndef PRODUCT if(TraceLoopOpts) { tty->print("OneIteration "); this->dump_head(); } #endif Node *init_n = cl->init_trip(); #ifdef ASSERT // Loop boundaries should be constant since trip count is exact. assert(init_n->get_int() + cl->stride_con() >= cl->limit()->get_int(), "should be one iteration"); #endif // Replace the phi at loop head with the value of the init_trip. // Then the CountedLoopEnd will collapse (backedge will not be taken) // and all loop-invariant uses of the exit values will be correct. phase->_igvn.replace_node(cl->phi(), cl->init_trip()); phase->C->set_major_progress(); return true; } //============================================================================= //------------------------------iteration_split_impl--------------------------- bool IdealLoopTree::iteration_split_impl( PhaseIdealLoop *phase, Node_List &old_new ) { // Compute exact loop trip count if possible. compute_exact_trip_count(phase); // Convert one iteration loop into normal code. if (policy_do_one_iteration_loop(phase)) return true; // Check and remove empty loops (spam micro-benchmarks) if (policy_do_remove_empty_loop(phase)) return true; // Here we removed an empty loop bool should_peel = policy_peeling(phase); // Should we peel? 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? #ifndef PRODUCT if (PrintOpto) tty->print_cr("should_peel"); #endif phase->do_peeling(this,old_new); } else if (should_unswitch) { phase->do_unswitching(this, old_new); } return true; } CountedLoopNode *cl = _head->as_CountedLoop(); if (!cl->is_valid_counted_loop()) return true; // Ignore various kinds of broken loops // Do nothing special to pre- and post- loops if (cl->is_pre_loop() || cl->is_post_loop()) return true; // Compute loop trip count from profile data 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) { phase->do_unswitching(this, old_new); return true; } bool should_maximally_unroll = policy_maximally_unroll(phase); if (should_maximally_unroll) { // 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; } } // Skip next optimizations if running low on nodes. Note that // policy_unswitching and policy_maximally_unroll have this check. uint nodes_left = MaxNodeLimit - phase->C->unique(); if ((2 * _body.size()) > nodes_left) { return true; } // 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. // The main loop will start cache-line aligned with at least 1 // iteration of the unrolled body (zero-trip test required) and // will have some range checks removed. // A post-loop will finish any odd iterations (leftover after // unrolling), plus any needed for RCE purposes. bool should_unroll = policy_unroll(phase); bool should_rce = policy_range_check(phase); bool should_align = policy_align(phase); // If not RCE'ing (iteration splitting) or Aligning, then we do not // need a pre-loop. We may still need to peel an initial iteration but // we will not be needing an unknown number of pre-iterations. // // Basically, if may_rce_align reports FALSE first time through, // we will not be able to later do RCE or Aligning on this loop. bool may_rce_align = !policy_peel_only(phase) || should_rce || should_align; // 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 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. if (should_rce) phase->do_range_check(this,old_new); // Double loop body for unrolling. Adjust the minimum-trip test (will do // twice as many iterations as before) and the main body limit (only do // an even number of trips). If we are peeling, we might enable some RCE // and we'd rather unroll the post-RCE'd loop SO... do not unroll if // peeling. if (should_unroll && !should_peel) phase->do_unroll(this,old_new, true); // Adjust the pre-loop limits to align the main body // iterations. 