Implement support for variable length arrays in C++. VLAs are limited

in several important ways:

  - VLAs of non-POD types are not permitted.
  - VLAs cannot be used in conjunction with C++ templates.

These restrictions are intended to keep VLAs out of the parts of the
C++ type system where they cause the most trouble. Fixes PR5678 and
<rdar://problem/8013618>.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@104443 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 80 insertions, 0 deletions

diff --git a/test/SemaCXX/c99-variable-length-array.cpp b/test/SemaCXX/c99-variable-length-array.cpp
new file mode 100644
index 0000000000..a792951252
--- /dev/null
+++ b/test/SemaCXX/c99-variable-length-array.cpp
@@ -0,0 +1,80 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s
+struct NonPOD {
+  NonPOD();
+};
+
+struct NonPOD2 {
+  NonPOD np;
+};
+
+struct POD {
+  int x;
+  int y;
+};
+
+// We allow VLAs of POD types, only.
+void vla(int N) {
+  int array1[N];
+  POD array2[N];
+  NonPOD array3[N]; // expected-error{{variable length array of non-POD element type 'NonPOD'}}
+  NonPOD2 array4[N][3]; // expected-error{{variable length array of non-POD element type 'NonPOD2'}}
+}
+
+// We disallow VLAs in templates
+template<typename T>
+void vla_in_template(int N, T t) {
+  int array1[N]; // expected-error{{variable length array cannot be used in a template definition}}
+}
+
+struct HasConstantValue {
+  static const unsigned int value = 2;
+};
+
+struct HasNonConstantValue {
+  static unsigned int value;
+};
+
+template<typename T>
+void vla_in_template(T t) {
+  int array2[T::value]; // expected-error{{variable length array cannot be used in a template instantiation}}
+}
+
+template void vla_in_template<HasConstantValue>(HasConstantValue);
+template void vla_in_template<HasNonConstantValue>(HasNonConstantValue); // expected-note{{instantiation of}}
+
+template<typename T> struct X0 { };
+
+// Cannot use any variably-modified type with a template parameter or
+// argument.
+void inst_with_vla(int N) {
+  int array[N];
+  X0<__typeof__(array)> x0a; // expected-error{{variably modified type 'typeof (array)' (aka 'int [N]') cannot be used as a template argument}}
+}
+
+template<typename T>
+struct X1 {
+  template<int (&Array)[T::value]> // expected-error{{variable length array cannot be used in a template instantiation}}
+  struct Inner {
+    
+  };
+};
+
+X1<HasConstantValue> x1a;
+X1<HasNonConstantValue> x1b; // expected-note{{in instantiation of}}
+
+// Template argument deduction does not allow deducing a size from a VLA.
+template<typename T, unsigned N>
+void accept_array(T (&array)[N]); // expected-note{{candidate template ignored: failed template argument deduction}}
+
+void test_accept_array(int N) {
+  int array[N];
+  accept_array(array); // expected-error{{no matching function for call to 'accept_array'}}
+}
+
+// Variably-modified types cannot be used in local classes.
+void local_classes(int N) {
+  struct X {
+    int size;
+    int array[N]; // expected-error{{fields must have a constant size: 'variable length array in structure' extension will never be supported}}
+  };
+}