8266542: Remove broken -XX:-UseLoopSafepoints flag

Reviewed-by: tschatzl, kvn

src/hotspot/share/opto/parse.hpp

@@ -480,7 +480,7 @@ class Parse : public GraphKit {
 
   // Insert a compiler safepoint into the graph, if there is a back-branch.
   void maybe_add_safepoint(int target_bci) {
-    if (UseLoopSafepoints && target_bci <= bci()) {
+    if (target_bci <= bci()) {
       add_safepoint();
     }
   }

src/hotspot/share/opto/parse2.cpp

@@ -485,7 +485,7 @@ void Parse::do_tableswitch() {
   }
 
   // Safepoint in case if backward branch observed
-  if (makes_backward_branch && UseLoopSafepoints) {
+  if (makes_backward_branch) {
     add_safepoint();
   }
 
@@ -579,7 +579,7 @@ void Parse::do_lookupswitch() {
   }
 
   // Safepoint in case backward branch observed
-  if (makes_backward_branch && UseLoopSafepoints) {
+  if (makes_backward_branch) {
     add_safepoint();
   }
 
@@ -2555,8 +2555,7 @@ void Parse::do_one_bytecode() {
     // a SafePoint here and have it dominate and kill the safepoint added at a
     // following backwards branch.  At this point the JVM state merely holds 2
     // longs but not the 3-way value.
-    if( UseLoopSafepoints ) {
-      switch( iter().next_bc() ) {
+    switch (iter().next_bc()) {
       case Bytecodes::_ifgt:
       case Bytecodes::_iflt:
       case Bytecodes::_ifge:
@@ -2567,7 +2566,6 @@ void Parse::do_one_bytecode() {
         maybe_add_safepoint(iter().next_get_dest());
       default:
         break;
-      }
     }
     b = pop_pair();
     a = pop_pair();

src/hotspot/share/opto/phaseX.cpp

@@ -407,10 +407,11 @@ void NodeHash::operator=(const NodeHash& nh) {
 //------------------------------PhaseRemoveUseless-----------------------------
 // 1) Use a breadthfirst walk to collect useful nodes reachable from root.
 PhaseRemoveUseless::PhaseRemoveUseless(PhaseGVN* gvn, Unique_Node_List* worklist, PhaseNumber phase_num) : Phase(phase_num) {
-
-  // Implementation requires 'UseLoopSafepoints == true' and an edge from root
-  // to each SafePointNode at a backward branch.  Inserted in add_safepoint().
-  if( !UseLoopSafepoints || !OptoRemoveUseless ) return;
+  // Implementation requires an edge from root to each SafePointNode
+  // at a backward branch. Inserted in add_safepoint().
+  if (!OptoRemoveUseless) {
+    return;
+  }
 
   // Identify nodes that are reachable from below, useful.
   C->identify_useful_nodes(_useful);
@@ -993,8 +994,7 @@ PhaseIterGVN::PhaseIterGVN(PhaseGVN* gvn) : PhaseGVN(gvn),
     if(n != NULL && n != _table.sentinel() && n->outcnt() == 0) {
       if( n->is_top() ) continue;
       // If remove_useless_nodes() has run, we expect no such nodes left.
-      assert(!UseLoopSafepoints || !OptoRemoveUseless,
-             "remove_useless_nodes missed this node");
+      assert(!OptoRemoveUseless, "remove_useless_nodes missed this node");
       hash_delete(n);
     }
   }

src/hotspot/share/runtime/globals.hpp

@@ -1146,9 +1146,6 @@ const intx ObjectAlignmentInBytes = 8;
   notproduct(bool, CollectIndexSetStatistics, false,                        \
           "Collect information about IndexSets")                            \
                                                                             \
-  develop(bool, UseLoopSafepoints, true,                                    \
-          "Generate Safepoint nodes in every loop")                         \
-                                                                            \
   develop(intx, FastAllocateSizeLimit, 128*K,                               \
           /* Note:  This value is zero mod 1<<13 for a cheap sparc set. */  \
           "Inline allocations larger than this in doublewords must go slow")\

test/hotspot/jtreg/compiler/arguments/TestDisableUseLoopSafepoints.java

@@ -1,41 +0,0 @@
-/*
- * Copyright (c) 2020, 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.
- */
-
-/**
- * @test
- * @bug 6232281
- * @requires vm.debug == true & vm.compiler2.enabled
- * @summary Tests that C2 does not crash trivially with a "remove_useless_nodes
- *          missed this node" message when UseLoopSafepoints is disabled.
- * @run main/othervm -Xcomp -XX:-TieredCompilation
-        -XX:CompileOnly=TestDisableUseLoopSafepoints -XX:-UseLoopSafepoints
- *      compiler.arguments.TestDisableUseLoopSafepoints
- */
-
-package compiler.arguments;
-
-public class TestDisableUseLoopSafepoints {
-    public static void main(String[] args) {
-        System.out.println("Passed");
-    }
-}