Fix stack indexing bugs

Author: PatrikScully

CHANGELOG.md

@@ -11,8 +11,6 @@ Currently the versioning policy of this project follows [Semantic Versioning v2.
 ### Added
 - New detector `SharedVariableAtomicityDetector` for new bug types `AT_NONATOMIC_OPERATIONS_ON_SHARED_VARIABLE`, `AT_NONATOMIC_64BIT_PRIMITIVE` and `AT_STALE_THREAD_WRITE_OF_PRIMITIVE` (See SEI CERT rules [VNA00-J](https://wiki.sei.cmu.edu/confluence/display/java/VNA00-J.+Ensure+visibility+when+accessing+shared+primitive+variables), [VNA02-J](https://wiki.sei.cmu.edu/confluence/display/java/VNA02-J.+Ensure+that+compound+operations+on+shared+variables+are+atomic) and [VNA05-J](https://wiki.sei.cmu.edu/confluence/display/java/VNA05-J.+Ensure+atomicity+when+reading+and+writing+64-bit+values)).
 - New detector `FindHiddenMethod` for bug type `HSM_HIDING_METHOD`. This bug is reported whenever a subclass method hides the static method of super class. (See [SEI CERT MET07-J](https://wiki.sei.cmu.edu/confluence/display/java/MET07-J.+Never+declare+a+class+method+that+hides+a+method+declared+in+a+superclass+or+superinterface)).
-- New detector `ResourceInMultipleThreadsDetector` and introduced new bug type:
-  - `AT_UNSAFE_RESOURCE_ACCESS_IN_THREAD` is reported in case of unsafe resource access in multiple threads.
 - New detector `AtomicOperationsCombinedDetector` and introduced new bug types:
   - `AT_COMBINED_ATOMIC_OPERATIONS_ARE_NOT_ATOMIC` is reported in case of combined atomic operations are not synchronized.
   - `AT_ATOMIC_OPERATION_NEEDS_SYNCHRONIZATION` is reported when an atomic operation is not synchronized, but should be because of thread safety.

spotbugs/src/main/java/edu/umd/cs/findbugs/detect/AtomicOperationsCombinedDetector.java

@@ -143,9 +143,11 @@ private void collectFieldsForAtomicityCheck(ClassContext classContext, Method me
 
             if (instruction instanceof PUTFIELD) {
                 OpcodeStack stack = OpcodeStackScanner.getStackAt(classContext.getJavaClass(), method, handle.getPosition());
-                OpcodeStack.Item stackItem = stack.getStackItem(0);
-                if (isAtomicField(stackItem.getReturnValueOf())) {
-                    fieldsForAtomicityCheck.add(XFactory.createXField((FieldInstruction) instruction, cpg));
+                if (stack.getStackDepth() > 0) {
+                    OpcodeStack.Item stackItem = stack.getStackItem(0);
+                    if (isAtomicField(stackItem.getReturnValueOf())) {
+                        fieldsForAtomicityCheck.add(XFactory.createXField((FieldInstruction) instruction, cpg));
+                    }
                 }
             }
         }
@@ -223,7 +225,7 @@ private void analyzeFieldsForAtomicityViolations(ClassContext classContext, Meth
     }
 
     private Optional<XField> findFieldRequiringAtomicityCheck(OpcodeStack stack) {
-        if (stack.getStackDepth() > 1 && stack.getStackItem(0).getReturnValueOf() != null) {
+        if (stack.getStackDepth() > 0 && stack.getStackItem(0).getReturnValueOf() != null) {
             return Optional.empty();
         }
         return IntStream.range(0, stack.getStackDepth())