diff --git a/clang/lib/AST/Interp/ByteCodeExprGen.cpp b/clang/lib/AST/Interp/ByteCodeExprGen.cpp
--- a/clang/lib/AST/Interp/ByteCodeExprGen.cpp
+++ b/clang/lib/AST/Interp/ByteCodeExprGen.cpp
@@ -362,13 +362,34 @@
   return this->visit(E->getSubExpr());
 }
 
+static CharUnits AlignOfType(QualType T, const ASTContext &ASTCtx,
+                             UnaryExprOrTypeTrait Kind) {
+  bool AlignOfReturnsPreferred =
+      ASTCtx.getLangOpts().getClangABICompat() <= LangOptions::ClangABI::Ver7;
+
+  // C++ [expr.alignof]p3:
+  //     When alignof is applied to a reference type, the result is the
+  //     alignment of the referenced type.
+  if (const auto *Ref = T->getAs<ReferenceType>())
+    T = Ref->getPointeeType();
+
+  // __alignof is defined to return the preferred alignment.
+  // Before 8, clang returned the preferred alignment for alignof and
+  // _Alignof as well.
+  if (Kind == UETT_PreferredAlignOf || AlignOfReturnsPreferred)
+    return ASTCtx.toCharUnitsFromBits(ASTCtx.getPreferredTypeAlign(T));
+
+  return ASTCtx.getTypeAlignInChars(T);
+}
+
 template <class Emitter>
 bool ByteCodeExprGen<Emitter>::VisitUnaryExprOrTypeTraitExpr(
     const UnaryExprOrTypeTraitExpr *E) {
+  UnaryExprOrTypeTrait Kind = E->getKind();
+  ASTContext &ASTCtx = Ctx.getASTContext();
 
-  if (E->getKind() == UETT_SizeOf) {
+  if (Kind == UETT_SizeOf) {
     QualType ArgType = E->getTypeOfArgument();
-
     CharUnits Size;
     if (ArgType->isVoidType() || ArgType->isFunctionType())
       Size = CharUnits::One();
@@ -376,7 +397,37 @@
       if (ArgType->isDependentType() || !ArgType->isConstantSizeType())
         return false;
 
-      Size = Ctx.getASTContext().getTypeSizeInChars(ArgType);
+      Size = ASTCtx.getTypeSizeInChars(ArgType);
+    }
+
+    return this->emitConst(Size.getQuantity(), E);
+  }
+
+  if (Kind == UETT_AlignOf || Kind == UETT_PreferredAlignOf) {
+    CharUnits Size;
+
+    if (E->isArgumentType()) {
+      QualType ArgType = E->getTypeOfArgument();
+
+      Size = AlignOfType(ArgType, ASTCtx, Kind);
+    } else {
+      // Argument is an expression, not a type.
+      const Expr *Arg = E->getArgumentExpr()->IgnoreParens();
+
+      // The kinds of expressions that we have special-case logic here for
+      // should be kept up to date with the special checks for those
+      // expressions in Sema.
+
+      // alignof decl is always accepted, even if it doesn't make sense: we
+      // default to 1 in those cases.
