Related to PR11848 and core-21989: switch ContainsUnexpandedParameterPack from
being a property of a canonical type to being a property of the fully-sugared
type. This should only make a difference in the case where an alias template
ignores one of its parameters, and that parameter is an unexpanded parameter
pack.

llvm-svn: 160244
diff --git a/clang/lib/AST/ASTContext.cpp b/clang/lib/AST/ASTContext.cpp
index b0351d6..c83e70a 100644
--- a/clang/lib/AST/ASTContext.cpp
+++ b/clang/lib/AST/ASTContext.cpp
@@ -2892,10 +2892,17 @@
 
   QualType Canon;
   if (!Pattern.isCanonical()) {
-    Canon = getPackExpansionType(getCanonicalType(Pattern), NumExpansions);
+    Canon = getCanonicalType(Pattern);
+    // The canonical type might not contain an unexpanded parameter pack, if it
+    // contains an alias template specialization which ignores one of its
+    // parameters.
+    if (Canon->containsUnexpandedParameterPack()) {
+      Canon = getPackExpansionType(getCanonicalType(Pattern), NumExpansions);
 
-    // Find the insert position again.
-    PackExpansionTypes.FindNodeOrInsertPos(ID, InsertPos);
+      // Find the insert position again, in case we inserted an element into
+      // PackExpansionTypes and invalidated our insert position.
+      PackExpansionTypes.FindNodeOrInsertPos(ID, InsertPos);
+    }
   }
 
   T = new (*this) PackExpansionType(Pattern, Canon, NumExpansions);