CodeHeap::verify fails extra_hops assertion in fastdebug test

When test with -XX:+VerifyCodeCache, many tests fail due to extra_hops assertion in CodeHeap::verify. hs_err is attached.

compiler/codegen/Test6875866.java
compiler/codegen/Test6935535.java
compiler/codegen/Test8005033.java

# Internal Error (/data/shihui/codes/shihui_jdk_master/src/hotspot/share/memory/heap.cpp:838), pid=1525697, tid=1525715
# assert((count == 0) || (extra_hops < (16 + 2*count))) failed: CodeHeap: many extra hops due to optimization. blocks: 234, extra hops: 484.


Check discussion in https://mail.openjdk.java.net/pipermail/hotspot-compiler-dev/2019-October/035508.html but didn't find where assertion (extra_hops < (16 + 2*count) comes from.

for example, before CodeHeap free, segmap is following extrem case.
|0|0|0|0|0|0|0|0|0|0|
after release, it will be
|0|1|1|1|1|1|1|1|1|1|
and increase 9 unnecessary hop for 1 segment.