+      if (const auto *DRE = dyn_cast<DeclRefExpr>(Arg))
+        Size = ASTCtx.getDeclAlign(DRE->getDecl(),
+                                   /*RefAsPointee*/ true);
+      else if (const auto *ME = dyn_cast<MemberExpr>(Arg))
+        Size = ASTCtx.getDeclAlign(ME->getMemberDecl(),
+                                   /*RefAsPointee*/ true);
+      else
+        Size = AlignOfType(Arg->getType(), ASTCtx, Kind);
     }
 
     return this->emitConst(Size.getQuantity(), E);
diff --git a/clang/test/AST/Interp/class-layout.cpp b/clang/test/AST/Interp/class-layout.cpp
new file mode 100644
--- /dev/null
+++ b/clang/test/AST/Interp/class-layout.cpp
@@ -0,0 +1,698 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-unknown %s -fsyntax-only -verify -fexperimental-new-constant-interpreter -std=c++98 -Wno-inaccessible-base -Wno-c++11-extensions
+// RUN: %clang_cc1 -triple x86_64-unknown-unknown %s -fsyntax-only -verify -fexperimental-new-constant-interpreter -std=c++11 -Wno-inaccessible-base
+// RUN: %clang_cc1 -triple x86_64-apple-darwin    %s -fsyntax-only -verify -fexperimental-new-constant-interpreter -std=c++11 -Wno-inaccessible-base -DCLANG_ABI_COMPAT=15
+// RUN: %clang_cc1 -triple x86_64-scei-ps4        %s -fsyntax-only -verify -fexperimental-new-constant-interpreter -std=c++11 -Wno-inaccessible-base -DCLANG_ABI_COMPAT=6
+// RUN: %clang_cc1 -triple x86_64-sie-ps5         %s -fsyntax-only -verify -fexperimental-new-constant-interpreter -std=c++11 -Wno-inaccessible-base -DCLANG_ABI_COMPAT=6
+// RUN: %clang_cc1 -triple x86_64-unknown-unknown %s -fsyntax-only -verify -fexperimental-new-constant-interpreter -std=c++11 -Wno-inaccessible-base -fclang-abi-compat=6 -DCLANG_ABI_COMPAT=6
+// RUN: %clang_cc1 -triple x86_64-unknown-unknown %s -fsyntax-only -verify -fexperimental-new-constant-interpreter -std=c++11 -Wno-inaccessible-base -fclang-abi-compat=14 -DCLANG_ABI_COMPAT=14
+// RUN: %clang_cc1 -triple x86_64-unknown-unknown %s -fsyntax-only -verify -fexperimental-new-constant-interpreter -std=c++11 -Wno-inaccessible-base -fclang-abi-compat=15 -DCLANG_ABI_COMPAT=15
+// RUN: %clang_cc1 -triple x86_64-unknown-unknown %s -fsyntax-only -verify -fexperimental-new-constant-interpreter -std=c++11 -Wno-inaccessible-base -fclang-abi-compat=16 -DCLANG_ABI_COMPAT=16
+// expected-no-diagnostics
+
+// FIXME: This is a copy of clang/test/SemaCXX/class-layout.cpp, but with the
+//   __builtin_offsetof calls commented out. Once that is supported in the
+//   new interpreter, we might as well remove this duplicated file and
+//   just use the one in SemaCXX/.
+
+#define SA(n, p) int a##n[(p) ? 1 : -1]
+
+struct A {
+  int a;
+  char b;
+};
+
+SA(0, sizeof(A) == 8);
+
+struct B : A {
+  char c;
+};
+
+SA(1, sizeof(B) == 12);
+
+struct C {
+// Make fields private so C won't be a POD type.
+private:
+  int a;
+  char b;
+};
+
+SA(2, sizeof(C) == 8);
+
+struct D : C {
+  char c;
+};
+
+SA(3, sizeof(D) == 8);
+
+struct __attribute__((packed)) E {
+  char b;
+  int a;
+};
+
+SA(4, sizeof(E) == 5);
+
+struct __attribute__((packed)) F : E {
+  char d;
+};
+
+SA(5, sizeof(F) == 6);
+
+struct G { G(); };
+struct H : G { };
+
+SA(6, sizeof(H) == 1);
+
+struct I {
+  char b;
+  int a;
+} __attribute__((packed));
+
+SA(6_1, sizeof(I) == 5);
+
+// PR5580
+namespace PR5580 {
+
+class A { bool iv0 : 1; };
+SA(7, sizeof(A) == 1);  
+
+class B : A { bool iv0 : 1; };
+SA(8, sizeof(B) == 2);
+
+struct C { bool iv0 : 1; };
+SA(9, sizeof(C) == 1);  
+
+struct D : C { bool iv0 : 1; };
+SA(10, sizeof(D) == 2);
+
+}
+
+namespace Test1 {
+
+// Test that we don't assert on this hierarchy.
