diff --git a/libcxx/cmake/caches/Generic-debug.cmake b/libcxx/cmake/caches/Generic-debug.cmake
new file mode 100644
--- /dev/null
+++ b/libcxx/cmake/caches/Generic-debug.cmake
@@ -0,0 +1,2 @@
+set(LIBCXX_TEST_PARAMS "std=c++2b" "debug_level=1" "additional_features=LIBCXX-DEBUG-FIXME" CACHE STRING "")
+set(LIBCXXABI_TEST_PARAMS "${LIBCXX_TEST_PARAMS}" CACHE STRING "")
diff --git a/libcxx/include/iterator b/libcxx/include/iterator
--- a/libcxx/include/iterator
+++ b/libcxx/include/iterator
@@ -476,10 +476,10 @@
 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
 void advance(_InputIter& __i, _Distance __orig_n)
 {
-    _LIBCPP_ASSERT(__orig_n >= 0 || __is_cpp17_bidirectional_iterator<_InputIter>::value,
-                   "Attempt to advance(it, n) with negative n on a non-bidirectional iterator");
     typedef decltype(_VSTD::__convert_to_integral(__orig_n)) _IntegralSize;
     _IntegralSize __n = __orig_n;
+    _LIBCPP_ASSERT(__n >= 0 || __is_cpp17_bidirectional_iterator<_InputIter>::value,
+                   "Attempt to advance(it, n) with negative n on a non-bidirectional iterator");
     _VSTD::__advance(__i, __n, typename iterator_traits<_InputIter>::iterator_category());
 }
 
diff --git a/libcxx/src/debug.cpp b/libcxx/src/debug.cpp
--- a/libcxx/src/debug.cpp
+++ b/libcxx/src/debug.cpp
@@ -438,7 +438,7 @@
     __i_node* j = __find_iterator(__j);
     __c_node* ci = i != nullptr ? i->__c_ : nullptr;
     __c_node* cj = j != nullptr ? j->__c_ : nullptr;
-    return ci != nullptr && ci == cj;
+    return ci == cj;
 }
 
 void
diff --git a/libcxx/test/libcxx/containers/sequences/vector/robust_against_adl.pass.cpp b/libcxx/test/libcxx/containers/sequences/vector/robust_against_adl.pass.cpp
--- a/libcxx/test/libcxx/containers/sequences/vector/robust_against_adl.pass.cpp
+++ b/libcxx/test/libcxx/containers/sequences/vector/robust_against_adl.pass.cpp
@@ -7,6 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: c++03
+// UNSUPPORTED: debug_level_0, debug_level_1
 
 // <vector>
 
diff --git a/libcxx/test/libcxx/diagnostics/nodiscard_extensions.pass.cpp b/libcxx/test/libcxx/diagnostics/nodiscard_extensions.pass.cpp
--- a/libcxx/test/libcxx/diagnostics/nodiscard_extensions.pass.cpp
+++ b/libcxx/test/libcxx/diagnostics/nodiscard_extensions.pass.cpp
@@ -18,6 +18,8 @@
 // UNSUPPORTED: apple-clang-9
 // UNSUPPORTED: gcc-5
 
+// XFAIL: LIBCXX-DEBUG-FIXME
+
 // All entities to which libc++ applies [[nodiscard]] as an extension should
 // be tested here and in nodiscard_extensions.fail.cpp. They should also
 // be listed in `UsingLibcxx.rst` in the documentation for the extension.
diff --git a/libcxx/test/std/algorithms/alg.sorting/alg.merge/inplace_merge_comp.pass.cpp b/libcxx/test/std/algorithms/alg.sorting/alg.merge/inplace_merge_comp.pass.cpp
--- a/libcxx/test/std/algorithms/alg.sorting/alg.merge/inplace_merge_comp.pass.cpp
+++ b/libcxx/test/std/algorithms/alg.sorting/alg.merge/inplace_merge_comp.pass.cpp
@@ -6,6 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
+// XFAIL: LIBCXX-DEBUG-FIXME
+
 // <algorithm>
 
 // template<BidirectionalIterator Iter, StrictWeakOrder<auto, Iter::value_type> Compare>
diff --git a/libcxx/test/std/containers/unord/unord.map/unord.map.modifiers/insert_hint_const_lvalue.pass.cpp b/libcxx/test/std/containers/unord/unord.map/unord.map.modifiers/insert_hint_const_lvalue.pass.cpp
--- a/libcxx/test/std/containers/unord/unord.map/unord.map.modifiers/insert_hint_const_lvalue.pass.cpp
+++ b/libcxx/test/std/containers/unord/unord.map/unord.map.modifiers/insert_hint_const_lvalue.pass.cpp
@@ -35,7 +35,7 @@
     assert(r->second == 3);
 
     const VT v2(3.5, 4);
-    r = c.insert(c.end(), v2);
+    r = c.insert(r, v2);
     assert(c.size() == 1);
     assert(r->first == 3.5);
     assert(r->second == 3);
diff --git a/libcxx/test/std/containers/unord/unord.map/unord.map.modifiers/insert_hint_rvalue.pass.cpp b/libcxx/test/std/containers/unord/unord.map/unord.map.modifiers/insert_hint_rvalue.pass.cpp
--- a/libcxx/test/std/containers/unord/unord.map/unord.map.modifiers/insert_hint_rvalue.pass.cpp
+++ b/libcxx/test/std/containers/unord/unord.map/unord.map.modifiers/insert_hint_rvalue.pass.cpp
@@ -38,7 +38,7 @@
         assert(r->first == 3.5);
         assert(r->second == 3);
 
-        r = c.insert(c.end(), P(3.5, static_cast<short>(4)));
+        r = c.insert(r, P(3.5, static_cast<short>(4)));
         assert(c.size() == 1);
         assert(r->first == 3.5);
         assert(r->second == 3);
@@ -64,7 +64,7 @@
         assert(r->first == 3);
         assert(r->second == 3);
 
-        r = c.insert(c.end(), P(3, 4));
+        r = c.insert(r, P(3, 4));
         assert(c.size() == 1);
         assert(r->first == 3);
         assert(r->second == 3);
@@ -91,7 +91,7 @@
         assert(r->first == 3.5);
         assert(r->second == 3);
 
-        r = c.insert(c.end(), P(3.5, static_cast<short>(4)));
+        r = c.insert(r, P(3.5, static_cast<short>(4)));
         assert(c.size() == 1);
         assert(r->first == 3.5);
         assert(r->second == 3);
@@ -118,7 +118,7 @@
         assert(r->first == 3);
         assert(r->second == 3);
 
-        r = c.insert(c.end(), P(3, 4));
+        r = c.insert(r, P(3, 4));
         assert(c.size() == 1);
         assert(r->first == 3);
         assert(r->second == 3);
@@ -143,7 +143,7 @@
         assert(r->first == 3.5);
         assert(r->second == 3);
 
