RenameDetector: Only scan deletes if adds exist

If there are only deletes, don't need perform rename or copy
detection.  There are no adds (aka destinations) for the deletes
to match against.

Change-Id: I00fb90c509fa26a053de561dd8506cc1e0f5799a
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

org.eclipse.jgit/src/org/eclipse/jgit/diff/RenameDetector.java

@@ -357,9 +357,17 @@ public class RenameDetector {
 
 			if (pm == null)
 				pm = NullProgressMonitor.INSTANCE;
+
+			if (0 < breakScore)
 				breakModifies(reader, pm);
+
+			if (!added.isEmpty() && !deleted.isEmpty())
 				findExactRenames(pm);
+
+			if (!added.isEmpty() && !deleted.isEmpty())
 				findContentRenames(reader, pm);
+
+			if (0 < breakScore && !added.isEmpty() && !deleted.isEmpty())
 				rejoinModifies(pm);
 
 			entries.addAll(added);
@@ -383,9 +391,6 @@ public class RenameDetector {
 
 	private void breakModifies(ContentSource.Pair reader, ProgressMonitor pm)
 			throws IOException {
-		if (breakScore <= 0)
-			return;
-
 		ArrayList<DiffEntry> newEntries = new ArrayList<DiffEntry>(entries.size());
 
 		pm.beginTask(JGitText.get().renamesBreakingModifies, entries.size());
@@ -469,9 +474,6 @@ public class RenameDetector {
 			ProgressMonitor pm)
 			throws IOException {
 		int cnt = Math.max(added.size(), deleted.size());
-		if (cnt == 0)
-			return;
-
 		if (getRenameLimit() == 0 || cnt <= getRenameLimit()) {
 			SimilarityRenameDetector d;
 
@@ -489,9 +491,6 @@ public class RenameDetector {
 
 	@SuppressWarnings("unchecked")
 	private void findExactRenames(ProgressMonitor pm) {
-		if (added.isEmpty() || deleted.isEmpty())
-			return;
-
 		pm.beginTask(JGitText.get().renamesFindingExact, //
 				added.size() + added.size() + deleted.size()
 						+ added.size() * deleted.size());