The following test failed in the JDK26 CI:

compiler/intrinsics/TestVerifyIntrinsicChecks.java

Here's a snippet from the log file:

#section:main
----------messages:(9/424)----------
command: main compiler.intrinsics.TestVerifyIntrinsicChecks verify
reason: User specified action: run main/othervm compiler.intrinsics.TestVerifyIntrinsicChecks verify
started: Thu Sep 18 16:43:43 GMT 2025
Mode: othervm [/othervm specified, test or library overrides a system module]
Process id: 61674
Timeout information:
--- Timeout information end.
finished: Thu Sep 18 16:50:27 GMT 2025
elapsed time (seconds): 403.733
----------configuration:(3/417)----------

<snip>

----------System.out:(7/2710)----------
2025-09-18T16:43:44.882415Z [MainThread] Starting JVM in a separate process to verify the crash
Command line: [/System/Volumes/Data/mesos/work_dir/jib-master/install/jdk-26+16-1655/macosx-x64-debug.jdk/jdk-26/fastdebug/bin/java -cp /System/Volumes/Data/mesos/work_dir/slaves/f7f8bd65-a387-4a2b-b519-702f2fefaf87-S168285/frameworks/1735e8a2-a1db-478c-8104-60c8b0af87dd-0196/executors/5f6eb4d3-0f51-4817-b5a6-7a459704175b/runs/3b729fd4-a9f0-4a5a-9063-303118d15337/testoutput/test-support/jtreg_open_test_hotspot_jtreg_tier1_compiler_3/classes/3/compiler/intrinsics/TestVerifyIntrinsicChecks.d:/System/Volumes/Data/mesos/work_dir/jib-master/install/jdk-26+16-1655/src.full/open/test/hotspot/jtreg/compiler/intrinsics:/System/Volumes/Data/mesos/work_dir/slaves/f7f8bd65-a387-4a2b-b519-702f2fefaf87-S168285/frameworks/1735e8a2-a1db-478c-8104-60c8b0af87dd-0196/executors/5f6eb4d3-0f51-4817-b5a6-7a459704175b/runs/3b729fd4-a9f0-4a5a-9063-303118d15337/testoutput/test-support/jtreg_open_test_hotspot_jtreg_tier1_compiler_3/classes/3/compiler/intrinsics/TestVerifyIntrinsicChecks.d/test/lib:/System/Volumes/Data/mesos/work_dir/jib-master/install/jdk-26+16-1655/src.full/open/test/lib:/System/Volumes/Data/mesos/work_dir/jib-master/install/jtreg/8/2/bundles/jtreg-8+2.zip/jtreg/lib/jtreg.jar -XX:MaxRAMPercentage=4.16667 -Dtest.boot.jdk=/System/Volumes/Data/mesos/work_dir/jib-master/install/jdk/24/36/bundles/macos-x64/jdk-24_macos-x64_bin.tar.gz/jdk-24.jdk/Contents/Home -Djava.io.tmpdir=/System/Volumes/Data/mesos/work_dir/slaves/f7f8bd65-a387-4a2b-b519-702f2fefaf87-S168285/frameworks/1735e8a2-a1db-478c-8104-60c8b0af87dd-0196/executors/5f6eb4d3-0f51-4817-b5a6-7a459704175b/runs/3b729fd4-a9f0-4a5a-9063-303118d15337/testoutput/test-support/jtreg_open_test_hotspot_jtreg_tier1_compiler_3/tmp -Xcomp -XX:-TieredCompilation -XX:CompileCommand=inline,java.lang.StringCoding::encodeAsciiArray0 -XX:+VerifyIntrinsicChecks --patch-module java.base=/System/Volumes/Data/mesos/work_dir/slaves/f7f8bd65-a387-4a2b-b519-702f2fefaf87-S168285/frameworks/1735e8a2-a1db-478c-8104-60c8b0af87dd-0196/executors/5f6eb4d3-0f51-4817-b5a6-7a459704175b/runs/3b729fd4-a9f0-4a5a-9063-303118d15337/testoutput/test-support/jtreg_open_test_hotspot_jtreg_tier1_compiler_3/classes/3/compiler/intrinsics/TestVerifyIntrinsicChecks.d/compiler/patches/java.base compiler.intrinsics.TestVerifyIntrinsicChecks crash ]
[2025-09-18T16:43:45.483032Z] Gathering output for process 61675
[2025-09-18T16:43:45.564438Z] Waiting for completion for process 61675
Timeout signalled after 120 seconds
[2025-09-18T16:45:46.835934Z] Waiting for completion finished for process 61675
Output and diagnostic info for process 61675 was saved into 'pid-61675-output.log'
----------System.err:(1/15)----------
STATUS:Passed.
----------rerun:(37/8683)*----------

<snip>

result: Error. Program `/System/Volumes/Data/mesos/work_dir/jib-master/install/jdk-26+16-1655/macosx-x64-debug.jdk/jdk-26/fastdebug/bin/java' timed out (timeout set to 120000ms, elapsed time including timeout handling was 403611ms).


test result: Error. Program `/System/Volumes/Data/mesos/work_dir/jib-master/install/jdk-26+16-1655/macosx-x64-debug.jdk/jdk-26/fastdebug/bin/java' timed out (timeout set to 120000ms, elapsed time including timeout handling was 403611ms).

Here's snippets from the hs_err_pid file:

# Internal Error (/System/Volumes/Data/mesos/work_dir/slaves/f7f8bd65-a387-4a2b-b519-702f2fefaf87-S168272/frameworks/1735e8a2-a1db-478c-8104-60c8b0af87dd-0196/executors/ca3eb868-c85a-4ee0-bb6a-36d5d1d78d50/runs/b6135b37-292e-4102-93c7-dcff927aa20d/workspace/open/src/hotspot/cpu/x86/macroAssembler_x86.cpp:442), pid=61675, tid=8963
# fatal error: DEBUG MESSAGE: unexpected null in intrinsic
#
# JRE version: Java(TM) SE Runtime Environment (26.0+16) (fastdebug build 26-ea+16-1655)
# Java VM: Java HotSpot(TM) 64-Bit Server VM (fastdebug 26-ea+16-1655, compiled mode, compressed oops, compressed class ptrs, g1 gc, bsd-amd64)
# Core dump will be written. Default location: core.61675

<snip>

--------------- T H R E A D ---------------

Current thread (0x00007fd448008e10): JavaThread "main" [_thread_in_Java, id=8963, stack(0x0000700005f10000,0x0000700006010000) (1024K)]

Stack: [0x0000700005f10000,0x0000700006010000], sp=0x000070000600f7c0, free space=1021k
Native frames: (J=compiled Java code, j=interpreted, Vv=VM code, C=native code)
V [libjvm.dylib+0x140fe44] VMError::report(outputStream*, bool)+0x1f14 (macroAssembler_x86.cpp:442)
V [libjvm.dylib+0x1413e0b] VMError::report_and_die(int, char const*, char const*, __va_list_tag*, Thread*, unsigned char*, void const*, void const*, char const*, int, unsigned long)+0x60b
V [libjvm.dylib+0x733ecb] report_fatal(VMErrorType, char const*, int, char const*, ...)+0xdb
V [libjvm.dylib+0xedb762] MacroAssembler::debug64(char*, long long, long long*)+0x42
Lock stack of current Java thread (top to bottom):

So we have an hs_err_pid file which shows a crash, BUT the
test PASSed while the timeout handler is running.

We have two problems here:

1) fatal error: DEBUG MESSAGE: unexpected null in intrinsic
2) the test is NOT detecting failure properly

Since this is a Tier1 failure, I'm starting this issue of as a P2.