-        r = c.insert(c.end(), {3.5, 4});
+        r = c.insert(r, {3.5, 4});
         assert(c.size() == 1);
         assert(r->first == 3.5);
         assert(r->second == 3);
diff --git a/libcxx/test/std/containers/unord/unord.multimap/unord.multimap.modifiers/insert_hint_const_lvalue.pass.cpp b/libcxx/test/std/containers/unord/unord.multimap/unord.multimap.modifiers/insert_hint_const_lvalue.pass.cpp
--- a/libcxx/test/std/containers/unord/unord.multimap/unord.multimap.modifiers/insert_hint_const_lvalue.pass.cpp
+++ b/libcxx/test/std/containers/unord/unord.multimap/unord.multimap.modifiers/insert_hint_const_lvalue.pass.cpp
@@ -35,7 +35,7 @@
     assert(r->second == 3);
 
     const VT v2(3.5, 4);
-    r = c.insert(c.end(), v2);
+    r = c.insert(r, v2);
     assert(c.size() == 2);
     assert(r->first == 3.5);
     assert(r->second == 4);
diff --git a/libcxx/test/std/containers/unord/unord.multiset/insert_hint_const_lvalue.pass.cpp b/libcxx/test/std/containers/unord/unord.multiset/insert_hint_const_lvalue.pass.cpp
--- a/libcxx/test/std/containers/unord/unord.multiset/insert_hint_const_lvalue.pass.cpp
+++ b/libcxx/test/std/containers/unord/unord.multiset/insert_hint_const_lvalue.pass.cpp
@@ -33,7 +33,7 @@
     assert(c.size() == 1);
     assert(*r == 3.5);
 
-    r = c.insert(c.end(), v1);
+    r = c.insert(r, v1);
     assert(c.size() == 2);
     assert(*r == 3.5);
 
diff --git a/libcxx/test/std/containers/unord/unord.set/insert_hint_const_lvalue.pass.cpp b/libcxx/test/std/containers/unord/unord.set/insert_hint_const_lvalue.pass.cpp
--- a/libcxx/test/std/containers/unord/unord.set/insert_hint_const_lvalue.pass.cpp
+++ b/libcxx/test/std/containers/unord/unord.set/insert_hint_const_lvalue.pass.cpp
@@ -33,17 +33,17 @@
     assert(c.size() == 1);
     assert(*r == 3.5);
 
-    r = c.insert(e, v1);
+    r = c.insert(r, v1);
     assert(c.size() == 1);
     assert(*r == 3.5);
 
     const VT v2(4.5);
-    r = c.insert(e, v2);
+    r = c.insert(c.end(), v2);
     assert(c.size() == 2);
     assert(*r == 4.5);
 
     const VT v3(5.5);
-    r = c.insert(e, v3);
+    r = c.insert(c.end(), v3);
     assert(c.size() == 3);
     assert(*r == 5.5);
 }
diff --git a/libcxx/test/std/containers/unord/unord.set/insert_hint_rvalue.pass.cpp b/libcxx/test/std/containers/unord/unord.set/insert_hint_rvalue.pass.cpp
--- a/libcxx/test/std/containers/unord/unord.set/insert_hint_rvalue.pass.cpp
+++ b/libcxx/test/std/containers/unord/unord.set/insert_hint_rvalue.pass.cpp
@@ -28,7 +28,8 @@
         typedef C::iterator R;
         typedef double P;
         C c;
-        R r = c.insert(c.end(), P(3.5));
+        typename C::const_iterator e = c.end();
+        R r = c.insert(e, P(3.5));
         assert(c.size() == 1);
         assert(*r == 3.5);
 
@@ -50,7 +51,8 @@
         typedef C::iterator R;
         typedef MoveOnly P;
         C c;
-        R r = c.insert(c.end(), P(3));
+        typename C::const_iterator e = c.end();
+        R r = c.insert(e, P(3));
         assert(c.size() == 1);
         assert(*r == 3);
 
@@ -72,7 +74,8 @@
         typedef C::iterator R;
         typedef double P;
         C c;
-        R r = c.insert(c.end(), P(3.5));
+        typename C::const_iterator e = c.end();
+        R r = c.insert(e, P(3.5));
         assert(c.size() == 1);
         assert(*r == 3.5);
 
@@ -94,7 +97,8 @@
         typedef C::iterator R;
         typedef MoveOnly P;
         C c;
-        R r = c.insert(c.end(), P(3));
+        typename C::const_iterator e = c.end();
+        R r = c.insert(e, P(3));
         assert(c.size() == 1);
         assert(*r == 3);
 
diff --git a/libcxx/test/std/containers/views/span.cons/deduct.pass.cpp b/libcxx/test/std/containers/views/span.cons/deduct.pass.cpp
--- a/libcxx/test/std/containers/views/span.cons/deduct.pass.cpp
+++ b/libcxx/test/std/containers/views/span.cons/deduct.pass.cpp
@@ -7,6 +7,7 @@
 //
 //===---------------------------------------------------------------------===//
 // UNSUPPORTED: c++03, c++11, c++14, c++17
+// XFAIL: LIBCXX-DEBUG-FIXME
 
 // <span>
 
diff --git a/libcxx/test/std/containers/views/span.iterators/begin.pass.cpp b/libcxx/test/std/containers/views/span.iterators/begin.pass.cpp
--- a/libcxx/test/std/containers/views/span.iterators/begin.pass.cpp
+++ b/libcxx/test/std/containers/views/span.iterators/begin.pass.cpp
@@ -6,6 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 // UNSUPPORTED: c++03, c++11, c++14, c++17
+// XFAIL: LIBCXX-DEBUG-FIXME
 
 // <span>
 
diff --git a/libcxx/test/std/containers/views/span.iterators/end.pass.cpp b/libcxx/test/std/containers/views/span.iterators/end.pass.cpp
--- a/libcxx/test/std/containers/views/span.iterators/end.pass.cpp
+++ b/libcxx/test/std/containers/views/span.iterators/end.pass.cpp
@@ -6,6 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 // UNSUPPORTED: c++03, c++11, c++14, c++17
+// XFAIL: LIBCXX-DEBUG-FIXME
 
 // <span>
 
diff --git a/libcxx/test/std/containers/views/span.iterators/rbegin.pass.cpp b/libcxx/test/std/containers/views/span.iterators/rbegin.pass.cpp
--- a/libcxx/test/std/containers/views/span.iterators/rbegin.pass.cpp
+++ b/libcxx/test/std/containers/views/span.iterators/rbegin.pass.cpp
@@ -6,6 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 // UNSUPPORTED: c++03, c++11, c++14, c++17
+// XFAIL: LIBCXX-DEBUG-FIXME
 
 // <span>
 
diff --git a/libcxx/test/std/containers/views/span.iterators/rend.pass.cpp b/libcxx/test/std/containers/views/span.iterators/rend.pass.cpp
--- a/libcxx/test/std/containers/views/span.iterators/rend.pass.cpp
+++ b/libcxx/test/std/containers/views/span.iterators/rend.pass.cpp
@@ -6,6 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 // UNSUPPORTED: c++03, c++11, c++14, c++17
+// XFAIL: LIBCXX-DEBUG-FIXME
 
 // <span>
 
diff --git a/libcxx/test/std/containers/views/span.sub/first.pass.cpp b/libcxx/test/std/containers/views/span.sub/first.pass.cpp
--- a/libcxx/test/std/containers/views/span.sub/first.pass.cpp
+++ b/libcxx/test/std/containers/views/span.sub/first.pass.cpp
@@ -7,6 +7,7 @@
 //
 //===---------------------------------------------------------------------===//
 // UNSUPPORTED: c++03, c++11, c++14, c++17
+// XFAIL: LIBCXX-DEBUG-FIXME
 
 // <span>
 
diff --git a/libcxx/test/std/containers/views/span.sub/last.pass.cpp b/libcxx/test/std/containers/views/span.sub/last.pass.cpp
--- a/libcxx/test/std/containers/views/span.sub/last.pass.cpp
+++ b/libcxx/test/std/containers/views/span.sub/last.pass.cpp
@@ -7,6 +7,7 @@
 //
 //===---------------------------------------------------------------------===//
 // UNSUPPORTED: c++03, c++11, c++14, c++17
+// XFAIL: LIBCXX-DEBUG-FIXME
 
