I noticed that attached JavaFuzzer generated test runs significantly longer with -Xcomp due to an increase in compilation time with C2.

Command line:
java -Xmx1G -Xcomp -Xbatch -XX:CompileOnly=Test -XX:MaxRAMPercentage=4.16667 Test

JDK 16
real 0m0,383s
user 0m0,326s
sys 0m0,029s

JDK 17+23 (contains JDK-8252372)
real 0m0,483s
user 0m0,421s
sys 0m0,032s

JDK 17+35
real 0m4,388s
user 0m4,310s
sys 0m0,056s

JDK 18 and later
real 0m10,312s
user 0m10,116s
sys 0m0,140s

With 5s test timeout it fails since JDK-8267988 in JDK 17 b27.
With 8s test timeout it fails since JDK-8272873 in JDK 18 b13.

We seem to spend most time in here:

#0 0x00007ffff70d9608 in Unique_Node_List::remove (n=<optimized out>, this=<optimized out>) at /oracle/valhalla/open/src/hotspot/share/opto/node.hpp:1590
#1 Unique_Node_List::remove (this=0x7fffac2ede30, n=0x7fffae517ae0) at /oracle/valhalla/open/src/hotspot/share/opto/node.cpp:2944
#2 0x00007ffff64ea758 in Compile::remove_modified_node (n=0x7fffae517ae0, this=0x7fffd47d4a30) at /oracle/valhalla/open/src/hotspot/share/opto/compile.cpp:1237
#3 Compile::remove_useless_node (this=0x7fffd47d4a30, dead=0x7fffae517ae0) at /oracle/valhalla/open/src/hotspot/share/opto/compile.cpp:374
#4 0x00007ffff71e9ceb in PhaseIterGVN::remove_globally_dead_node (this=this@entry=0x7fffd47d23f0, dead=dead@entry=0x7fffae517ae0) at /oracle/valhalla/open/src/hotspot/share/opto/phaseX.cpp:1442
#5 0x00007ffff71eae1e in PhaseIterGVN::remove_dead_node (dead=0x7fffae517ae0, this=0x7fffd47d23f0) at /oracle/valhalla/open/src/hotspot/share/opto/phaseX.hpp:507
#6 PhaseIterGVN::subsume_node (this=0x7fffd47d23f0, old=0x7fffae517ae0, nn=0x7fffaea5fae0) at /oracle/valhalla/open/src/hotspot/share/opto/phaseX.cpp:1491
#7 0x00007ffff6ee8878 in PhaseIdealLoop::try_sink_out_of_loop (n=<optimized out>, this=0x7fffd47d1720) at /oracle/valhalla/open/src/hotspot/share/opto/loopopts.cpp:1821
#8 PhaseIdealLoop::try_sink_out_of_loop (this=0x7fffd47d1720, n=<optimized out>) at /oracle/valhalla/open/src/hotspot/share/opto/loopopts.cpp:1763
#9 0x00007ffff6ee8ad5 in PhaseIdealLoop::split_if_with_blocks_post (this=0x7fffd47d1720, n=<optimized out>) at /oracle/valhalla/open/src/hotspot/share/opto/loopopts.cpp:1618
#10 0x00007ffff6ee9eb4 in PhaseIdealLoop::split_if_with_blocks_post (n=0x7fffac383d08, this=0x7fffd47d1720) at /oracle/valhalla/open/src/hotspot/share/opto/loopopts.cpp:2001
#11 PhaseIdealLoop::split_if_with_blocks (this=this@entry=0x7fffd47d1720, visited=..., nstack=...) at /oracle/valhalla/open/src/hotspot/share/opto/loopopts.cpp:2001
#12 0x00007ffff6eda5cf in PhaseIdealLoop::build_and_optimize (this=this@entry=0x7fffd47d1720) at /oracle/valhalla/open/src/hotspot/share/opto/loopnode.cpp:4517
#13 0x00007ffff650d674 in PhaseIdealLoop::PhaseIdealLoop (mode=LoopOptsDefault, igvn=..., this=0x7fffd47d1720) at /oracle/valhalla/open/src/hotspot/share/opto/loopnode.hpp:1101

Running with -XX:-SplitIfBlocks or explicitly disabling PhaseIdealLoop::try_sink_out_of_loop brings back old speed.

This also shows with -XX:+CITime:

JDK 16:
Accumulated compiler times
----------------------------------------------------------
  Total compilation time : 0,293 s

JDK 21:
Accumulated compiler times
----------------------------------------------------------
  Total compilation time : 9,049 s