Index: lib/Format/WhitespaceManager.cpp
===================================================================
--- lib/Format/WhitespaceManager.cpp
+++ lib/Format/WhitespaceManager.cpp
@@ -100,14 +100,52 @@
   Changes[0].PreviousEndOfTokenColumn = 0;
   Change *LastOutsideTokenChange = &Changes[0];
   for (unsigned i = 1, e = Changes.size(); i != e; ++i) {
-    unsigned OriginalWhitespaceStart =
-        SourceMgr.getFileOffset(Changes[i].OriginalWhitespaceRange.getBegin());
-    unsigned PreviousOriginalWhitespaceEnd = SourceMgr.getFileOffset(
-        Changes[i - 1].OriginalWhitespaceRange.getEnd());
-    Changes[i - 1].TokenLength = OriginalWhitespaceStart -
-                                 PreviousOriginalWhitespaceEnd +
-                                 Changes[i].PreviousLinePostfix.size() +
-                                 Changes[i - 1].CurrentLinePrefix.size();
+    SourceLocation OriginalWhitespaceStart =
+        Changes[i].OriginalWhitespaceRange.getBegin();
+    SourceLocation PreviousOriginalWhitespaceEnd =
+        Changes[i - 1].OriginalWhitespaceRange.getEnd();
+    unsigned OriginalWhitespaceStartOffset =
+        SourceMgr.getFileOffset(OriginalWhitespaceStart);
+    unsigned PreviousOriginalWhitespaceEndOffset =
+        SourceMgr.getFileOffset(PreviousOriginalWhitespaceEnd);
+    assert(PreviousOriginalWhitespaceEndOffset <=
+           OriginalWhitespaceStartOffset);
+    const char *const PreviousOriginalWhitespaceEndData =
+        SourceMgr.getCharacterData(PreviousOriginalWhitespaceEnd);
+    StringRef Text(PreviousOriginalWhitespaceEndData,
+                   SourceMgr.getCharacterData(OriginalWhitespaceStart) -
+                       PreviousOriginalWhitespaceEndData);
+    // Usually consecutive changes would occur in consecutive tokens. This is
+    // not the case however when analyzing some preprocessor runs of the
+    // annotated lines. For example, in this code:
+    //
+    // #if A // line 1
+    // int i = 1;
+    // #else B // line 2
+    // int i = 2;
+    // #endif // line 3
+    //
+    // one of the runs will produce the sequence of lines marked with line 1, 2
+    // and 3. So the two consecutive whitespace changes just before '// line 2'
+    // and before '#endif // line 3' span multiple lines and tokens:
+    //
+    // #else B{change X}[// line 2
+    // int i = 2;
+    // ]{change Y}#endif // line 3
+    //
+    // For this reason, if the text between consecutive changes spans multiple
+    // newlines, the token length must be adjusted to the end of the original
+    // line of the token.
+    auto NewlinePos = Text.find_first_of('\n');
+    if (NewlinePos == StringRef::npos) {
+      Changes[i - 1].TokenLength = OriginalWhitespaceStartOffset -
+                                   PreviousOriginalWhitespaceEndOffset +
+                                   Changes[i].PreviousLinePostfix.size() +
+                                   Changes[i - 1].CurrentLinePrefix.size();
+    } else {
+      Changes[i - 1].TokenLength =
+          NewlinePos + Changes[i - 1].CurrentLinePrefix.size();
+    }
 
     // If there are multiple changes in this token, sum up all the changes until
     // the end of the line.
Index: unittests/Format/FormatTestComments.cpp
===================================================================
--- unittests/Format/FormatTestComments.cpp
+++ unittests/Format/FormatTestComments.cpp
@@ -1052,6 +1052,30 @@
                "}", getLLVMStyleWithColumns(80));
 }
 
+TEST_F(FormatTestComments, AlignsPPElseEndifComments) {
+  verifyFormat("#if A\n"
+               "#else  // A\n"
+               "int iiii;\n"
+               "#endif // B",
+               getLLVMStyleWithColumns(20));
+  verifyFormat("#if A\n"
+               "#else  // A\n"
+               "int iiii; // CC\n"
+               "#endif // B",
+               getLLVMStyleWithColumns(20));
+  EXPECT_EQ("#if A\n"
+            "#else  // A1\n"
+            "       // A2\n"
+            "int ii;\n"
+            "#endif // B",
+            format("#if A\n"
+                   "#else  // A1\n"
+                   "       // A2\n"
+                   "int ii;\n"
+                   "#endif // B",
+                   getLLVMStyleWithColumns(20)));
+}
+
 TEST_F(FormatTestComments, CommentsInStaticInitializers) {
   EXPECT_EQ(
       "static SomeType type = {aaaaaaaaaaaaaaaaaaaa, /* comment */\n"