[Sema][SVE] Reject arrays of sizeless types

The SVE ACLE doesn't allow arrays of sizeless types.  At the moment
clang accepts the TU:

  __SVInt8_t x[2];

but trying to code-generate it triggers the LLVM assertion:

  llvm/lib/IR/Type.cpp:588: static llvm::ArrayType* llvm::ArrayType::get(llvm::Type*, uint64_t): Assertion `isValidElementType(ElementType) && "Invalid type for array element!"' failed.

This patch reports an appropriate error instead.

The rules are slightly more restrictive than for general incomplete types.
For example:

  struct s;
  typedef struct s arr[2];

is valid as far as it goes, whereas arrays of sizeless types are
invalid in all contexts.  BuildArrayType therefore needs a specific
check for isSizelessType in addition to the usual handling of
incomplete types.

Differential Revision: https://reviews.llvm.org/D76082

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -5895,8 +5895,8 @@ def err_flexible_array_init_needs_braces : Error<
   "flexible array requires brace-enclosed initializer">;
 def err_illegal_decl_array_of_functions : Error<
   "'%0' declared as array of functions of type %1">;
-def err_illegal_decl_array_incomplete_type : Error<
-  "array has incomplete element type %0">;
+def err_array_incomplete_or_sizeless_type : Error<
+  "array has %select{incomplete|sizeless}0 element type %1">;
 def err_illegal_message_expr_incomplete_type : Error<
   "Objective-C message has incomplete result type %0">;
 def err_illegal_decl_array_of_references : Error<

clang/lib/Sema/SemaDecl.cpp

@@ -12385,9 +12385,9 @@ void Sema::ActOnUninitializedDecl(Decl *RealDecl) {
       if (!Var->isInvalidDecl()) {
         if (const IncompleteArrayType *ArrayT
                                     = Context.getAsIncompleteArrayType(Type)) {
-          if (RequireCompleteType(Var->getLocation(),
-                                  ArrayT->getElementType(),
-                                  diag::err_illegal_decl_array_incomplete_type))
+          if (RequireCompleteSizedType(
+                  Var->getLocation(), ArrayT->getElementType(),
+                  diag::err_array_incomplete_or_sizeless_type))
             Var->setInvalidDecl();
         } else if (Var->getStorageClass() == SC_Static) {
           // C99 6.9.2p3: If the declaration of an identifier for an object is

clang/lib/Sema/SemaExpr.cpp

@@ -6175,10 +6175,10 @@ Sema::BuildCompoundLiteralExpr(SourceLocation LParenLoc, TypeSourceInfo *TInfo,
   QualType literalType = TInfo->getType();
 
   if (literalType->isArrayType()) {
-    if (RequireCompleteType(LParenLoc, Context.getBaseElementType(literalType),
-          diag::err_illegal_decl_array_incomplete_type,
-          SourceRange(LParenLoc,
-                      LiteralExpr->getSourceRange().getEnd())))
+    if (RequireCompleteSizedType(
+            LParenLoc, Context.getBaseElementType(literalType),
+            diag::err_array_incomplete_or_sizeless_type,
+            SourceRange(LParenLoc, LiteralExpr->getSourceRange().getEnd())))
       return ExprError();
     if (literalType->isVariableArrayType())
       return ExprError(Diag(LParenLoc, diag::err_variable_object_no_init)

clang/lib/Sema/SemaType.cpp

@@ -2214,7 +2214,7 @@ QualType Sema::BuildArrayType(QualType T, ArrayType::ArraySizeModifier ASM,
     }
 
     if (T->isVoidType() || T->isIncompleteArrayType()) {
-      Diag(Loc, diag::err_illegal_decl_array_incomplete_type) << T;
+      Diag(Loc, diag::err_array_incomplete_or_sizeless_type) << 0 << T;
       return QualType();
     }
 
@@ -2232,11 +2232,16 @@ QualType Sema::BuildArrayType(QualType T, ArrayType::ArraySizeModifier ASM,
   } else {
     // C99 6.7.5.2p1: If the element type is an incomplete or function type,
     // reject it (e.g. void ary[7], struct foo ary[7], void ary[7]())
-    if (RequireCompleteType(Loc, T,
-                            diag::err_illegal_decl_array_incomplete_type))
+    if (RequireCompleteSizedType(Loc, T,
+                                 diag::err_array_incomplete_or_sizeless_type))
       return QualType();
   }
 
