[clang] [clang] Preserve ext_vector_type locations during template substitution (PR #229328)

[Chen Miao via cfe-commits]

================
@@ -525,7 +525,16 @@ class ASTNodeTraverser
     Visit(TL.getSizeExpr());
   }
   void VisitDependentSizedExtVectorTypeLoc(DependentSizedExtVectorTypeLoc TL) {
-    Visit(cast<DependentSizedExtVectorType>(TL.getType())->getSizeExpr());
+    Expr *Size = TL.getSizeExpr();
+    Visit(Size ? Size : TL.getTypePtr()->getSizeExpr());
+  }
+  void VisitVectorTypeLoc(VectorTypeLoc TL) {
+    if (Expr *Size = TL.getSizeExpr())
+      Visit(Size);
+  }
+  void VisitDependentVectorTypeLoc(DependentVectorTypeLoc TL) {
+    Expr *Size = TL.getSizeExpr();
+    Visit(Size ? Size : TL.getTypePtr()->getSizeExpr());
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ChenMiaoi wrote:

This happens because the patch adds a separate `SizeExpr` field to the dependent vector TypeLocs and initializes it to nullptr. For example:

``` cc
template<int N> struct V {
  typedef int type __attribute__((ext_vector_type(N)));
};
```

The Type retains the expression N, but the current TypeLoc-building path does not populate the new TypeLoc field after initialization.

Looking at this again, initializing the field with `setSizeExpr(getTypePtr()->getSizeExpr())`, as `DependentSizedArrayTypeLoc` does, seems better and should allow us to simplify the fallback logic?

https://github.com/llvm/llvm-project/pull/229328