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

diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/diff/RenameDetector.java b/org.eclipse.jgit/src/org/eclipse/jgit/diff/RenameDetector.java
index 9d9a96d..dfaf588 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/diff/RenameDetector.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/diff/RenameDetector.java
@@ -357,9 +357,17 @@ public List<DiffEntry> compute(ContentSource.Pair reader, ProgressMonitor pm)
 
 			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 void reset() {
 
 	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 @@ private void findContentRenames(ContentSource.Pair reader,
 			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 @@ private void findContentRenames(ContentSource.Pair reader,
 
 	@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());