compiler/debug/TestStressCM.java failed with "RuntimeException: got the same optimization stats for different seeds: expected 45"

The following test failed in the JDK16 CI:

compiler/debug/TestStressCM.java

Here's a snippet from the log file:

----------System.err:(47/2272)----------
java.lang.RuntimeException: got the same optimization stats for different seeds: expected 45
--- Compiler Statistics ---
Methods seen: 1 Methods parsed: 1 Nodes created: 1979
Blocks parsed: 5 Blocks seen: 5
0 made implicit ( 0%)
CCP: 1 constants found: 0
Total frameslots = 0, Max frameslots = 0
Inserted 0 spill loads, 0 spill stores, 0 mem-mem moves and 0 copies.
Total load cost= 0, store cost = 0, mem-mem cost = 0.00, copy cost = 0.
Adjusted spill cost = 0.
Conservatively coalesced 37 copies, 0 pairs, 0 post alloc.
Average allocation trips 1.000000
High Pressure Blocks = 29, Low Pressure Blocks = 103
Nops added 0 bytes to total of 1936 bytes, for 0.00%
Peephole: peephole rules applied: 0
PhaseIdealLoop=7, sum _unique=1744
 to not equal 45
--- Compiler Statistics ---
Methods seen: 1 Methods parsed: 1 Nodes created: 1979
Blocks parsed: 5 Blocks seen: 5
0 made implicit ( 0%)
CCP: 1 constants found: 0
Total frameslots = 0, Max frameslots = 0
Inserted 0 spill loads, 0 spill stores, 0 mem-mem moves and 0 copies.
Total load cost= 0, store cost = 0, mem-mem cost = 0.00, copy cost = 0.
Adjusted spill cost = 0.
Conservatively coalesced 37 copies, 0 pairs, 0 post alloc.
Average allocation trips 1.000000
High Pressure Blocks = 29, Low Pressure Blocks = 103
Nops added 0 bytes to total of 1936 bytes, for 0.00%
Peephole: peephole rules applied: 0
PhaseIdealLoop=7, sum _unique=1744

at jdk.test.lib.Asserts.fail(Asserts.java:594)
at jdk.test.lib.Asserts.assertNotEquals(Asserts.java:394)
at jdk.test.lib.Asserts.assertNE(Asserts.java:367)
at compiler.debug.TestStressCM.main(TestStressCM.java:70)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:64)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:564)
at com.sun.javatest.regtest.agent.MainActionHelper$AgentVMRunnable.run(MainActionHelper.java:298)
at java.base/java.lang.Thread.run(Thread.java:832)

JavaTest Message: Test threw exception: java.lang.RuntimeException
JavaTest Message: shutting down test

Normally a Tier2 failure would start out at P3, but this test
failure appears to be generating two sightings on linux-aarch64
per Tier2 job set starting with jdk-16+20-1053-tier2. That's a bit
noisy so I'm starting this bug off as a P2.