make
Building target 'default (exploded-image)' in configuration 'linux-x86_64-normal-server-release'
Updating support/modules_libs/java.base/server/libjvm.so due to 1 file(s)
/client/hotspot/src/share/vm/opto/library_call.cpp: In member function ‘bool LibraryCallKit::inline_unsafe_access(bool, BasicType, LibraryCallKit::AccessKind, bool)’:
client/hotspot/src/share/vm/opto/library_call.cpp:2578:3: error: ‘need_mem_bar’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
   if (need_mem_bar) insert_mem_bar(Op_MemBarCPUOrder);
   ^
cc1plus: all warnings being treated as errors
make[3]: *** /client/build/linux-x86_64-normal-server-release/hotspot/variant-server/libjvm/objs/library_call.o] Error 1
lib/CompileJvm.gmk:201: recipe for target '/client/build/linux-x86_64-normal-server-release/hotspot/variant-server/libjvm/objs/library_call.o' failed
make[2]: *** [hotspot-server-libs] Error 1
make/Main.gmk:263: recipe for target 'hotspot-server-libs' failed

This is a warnings-as-errors failure and whilst I don't see that this
specific change did anything wrong it was enough to 'wake up'
the compiler to this pattern which it probably should have
complained about all along ..

Clearly the hotspot code does not expect this to actually occur,
but the compiler can't be expected to know this.

The fix should be as simple as
- bool need_mem_bar;
+ bool need_mem_bar = false