[libc++] Remove redundant assertion in std::span::subspan

That is already checked later in the function as `__count <= size() - __offset`.

rdar://107884996

Differential Revision: https://reviews.llvm.org/D148030

Author: ldionne

libcxx/include/span

@@ -327,7 +327,6 @@ public:
        subspan(size_type __offset, size_type __count = dynamic_extent) const noexcept
     {
         _LIBCPP_ASSERT(__offset <= size(), "span<T, N>::subspan(offset, count): offset out of range");
-        _LIBCPP_ASSERT(__count  <= size() || __count == dynamic_extent, "span<T, N>::subspan(offset, count): count out of range");
         if (__count == dynamic_extent)
             return {data() + __offset, size() - __offset};
         _LIBCPP_ASSERT(__count <= size() - __offset, "span<T, N>::subspan(offset, count): offset + count out of range");
@@ -493,7 +492,6 @@ public:
     subspan(size_type __offset, size_type __count = dynamic_extent) const noexcept
     {
         _LIBCPP_ASSERT(__offset <= size(), "span<T>::subspan(offset, count): offset out of range");
-        _LIBCPP_ASSERT(__count <= size() || __count == dynamic_extent, "span<T>::subspan(offset, count): count out of range");
         if (__count == dynamic_extent)
             return {data() + __offset, size() - __offset};
         _LIBCPP_ASSERT(__count <= size() - __offset, "span<T>::subspan(offset, count): offset + count out of range");

libcxx/test/libcxx/containers/views/views.span/span.sub/assert.subspan.pass.cpp

@@ -38,7 +38,7 @@ int main(int, char**) {
         TEST_LIBCPP_ASSERT_FAILURE(s.subspan(4), "span<T>::subspan(offset, count): offset out of range");
         TEST_LIBCPP_ASSERT_FAILURE(s.subspan<4>(), "span<T>::subspan<Offset, Count>(): Offset out of range");
 
-        TEST_LIBCPP_ASSERT_FAILURE(s.subspan(0, 4), "span<T>::subspan(offset, count): count out of range");
+        TEST_LIBCPP_ASSERT_FAILURE(s.subspan(0, 4), "span<T>::subspan(offset, count): offset + count out of range");
         TEST_LIBCPP_ASSERT_FAILURE((s.subspan<0, 4>()), "span<T>::subspan<Offset, Count>(): Offset + Count out of range");
 
         TEST_LIBCPP_ASSERT_FAILURE(s.subspan(1, 3), "span<T>::subspan(offset, count): offset + count out of range");
@@ -50,7 +50,7 @@ int main(int, char**) {
         TEST_LIBCPP_ASSERT_FAILURE(s.subspan(4), "span<T, N>::subspan(offset, count): offset out of range");
         // s.subspan<4>() caught at compile-time (tested in libcxx/test/std/containers/views/views.span/span.sub/subspan.verify.cpp)
 
-        TEST_LIBCPP_ASSERT_FAILURE(s.subspan(0, 4), "span<T, N>::subspan(offset, count): count out of range");
+        TEST_LIBCPP_ASSERT_FAILURE(s.subspan(0, 4), "span<T, N>::subspan(offset, count): offset + count out of range");
         // s.subspan<0, 4>() caught at compile-time (tested in libcxx/test/std/containers/views/views.span/span.sub/subspan.verify.cpp)
 
         TEST_LIBCPP_ASSERT_FAILURE(s.subspan(1, 3), "span<T, N>::subspan(offset, count): offset + count out of range");