ADDITIONAL SYSTEM INFORMATION :
# JRE version: OpenJDK Runtime Environment (8.0_392) (build 1.8.0_392-internal-fastdebug--b00)
# Java VM: OpenJDK 64-Bit Server VM (25.392-b00-fastdebug compiled mode linux-amd64 compressed oops)

A DESCRIPTION OF THE PROBLEM :
I ran a modified regression testcase on JDK8u392 and found that the JVM crashed with -Xcomp -XX:-TieredCompilation options.

#
# A fatal error has been detected by the Java Runtime Environment:
#
# Internal Error (/data//jdk8u/hotspot/src/share/vm/opto/node.hpp:792), pid=84055, tid=0x00007f9f7a252700
# assert(is_Loop()) failed: invalid node class
#
# JRE version: OpenJDK Runtime Environment (8.0_392) (build 1.8.0_392-internal-fastdebug--b00)
# Java VM: OpenJDK 64-Bit Server VM (25.392-b00-fastdebug compiled mode linux-amd64 compressed oops)
# Failed to write core dump. Core dumps have been disabled. To enable core dumping, try "ulimit -c unlimited" before starting Java again
#
# If you would like to submit a bug report, please visit:
# http://bugreport.java.com/bugreport/crash.jsp
#

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
java -Xcomp -XX:-TieredCompilation compiler.loopopts.TestIterationSplitWithRegionHead

ACTUAL -
# To suppress the following error report, specify this argument
# after -XX: or in .hotspotrc: SuppressErrorAt=/node.hpp:792
#
# A fatal error has been detected by the Java Runtime Environment:
#
# Internal Error (/data//jdk8u/hotspot/src/share/vm/opto/node.hpp:792), pid=84055, tid=0x00007f9f7a252700
# assert(is_Loop()) failed: invalid node class
#
# JRE version: OpenJDK Runtime Environment (8.0_392) (build 1.8.0_392-internal-fastdebug--b00)
# Java VM: OpenJDK 64-Bit Server VM (25.392-b00-fastdebug compiled mode linux-amd64 compressed oops)
# Failed to write core dump. Core dumps have been disabled. To enable core dumping, try "ulimit -c unlimited" before starting Java again
#
# An error report file with more information is saved as:
# /home//repository//toreport/TestIterationSplitWithRegionHead_09_24_02_02_31/hs_err_pid84055.log
#
# Compiler replay data is saved as:
# /home//repository//toreport/TestIterationSplitWithRegionHead_09_24_02_02_31/replay_pid84055.log
#
# If you would like to submit a bug report, please visit:
# http://bugreport.java.com/bugreport/crash.jsp
#

---------- BEGIN SOURCE ----------
package compiler.loopopts;

public class TestIterationSplitWithRegionHead {

    static boolean flagFalse = false;

    public static void main(String[] args) {

// modified code
try {
Class <?> Class0 = Class.forName("compiler.loopopts.TestIterationSplitWithRegionHead");
Class0.getDeclaredMethod("test").invoke(null);
}catch (Exception eeeeeeee){throw new RuntimeException(eeeeeeee);}
// test();

    }

    public static void test() {
        // 1) The loop tree is built. We find that nested loop N2 is an infinite loop and add a NeverBranch
        // to the inner loop to make it reachable. But the current loop tree does not have N2, yet. The
        // resulting loop tree is:
        //
        // Loop: N0/N0 has_call has_sfpt
        // Loop: N77/N121 has_call // N1 outer
        // Loop: N77/N111 has_call sfpts={ 111 97 } // N1 inner
        //
        // 2) beautify_loops() finds that the outer loop head of N1 is shared and thus adds a new region
        // in merge_many_backedges(). As a result, the loop tree is built again. This time, the NeverBranch
        // in the inner loop of N2 allows that a loop tree can be built for it:
        //
        // Loop: N0/N0 has_call has_sfpt
        // Loop: N216/N213 limit_check profile_predicated predicated has_call sfpts={ 111 97 } // N1 shared loop head
        // Loop: N196/N201 sfpts={ 201 } // N2 inner loop now discovered with the new NeverBranch
        //
        // However, a LoopNode is only added by beautify_loops() which won't be called until the next iteration of loop opts.
        // This means that we have a Region node (N196) as head in the loop tree which cannot be handled by iteration_split_impl()
        // resulting in an assertion failure.

        // Nested loop N1
        while (flagFalse) {
            while (dontInlineFalse()) {
            }
        }
        dontInlineFalse();

        // Nested loop N2
        while (flagFalse) {
            while (true) ; // Detected as infinite inner loop by C2 -> NeverBranch added
        }
    }

    public static boolean dontInlineFalse() {
        return false;
    }
}

---------- END SOURCE ----------

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