[Sema] Fix ExtVectorElementExpr tree transform for the isArrow case.

Make sure we propagate the value for `IsArrow` to
`RebuildExtVectorElementExpr` in order to be able to handle correctly
vector component accesses where the base value is a pointer.

Reviewed By: rjmccall

Differential Revision: https://reviews.llvm.org/D131698

Author: michele-scandale

clang/lib/Sema/TreeTransform.h

@@ -2814,20 +2814,18 @@ class TreeTransform {
   ///
   /// By default, performs semantic analysis to build the new expression.
   /// Subclasses may override this routine to provide different behavior.
-  ExprResult RebuildExtVectorElementExpr(Expr *Base,
-                                               SourceLocation OpLoc,
-                                               SourceLocation AccessorLoc,
-                                               IdentifierInfo &Accessor) {
+  ExprResult RebuildExtVectorElementExpr(Expr *Base, SourceLocation OpLoc,
+                                         bool IsArrow,
+                                         SourceLocation AccessorLoc,
+                                         IdentifierInfo &Accessor) {
 
     CXXScopeSpec SS;
     DeclarationNameInfo NameInfo(&Accessor, AccessorLoc);
-    return getSema().BuildMemberReferenceExpr(Base, Base->getType(),
-                                              OpLoc, /*IsArrow*/ false,
-                                              SS, SourceLocation(),
-                                              /*FirstQualifierInScope*/ nullptr,
-                                              NameInfo,
-                                              /* TemplateArgs */ nullptr,
-                                              /*S*/ nullptr);
+    return getSema().BuildMemberReferenceExpr(
+        Base, Base->getType(), OpLoc, IsArrow, SS, SourceLocation(),
+        /*FirstQualifierInScope*/ nullptr, NameInfo,
+        /* TemplateArgs */ nullptr,
+        /*S*/ nullptr);
   }
 
   /// Build a new initializer list expression.
@@ -11424,9 +11422,9 @@ TreeTransform<Derived>::TransformExtVectorElementExpr(ExtVectorElementExpr *E) {
   // FIXME: Bad source location
   SourceLocation FakeOperatorLoc =
       SemaRef.getLocForEndOfToken(E->getBase()->getEndLoc());
-  return getDerived().RebuildExtVectorElementExpr(Base.get(), FakeOperatorLoc,
-                                                  E->getAccessorLoc(),
-                                                  E->getAccessor());
+  return getDerived().RebuildExtVectorElementExpr(
+      Base.get(), FakeOperatorLoc, E->isArrow(), E->getAccessorLoc(),
+      E->getAccessor());
 }
 
 template<typename Derived>

clang/test/SemaTemplate/instantiate-clang.cpp

@@ -18,7 +18,15 @@ struct ExtVectorAccess0 {
 template struct ExtVectorAccess0<double2>;
 template struct ExtVectorAccess0<double4>;
 
-typedef __attribute__(( ext_vector_type(2) )) double double2;
+template<typename T>
+struct ExtVectorAccess1 {
+  void f(T *v1, double4 *v2) {
+    v1->xy = v2->yx;
+  }
+};
+
+template struct ExtVectorAccess1<double2>;
+template struct ExtVectorAccess1<double4>;
 
 template<typename T, typename U, int N, int M>
 struct ShuffleVector0 {