CppTools: CppPreprocessor: Read file only if necessary

Change-Id: Ia60d3e1907f9238f873f016d844095084b76ad6b
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>

src/plugins/cpptools/cpppreprocessor.cpp

@@ -410,6 +410,14 @@ void CppPreprocessor::sourceNeeded(unsigned line, const QString &fileName, Inclu
     if (absoluteFileName != modelManager()->configurationFileName())
         m_included.insert(absoluteFileName);
 
+    // Already in snapshot? Use it!
+    Document::Ptr doc = m_snapshot.document(absoluteFileName);
+    if (doc) {
+        mergeEnvironment(doc);
+        return;
+    }
+
+    // Otherwise get file contents
     unsigned editorRevision = 0;
     QByteArray contents;
     const bool gotFileContents = getFileContents(absoluteFileName, &contents, &editorRevision);
@@ -427,12 +435,6 @@ void CppPreprocessor::sourceNeeded(unsigned line, const QString &fileName, Inclu
                  << "contents:" << contents.size() << "bytes";
     }
 
-    Document::Ptr doc = m_snapshot.document(absoluteFileName);
-    if (doc) {
-        mergeEnvironment(doc);
-        return;
-    }
-
     doc = Document::create(absoluteFileName);
     doc->setRevision(m_revision);
     doc->setEditorRevision(editorRevision);