+struct A { };
+struct B : A { virtual void b(); };
+class C : virtual A { int c; };
+struct D : virtual B { };
+struct E : C, virtual D { };
+class F : virtual E { };
+struct G : virtual E, F { };
+
+SA(0, sizeof(G) == 24);
+
+}
+
+namespace Test2 {
+
+// Test that this somewhat complex class structure is laid out correctly.
+struct A { };
+struct B : A { virtual void b(); };
+struct C : virtual B { };
+struct D : virtual A { };
+struct E : virtual B, D { };
+struct F : E, virtual C { };
+struct G : virtual F, A { };
+struct H { G g; };
+
+SA(0, sizeof(H) == 24);
+
+}
+
+namespace PR16537 {
+namespace test1 {
+  struct pod_in_11_only {
+  private:
+    long long x;
+  };
+   
+  struct tail_padded_pod_in_11_only {
+    pod_in_11_only pod11;
+    char tail_padding;
+  };
+    
+  struct might_use_tail_padding : public tail_padded_pod_in_11_only {
+    char may_go_into_tail_padding;
+  };
+
+  SA(0, sizeof(might_use_tail_padding) == 16);
+}
+
+namespace test2 {
+  struct pod_in_11_only {
+  private:
+    long long x;
+  };
+   
+  struct tail_padded_pod_in_11_only {
+    pod_in_11_only pod11 __attribute__((aligned(16)));
+  };
+    
+  struct might_use_tail_padding : public tail_padded_pod_in_11_only {
+    char may_go_into_tail_padding;
+  };
+
+  SA(0, sizeof(might_use_tail_padding) == 16);
+}
+
+namespace test3 {
+  struct pod_in_11_only {
+  private:
+    long long x;
+  };
+   
+  struct tail_padded_pod_in_11_only {
+    pod_in_11_only pod11;
+    char tail_padding;
+  };
+
+  struct second_base {
+      char foo;
+  };
+    
+  struct might_use_tail_padding : public tail_padded_pod_in_11_only, public second_base {
+
+  };
+  SA(0, sizeof(might_use_tail_padding) == 16);
+}
+
+namespace test4 {
+  struct pod_in_11_only {
+  private:
+    long long x;
+  };
+   
+  struct tail_padded_pod_in_11_only {
+    pod_in_11_only pod11;
+    char tail_padding;
+  };
+
+  struct second_base {
+    char foo;
+  };
+    
+  struct might_use_tail_padding : public tail_padded_pod_in_11_only, public second_base {
+    char may_go_into_tail_padding;
+  };
+  SA(0, sizeof(might_use_tail_padding) == 16);
+}
+
+namespace test5 {
+  struct pod_in_11_only {
+  private:
+    long long x;
+  };
+
+  struct pod_in_11_only2 {
+  private:
+    long long x;
+  };
+   
+  struct tail_padded_pod_in_11_only {
+    pod_in_11_only pod11;
+    char tail_padding;
+  };
+
+  struct second_base {
+    pod_in_11_only2 two;
+    char foo;
+  };
+    
+  struct might_use_tail_padding : public tail_padded_pod_in_11_only, public second_base {
+    char may_go_into_tail_padding;
+  };
+  SA(0, sizeof(might_use_tail_padding) == 32);
+}
+
+namespace test6 {
+  struct pod_in_11_only {
+  private:
+    long long x;
+  };
+
+  struct pod_in_11_only2 {
+  private:
+    long long x;
+  };
+   
+  struct tail_padded_pod_in_11_only {
+    pod_in_11_only pod11;
+    char tail_padding;
+  };
+
+  struct second_base {
+    pod_in_11_only2 two;
+    char foo;
+  };
+    
+  struct might_use_tail_padding : public tail_padded_pod_in_11_only, public second_base {
+    char may_go_into_tail_padding;
