openpic: Accelerate pending irq search

When we're done with one interrupt, we need to search for the next pending
interrupt in the queue. This search has grown quite big now that we have
more than 256 possible irq lines.

So let's memorize how many interrupts we have pending in our bitmaps, so
that we can always bail out in the usual case - the one where we're all done.
Signed-off-by: NAlexander Graf <agraf@suse.de>

hw/openpic.c

@@ -169,6 +169,7 @@ typedef struct IRQ_queue_t {
     uint32_t queue[BF_WIDTH(MAX_IRQ)];
     int next;
     int priority;
+    int pending;    /* nr of pending bits in queue */
 } IRQ_queue_t;
 
 typedef struct IRQ_src_t {
@@ -251,11 +252,13 @@ static void openpic_irq_raise(OpenPICState *opp, int n_CPU, IRQ_src_t *src);
 
 static inline void IRQ_setbit(IRQ_queue_t *q, int n_IRQ)
 {
+    q->pending++;
     set_bit(q->queue, n_IRQ);
 }
 
 static inline void IRQ_resetbit(IRQ_queue_t *q, int n_IRQ)
 {
+    q->pending--;
     reset_bit(q->queue, n_IRQ);
 }
 
@@ -271,6 +274,12 @@ static void IRQ_check(OpenPICState *opp, IRQ_queue_t *q)
 
     next = -1;
     priority = -1;
+
+    if (!q->pending) {
+        /* IRQ bitmap is empty */
+        goto out;
+    }
+
     for (i = 0; i < opp->max_irq; i++) {
         if (IRQ_testbit(q, i)) {
             DPRINTF("IRQ_check: irq %d set ipvp_pr=%d pr=%d\n",
@@ -281,6 +290,8 @@ static void IRQ_check(OpenPICState *opp, IRQ_queue_t *q)
             }
         }
     }
+
+out:
     q->next = next;
     q->priority = priority;
 }