early experimental version of the bytecode library is bundled under:
test/jdk/lib/testlibrary/bytecode

following tests reference it:
test/jdk/java/lang/invoke/common/test/java/lang/invoke/lib/InstructionHelper.java
test/jdk/java/lang/invoke/condy/CondyWithGarbageTest.java
test/jdk/java/lang/invoke/condy/CondyReturnPrimitiveTest.java
test/jdk/java/lang/invoke/condy/CondyWrongType.java
test/jdk/java/lang/invoke/condy/CondyNestedTest.java
test/jdk/java/lang/invoke/condy/CondyStaticArgumentsTest.java
test/jdk/java/lang/invoke/condy/BootstrapMethodJumboArgsTest.java
test/jdk/java/lang/invoke/condy/ConstantBootstrapsTest.java
test/jdk/java/lang/invoke/condy/CondyRepeatFailedResolution.java
test/jdk/java/lang/invoke/condy/CondyBSMInvocation.java
test/jdk/java/lang/invoke/condy/CondyTypeValidationTest.java
test/jdk/java/lang/invoke/condy/CondyBSMValidationTest.java
test/jdk/java/lang/invoke/condy/CondyNameValidationTest.java
test/jdk/java/lang/invoke/condy/CondyBSMException.java
test/jdk/java/lang/invoke/condy/CondyInterfaceWithOverpassMethods.java