[clang][Interp] Start implementing vector types

Map them to primtive arrays, much like complex types.

clang/lib/AST/Interp/ByteCodeExprGen.cpp

@@ -1033,6 +1033,34 @@ bool ByteCodeExprGen<Emitter>::VisitInitListExpr(const InitListExpr *E) {
     return true;
   }
 
+  if (const auto *VecT = E->getType()->getAs<VectorType>()) {
+    unsigned NumVecElements = VecT->getNumElements();
+    assert(NumVecElements >= E->getNumInits());
+
+    QualType ElemQT = VecT->getElementType();
+    PrimType ElemT = classifyPrim(ElemQT);
+
+    // All initializer elements.
+    unsigned InitIndex = 0;
+    for (const Expr *Init : E->inits()) {
+      if (!this->visit(Init))
+        return false;
+
+      if (!this->emitInitElem(ElemT, InitIndex, E))
+        return false;
+      ++InitIndex;
+    }
+
+    // Fill the rest with zeroes.
+    for (; InitIndex != NumVecElements; ++InitIndex) {
+      if (!this->visitZeroInitializer(ElemT, ElemQT, E))
+        return false;
+      if (!this->emitInitElem(ElemT, InitIndex, E))
+        return false;
+    }
+    return true;
+  }
+
   return false;
 }
 

clang/lib/AST/Interp/Context.cpp

@@ -120,7 +120,8 @@ std::optional<PrimType> Context::classify(QualType T) const {
   if (T->isBooleanType())
     return PT_Bool;
 
-  if (T->isAnyComplexType())
+  // We map these to primitive arrays.
+  if (T->isAnyComplexType() || T->isVectorType())
     return std::nullopt;
 
   if (T->isSignedIntegerOrEnumerationType()) {

clang/lib/AST/Interp/EvalEmitter.cpp

@@ -51,7 +51,8 @@ EvaluationResult EvalEmitter::interpretDecl(const VarDecl *VD,
   this->CheckFullyInitialized = CheckFullyInitialized;
   this->ConvertResultToRValue =
       VD->getAnyInitializer() &&
-      (VD->getAnyInitializer()->getType()->isAnyComplexType());
+      (VD->getAnyInitializer()->getType()->isAnyComplexType() ||
+       VD->getAnyInitializer()->getType()->isVectorType());
   EvalResult.setSource(VD);
 
   if (!this->visitDecl(VD) && EvalResult.empty())

clang/lib/AST/Interp/Pointer.cpp

@@ -342,6 +342,25 @@ std::optional<APValue> Pointer::toRValue(const Context &Ctx) const {
       return false;
     }
 
+    // Vector types.
+    if (const auto *VT = Ty->getAs<VectorType>()) {
+      assert(Ptr.getFieldDesc()->isPrimitiveArray());
+      QualType ElemTy = VT->getElementType();
+      PrimType ElemT = *Ctx.classify(ElemTy);
+
+      SmallVector<APValue> Values;
+      Values.reserve(VT->getNumElements());
+      for (unsigned I = 0; I != VT->getNumElements(); ++I) {
+        TYPE_SWITCH(ElemT, {
+          Values.push_back(Ptr.atIndex(I).deref<T>().toAPValue());
+        });
+      }
+
+      assert(Values.size() == VT->getNumElements());
+      R = APValue(Values.data(), Values.size());
+      return true;
+    }
+
     llvm_unreachable("invalid value to return");
   };
 

clang/lib/AST/Interp/Program.cpp

@@ -411,5 +411,12 @@ Descriptor *Program::createDescriptor(const DeclTy &D, const Type *Ty,
                               IsMutable);
   }
 
+  // Same with vector types.
+  if (const auto *VT = Ty->getAs<VectorType>()) {
+    PrimType ElemTy = *Ctx.classify(VT->getElementType());
+    return allocateDescriptor(D, ElemTy, MDSize, VT->getNumElements(), IsConst,
+                              IsTemporary, IsMutable);
+  }
+
   return nullptr;
 }

clang/test/AST/Interp/vectors.cpp

@@ -0,0 +1,22 @@
+// RUN: %clang_cc1 -fexperimental-new-constant-interpreter -verify=expected,both %s
+// RUN: %clang_cc1 -verify=ref,both %s
+
+// both-no-diagnostics
+
+typedef int __attribute__((vector_size(16))) VI4;
+constexpr VI4 A = {1,2,3,4};
+
+/// From constant-expression-cxx11.cpp
+namespace Vector {
+  typedef int __attribute__((vector_size(16))) VI4;
+  constexpr VI4 f(int n) {
+    return VI4 { n * 3, n + 4, n - 5, n / 6 };
+  }
+  constexpr auto v1 = f(10);
+
+  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);
+}