+  };
+  SA(0, sizeof(might_use_tail_padding) == 32);
+}
+
+namespace test7 {
+  struct pod_in_11_only {
+  private:
+    long long x;
+  };
+   
+  struct tail_padded_pod_in_11_only {
+    pod_in_11_only pod11;
+    pod_in_11_only pod12;
+    char tail_padding;
+  };
+    
+  struct might_use_tail_padding : public tail_padded_pod_in_11_only {
+    char may_go_into_tail_padding;
+  };
+
+  SA(0, sizeof(might_use_tail_padding) == 24);
+}
+
+namespace test8 {
+  struct pod_in_11_only {
+  private:
+    long long x;
+  };
+   
+  struct tail_padded_pod_in_11_only {
+    pod_in_11_only pod11;
+    char tail_padding;
+  };
+
+  struct another_layer {
+    tail_padded_pod_in_11_only pod;
+    char padding;
+  };
+    
+  struct might_use_tail_padding : public another_layer {
+    char may_go_into_tail_padding;
+  };
+
+  SA(0, sizeof(might_use_tail_padding) == 24);
+}
+
+namespace test9 {
+  struct pod_in_11_only {
+  private:
+    long long x;
+  };
+   
+  struct tail_padded_pod_in_11_only {
+    pod_in_11_only pod11;
+    char tail_padding;
+  };
+
+  struct another_layer : tail_padded_pod_in_11_only {
+  };
+    
+  struct might_use_tail_padding : public another_layer {
+    char may_go_into_tail_padding;
+  };
+
+  SA(0, sizeof(might_use_tail_padding) == 16);
+}
+
+namespace test10 {
+  struct pod_in_11_only {
+  private:
+    long long x;
+  };
+   
+  struct A {
+    pod_in_11_only a;
+    char apad;
+  };
+
+  struct B {
+    char b;
+  };
+
+  struct C {
+    pod_in_11_only c;
+    char cpad;
+  };
+
+  struct D {
+    char d;
+  };
+    
+  struct might_use_tail_padding : public A, public B, public C, public D {
+  };
+
+  SA(0, sizeof(might_use_tail_padding) == 32);
+}
+
+namespace test11 {
+  struct pod_in_11_only {
+  private:
+    long long x;
+  };
+   
+  struct A {
+    pod_in_11_only a;
+    char apad;
+  };
+
+  struct B {
+    char b_pre;
+    pod_in_11_only b;
+    char bpad;
+  };
+
+  struct C {
+    char c_pre;
+    pod_in_11_only c;
+    char cpad;
+  };
+
+  struct D {
+    char d_pre;
+    pod_in_11_only d;
+    char dpad;
+  };
+    
+  struct might_use_tail_padding : public A, public B, public C, public D {
+    char m;
+  };
+
+  SA(0, sizeof(might_use_tail_padding) == 88);
+}
+
+namespace test12 {
+  struct pod_in_11_only {
+  private:
+    long long x;
+  };
+   
+  struct A {
+    pod_in_11_only a __attribute__((aligned(128)));
+  };
+
+  struct B {
+    char bpad;
+  };
+
+  struct C {
+    char cpad;
+  };
+
+  struct D {
+    char dpad;
+  };
+    
+  struct might_use_tail_padding : public A, public B, public C, public D {
+    char m;
+  };
+  SA(0, sizeof(might_use_tail_padding) == 128);
+}
+
+namespace test13 {
+  struct pod_in_11_only {
+  private:
+    long long x;
+  };
+   
+  struct A {
+    pod_in_11_only a;
+    char apad;
+  };
+
+  struct B {
+  };
+
+  struct C {
+    char c_pre;
+    pod_in_11_only c;
+    char cpad;
+  };
+
+  struct D {
+  };
+    
+  struct might_use_tail_padding : public A, public B, public C, public D {
+    char m;
+  };
+  SA(0, sizeof(might_use_tail_padding) == 40);
