[clang][Interp] Support __builtin_vectorelements

Author: tbaederr

clang/lib/AST/Interp/ByteCodeExprGen.cpp

@@ -1251,6 +1251,15 @@ bool ByteCodeExprGen<Emitter>::VisitUnaryExprOrTypeTraitExpr(
     return this->emitConst(Size.getQuantity(), E);
   }
 
+  if (Kind == UETT_VectorElements) {
+    if (const auto *VT = E->getTypeOfArgument()->getAs<VectorType>())
+      return this->emitConst(VT->getNumElements(), E);
+
+    // FIXME: Apparently we need to catch the fact that a sizeless vector type
+    // has been passed and diagnose that (at run time).
+    assert(E->getTypeOfArgument()->isSizelessVectorType());
+  }
+
   return false;
 }
 

clang/test/AST/Interp/vectors.cpp

@@ -13,12 +13,14 @@ namespace Vector {
     return VI4 { n * 3, n + 4, n - 5, n / 6 };
   }
   constexpr auto v1 = f(10);
+  static_assert(__builtin_vectorelements(v1) == (16 / sizeof(int)), "");
 
   typedef double __attribute__((vector_size(32))) VD4;
   constexpr VD4 g(int n) {
     return (VD4) { n / 2.0, n + 1.5, n - 5.4, n * 0.9 };
   }
   constexpr auto v2 = g(4);
+  static_assert(__builtin_vectorelements(v2) == (32 / sizeof(double)), "");
 }
 
 /// FIXME: We need to support BitCasts between vector types.