[Truffle] Avoid splicing together empty strings.

A semi-common case is using String#slice! to truncate a string. In this case we'd like to model the operation as a simple substring. However, splicing assumed a string would be inserted in the middle of another and thus generated superfluous ropes for the truncation case.
jruby · Apr 21, 2016 · 84a785c · 84a785c
1 parent 2de4aa9
commit 84a785c
Showing 1 changed file with 17 additions and 3 deletions.
diff --git a/truffle/src/main/java/org/jruby/truffle/core/rubinius/StringPrimitiveNodes.java b/truffle/src/main/java/org/jruby/truffle/core/rubinius/StringPrimitiveNodes.java
@@ -1448,7 +1448,9 @@ public Object spliceAppend(DynamicObject string, DynamicObject other, int splice
         }
 
         @Specialization(guards = { "!indexAtEitherBounds(string, spliceByteIndex)", "isRubyString(other)", "isRubyEncoding(rubyEncoding)", "!isRopeBuffer(string)" })
-        public DynamicObject splice(DynamicObject string, DynamicObject other, int spliceByteIndex, int byteCountToReplace, DynamicObject rubyEncoding) {
+        public DynamicObject splice(DynamicObject string, DynamicObject other, int spliceByteIndex, int byteCountToReplace, DynamicObject rubyEncoding,
+                                    @Cached("createBinaryProfile()") ConditionProfile insertStringIsEmptyProfile,
+                                    @Cached("createBinaryProfile()") ConditionProfile splitRightIsEmptyProfile) {
             if (leftMakeSubstringNode == null) {
                 CompilerDirectives.transferToInterpreter();
                 leftMakeSubstringNode = insert(RopeNodesFactory.MakeSubstringNodeGen.create(null, null, null));
@@ -1476,8 +1478,20 @@ public DynamicObject splice(DynamicObject string, DynamicObject other, int splic
 
             final Rope splitLeft = leftMakeSubstringNode.executeMake(source, 0, spliceByteIndex);
             final Rope splitRight = rightMakeSubstringNode.executeMake(source, rightSideStartingIndex, source.byteLength() - rightSideStartingIndex);
-            final Rope joinedLeft = leftMakeConcatNode.executeMake(splitLeft, insert, encoding);
-            final Rope joinedRight = rightMakeConcatNode.executeMake(joinedLeft, splitRight, encoding);
+
+            final Rope joinedLeft;
+            if (insertStringIsEmptyProfile.profile(insert.isEmpty())) {
+                joinedLeft = splitLeft;
+            } else {
+                joinedLeft = leftMakeConcatNode.executeMake(splitLeft, insert, encoding);
+            }
+
+            final Rope joinedRight;
+            if (splitRightIsEmptyProfile.profile(splitRight.isEmpty())) {
+                joinedRight = joinedLeft;
+            } else {
+                joinedRight = rightMakeConcatNode.executeMake(joinedLeft, splitRight, encoding);
+            }
 
             StringOperations.setRope(string, joinedRight);