Bytecode DSL: fix bug in BinarySubscript, initialize empty lists to empty storage

Author: steve-s

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/nodes/bytecode_dsl/PBytecodeDSLRootNode.java

@@ -220,6 +220,7 @@
 import com.oracle.graal.python.runtime.sequence.PSequenceWithStorage;
 import com.oracle.graal.python.runtime.sequence.storage.BoolSequenceStorage;
 import com.oracle.graal.python.runtime.sequence.storage.DoubleSequenceStorage;
+import com.oracle.graal.python.runtime.sequence.storage.EmptySequenceStorage;
 import com.oracle.graal.python.runtime.sequence.storage.IntSequenceStorage;
 import com.oracle.graal.python.runtime.sequence.storage.LongSequenceStorage;
 import com.oracle.graal.python.runtime.sequence.storage.ObjectSequenceStorage;
@@ -1636,7 +1637,16 @@ public static Object perform(VirtualFrame frame,
 
     @Operation(storeBytecodeIndex = false)
     public static final class MakeList {
-        @Specialization
+        @Specialization(guards = "elements.length == 0")
+        public static PList doEmpty(@Variadic Object[] elements,
+                        @Bind PBytecodeDSLRootNode rootNode) {
+            // Common pattern is to create an empty list and then add items.
+            // We need to start from empty storage, so that we can specialize to, say, int storage
+            // if only ints are appended to this list
+            return PFactory.createList(rootNode.getLanguage(), EmptySequenceStorage.INSTANCE);
+        }
+
+        @Specialization(guards = "elements.length > 0")
         public static PList perform(@Variadic Object[] elements,
                         @Bind PBytecodeDSLRootNode rootNode) {
             return PFactory.createList(rootNode.getLanguage(), elements);
@@ -3210,7 +3220,7 @@ public static boolean doObject(long typeFlags, Object value,
     @ImportStatic(PGuards.class)
     public static final class BinarySubscript {
         static boolean isBuiltinListOrTuple(PSequenceWithStorage s) {
-            return PGuards.isBuiltinTuple(s) && PGuards.isBuiltinList(s);
+            return PGuards.isBuiltinTuple(s) || PGuards.isBuiltinList(s);
         }
 
         public static boolean isIntBuiltinListOrTuple(PSequenceWithStorage s) {