 // <span>
 
diff --git a/libcxx/test/std/containers/views/span.sub/subspan.pass.cpp b/libcxx/test/std/containers/views/span.sub/subspan.pass.cpp
--- a/libcxx/test/std/containers/views/span.sub/subspan.pass.cpp
+++ b/libcxx/test/std/containers/views/span.sub/subspan.pass.cpp
@@ -7,6 +7,7 @@
 //
 //===---------------------------------------------------------------------===//
 // UNSUPPORTED: c++03, c++11, c++14, c++17
+// XFAIL: LIBCXX-DEBUG-FIXME
 
 // <span>
 
diff --git a/libcxx/test/std/input.output/filesystems/class.path/path.nonmember/path.factory.pass.cpp b/libcxx/test/std/input.output/filesystems/class.path/path.nonmember/path.factory.pass.cpp
--- a/libcxx/test/std/input.output/filesystems/class.path/path.nonmember/path.factory.pass.cpp
+++ b/libcxx/test/std/input.output/filesystems/class.path/path.nonmember/path.factory.pass.cpp
@@ -6,6 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
+// XFAIL: LIBCXX-DEBUG-FIXME
+
 // UNSUPPORTED: c++03
 // ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_DISABLE_DEPRECATION_WARNINGS
 
diff --git a/libcxx/test/std/input.output/filesystems/fs.op.funcs/fs.op.proximate/proximate.pass.cpp b/libcxx/test/std/input.output/filesystems/fs.op.funcs/fs.op.proximate/proximate.pass.cpp
--- a/libcxx/test/std/input.output/filesystems/fs.op.funcs/fs.op.proximate/proximate.pass.cpp
+++ b/libcxx/test/std/input.output/filesystems/fs.op.funcs/fs.op.proximate/proximate.pass.cpp
@@ -6,6 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
+// XFAIL: LIBCXX-DEBUG-FIXME
+
 // UNSUPPORTED: c++03
 
 // <filesystem>
diff --git a/libcxx/test/std/numerics/numeric.ops/exclusive.scan/exclusive_scan.pass.cpp b/libcxx/test/std/numerics/numeric.ops/exclusive.scan/exclusive_scan.pass.cpp
--- a/libcxx/test/std/numerics/numeric.ops/exclusive.scan/exclusive_scan.pass.cpp
+++ b/libcxx/test/std/numerics/numeric.ops/exclusive.scan/exclusive_scan.pass.cpp
@@ -6,11 +6,12 @@
 //
 //===----------------------------------------------------------------------===//
 
-// <numeric>
 // UNSUPPORTED: c++03, c++11, c++14
 // UNSUPPORTED: clang-8
 // UNSUPPORTED: gcc-9
 
+// <numeric>
+
 // Became constexpr in C++20
 // template<class InputIterator, class OutputIterator, class T>
 //     OutputIterator exclusive_scan(InputIterator first, InputIterator last,
@@ -23,55 +24,39 @@
 #include <cassert>
 #include <functional>
 #include <iterator>
-#include <vector>
 
 #include "test_macros.h"
 #include "test_iterators.h"
-// FIXME Remove constexpr vector workaround introduced in D90569
-#if TEST_STD_VER > 17
-#include <span>
-#endif
 
-template <class Iter1, class T, class Iter2>
+template <class Iter1, class T>
 TEST_CONSTEXPR_CXX20 void
-test(Iter1 first, Iter1 last, T init, Iter2 rFirst, Iter2 rLast)
+test(Iter1 first, Iter1 last, T init, const T *rFirst, const T *rLast)
 {
-    // C++17 doesn't test constexpr so can use a vector.
-    // C++20 can use vector in constexpr evaluation, but both libc++ and MSVC
-    // don't have the support yet. In these cases use a std::span for the test.
-    // FIXME Remove constexpr vector workaround introduced in D90569
-    size_t size = std::distance(first, last);
-#if TEST_STD_VER < 20 || \
-    (defined(__cpp_lib_constexpr_vector) && __cpp_lib_constexpr_vector >= 201907L)
-
-    std::vector<typename std::iterator_traits<Iter1>::value_type> v(size);
-#else
-    assert((size <= 5) && "Increment the size of the array");
-    typename std::iterator_traits<Iter1>::value_type b[5];
-    std::span<typename std::iterator_traits<Iter1>::value_type> v{b, size};
-#endif
+    assert((rLast - rFirst) <= 5);  // or else increase the size of "out"
+    T out[5];
 
-//  Not in place
-    std::exclusive_scan(first, last, v.begin(), init);
-    assert(std::equal(v.begin(), v.end(), rFirst, rLast));
+    // Not in place
+    T *end = std::exclusive_scan(first, last, out, init);
+    assert(std::equal(out, end, rFirst, rLast));
 
-//  In place
-    std::copy(first, last, v.begin());
-    std::exclusive_scan(v.begin(), v.end(), v.begin(), init);
-    assert(std::equal(v.begin(), v.end(), rFirst, rLast));
+    // In place
+    std::copy(first, last, out);
+    end = std::exclusive_scan(out, end, out, init);
+    assert(std::equal(out, end, rFirst, rLast));
 }
 
 template <class Iter>
 TEST_CONSTEXPR_CXX20 void
 test()
 {
-          int ia[]   = {1, 3, 5, 7,  9};
+    int ia[]         = {1, 3, 5, 7,  9};
     const int pRes[] = {0, 1, 4, 9, 16};
     const unsigned sa = sizeof(ia) / sizeof(ia[0]);
     static_assert(sa == sizeof(pRes) / sizeof(pRes[0]));       // just to be sure
 
-    for (unsigned int i = 0; i < sa; ++i )
+    for (unsigned int i = 0; i < sa; ++i) {
         test(Iter(ia), Iter(ia + i), 0, pRes, pRes + i);
+    }
 }
 
 constexpr size_t triangle(size_t n) { return n*(n+1)/2; }
diff --git a/libcxx/test/std/numerics/numeric.ops/exclusive.scan/exclusive_scan_init_op.pass.cpp b/libcxx/test/std/numerics/numeric.ops/exclusive.scan/exclusive_scan_init_op.pass.cpp
--- a/libcxx/test/std/numerics/numeric.ops/exclusive.scan/exclusive_scan_init_op.pass.cpp
+++ b/libcxx/test/std/numerics/numeric.ops/exclusive.scan/exclusive_scan_init_op.pass.cpp
@@ -6,11 +6,12 @@
 //
 //===----------------------------------------------------------------------===//
 
-// <numeric>
 // UNSUPPORTED: c++03, c++11, c++14
 // UNSUPPORTED: clang-8
 // UNSUPPORTED: gcc-9
 
+// <numeric>
+
 // Became constexpr in C++20
 // template<class InputIterator, class OutputIterator, class T, class BinaryOperation>
 //     OutputIterator
@@ -24,42 +25,25 @@
 #include <cassert>
 #include <functional>
 #include <iterator>
-#include <vector>
 
 #include "test_macros.h"
 #include "test_iterators.h"
-// FIXME Remove constexpr vector workaround introduced in D90569
-#if TEST_STD_VER > 17
-#include <span>
-#endif
 