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); } return true; } //============================================================================= //------------------------------iteration_split-------------------------------- bool IdealLoopTree::iteration_split( PhaseIdealLoop *phase, Node_List &old_new ) { // Recursively iteration split nested loops if (_child && !_child->iteration_split(phase, old_new)) return false; // Clean out prior deadwood DCE_loop_body(); // Look for loop-exit tests with my 50/50 guesses from the Parsing stage. // Replace with a 1-in-10 exit guess. if (_parent /*not the root loop*/ && !_irreducible && // Also ignore the occasional dead backedge !tail()->is_top()) { adjust_loop_exit_prob(phase); } // Gate unrolling, RCE and peeling efforts. if (!_child && // If not an inner loop, do not split !_irreducible && _allow_optimizations && !tail()->is_top()) { // Also ignore the occasional dead backedge if (!_has_call) { if (!iteration_split_impl(phase, old_new)) { return false; } } else if (policy_unswitching(phase)) { phase->do_unswitching(this, old_new); } } // Minor offset re-organization to remove loop-fallout uses of // trip counter when there was no major reshaping. phase->reorg_offsets(this); if (_next && !_next->iteration_split(phase, old_new)) return false; return true; } //============================================================================= // Process all the loops in the loop tree and replace any fill // patterns with an intrisc version. bool PhaseIdealLoop::do_intrinsify_fill() { bool changed = false; for (LoopTreeIterator iter(_ltree_root); !iter.done(); iter.next()) { IdealLoopTree* lpt = iter.current(); changed |= intrinsify_fill(lpt); } return changed; } // Examine an inner loop looking for a a single store of an invariant // value in a unit stride loop, bool PhaseIdealLoop::match_fill_loop(IdealLoopTree* lpt, Node*& store, Node*& store_value, Node*& shift, Node*& con) { const char* msg = NULL; Node* msg_node = NULL; store_value = NULL; con = NULL; shift = NULL; // Process the loop looking for stores. If there are multiple // stores or extra control flow give at this point. CountedLoopNode* head = lpt->_head->as_CountedLoop(); for (uint i = 0; msg == NULL && i < lpt->_body.size(); i++) { Node* n = lpt->_body.at(i); if (n->outcnt() == 0) continue; // Ignore dead if (n->is_Store()) { if (store != NULL) { msg = "multiple stores"; break; } int opc = n->Opcode(); if (opc == Op_StoreP || opc == Op_StoreN || opc == Op_StoreCM) { msg = "oop fills not handled"; break; } Node* value = n->in(MemNode::ValueIn); if (!lpt->is_invariant(value)) { msg = "variant store value"; } else if (!_igvn.type(n->in(MemNode::Address))->isa_aryptr()) { msg = "not array address"; } store = n; store_value = value; } else if (n->is_If() && n != head->loopexit()) { msg = "extra control flow"; msg_node = n; } } if (store == NULL) { // No store in loop return false; } if (msg == NULL && head->stride_con() != 1) { // could handle negative strides too if (head->stride_con() < 0) { msg = "negative stride"; } else { msg = "non-unit stride"; } } if (msg == NULL && !store->in(MemNode::Address)->is_AddP()) { msg = "can't handle store address"; msg_node = store->in(MemNode::Address); } if (msg == NULL && (!store->in(MemNode::Memory)->is_Phi() || store->in(MemNode::Memory)->in(LoopNode::LoopBackControl) != store)) { msg = "store memory isn't proper phi"; msg_node = store->in(MemNode::Memory); } // Make sure there is an appropriate fill routine BasicType t = store->as_Mem()->memory_type(); const char* fill_name; if (msg == NULL && StubRoutines::select_fill_function(t, false, fill_name) == NULL) { msg = "unsupported store"; msg_node = store; } if (msg != NULL) { #ifndef PRODUCT if (TraceOptimizeFill) { tty->print_cr("not fill intrinsic candidate: %s", msg); if (msg_node != NULL) msg_node->dump(); } #endif return false; } // Make sure the address expression can be handled. It should be // head->phi * elsize + con. head->phi might have a ConvI2L. Node* elements[4]; Node* conv = NULL; bool found_index = false; int count = store->in(MemNode::Address)->as_AddP()->unpack_offsets(elements, ARRAY_SIZE(elements)); for (int e = 0; e < count; e++) { Node* n = elements[e]; if (n->is_Con() && con == NULL) { con = n; } else if (n->Opcode() == Op_LShiftX && shift == NULL) { Node* value = n->in(1); #ifdef _LP64 if (value->Opcode() == Op_ConvI2L) { conv = value; value = value->in(1); } #endif if (value != head->phi()) { msg = "unhandled shift in address"; } else { if (type2aelembytes(store->as_Mem()->memory_type(), true) != (1 << n->in(2)->get_int())) { msg = "scale doesn't match"; } else { found_index = true; shift = n; } } } else if (n->Opcode() == Op_ConvI2L && conv == NULL) { if (n->in(1) == head->phi()) { found_index = true; conv = n; } else { msg = "unhandled input to ConvI2L"; } } else if (n == head->phi()) { // no shift, check below for allowed cases found_index = true; } else { msg = "unhandled node in address"; msg_node = n; } } if (count == -1) { msg = "malformed address expression"; msg_node = store; } if (!found_index) { msg = "missing use of index"; } // byte sized items won't have a shift if (msg == NULL && shift == NULL && t != T_BYTE && t != T_BOOLEAN) { msg = "can't find shift"; msg_node = store; } if (msg != NULL) { #ifndef PRODUCT if (TraceOptimizeFill) { tty->print_cr("not fill intrinsic: %s", msg); if (msg_node != NULL) msg_node->dump(); } #endif return false; } // No make sure all the other nodes in the loop can be handled VectorSet ok(Thread::current()->resource_area()); // store related values are ok ok.set(store->_idx); ok.set(store->in(MemNode::Memory)->_idx); // Loop structure is ok ok.set(head->_idx); ok.set(head->loopexit()->_idx); ok.set(head->phi()->_idx); ok.set(head->incr()->_idx); ok.set(head->loopexit()->cmp_node()->_idx); ok.set(head->loopexit()->in(1)->_idx); // Address elements are ok if (con) ok.set(con->_idx); if (shift) ok.set(shift->_idx); if (conv) ok.set(conv->_idx); for (uint i = 0; msg == NULL && i < lpt->_body.size(); i++) { Node* n = lpt->_body.at(i); if (n->outcnt() == 0) continue; // Ignore dead if (ok.test(n->_idx)) continue; // Backedge projection is ok if (n->is_IfTrue() && n->in(0) == head->loopexit()) continue; if (!n->is_AddP()) { msg = "unhandled node"; msg_node = n; break; } } // Make sure no unexpected values are used outside the loop for (uint i = 0; msg == NULL && i < lpt->_body.size(); i++) { Node* n = lpt->_body.at(i); // These values can be replaced with other nodes if they are used // outside the loop. if (n == store || n == head->loopexit() || n == head->incr() || n == store->in(MemNode::Memory)) continue; for (SimpleDUIterator iter(n); iter.has_next(); iter.next()) { Node* use = iter.get(); if (!lpt->_body.contains(use)) { msg = "node is used outside loop"; // lpt->_body.dump(); msg_node = n; break; } } } #ifdef ASSERT if (TraceOptimizeFill) { if (msg != NULL) { tty->print_cr("no fill intrinsic: %s", msg); if (msg_node != NULL) msg_node->dump(); } else { tty->print_cr("fill intrinsic for:"); } store->dump(); if (Verbose) { lpt->_body.dump(); } } #endif return msg == NULL; } bool PhaseIdealLoop::intrinsify_fill(IdealLoopTree* lpt) { // Only for counted inner loops if (!lpt->is_counted() || !lpt->is_inner()) { return false; } // Must have constant stride CountedLoopNode* head = lpt->_head->as_CountedLoop(); if (!head->is_valid_counted_loop() || !head->is_normal_loop()) { return false; } // Check that the body only contains a store of a loop invariant // value that is indexed by the loop phi. Node* store = NULL; Node* store_value = NULL; Node* shift = NULL; Node* offset = NULL; if (!match_fill_loop(lpt, store, store_value, shift, offset)) { return false; } #ifndef PRODUCT if (TraceLoopOpts) { tty->print("ArrayFill "); lpt->dump_head(); } #endif // Now replace the whole loop body by a call to a fill routine that // covers the same region as the loop. Node* base = store->in(MemNode::Address)->as_AddP()->in(AddPNode::Base); // Build an expression for the beginning