BuildVectorType with a dependent (array) type is crashing the compiler - Fix for PR-47542

[rnk]

clang/lib/Sema/SemaType.cpp

2523

It looks like clang and gcc treat this attribute on array types differently. Consider the non-dependent case:
https://gcc.godbolt.org/z/n6Prfd

typedef int myvect[4] __attribute__((vector_size(16)));

GCC treats this as an array of four 16 byte vectors. Clang tries to apply the attribute to the array type and rejects it here, rather than applying it to the inner type.

I think the change is correct, but I'd suggest simplifying the condition: we can reject the vector_size attribute on all array types, whether they are dependent or not. You should be able to remove the CurType->isDependentType() && clause. Can you make sure we have a test for the non-dependent array type case? You can use the typedef I have above.

[rnk]

Thanks!

[zahiraam]

In D88150#2298923, @rnk wrote:

Thanks!

Thank you! Would you mind merge it in please? Thanks.

clang/lib/Sema/SemaType.cpp

QualType Sema::BuildArrayType(QualType T, ArrayType::ArraySizeModifier ASM,
 
   return T;
 }
 
 QualType Sema::BuildVectorType(QualType CurType, Expr *SizeExpr,
                                SourceLocation AttrLoc) {
   // The base type must be integer (not Boolean or enumeration) or float, and
   // can't already be a vector.
-  if (!CurType->isDependentType() &&
+  if ((!CurType->isDependentType() &&
        (!CurType->isBuiltinType() || CurType->isBooleanType() ||
-       (!CurType->isIntegerType() && !CurType->isRealFloatingType()))) {
+        (!CurType->isIntegerType() && !CurType->isRealFloatingType()))) ||
+      CurType->isArrayType()) {
     Diag(AttrLoc, diag::err_attribute_invalid_vector_type) << CurType;
     return QualType();
   }
 
   if (SizeExpr->isTypeDependent() || SizeExpr->isValueDependent())
     return Context.getDependentVectorType(CurType, SizeExpr, AttrLoc,
                                                VectorType::GenericVector);
 

clang/test/SemaCXX/attr-gnu.cpp

 // RUN: %clang_cc1 -std=gnu++17 -fsyntax-only -fms-compatibility -verify %s
 
 void f() {
   // GNU-style attributes are prohibited in this position.
   auto P = new int * __attribute__((vector_size(8))); // expected-error {{an attribute list cannot appear here}} \
                                                       // expected-error {{invalid vector element type 'int *'}}
 
   // Ensure that MS type attribute keywords are still supported in this
   // position.
   auto P2 = new int * __sptr; // Ok
 }
 
 void g(int a[static [[]] 5]); // expected-error {{static array size is a C99 feature, not permitted in C++}}
 
+template<typename T> struct A {
+  int x[sizeof(T)] __attribute((vector_size(8))); // expected-error {{invalid vector element type 'int [sizeof(T)]'}}
+};
+
+typedef int myvect[4] __attribute__((vector_size(16))); // expected-error {{invalid vector element type 'int [4]'}}
+void foo(myvect *in, myvect *out) { (*out)[0] = (*in)[0]; }
+
 namespace {
 class B {
 public:
   virtual void test() {}
   virtual void test2() {}
   virtual void test3() {}
 };