support longs as slice start

Author: timfel

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/nodes/subscript/SliceLiteralNode.java

@@ -78,6 +78,16 @@ public PSlice doSlice(int start, @SuppressWarnings("unused") PNone stop, @Suppre
         return factory().createSlice(start, MISSING_INDEX, MISSING_INDEX);
     }
 
+    @TruffleBoundary
+    @Specialization
+    public PSlice doPSlice(long start, @SuppressWarnings("unused") PNone stop, @SuppressWarnings("unused") PNone step) {
+        try {
+            return factory().createSlice(Math.toIntExact(start), MISSING_INDEX, 1);
+        } catch (ArithmeticException e) {
+            throw raise(IndexError, "cannot fit 'int' into an index-sized integer");
+        }
+    }
+
     @Specialization
     public PSlice doSlice(int start, @SuppressWarnings("unused") PNone stop, int step) {
         return factory().createSlice(start, MISSING_INDEX, step);