+}
+
+namespace test14 {
+  struct pod_in_11_only {
+  private:
+    long long x;
+  };
+   
+  struct A {
+    pod_in_11_only a;
+    char apad;
+  };
+
+  struct might_use_tail_padding : public A {
+    struct {
+      int : 0;
+    } x;
+  };
+  SA(0, sizeof(might_use_tail_padding) == 16);
+}
+
+namespace test15 {
+  struct pod_in_11_only {
+  private:
+    long long x;
+  };
+   
+  struct A {
+    pod_in_11_only a;
+    char apad;
+  };
+
+  struct might_use_tail_padding : public A {
+    struct {
+      char a:1;
+      char b:2;
+      char c:2;
+      char d:2;
+      char e:1;
+    } x;
+  };
+  SA(0, sizeof(might_use_tail_padding) == 16);
+}
+
+namespace test16 {
+  struct pod_in_11_only {
+  private:
+    long long x;
+  };
+   
+  struct A  {
+    pod_in_11_only a;
+    char apad;
+  };
+
+  struct B {
+    char bpod;
+    pod_in_11_only b;
+    char bpad;
+  };
+
+  struct C : public A, public B {
+  };
+  
+  struct D : public C {
+  };
+
+  struct might_use_tail_padding : public D {
+    char m;
+  };
+  SA(0, sizeof(might_use_tail_padding) == 40);
+}
+
+namespace test17 {
+  struct pod_in_11_only {
+  private:
+    long long x;
+  };
+   
+  struct A {
+    pod_in_11_only a __attribute__((aligned(512)));
+  };
+
+  struct B {
+    char bpad;
+    pod_in_11_only foo;
+    char btail;
+  };
+
+  struct C {
+    char cpad;
+  };
+
+  struct D {
+    char dpad;
+  };
+    
+  struct might_use_tail_padding : public A, public B, public C, public D {
+    char a;
+  };
+  SA(0, sizeof(might_use_tail_padding) == 512);
+}
+
+namespace test18 {
+  struct pod_in_11_only {
+  private:
+    long long x;
+  };
+   
+  struct A  {
+    pod_in_11_only a;
+    char apad;
+  };
+
+  struct B {
+    char bpod;
+    pod_in_11_only b;
+    char bpad;
+  };
+
+  struct A1  {
+    pod_in_11_only a;
+    char apad;
+  };
+
+  struct B1 {
+    char bpod;
+    pod_in_11_only b;
+    char bpad;
+  };
+
+  struct C : public A, public B {
+  };
+
+  struct D : public A1, public B1 {
+  };
+
+  struct E : public D, public C {
+  };
+
+  struct F : public E {
+  };
+
+  struct might_use_tail_padding : public F {
+    char m;
+  };
+  SA(0, sizeof(might_use_tail_padding) == 80);
+}
+} // namespace PR16537
+
+namespace PR37275 {
+  struct X { char c; };
+
+  struct A { int n; };
+  _Static_assert(_Alignof(A) == _Alignof(int), "");
+  _Static_assert(_Alignof(A[]) == _Alignof(A), "");
+
+  _Static_assert(_Alignof(int[]) == _Alignof(int), "");
+  _Static_assert(_Alignof(char[]) == _Alignof(char), "");
+
+  // __attribute__((packed)) does not apply to base classes.
+  struct __attribute__((packed)) B : X, A {};
+#if defined(CLANG_ABI_COMPAT) && CLANG_ABI_COMPAT <= 6
+  _Static_assert(_Alignof(B) == 1, "");
+  _Static_assert(_Alignof(B[]) == 1, "");
+  //_Static_assert(__builtin_offsetof(B, n) == 1, ""); FIXME
+#else
+  _Static_assert(_Alignof(B) == _Alignof(int), "");
+  _Static_assert(_Alignof(B[]) == _Alignof(int), "");
+  //_Static_assert(__builtin_offsetof(B, n) == 4, ""); FIXME
+#endif
+
+  // #pragma pack does, though.