-template <class Iter1, class T, class Op, class Iter2>
+template <class Iter1, class T, class Op>
 TEST_CONSTEXPR_CXX20 void
-test(Iter1 first, Iter1 last, T init, Op op, Iter2 rFirst, Iter2 rLast)
+test(Iter1 first, Iter1 last, T init, Op op, const T *rFirst, const T *rLast)
 {
-    // C++17 doesn't test constexpr so can use a vector.
-    // C++20 can use vector in constexpr evaluation, but both libc++ and MSVC
-    // don't have the support yet. In these cases use a std::span for the test.
-    // FIXME Remove constexpr vector workaround introduced in D90569
-    size_t size = std::distance(first, last);
-#if TEST_STD_VER < 20 || \
-    (defined(__cpp_lib_constexpr_vector) && __cpp_lib_constexpr_vector >= 201907L)
-
-    std::vector<typename std::iterator_traits<Iter1>::value_type> v(size);
-#else
-    assert((size <= 5) && "Increment the size of the array");
-    typename std::iterator_traits<Iter1>::value_type b[5];
-    std::span<typename std::iterator_traits<Iter1>::value_type> v{b, size};
-#endif
+    assert((rLast - rFirst) <= 5);  // or else increase the size of "out"
+    T out[5];
 
-//  Not in place
-    std::exclusive_scan(first, last, v.begin(), init, op);
-    assert(std::equal(v.begin(), v.end(), rFirst, rLast));
+    // Not in place
+    T *end = std::exclusive_scan(first, last, out, init, op);
+    assert(std::equal(out, end, rFirst, rLast));
 
-//  In place
-    std::copy(first, last, v.begin());
-    std::exclusive_scan(v.begin(), v.end(), v.begin(), init, op);
-    assert(std::equal(v.begin(), v.end(), rFirst, rLast));
+    // In place
+    std::copy(first, last, out);
+    end = std::exclusive_scan(out, end, out, init, op);
+    assert(std::equal(out, end, rFirst, rLast));
 }
 
 
@@ -67,7 +51,7 @@
 TEST_CONSTEXPR_CXX20 void
 test()
 {
-          int ia[]   = {1, 3, 5,  7,   9};
+    int ia[]         = {1, 3, 5,  7,   9};
     const int pRes[] = {0, 1, 4,  9,  16};
     const int mRes[] = {1, 1, 3, 15, 105};
     const unsigned sa = sizeof(ia) / sizeof(ia[0]);
@@ -77,7 +61,7 @@
     for (unsigned int i = 0; i < sa; ++i ) {
         test(Iter(ia), Iter(ia + i), 0, std::plus<>(),       pRes, pRes + i);
         test(Iter(ia), Iter(ia + i), 1, std::multiplies<>(), mRes, mRes + i);
-        }
+    }
 }
 
 TEST_CONSTEXPR_CXX20 bool
@@ -95,18 +79,8 @@
     {
     std::array<unsigned char, 10> v;
     std::iota(v.begin(), v.end(), static_cast<unsigned char>(1));
-    // C++17 doesn't test constexpr so can use a vector.
-    // C++20 can use vector in constexpr evaluation, but both libc++ and MSVC
-    // don't have the support yet. In these cases use a std::span for the test.
-    // FIXME Remove constexpr vector workaround introduced in D90569
-#if TEST_STD_VER < 20 || \
-    (defined(__cpp_lib_constexpr_vector) && __cpp_lib_constexpr_vector >= 201907L)
-    std::vector<size_t> res;
-    std::exclusive_scan(v.begin(), v.end(), std::back_inserter(res), 1, std::multiplies<>());
-#else
     std::array<size_t, 10> res;
     std::exclusive_scan(v.begin(), v.end(), res.begin(), 1, std::multiplies<>());
-#endif
 
     assert(res.size() == 10);
     size_t j = 1;
diff --git a/libcxx/test/std/numerics/numeric.ops/inclusive.scan/inclusive_scan.pass.cpp b/libcxx/test/std/numerics/numeric.ops/inclusive.scan/inclusive_scan.pass.cpp
--- a/libcxx/test/std/numerics/numeric.ops/inclusive.scan/inclusive_scan.pass.cpp
+++ b/libcxx/test/std/numerics/numeric.ops/inclusive.scan/inclusive_scan.pass.cpp
@@ -6,11 +6,12 @@
 //
 //===----------------------------------------------------------------------===//
 
-// <numeric>
 // UNSUPPORTED: c++03, c++11, c++14
 // UNSUPPORTED: clang-8
 // UNSUPPORTED: gcc-9
 
+// <numeric>
+
 // Became constexpr in C++20
 // template<class InputIterator, class OutputIterator, class T>
 //     OutputIterator inclusive_scan(InputIterator first, InputIterator last,
@@ -23,42 +24,25 @@
 #include <cassert>
 #include <functional>
 #include <iterator>
-#include <vector>
 
 #include "test_macros.h"
 #include "test_iterators.h"
-// FIXME Remove constexpr vector workaround introduced in D90569
-#if TEST_STD_VER > 17
-#include <span>
-#endif
 
-template <class Iter1, class Iter2>
+template <class Iter1, class T>
 TEST_CONSTEXPR_CXX20 void
-test(Iter1 first, Iter1 last, Iter2 rFirst, Iter2 rLast)
+test(Iter1 first, Iter1 last, const T *rFirst, const T *rLast)
 {
-    // C++17 doesn't test constexpr so can use a vector.
-    // C++20 can use vector in constexpr evaluation, but both libc++ and MSVC
-    // don't have the support yet. In these cases use a std::span for the test.
-    // FIXME Remove constexpr vector workaround introduced in D90569
-    size_t size = std::distance(first, last);
-#if TEST_STD_VER < 20 || \
-    (defined(__cpp_lib_constexpr_vector) && __cpp_lib_constexpr_vector >= 201907L)
-
-    std::vector<typename std::iterator_traits<Iter1>::value_type> v(size);
-#else
-    assert((size <= 5) && "Increment the size of the array");
-    typename std::iterator_traits<Iter1>::value_type b[5];
-    std::span<typename std::iterator_traits<Iter1>::value_type> v{b, size};
-#endif
+    assert((rLast - rFirst) <= 5);  // or else increase the size of "out"
+    T out[5];
 
-//  Not in place
-    std::inclusive_scan(first, last, v.begin());
-    assert(std::equal(v.begin(), v.end(), rFirst, rLast));
+    // Not in place
+    T *end = std::inclusive_scan(first, last, out);
+    assert(std::equal(out, end, rFirst, rLast));
 
-//  In place
-    std::copy(first, last, v.begin());
-    std::inclusive_scan(v.begin(), v.end(), v.begin());
-    assert(std::equal(v.begin(), v.end(), rFirst, rLast));
+    // In place
+    std::copy(first, last, out);
+    end = std::inclusive_scan(out, end, out);
+    assert(std::equal(out, end, rFirst, rLast));
 }
 
 
@@ -66,13 +50,14 @@
 TEST_CONSTEXPR_CXX20 void
 test()
 {
-          int ia[]   = {1, 3, 5, 7,  9};
+    int ia[]         = {1, 3, 5, 7,  9};
     const int pRes[] = {1, 4, 9, 16, 25};
     const unsigned sa = sizeof(ia) / sizeof(ia[0]);
     static_assert(sa == sizeof(pRes) / sizeof(pRes[0]));       // just to be sure
 
-    for (unsigned int i = 0; i < sa; ++i )
+    for (unsigned int i = 0; i < sa; ++i ) {
         test(Iter(ia), Iter(ia + i), pRes, pRes + i);
+    }
 }
 
 constexpr size_t triangle(size_t n) { return n*(n+1)/2; }
@@ -106,18 +91,8 @@
     }
 
