Initial bisection points at JDK-8343148.

Reliably reproduces like this on current tip:

$ export JAVA_HOME=<point to fastdebug build>
$ export PATH=$JAVA_HOME/bin:$PATH
$ cd test/hotspot/jtreg/testlibrary/ctw
$ make
$ cd dist
$ wget https://repo1.maven.org/maven2/edu/gmu/cs/ecj/20.0/ecj-20.0.jar
$ ./ctw.sh ecj-20.0.jar

# A fatal error has been detected by the Java Runtime Environment:
#
# Internal Error (/home/shipilev/shipilev-jdk/src/hotspot/share/opto/loopnode.hpp:1003), pid=35182, tid=35202
# Error: assert(has_node(i)) failed
#
# JRE version: OpenJDK Runtime Environment (25.0) (fastdebug build 25-internal-adhoc.shipilev.shipilev-jdk)
# Java VM: OpenJDK 64-Bit Server VM (fastdebug 25-internal-adhoc.shipilev.shipilev-jdk, mixed mode, sharing, tiered, compressed oops, compressed class ptrs, g1 gc, linux-amd64)
# Problematic frame:
# V [libjvm.so+0x11e719e] PhaseIdealLoop::get_ctrl(Node const*)+0x24e

Current CompileTask:
C2:4883 7338 b 4 ec.gp.koza.KozaShortStatistics::_postEvaluationStatistics (1475 bytes)

Stack: [0x00007f900ee4e000,0x00007f900ef4f000], sp=0x00007f900ef49d60, free space=1007k
Native frames: (J=compiled Java code, j=interpreted, Vv=VM code, C=native code)
V [libjvm.so+0x11e719e] PhaseIdealLoop::get_ctrl(Node const*)+0x24e (loopnode.hpp:1003)
V [libjvm.so+0x1224e9b] PhaseIdealLoop::split_thru_phi(Node*, Node*, int)+0x46b (loopopts.cpp:192)
V [libjvm.so+0x1229438] PhaseIdealLoop::split_if_with_blocks_pre(Node*)+0x258 (loopopts.cpp:1226)
V [libjvm.so+0x122e520] PhaseIdealLoop::split_if_with_blocks(VectorSet&, Node_Stack&)+0x100 (loopopts.cpp:1982)
V [libjvm.so+0x1221458] PhaseIdealLoop::build_and_optimize()+0x10c8 (loopnode.cpp:4889)
V [libjvm.so+0xa06d84] PhaseIdealLoop::optimize(PhaseIterGVN&, LoopOptsMode)+0x344 (loopnode.hpp:1113)
V [libjvm.so+0xa006e9] Compile::optimize_loops(PhaseIterGVN&, LoopOptsMode) [clone .part.486]+0x89 (compile.cpp:2183)
V [libjvm.so+0xa0308b] Compile::Optimize()+0x114b (compile.hpp:831)
V [libjvm.so+0xa05079] Compile::Compile(ciEnv*, ciMethod*, int, Options, DirectiveSet*)+0x1ae9 (compile.cpp:852)
V [libjvm.so+0x86b5b5] C2Compiler::compile_method(ciEnv*, ciMethod*, int, bool, DirectiveSet*)+0x305 (c2compiler.cpp:142)
V [libjvm.so+0xa0eb3b] CompileBroker::invoke_compiler_on_method(CompileTask*)+0x49b (compileBroker.cpp:2319)
V [libjvm.so+0xa0fa17] CompileBroker::compiler_thread_loop()+0x307 (compileBroker.cpp:1977)
V [libjvm.so+0xe6d167] JavaThread::thread_main_inner()+0x1b7 (javaThread.cpp:777)
V [libjvm.so+0x18ad09e] Thread::call_run()+0x13e (thread.cpp:232)
V [libjvm.so+0x1413e40] thread_native_entry(Thread*)+0x120 (os_linux.cpp:860)