Dependencies::find_unique_concrete_method() doesn't filter out non-virtual (static & private) methods. For C1/C2, the proper checks happen in ciMethod::find_monomorphic_target(), but JVMCI doesn't have them.

Non-virtual methods are problematic because ClassHierarchyWalker operates on symbolic info when looking for overrides.

With the following patch compiler/jvmci/compilerToVM/FindUniqueConcreteMethodTest.java hits the assert:
diff --git a/src/hotspot/share/code/dependencies.cpp b/src/hotspot/share/code/dependencies.cpp
--- a/src/hotspot/share/code/dependencies.cpp
+++ b/src/hotspot/share/code/dependencies.cpp
@@ -1099,6 +1099,7 @@
 
   void initialize_from_method(Method* m) {
     assert(m != NULL && m->is_method(), "sanity");
+ assert(!m->is_static() && !m->is_private(), "sanity");
     _name = m->name();
     _signature = m->signature();
   }

----------System.out:(28/2434)----------
CASE: receiver=compiler.jvmci.common.testcases.SingleSubclass, holder=compiler.jvmci.common.testcases.SingleSubclass, method=overridenMethod, isPositive=true
CASE: receiver=compiler.jvmci.common.testcases.SingleSubclass, holder=compiler.jvmci.common.testcases.SingleSubclass, method=protectedMethod, isPositive=true
CASE: receiver=compiler.jvmci.common.testcases.MultipleImplementer1, holder=compiler.jvmci.common.testcases.MultipleImplementer1, method=testMethod, isPositive=true
CASE: receiver=compiler.jvmci.common.testcases.SingleSubclass, holder=compiler.jvmci.common.testcases.SingleSubclass, method=usualMethod, isPositive=true
CASE: receiver=compiler.jvmci.common.testcases.SingleSubclass, holder=compiler.jvmci.common.testcases.SingleSubclass, method=defaultAccessMethod, isPositive=true
CASE: receiver=compiler.jvmci.common.testcases.MultipleSuperImplementers, holder=compiler.jvmci.common.testcases.SimpleSingleImplementerInterface, method=interfaceMethod, isPositive=false
CASE: receiver=compiler.jvmci.common.testcases.MultipleSuperImplementers, holder=compiler.jvmci.common.testcases. DuplicateSimpleSingleImplementerInterface, method=interfaceMethod, isPositive=false
CASE: receiver=compiler.jvmci.common.testcases.SingleSubclass, holder=compiler.jvmci.common.testcases.SingleSubclass, method=privateMethod, isPositive=true
# To suppress the following error report, specify this argument
# after -XX: or in .hotspotrc: SuppressErrorAt=/dependencies.cpp:1102
#
# A fatal error has been detected by the Java Runtime Environment:
#
# Internal Error (/Users/vlivanov/ws/jdk/open/jdk/src/hotspot/share/code/dependencies.cpp:1102), pid=4536, tid=39939
# assert(!m->is_static() && !m->is_private()) failed: sanity
#
# JRE version: OpenJDK Runtime Environment (13.0) (slowdebug build 13-internal+0-adhoc.vlivanov.jdk)
# Java VM: OpenJDK 64-Bit Server VM (slowdebug 13-internal+0-adhoc.vlivanov.jdk, mixed mode, tiered, jvmci, compressed oops, g1 gc, bsd-amd64)