8014431: cleanup warnings indicated by the -Wunused-value compiler option on linux

Reviewed-by: dholmes, coleenp
Contributed-by: jeremymanson@google.com, calvin.cheung@oracle.com

2 files changed, 29 insertions, 11 deletions

diff --git a/src/share/vm/utilities/exceptions.hpp b/src/share/vm/utilities/exceptions.hpp
index 089cd3e08..32c6f35d8 100644
--- a/src/share/vm/utilities/exceptions.hpp
+++ b/src/share/vm/utilities/exceptions.hpp
@@ -194,15 +194,15 @@ class Exceptions {
 #define HAS_PENDING_EXCEPTION                    (((ThreadShadow*)THREAD)->has_pending_exception())
 #define CLEAR_PENDING_EXCEPTION                  (((ThreadShadow*)THREAD)->clear_pending_exception())
 
-#define CHECK                                    THREAD); if (HAS_PENDING_EXCEPTION) return       ; (0
-#define CHECK_(result)                           THREAD); if (HAS_PENDING_EXCEPTION) return result; (0
+#define CHECK                                    THREAD); if (HAS_PENDING_EXCEPTION) return       ; (void)(0
+#define CHECK_(result)                           THREAD); if (HAS_PENDING_EXCEPTION) return result; (void)(0
 #define CHECK_0                                  CHECK_(0)
 #define CHECK_NH                                 CHECK_(Handle())
 #define CHECK_NULL                               CHECK_(NULL)
 #define CHECK_false                              CHECK_(false)
 
-#define CHECK_AND_CLEAR                         THREAD); if (HAS_PENDING_EXCEPTION) { CLEAR_PENDING_EXCEPTION; return;        } (0
-#define CHECK_AND_CLEAR_(result)                THREAD); if (HAS_PENDING_EXCEPTION) { CLEAR_PENDING_EXCEPTION; return result; } (0
+#define CHECK_AND_CLEAR                         THREAD); if (HAS_PENDING_EXCEPTION) { CLEAR_PENDING_EXCEPTION; return;        } (void)(0
+#define CHECK_AND_CLEAR_(result)                THREAD); if (HAS_PENDING_EXCEPTION) { CLEAR_PENDING_EXCEPTION; return result; } (void)(0
 #define CHECK_AND_CLEAR_0                       CHECK_AND_CLEAR_(0)
 #define CHECK_AND_CLEAR_NH                      CHECK_AND_CLEAR_(Handle())
 #define CHECK_AND_CLEAR_NULL                    CHECK_AND_CLEAR_(NULL)
@@ -282,7 +282,7 @@ class Exceptions {
     CLEAR_PENDING_EXCEPTION;               \
     ex->print();                           \
     ShouldNotReachHere();                  \
-  } (0
+  } (void)(0
 
 // ExceptionMark is a stack-allocated helper class for local exception handling.
 // It is used with the EXCEPTION_MARK macro.
diff --git a/src/share/vm/utilities/taskqueue.hpp b/src/share/vm/utilities/taskqueue.hpp
index 980b7e973..aea96c858 100644
--- a/src/share/vm/utilities/taskqueue.hpp
+++ b/src/share/vm/utilities/taskqueue.hpp
@@ -340,8 +340,12 @@ bool GenericTaskQueue<E, F, N>::push_slow(E t, uint dirty_n_elems) {
   if (dirty_n_elems == N - 1) {
     // Actually means 0, so do the push.
     uint localBot = _bottom;
-    // g++ complains if the volatile result of the assignment is unused.
-    const_cast<E&>(_elems[localBot] = t);
+    // g++ complains if the volatile result of the assignment is
+    // unused, so we cast the volatile away.  We cannot cast directly
+    // to void, because gcc treats that as not using the result of the
+    // assignment.  However, casting to E& means that we trigger an
+    // unused-value warning.  So, we cast the E& to void.
+    (void)const_cast<E&>(_elems[localBot] = t);
     OrderAccess::release_store(&_bottom, increment_index(localBot));
     TASKQUEUE_STATS_ONLY(stats.record_push());
     return true;
@@ -397,7 +401,12 @@ bool GenericTaskQueue<E, F, N>::pop_global(E& t) {
     return false;
   }
 
-  const_cast<E&>(t = _elems[oldAge.top()]);
+  // g++ complains if the volatile result of the assignment is
+  // unused, so we cast the volatile away.  We cannot cast directly
+  // to void, because gcc treats that as not using the result of the
+  // assignment.  However, casting to E& means that we trigger an
+  // unused-value warning.  So, we cast the E& to void.
+  (void) const_cast<E&>(t = _elems[oldAge.top()]);
   Age newAge(oldAge);
   newAge.increment();
   Age resAge = _age.cmpxchg(newAge, oldAge);
@@ -640,8 +649,12 @@ GenericTaskQueue<E, F, N>::push(E t) {
   uint dirty_n_elems = dirty_size(localBot, top);
   assert(dirty_n_elems < N, "n_elems out of range.");
   if (dirty_n_elems < max_elems()) {
-    // g++ complains if the volatile result of the assignment is unused.
-    const_cast<E&>(_elems[localBot] = t);
+    // g++ complains if the volatile result of the assignment is
+    // unused, so we cast the volatile away.  We cannot cast directly
+    // to void, because gcc treats that as not using the result of the
+    // assignment.  However, casting to E& means that we trigger an
+    // unused-value warning.  So, we cast the E& to void.
+    (void) const_cast<E&>(_elems[localBot] = t);
     OrderAccess::release_store(&_bottom, increment_index(localBot));
     TASKQUEUE_STATS_ONLY(stats.record_push());
     return true;
@@ -665,7 +678,12 @@ GenericTaskQueue<E, F, N>::pop_local(E& t) {
   // This is necessary to prevent any read below from being reordered
   // before the store just above.
   OrderAccess::fence();
-  const_cast<E&>(t = _elems[localBot]);
+  // g++ complains if the volatile result of the assignment is
+  // unused, so we cast the volatile away.  We cannot cast directly
+  // to void, because gcc treats that as not using the result of the
+  // assignment.  However, casting to E& means that we trigger an
+  // unused-value warning.  So, we cast the E& to void.
+  (void) const_cast<E&>(t = _elems[localBot]);
   // This is a second read of "age"; the "size()" above is the first.
   // If there's still at least one element in the queue, based on the
   // "_bottom" and "age" we've read, then there can be no interference with