of the copy region Node* index = head->init_trip(); #ifdef _LP64 index = new (C) ConvI2LNode(index); _igvn.register_new_node_with_optimizer(index); #endif if (shift != NULL) { // byte arrays don't require a shift but others do. index = new (C) LShiftXNode(index, shift->in(2)); _igvn.register_new_node_with_optimizer(index); } index = new (C) AddPNode(base, base, index); _igvn.register_new_node_with_optimizer(index); Node* from = new (C) AddPNode(base, index, offset); _igvn.register_new_node_with_optimizer(from); // Compute the number of elements to copy Node* len = new (C) SubINode(head->limit(), head->init_trip()); _igvn.register_new_node_with_optimizer(len); BasicType t = store->as_Mem()->memory_type(); bool aligned = false; if (offset != NULL && head->init_trip()->is_Con()) { int element_size = type2aelembytes(t); aligned = (offset->find_intptr_t_type()->get_con() + head->init_trip()->get_int() * element_size) % HeapWordSize == 0; } // Build a call to the fill routine const char* fill_name; address fill = StubRoutines::select_fill_function(t, aligned, fill_name); assert(fill != NULL, "what?"); // Convert float/double to int/long for fill routines if (t == T_FLOAT) { store_value = new (C) MoveF2INode(store_value); _igvn.register_new_node_with_optimizer(store_value); } else if (t == T_DOUBLE) { store_value = new (C) MoveD2LNode(store_value); _igvn.register_new_node_with_optimizer(store_value); } Node* mem_phi = store->in(MemNode::Memory); Node* result_ctrl; Node* result_mem; const TypeFunc* call_type = OptoRuntime::array_fill_Type(); CallLeafNode *call = new (C) CallLeafNoFPNode(call_type, fill, fill_name, TypeAryPtr::get_array_body_type(t)); call->init_req(TypeFunc::Parms+0, from); call->init_req(TypeFunc::Parms+1, store_value); #ifdef _LP64 len = new (C) ConvI2LNode(len); _igvn.register_new_node_with_optimizer(len); #endif call->init_req(TypeFunc::Parms+2, len); #ifdef _LP64 call->init_req(TypeFunc::Parms+3, C->top()); #endif call->init_req( TypeFunc::Control, head->init_control()); call->init_req( TypeFunc::I_O , C->top() ) ; // does no i/o call->init_req( TypeFunc::Memory , mem_phi->in(LoopNode::EntryControl) ); call->init_req( TypeFunc::ReturnAdr, C->start()->proj_out(TypeFunc::ReturnAdr) ); call->init_req( TypeFunc::FramePtr, C->start()->proj_out(TypeFunc::FramePtr) ); _igvn.register_new_node_with_optimizer(call); result_ctrl = new (C) ProjNode(call,TypeFunc::Control); _igvn.register_new_node_with_optimizer(result_ctrl); result_mem = new (C) ProjNode(call,TypeFunc::Memory); _igvn.register_new_node_with_optimizer(result_mem); // If this fill is tightly coupled to an allocation and overwrites // the whole body, allow it to take over the zeroing. AllocateNode* alloc = AllocateNode::Ideal_allocation(base, this); if (alloc != NULL && alloc->is_AllocateArray()) { Node* length = alloc->as_AllocateArray()->Ideal_length(); if (head->limit() == length && head->init_trip() == _igvn.intcon(0)) { if (TraceOptimizeFill) { tty->print_cr("Eliminated zeroing in allocation"); } alloc->maybe_set_complete(&_igvn); } else { #ifdef ASSERT if (TraceOptimizeFill) { tty->print_cr("filling array but bounds don't match"); alloc->dump(); head->init_trip()->dump(); head->limit()->dump(); length->dump(); } #endif } } // Redirect the old control and memory edges that are outside the loop. Node* exit = head->loopexit()->proj_out(0); // Sometimes the memory phi of the head is used as the outgoing // state of the loop. It's safe in this case to replace it with the // result_mem. _igvn.replace_node(store->in(MemNode::Memory), result_mem); _igvn.replace_node(exit, result_ctrl); _igvn.replace_node(store, result_mem); // Any uses the increment outside of the loop become the loop limit. _igvn.replace_node(head->incr(), head->limit()); // Disconnect the head from the loop. for (uint i = 0; i < lpt->_body.size(); i++) { Node* n = lpt->_body.at(i); _igvn.replace_node(n, C->top()); } return true; }