8297642: PhaseIdealLoop::only_has_infinite_loops must detect all loops that never lead to termination
Reviewed-by: thartmann, roland
This commit is contained in:
Emanuel Peter
parent
fc52f21f9a
commit
d562d3fcbe
@ -4190,45 +4190,40 @@ bool PhaseIdealLoop::process_expensive_nodes() {
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}
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#ifdef ASSERT
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// Goes over all children of the root of the loop tree, collects all controls for the loop and its inner loops then
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// checks whether any control is a branch out of the loop and if it is, whether it's not a NeverBranch.
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// Goes over all children of the root of the loop tree. Check if any of them have a path
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// down to Root, that does not go via a NeverBranch exit.
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bool PhaseIdealLoop::only_has_infinite_loops() {
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ResourceMark rm;
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Unique_Node_List worklist;
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// start traversal at all loop heads of first-level loops
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for (IdealLoopTree* l = _ltree_root->_child; l != NULL; l = l->_next) {
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Unique_Node_List wq;
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Node* head = l->_head;
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assert(head->is_Region(), "");
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for (uint i = 1; i < head->req(); ++i) {
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Node* in = head->in(i);
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if (get_loop(in) != _ltree_root) {
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wq.push(in);
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worklist.push(head);
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}
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}
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for (uint i = 0; i < wq.size(); ++i) {
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Node* c = wq.at(i);
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if (c == head) {
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continue;
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} else if (c->is_Region()) {
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for (uint j = 1; j < c->req(); ++j) {
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wq.push(c->in(j));
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}
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} else {
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wq.push(c->in(0));
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}
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}
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assert(wq.member(head), "");
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for (uint i = 0; i < wq.size(); ++i) {
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Node* c = wq.at(i);
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if (c->is_MultiBranch()) {
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for (DUIterator_Fast jmax, j = c->fast_outs(jmax); j < jmax; j++) {
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Node* u = c->fast_out(j);
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assert(u->is_CFG(), "");
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if (!wq.member(u) && c->Opcode() != Op_NeverBranch) {
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// BFS traversal down the CFG, except through NeverBranch exits
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for (uint i = 0; i < worklist.size(); ++i) {
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Node* n = worklist.at(i);
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assert(n->is_CFG(), "only traverse CFG");
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if (n->is_Root()) {
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// Found root -> there was an exit!
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return false;
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} else if (n->Opcode() == Op_NeverBranch) {
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// Only follow the loop-internal projection, not the NeverBranch exit
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ProjNode* proj = n->as_Multi()->proj_out_or_null(0);
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assert(proj != nullptr, "must find loop-internal projection of NeverBranch");
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worklist.push(proj);
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} else {
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// Traverse all CFG outputs
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for (DUIterator_Fast imax, i = n->fast_outs(imax); i < imax; i++) {
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Node* use = n->fast_out(i);
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if (use->is_CFG()) {
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worklist.push(use);
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}
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}
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}
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}
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}
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// No exit found for any loop -> all are infinite
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return true;
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}
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#endif
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@ -0,0 +1,96 @@
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/*
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* Copyright (c) 2022, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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super public class TestOnlyInfiniteLoops
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{
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public Method "<init>":"()V"
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stack 2 locals 1
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{
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aload_0;
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invokespecial Method java/lang/Object."<init>":"()V";
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return;
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}
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static Method test_simple:"(III)I"
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stack 200 locals 10
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{
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// Nested infinite loop, where inner loop eventually
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// looses exit to outer loop. Then, the inner loop
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// floats outside the inner loop. The entry from
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// outer to inner loop now becomes an exit for the
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// outer loop, where it now enters the next loop, that
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// used to be the inner loop.
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iconst_0;
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istore 9;
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iload 0;
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ifeq LEND; // skip
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LOOP1:
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iload 1;
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ifeq LOOP1; // dominates
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LOOP2:
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// SKIP: prevent loop-exit from becoming zero-trip guard
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iload 2;
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ifeq SKIP;
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iinc 9, 1;
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SKIP:
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iload 1;
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ifeq LOOP1; // is dominated
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goto LOOP2;
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LEND:
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iload 9;
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ireturn;
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}
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static Method test_irreducible:"(IIII)V"
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stack 200 locals 200
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{
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iload_0;
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ifeq LEND; // skip
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L1:
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iload 1;
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ifgt MERGE;
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L2:
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iload 2;
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ifge MERGE;
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goto L1;
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MERGE:
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nop;
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LOOP:
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iload 3;
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ifle L2;
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iconst_0; // always true
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ifeq LOOP;
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iconst_0; // always true
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ifeq LOOP;
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INFTY:
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goto INFTY; // infinite loop
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LEND:
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return;
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}
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}
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@ -0,0 +1,53 @@
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/*
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* Copyright (c) 2022, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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/*
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* @test
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* @bug 8297642
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* @compile TestOnlyInfiniteLoops.jasm
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* @summary Nested irreducible loops, where the inner loop floats out of the outer
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* @run main/othervm
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* -XX:CompileCommand=compileonly,TestOnlyInfiniteLoops::test*
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* -XX:-TieredCompilation -Xcomp
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* TestOnlyInfiniteLoopsMain
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*
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* @test
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* @bug 8297642
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* @compile TestOnlyInfiniteLoops.jasm
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* @summary Nested irreducible loops, where the inner loop floats out of the outer
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* @run main/othervm
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* -XX:CompileCommand=compileonly,TestOnlyInfiniteLoops::test*
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* -XX:-TieredCompilation -Xcomp
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* -XX:PerMethodTrapLimit=0
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* TestOnlyInfiniteLoopsMain
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*/
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public class TestOnlyInfiniteLoopsMain {
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public static void main(String[] args) {
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TestOnlyInfiniteLoops t = new TestOnlyInfiniteLoops();
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System.out.println("test_simple");
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t.test_simple(0, 0, 0);
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System.out.println("test_irreducible");
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t.test_irreducible(0, 0, 0, 0);
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}
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}
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