+  if (T->isSizelessType()) {
+    Diag(Loc, diag::err_array_incomplete_or_sizeless_type) << 1 << T;
+    return QualType();
+  }
+
   if (T->isFunctionType()) {
     Diag(Loc, diag::err_illegal_decl_array_of_functions)
       << getPrintableNameForEntity(Entity) << T;

clang/test/Sema/sizeless-1.c

@@ -51,6 +51,8 @@ void unused() {
 
 struct incomplete_struct *incomplete_ptr;
 
+typedef svint8_t sizeless_array[1]; // expected-error {{array has sizeless element type}}
+
 void func(int sel) {
   static svint8_t static_int8; // expected-error {{non-local variable with sizeless type 'svint8_t'}}
 
@@ -93,6 +95,9 @@ void func(int sel) {
   _Atomic svint8_t atomic_int8;      // expected-error {{_Atomic cannot be applied to sizeless type 'svint8_t'}}
   __restrict svint8_t restrict_int8; // expected-error {{requires a pointer or reference}}
 
+  svint8_t array_int8[1];          // expected-error {{array has sizeless element type}}
+  svint8_t array_int8_init[] = {}; // expected-error {{array has sizeless element type}}
+
   _Bool test_int8 = init_int8; // expected-error {{initializing '_Bool' with an expression of incompatible type 'svint8_t'}}
 
   int int_int8 = init_int8; // expected-error {{initializing 'int' with an expression of incompatible type 'svint8_t'}}

clang/test/SemaCXX/sizeless-1.cpp

@@ -61,6 +61,8 @@ void unused() {
 
 struct incomplete_struct *incomplete_ptr;
 
+typedef svint8_t sizeless_array[1]; // expected-error {{array has sizeless element type}}
+
 void func(int sel) {
   static svint8_t static_int8; // expected-error {{non-local variable with sizeless type 'svint8_t'}}
 
@@ -107,6 +109,9 @@ void func(int sel) {
   _Atomic svint8_t atomic_int8;      // expected-error {{_Atomic cannot be applied to sizeless type 'svint8_t'}}
   __restrict svint8_t restrict_int8; // expected-error {{requires a pointer or reference}}
 
+  svint8_t array_int8[1];          // expected-error {{array has sizeless element type}}
+  svint8_t array_int8_init[] = {}; // expected-error {{array has sizeless element type}}
+
   bool test_int8 = init_int8; // expected-error {{cannot initialize a variable of type 'bool' with an lvalue of type 'svint8_t'}}
 
   int int_int8 = init_int8; // expected-error {{cannot initialize a variable of type 'int' with an lvalue of type 'svint8_t'}}
@@ -283,6 +288,11 @@ struct s_ptr_template {
   T *y;
 };
 
+template <typename T>
+struct s_array_template {
+  T y[1]; // expected-error {{array has sizeless element type}}
+};
+
 struct widget {
   widget(s_ptr_template<int>);
   svint8_t operator[](int);
@@ -330,6 +340,13 @@ template <typename T>
 void template_fn_rvalue_ref(T &&) {}
 #endif
 
+#if __cplusplus >= 201103L
+template <typename T>
+using array_alias = T[1]; // expected-error {{array has sizeless element type '__SVInt8_t'}}
+extern array_alias<int> *array_alias_int_ptr;
+extern array_alias<svint8_t> *array_alias_int8_ptr; // expected-note {{in instantiation of template type alias 'array_alias' requested here}}
+#endif
+
 void cxx_only(int sel) {
   svint8_t local_int8;
   svint16_t local_int16;
@@ -372,6 +389,9 @@ void cxx_only(int sel) {
   widget w(1);
   local_int8 = w[1];
 
+  s_array_template<int> st_array_int;
+  s_array_template<svint8_t> st_array_svint8; // expected-note {{in instantiation}}
+
   local_int8 = static_cast<svint8_t>(wrapper<svint8_t>());
   local_int16 = static_cast<svint8_t>(wrapper<svint8_t>()); // expected-error {{assigning to 'svint16_t' (aka '__SVInt16_t') from incompatible type 'svint8_t'}}