     {
-    // C++17 doesn't test constexpr so can use a vector.
-    // C++20 can use vector in constexpr evaluation, but both libc++ and MSVC
-    // don't have the support yet. In these cases use a std::span for the test.
-    // FIXME Remove constexpr vector workaround introduced in D90569
-#if TEST_STD_VER < 20 || \
-    (defined(__cpp_lib_constexpr_vector) && __cpp_lib_constexpr_vector >= 201907L)
-    std::vector<size_t> v, res;
-    std::inclusive_scan(v.begin(), v.end(), std::back_inserter(res));
-#else
     std::array<size_t, 0> v, res;
     std::inclusive_scan(v.begin(), v.end(), res.begin());
-#endif
     assert(res.empty());
     }
 }
diff --git a/libcxx/test/std/numerics/numeric.ops/inclusive.scan/inclusive_scan_op.pass.cpp b/libcxx/test/std/numerics/numeric.ops/inclusive.scan/inclusive_scan_op.pass.cpp
--- a/libcxx/test/std/numerics/numeric.ops/inclusive.scan/inclusive_scan_op.pass.cpp
+++ b/libcxx/test/std/numerics/numeric.ops/inclusive.scan/inclusive_scan_op.pass.cpp
@@ -6,11 +6,12 @@
 //
 //===----------------------------------------------------------------------===//
 
-// <numeric>
 // UNSUPPORTED: c++03, c++11, c++14
 // UNSUPPORTED: clang-8
 // UNSUPPORTED: gcc-9
 
+// <numeric>
+
 // Became constexpr in C++20
 // template<class InputIterator, class OutputIterator, class T, class BinaryOperation>
 //     OutputIterator
@@ -24,42 +25,25 @@
 #include <cassert>
 #include <functional>
 #include <iterator>
-#include <vector>
 
 #include "test_macros.h"
 #include "test_iterators.h"
-// FIXME Remove constexpr vector workaround introduced in D90569
-#if TEST_STD_VER > 17
-#include <span>
-#endif
 
-template <class Iter1, class Op, class Iter2>
+template <class Iter1, class Op, class T>
 TEST_CONSTEXPR_CXX20 void
-test(Iter1 first, Iter1 last, Op op, Iter2 rFirst, Iter2 rLast)
+test(Iter1 first, Iter1 last, Op op, const T *rFirst, const T *rLast)
 {
-    // C++17 doesn't test constexpr so can use a vector.
-    // C++20 can use vector in constexpr evaluation, but both libc++ and MSVC
-    // don't have the support yet. In these cases use a std::span for the test.
-    // FIXME Remove constexpr vector workaround introduced in D90569
-    size_t size = std::distance(first, last);
-#if TEST_STD_VER < 20 || \
-    (defined(__cpp_lib_constexpr_vector) && __cpp_lib_constexpr_vector >= 201907L)
-
-    std::vector<typename std::iterator_traits<Iter1>::value_type> v(size);
-#else
-    assert((size <= 5) && "Increment the size of the array");
-    typename std::iterator_traits<Iter1>::value_type b[5];
-    std::span<typename std::iterator_traits<Iter1>::value_type> v{b, size};
-#endif
+    assert((rLast - rFirst) <= 5);  // or else increase the size of "out"
+    T out[5];
 
-//  Not in place
-    std::inclusive_scan(first, last, v.begin(), op);
-    assert(std::equal(v.begin(), v.end(), rFirst, rLast));
+    // Not in place
+    T *end = std::inclusive_scan(first, last, out, op);
+    assert(std::equal(out, end, rFirst, rLast));
 
-//  In place
-    std::copy(first, last, v.begin());
-    std::inclusive_scan(v.begin(), v.end(), v.begin(), op);
-    assert(std::equal(v.begin(), v.end(), rFirst, rLast));
+    // In place
+    std::copy(first, last, out);
+    end = std::inclusive_scan(out, end, out, op);
+    assert(std::equal(out, end, rFirst, rLast));
 }
 
 
@@ -67,7 +51,7 @@
 TEST_CONSTEXPR_CXX20 void
 test()
 {
-          int ia[]   = {1, 3,  5,   7,   9};
+    int ia[]         = {1, 3,  5,   7,   9};
     const int pRes[] = {1, 4,  9,  16,  25};
     const int mRes[] = {1, 3, 15, 105, 945};
     const unsigned sa = sizeof(ia) / sizeof(ia[0]);
@@ -77,7 +61,7 @@
     for (unsigned int i = 0; i < sa; ++i ) {
         test(Iter(ia), Iter(ia + i), std::plus<>(),       pRes, pRes + i);
         test(Iter(ia), Iter(ia + i), std::multiplies<>(), mRes, mRes + i);
-        }
+    }
 }
 
 constexpr size_t triangle(size_t n) { return n*(n+1)/2; }
@@ -111,18 +95,8 @@
     }
 
     {
-    // C++17 doesn't test constexpr so can use a vector.
-    // C++20 can use vector in constexpr evaluation, but both libc++ and MSVC
-    // don't have the support yet. In these cases use a std::span for the test.
-    // FIXME Remove constexpr vector workaround introduced in D90569
-#if TEST_STD_VER < 20 || \
-    (defined(__cpp_lib_constexpr_vector) && __cpp_lib_constexpr_vector >= 201907L)
-    std::vector<size_t> v, res;
-    std::inclusive_scan(v.begin(), v.end(), std::back_inserter(res), std::plus<>());
-#else
     std::array<size_t, 0> v, res;
     std::inclusive_scan(v.begin(), v.end(), res.begin(), std::plus<>());
-#endif
     assert(res.empty());
     }
 }
diff --git a/libcxx/test/std/numerics/numeric.ops/inclusive.scan/inclusive_scan_op_init.pass.cpp b/libcxx/test/std/numerics/numeric.ops/inclusive.scan/inclusive_scan_op_init.pass.cpp
--- a/libcxx/test/std/numerics/numeric.ops/inclusive.scan/inclusive_scan_op_init.pass.cpp
+++ b/libcxx/test/std/numerics/numeric.ops/inclusive.scan/inclusive_scan_op_init.pass.cpp
@@ -6,11 +6,12 @@
 //
 //===----------------------------------------------------------------------===//
 
-// <numeric>
 // UNSUPPORTED: c++03, c++11, c++14
 // UNSUPPORTED: clang-8
 // UNSUPPORTED: gcc-9
 
+// <numeric>
+
 // Became constexpr in C++20
 // template<class InputIterator, class OutputIterator, class T, class BinaryOperation>
 //     OutputIterator
@@ -24,42 +25,25 @@
 #include <cassert>
 #include <functional>
 #include <iterator>
-#include <vector>
 
 #include "test_macros.h"
 #include "test_iterators.h"
-// FIXME Remove constexpr vector workaround introduced in D90569
-#if TEST_STD_VER > 17
-#include <span>
-#endif
 
-template <class Iter1, class T, class Op, class Iter2>
+template <class Iter1, class T, class Op>
 TEST_CONSTEXPR_CXX20 void
-test(Iter1 first, Iter1 last, Op op, T init, Iter2 rFirst, Iter2 rLast)
+test(Iter1 first, Iter1 last, Op op, T init, const T *rFirst, const T *rLast)
 {
-    // C++17 doesn't test constexpr so can use a vector.
-    // C++20 can use vector in constexpr evaluation, but both libc++ and MSVC
-    // don't have the support yet. In these cases use a std::span for the test.
-    // FIXME Remove constexpr vector workaround introduced in D90569
-    size_t size = std::distance(first, last);
-#if TEST_STD_VER < 20 || \
-    (defined(__cpp_lib_constexpr_vector) && __cpp_lib_constexpr_vector >= 201907L)
-
-    std::vector<typename std::iterator_traits<Iter1>::value_type> v(size);
-#else
-    assert((size <= 5) && "Increment the size of the array");
-    typename std::iterator_traits<Iter1>::value_type b[5];
-    std::span<typename std::iterator_traits<Iter1>::value_type> v{b, size};
-#endif
+    assert((rLast - rFirst) <= 5);  // or else increase the size of "out"
+    T out[5];
 
