A bit optimization for tlb_set_page()

This patch avoids handling write watchpoints on read-only memory access.
It also breaks the searching loop for watchpoint once the setup for
handling watchpoint later is done.
Signed-off-by: NJun Koi <junkoi2004@gmail.com>
Signed-off-by: NAurelien Jarno <aurelien@aurel32.net>

exec.c

@@ -2209,10 +2209,12 @@ void tlb_set_page(CPUState *env, target_ulong vaddr,
        watchpoint trap routines.  */
     QTAILQ_FOREACH(wp, &env->watchpoints, entry) {
         if (vaddr == (wp->vaddr & TARGET_PAGE_MASK)) {
-            iotlb = io_mem_watch + paddr;
-            /* TODO: The memory case can be optimized by not trapping
-               reads of pages with a write breakpoint.  */
-            address |= TLB_MMIO;
+            /* Avoid trapping reads of pages with a write breakpoint. */
+            if ((prot & PAGE_WRITE) || (wp->flags & BP_MEM_READ)) {
+                iotlb = io_mem_watch + paddr;
+                address |= TLB_MMIO;
+                break;
+            }
         }
     }