+#pragma pack(push, 2)
+  struct C : X, A {};
+  _Static_assert(_Alignof(C) == 2, "");
+  _Static_assert(_Alignof(C[]) == 2, "");
+  //_Static_assert(__builtin_offsetof(C, n) == 2, ""); FIXME
+
+  struct __attribute__((packed)) D : X, A {};
+#if defined(CLANG_ABI_COMPAT) && CLANG_ABI_COMPAT <= 6
+  _Static_assert(_Alignof(D) == 1, "");
+  //_Static_assert(__builtin_offsetof(D, n) == 1, ""); FIXME
+#else
+  _Static_assert(_Alignof(D) == 2, "");
+  //_Static_assert(__builtin_offsetof(D, n) == 2, ""); FIXME
+#endif
+#pragma pack(pop)
+}
+
+namespace non_pod {
+struct t1 {
+protected:
+  int a;
+};
+// GCC prints warning: ignoring packed attribute because of unpacked non-POD field 't1 t2::v1'`
+struct t2 {
+  char c1;
+  short s1;
+  char c2;
+  t1 v1;
+} __attribute__((packed));
+#if defined(CLANG_ABI_COMPAT) && CLANG_ABI_COMPAT <= 15
+_Static_assert(_Alignof(t1) == 4, "");
+_Static_assert(_Alignof(t1[]) == 4, "");
+_Static_assert(_Alignof(t2) == 1, "");
+_Static_assert(_Alignof(t2[]) == 1, "");
+#else
+_Static_assert(_Alignof(t1) == 4, "");
+_Static_assert(_Alignof(t1[]) == 4, "");
+_Static_assert(_Alignof(t2) == 4, "");
+_Static_assert(_Alignof(t2[]) == 4, "");
+#endif
+_Static_assert(sizeof(t2) == 8, ""); // it's still packing the rest of the struct
+} // namespace non_pod
+
+namespace non_pod_packed {
+struct t1 {
+protected:
+  int a;
+} __attribute__((packed));
+struct t2 {
+  t1 v1;
+} __attribute__((packed));
+_Static_assert(_Alignof(t1) == 1, "");
+_Static_assert(_Alignof(t2) == 1, "");
+} // namespace non_pod_packed
+
+namespace non_pod_packed_packed {
+struct B {
+  int b;
+};
+struct  FromB : B {
+} __attribute__((packed));
+struct C {
+  char a[3];
+  FromB b;
+} __attribute__((packed));
+//_Static_assert(__builtin_offsetof(C, b) == 3, ""); FIXME
+}
+
+namespace cxx11_pod {
+struct t1 {
+  t1() = default;
+  t1(const t1&) = delete;
+  ~t1() = delete;
+  t1(t1&&) = default;
+  int a;
+  char c;
+};
+struct t2 {
+  t1 v1;
+} __attribute__((packed));
+_Static_assert(_Alignof(t2) == 1, "");
+struct t3 : t1 {
+  char c;
+};
+#if defined(CLANG_ABI_COMPAT) && CLANG_ABI_COMPAT <= 15
+_Static_assert(sizeof(t3) == 8, "");
+#else
+_Static_assert(sizeof(t3) == 12, "");
+#endif
+}
diff --git a/clang/test/AST/Interp/cxx20.cpp b/clang/test/AST/Interp/cxx20.cpp
--- a/clang/test/AST/Interp/cxx20.cpp
+++ b/clang/test/AST/Interp/cxx20.cpp
@@ -1,6 +1,10 @@
 // RUN: %clang_cc1 -fexperimental-new-constant-interpreter -std=c++20 -verify %s
 // RUN: %clang_cc1 -std=c++20 -verify=ref %s
 
+void test_alignas_operand() {
+  alignas(8) char dummy;
+  static_assert(__alignof(dummy) == 8);
+}
 
 constexpr int getMinus5() {
   int a = 10;