-//  Not in place
-    std::inclusive_scan(first, last, v.begin(), op, init);
-    assert(std::equal(v.begin(), v.end(), rFirst, rLast));
+    // Not in place
+    T *end = std::inclusive_scan(first, last, out, op, init);
+    assert(std::equal(out, end, rFirst, rLast));
 
-//  In place
-    std::copy(first, last, v.begin());
-    std::inclusive_scan(v.begin(), v.end(), v.begin(), op, init);
-    assert(std::equal(v.begin(), v.end(), rFirst, rLast));
+    // In place
+    std::copy(first, last, out);
+    end = std::inclusive_scan(out, end, out, op, init);
+    assert(std::equal(out, end, rFirst, rLast));
 }
 
 
@@ -67,7 +51,7 @@
 TEST_CONSTEXPR_CXX20 void
 test()
 {
-          int ia[]   = {1, 3,  5,   7,   9};
+    int ia[]         = {1, 3,  5,   7,   9};
     const int pRes[] = {1, 4,  9,  16,  25};
     const int mRes[] = {1, 3, 15, 105, 945};
     const unsigned sa = sizeof(ia) / sizeof(ia[0]);
@@ -77,7 +61,7 @@
     for (unsigned int i = 0; i < sa; ++i ) {
         test(Iter(ia), Iter(ia + i), std::plus<>(),       0, pRes, pRes + i);
         test(Iter(ia), Iter(ia + i), std::multiplies<>(), 1, mRes, mRes + i);
-        }
+    }
 }
 
 constexpr size_t triangle(size_t n) { return n*(n+1)/2; }
@@ -111,18 +95,8 @@
     }
 
     {
-    // C++17 doesn't test constexpr so can use a vector.
-    // C++20 can use vector in constexpr evaluation, but both libc++ and MSVC
-    // don't have the support yet. In these cases use a std::span for the test.
-    // FIXME Remove constexpr vector workaround introduced in D90569
-#if TEST_STD_VER < 20 || \
-    (defined(__cpp_lib_constexpr_vector) && __cpp_lib_constexpr_vector >= 201907L)
-    std::vector<size_t> v, res;
-    std::inclusive_scan(v.begin(), v.end(), std::back_inserter(res), std::plus<>(), size_t{40});
-#else
     std::array<size_t, 0> v, res;
     std::inclusive_scan(v.begin(), v.end(), res.begin(), std::plus<>(), size_t{40});
-#endif
     assert(res.empty());
     }
 
@@ -130,18 +104,8 @@
     {
     std::array<unsigned char, 10> v;
     std::iota(v.begin(), v.end(), static_cast<unsigned char>(1));
-    // C++17 doesn't test constexpr so can use a vector.
-    // C++20 can use vector in constexpr evaluation, but both libc++ and MSVC
-    // don't have the support yet. In these cases use a std::span for the test.
-    // FIXME Remove constexpr vector workaround introduced in D90569
-#if TEST_STD_VER < 20 || \
-    (defined(__cpp_lib_constexpr_vector) && __cpp_lib_constexpr_vector >= 201907L)
-    std::vector<size_t> res;
-    std::inclusive_scan(v.begin(), v.end(), std::back_inserter(res), std::multiplies<>(), size_t{1});
-#else
     std::array<size_t, 10> res;
     std::inclusive_scan(v.begin(), v.end(), res.begin(), std::multiplies<>(), size_t{1});
-#endif
 
     assert(res.size() == 10);
     size_t j = 1;
diff --git a/libcxx/test/std/numerics/numeric.ops/transform.exclusive.scan/transform_exclusive_scan_init_bop_uop.pass.cpp b/libcxx/test/std/numerics/numeric.ops/transform.exclusive.scan/transform_exclusive_scan_init_bop_uop.pass.cpp
--- a/libcxx/test/std/numerics/numeric.ops/transform.exclusive.scan/transform_exclusive_scan_init_bop_uop.pass.cpp
+++ b/libcxx/test/std/numerics/numeric.ops/transform.exclusive.scan/transform_exclusive_scan_init_bop_uop.pass.cpp
@@ -6,11 +6,12 @@
 //
 //===----------------------------------------------------------------------===//
 
-// <numeric>
 // UNSUPPORTED: c++03, c++11, c++14
 // UNSUPPORTED: clang-8
 // UNSUPPORTED: gcc-9
 
+// <numeric>
+
 // Became constexpr in C++20
 // template<class InputIterator, class OutputIterator, class T,
 //          class BinaryOperation, class UnaryOperation>
@@ -26,14 +27,9 @@
 #include <cassert>
 #include <functional>
 #include <iterator>
-#include <vector>
 
 #include "test_macros.h"
 #include "test_iterators.h"
-// FIXME Remove constexpr vector workaround introduced in D90569
-#if TEST_STD_VER > 17
-#include <span>
-#endif
 
 struct add_one {
     template <typename T>
@@ -42,41 +38,28 @@
     }
 };
 
-template <class Iter1, class BOp, class UOp, class T, class Iter2>
+template <class Iter1, class BOp, class UOp, class T>
 TEST_CONSTEXPR_CXX20 void
-test(Iter1 first, Iter1 last, BOp bop, UOp uop, T init, Iter2 rFirst, Iter2 rLast)
+test(Iter1 first, Iter1 last, BOp bop, UOp uop, T init, const T *rFirst, const T *rLast)
 {
-    // C++17 doesn't test constexpr so can use a vector.
-    // C++20 can use vector in constexpr evaluation, but both libc++ and MSVC
-    // don't have the support yet. In these cases use a std::span for the test.
-    // FIXME Remove constexpr vector workaround introduced in D90569
-    size_t size = std::distance(first, last);
-#if TEST_STD_VER < 20 || \
-    (defined(__cpp_lib_constexpr_vector) && __cpp_lib_constexpr_vector >= 201907L)
-
-    std::vector<typename std::iterator_traits<Iter1>::value_type> v(size);
-#else
-    assert((size <= 5) && "Increment the size of the array");
-    typename std::iterator_traits<Iter1>::value_type b[5];
-    std::span<typename std::iterator_traits<Iter1>::value_type> v{b, size};
-#endif
+    assert((rLast - rFirst) <= 5);  // or else increase the size of "out"
+    T out[5];
 
-//  Test not in-place
-    std::transform_exclusive_scan(first, last, v.begin(), init, bop, uop);
-    assert(std::equal(v.begin(), v.end(), rFirst, rLast));
+    // Not in place
+    T *end = std::transform_exclusive_scan(first, last, out, init, bop, uop);
+    assert(std::equal(out, end, rFirst, rLast));
 
-//  Test in-place
-    std::copy(first, last, v.begin());
-    std::transform_exclusive_scan(v.begin(), v.end(), v.begin(), init, bop, uop);
-    assert(std::equal(v.begin(), v.end(), rFirst, rLast));
+    // In place
+    std::copy(first, last, out);
+    end = std::transform_exclusive_scan(out, end, out, init, bop, uop);
+    assert(std::equal(out, end, rFirst, rLast));
 }
 
