convert Bpred from linked list to Barray (#23180)

Author: WalterBright

compiler/src/dmd/backend/barray.d

@@ -112,6 +112,45 @@ struct Barray(T)
         setLength(len);
     }
 
+    /**********************
+     * Subtract element at index i from the array.
+     * Ripple the elements after i to the left 1 place.
+     * Reduce the array length by one.
+     * Params:
+     *  i = index of element to subtract
+     */
+    void subtracti(size_t i)
+    {
+        while (i + 1 < array.length)
+        {
+            array[i] = array[i + 1];
+            ++i;
+        }
+        setLength(array.length - 1);
+    }
+
+    /**********************
+     * Subtract element from the array.
+     * Ripple the elements after it to the left 1 place.
+     * Reduce the array length by one.
+     * Params:
+     *  t = element to subtract
+     * Returns:
+     *  true if element was found and subtracted
+     */
+    bool subtract(T t)
+    {
+        foreach (i, ref e; array)
+        {
+            if (t == e)
+            {
+                subtracti(i);
+                return true; // t was found at index i
+            }
+        }
+        return false; // t is not in array
+    }
+
     /******************
      * Release all memory used.
      */
@@ -146,6 +185,8 @@ unittest
     a.push(50);
     a.remove(1);
     assert(a[1] == 50);
+    a.subtracti(0);
+    assert(a[0] == 50);
     a.dtor();
     assert(a.length == 0);
 }