-
 template <class Iter>
 TEST_CONSTEXPR_CXX20 void
 test()
 {
-          int ia[]     = { 1,  3,  5,    7,   9 };
+    int ia[]           = { 1,  3,  5,    7,   9 };
     const int pResI0[] = { 0,  2,  6,   12,  20 };        // with add_one
     const int mResI0[] = { 0,  0,  0,    0,   0 };
     const int pResN0[] = { 0, -1, -4,   -9, -16 };        // with negate
@@ -104,7 +87,7 @@
         test(Iter(ia), Iter(ia + i), std::multiplies<>(), add_one{},       2, mResI2, mResI2 + i);
         test(Iter(ia), Iter(ia + i), std::plus<>(),       std::negate<>(), 2, pResN2, pResN2 + i);
         test(Iter(ia), Iter(ia + i), std::multiplies<>(), std::negate<>(), 2, mResN2, mResN2 + i);
-        }
+    }
 }
 
 constexpr size_t triangle(size_t n) { return n*(n+1)/2; }
@@ -138,18 +121,8 @@
     }
 
     {
-    // C++17 doesn't test constexpr so can use a vector.
-    // C++20 can use vector in constexpr evaluation, but both libc++ and MSVC
-    // don't have the support yet. In these cases use a std::span for the test.
-    // FIXME Remove constexpr vector workaround introduced in D90569
-#if TEST_STD_VER < 20 || \
-    (defined(__cpp_lib_constexpr_vector) && __cpp_lib_constexpr_vector >= 201907L)
-    std::vector<size_t> v, res;
-    std::transform_exclusive_scan(v.begin(), v.end(), std::back_inserter(res), size_t{40}, std::plus<>(), add_one{});
-#else
     std::array<size_t, 0> v, res;
     std::transform_exclusive_scan(v.begin(), v.end(), res.begin(), size_t{40}, std::plus<>(), add_one{});
-#endif
     assert(res.empty());
     }
 
@@ -157,18 +130,8 @@
     {
     std::array<unsigned char, 10> v;
     std::iota(v.begin(), v.end(), static_cast<unsigned char>(1));
-    // C++17 doesn't test constexpr so can use a vector.
-    // C++20 can use vector in constexpr evaluation, but both libc++ and MSVC
-    // don't have the support yet. In these cases use a std::span for the test.
-    // FIXME Remove constexpr vector workaround introduced in D90569
-#if TEST_STD_VER < 20 || \
-    (defined(__cpp_lib_constexpr_vector) && __cpp_lib_constexpr_vector >= 201907L)
-    std::vector<size_t> res;
-    std::transform_exclusive_scan(v.begin(), v.end(), std::back_inserter(res), size_t{1}, std::multiplies<>(), add_one{});
-#else
     std::array<size_t, 10> res;
     std::transform_exclusive_scan(v.begin(), v.end(), res.begin(), size_t{1}, std::multiplies<>(), add_one{});
-#endif
 
     assert(res.size() == 10);
     size_t j = 1;
diff --git a/libcxx/test/std/numerics/numeric.ops/transform.inclusive.scan/transform_inclusive_scan_bop_uop.pass.cpp b/libcxx/test/std/numerics/numeric.ops/transform.inclusive.scan/transform_inclusive_scan_bop_uop.pass.cpp
--- a/libcxx/test/std/numerics/numeric.ops/transform.inclusive.scan/transform_inclusive_scan_bop_uop.pass.cpp
+++ b/libcxx/test/std/numerics/numeric.ops/transform.inclusive.scan/transform_inclusive_scan_bop_uop.pass.cpp
@@ -1,4 +1,3 @@
-
 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
@@ -7,11 +6,12 @@
 //
 //===----------------------------------------------------------------------===//
 
-// <numeric>
 // UNSUPPORTED: c++03, c++11, c++14
 // UNSUPPORTED: clang-8
 // UNSUPPORTED: gcc-9
 
+// <numeric>
+
 // Became constexpr in C++20
 // template<class InputIterator, class OutputIterator, class T,
 //          class BinaryOperation, class UnaryOperation>
@@ -27,49 +27,32 @@
 #include <cassert>
 #include <functional>
 #include <iterator>
-#include <vector>
 
 #include "test_macros.h"
 #include "test_iterators.h"
-// FIXME Remove constexpr vector workaround introduced in D90569
-#if TEST_STD_VER > 17
-#include <span>
-#endif
 
 struct add_one {
     template <typename T>
-    constexpr auto operator()(T x) const noexcept {
-        return static_cast<T>(x + 1);
+    constexpr T operator()(T x) const {
+        return x + 1;
     }
 };
 
-template <class Iter1, class BOp, class UOp, class Iter2>
+template <class Iter1, class BOp, class UOp, class T>
 TEST_CONSTEXPR_CXX20 void
-test(Iter1 first, Iter1 last, BOp bop, UOp uop, Iter2 rFirst, Iter2 rLast)
+test(Iter1 first, Iter1 last, BOp bop, UOp uop, const T *rFirst, const T *rLast)
 {
-    // C++17 doesn't test constexpr so can use a vector.
-    // C++20 can use vector in constexpr evaluation, but both libc++ and MSVC
-    // don't have the support yet. In these cases use a std::span for the test.
-    // FIXME Remove constexpr vector workaround introduced in D90569
-    size_t size = std::distance(first, last);
-#if TEST_STD_VER < 20 || \
-    (defined(__cpp_lib_constexpr_vector) && __cpp_lib_constexpr_vector >= 201907L)
-
-    std::vector<typename std::iterator_traits<Iter1>::value_type> v(size);
-#else
-    assert((size <= 5) && "Increment the size of the array");
-    typename std::iterator_traits<Iter1>::value_type b[5];
-    std::span<typename std::iterator_traits<Iter1>::value_type> v{b, size};
-#endif
+    assert((rLast - rFirst) <= 5);  // or else increase the size of "out"
+    T out[5];
 
-//  Test not in-place
-    std::transform_inclusive_scan(first, last, v.begin(), bop, uop);
-    assert(std::equal(v.begin(), v.end(), rFirst, rLast));
+    // Not in place
+    T *end = std::transform_inclusive_scan(first, last, out, bop, uop);
+    assert(std::equal(out, end, rFirst, rLast));
 
-//  Test in-place
-    std::copy(first, last, v.begin());
-    std::transform_inclusive_scan(v.begin(), v.end(), v.begin(), bop, uop);
-    assert(std::equal(v.begin(), v.end(), rFirst, rLast));
+    // In place
+    std::copy(first, last, out);
+    end = std::transform_inclusive_scan(out, end, out, bop, uop);
+    assert(std::equal(out, end, rFirst, rLast));
 }
 
 
@@ -77,7 +60,7 @@
 TEST_CONSTEXPR_CXX20 void
 test()
 {
-          int ia[]     = {  1,  3,   5,   7,    9 };
+    int ia[]           = {  1,  3,   5,   7,    9 };
     const int pResI0[] = {  2,  6,  12,  20,   30 };        // with add_one
     const int mResI0[] = {  2,  8, 48,  384, 3840 };
     const int pResN0[] = { -1, -4,  -9, -16,  -25 };        // with negate
@@ -93,7 +76,7 @@
         test(Iter(ia), Iter(ia + i), std::multiplies<>(), add_one{},       mResI0, mResI0 + i);
         test(Iter(ia), Iter(ia + i), std::plus<>(),       std::negate<>(), pResN0, pResN0 + i);
         test(Iter(ia), Iter(ia + i), std::multiplies<>(), std::negate<>(), mResN0, mResN0 + i);
-        }
+    }
 }
 
 constexpr size_t triangle(size_t n) { return n*(n+1)/2; }
@@ -127,18 +110,8 @@
     }
 
     {
-    // C++17 doesn't test constexpr so can use a vector.
-    // C++20 can use vector in constexpr evaluation, but both libc++ and MSVC
-    // don't have the support yet. In these cases use a std::span for the test.
-    // FIXME Remove constexpr vector workaround introduced in D90569
-#if TEST_STD_VER < 20 || \
-    (defined(__cpp_lib_constexpr_vector) && __cpp_lib_constexpr_vector >= 201907L)
-    std::vector<size_t> v, res;
-    std::transform_inclusive_scan(v.begin(), v.end(), std::back_inserter(res), std::plus<>(), add_one{});
-#else
     std::array<size_t, 0> v, res;
     std::transform_inclusive_scan(v.begin(), v.end(), res.begin(), std::plus<>(), add_one{});
-#endif
     assert(res.empty());
     }
 }
diff --git a/libcxx/test/std/numerics/numeric.ops/transform.inclusive.scan/transform_inclusive_scan_bop_uop_init.pass.cpp b/libcxx/test/std/numerics/numeric.ops/transform.inclusive.scan/transform_inclusive_scan_bop_uop_init.pass.cpp
--- a/libcxx/test/std/numerics/numeric.ops/transform.inclusive.scan/transform_inclusive_scan_bop_uop_init.pass.cpp
+++ b/libcxx/test/std/numerics/numeric.ops/transform.inclusive.scan/transform_inclusive_scan_bop_uop_init.pass.cpp
@@ -6,11 +6,12 @@
 //
 //===----------------------------------------------------------------------===//
 
-// <numeric>
 // UNSUPPORTED: c++03, c++11, c++14
 // UNSUPPORTED: clang-8
 // UNSUPPORTED: gcc-9
 
+// <numeric>
+
 // Became constexpr in C++20
 // template<class InputIterator, class OutputIterator, class T,
 //          class BinaryOperation, class UnaryOperation>
@@ -27,49 +28,32 @@
 #include <cassert>
 #include <functional>
 #include <iterator>
-#include <vector>
 
 #include "test_macros.h"
 #include "test_iterators.h"
-// FIXME Remove constexpr vector workaround introduced in D90569
-#if TEST_STD_VER > 17
-#include <span>
-#endif
 
 struct add_one {
     template <typename T>
-    constexpr auto operator()(T x) const noexcept {
-        return static_cast<T>(x + 1);
+    constexpr T operator()(T x) const {
+        return x + 1;
     }
 };
 
-template <class Iter1, class BOp, class UOp, class T, class Iter2>
+template <class Iter1, class BOp, class UOp, class T>
 TEST_CONSTEXPR_CXX20 void
-test(Iter1 first, Iter1 last, BOp bop, UOp uop, T init, Iter2 rFirst, Iter2 rLast)
+test(Iter1 first, Iter1 last, BOp bop, UOp uop, T init, const T *rFirst, const T *rLast)
 {
-    // C++17 doesn't test constexpr so can use a vector.
-    // C++20 can use vector in constexpr evaluation, but both libc++ and MSVC
-    // don't have the support yet. In these cases use a std::span for the test.
-    // FIXME Remove constexpr vector workaround introduced in D90569
-    size_t size = std::distance(first, last);
-#if TEST_STD_VER < 20 || \
-    (defined(__cpp_lib_constexpr_vector) && __cpp_lib_constexpr_vector >= 201907L)
-
-    std::vector<typename std::iterator_traits<Iter1>::value_type> v(size);
-#else
-    assert((size <= 5) && "Increment the size of the array");
-    typename std::iterator_traits<Iter1>::value_type b[5];
-    std::span<typename std::iterator_traits<Iter1>::value_type> v{b, size};
-#endif
+    assert((rLast - rFirst) <= 5);  // or else increase the size of "out"
+    T out[5];
 
-//  Test not in-place
-    std::transform_inclusive_scan(first, last, v.begin(), bop, uop, init);
-    assert(std::equal(v.begin(), v.end(), rFirst, rLast));
+    // Not in place
+    T *end = std::transform_inclusive_scan(first, last, out, bop, uop, init);
+    assert(std::equal(out, end, rFirst, rLast));
 
-//  Test in-place
-    std::copy(first, last, v.begin());
-    std::transform_inclusive_scan(v.begin(), v.end(), v.begin(), bop, uop, init);
-    assert(std::equal(v.begin(), v.end(), rFirst, rLast));
+    // In place
+    std::copy(first, last, out);
+    end = std::transform_inclusive_scan(out, end, out, bop, uop, init);
+    assert(std::equal(out, end, rFirst, rLast));
 }
 
 
@@ -77,7 +61,7 @@
 TEST_CONSTEXPR_CXX20 void
 test()
 {
-          int ia[]     = {  1,  3,   5,    7,     9 };
+    int ia[]           = {  1,  3,   5,    7,     9 };
     const int pResI0[] = {  2,  6,  12,   20,    30 };        // with add_one
     const int mResI0[] = {  0,  0,   0,    0,     0 };
     const int pResN0[] = { -1, -4,  -9,  -16,   -25 };        // with negate
@@ -105,7 +89,7 @@
         test(Iter(ia), Iter(ia + i), std::multiplies<>(), add_one{},       2, mResI2, mResI2 + i);
         test(Iter(ia), Iter(ia + i), std::plus<>(),       std::negate<>(), 2, pResN2, pResN2 + i);
         test(Iter(ia), Iter(ia + i), std::multiplies<>(), std::negate<>(), 2, mResN2, mResN2 + i);
-        }
+    }
 }
 
 constexpr size_t triangle(size_t n) { return n*(n+1)/2; }
@@ -139,18 +123,8 @@
     }
 
     {
-    // C++17 doesn't test constexpr so can use a vector.
-    // C++20 can use vector in constexpr evaluation, but both libc++ and MSVC
-    // don't have the support yet. In these cases use a std::span for the test.
-    // FIXME Remove constexpr vector workaround introduced in D90569
-#if TEST_STD_VER < 20 || \
-    (defined(__cpp_lib_constexpr_vector) && __cpp_lib_constexpr_vector >= 201907L)
-    std::vector<size_t> v, res;
-    std::transform_inclusive_scan(v.begin(), v.end(), std::back_inserter(res), std::plus<>(), add_one{}, size_t{1});
-#else
     std::array<size_t, 0> v, res;
     std::transform_inclusive_scan(v.begin(), v.end(), res.begin(), std::plus<>(), add_one{}, size_t{1});
-#endif
     assert(res.empty());
     }
 
@@ -158,18 +132,8 @@
     {
     std::array<unsigned char, 10> v;
     std::iota(v.begin(), v.end(), static_cast<unsigned char>(1));
-    // C++17 doesn't test constexpr so can use a vector.
-    // C++20 can use vector in constexpr evaluation, but both libc++ and MSVC
-    // don't have the support yet. In these cases use a std::span for the test.
-    // FIXME Remove constexpr vector workaround introduced in D90569
-#if TEST_STD_VER < 20 || \
-    (defined(__cpp_lib_constexpr_vector) && __cpp_lib_constexpr_vector >= 201907L)
-    std::vector<size_t> res;
-    std::transform_inclusive_scan(v.begin(), v.end(), std::back_inserter(res), std::multiplies<>(), add_one{}, size_t{1});
-#else
     std::array<size_t, 10> res;
     std::transform_inclusive_scan(v.begin(), v.end(), res.begin(), std::multiplies<>(), add_one{}, size_t{1});
-#endif
 
     assert(res.size() == 10);
     size_t j = 2;
diff --git a/libcxx/test/std/strings/basic.string/string.iterators/iterators.pass.cpp b/libcxx/test/std/strings/basic.string/string.iterators/iterators.pass.cpp
--- a/libcxx/test/std/strings/basic.string/string.iterators/iterators.pass.cpp
+++ b/libcxx/test/std/strings/basic.string/string.iterators/iterators.pass.cpp
@@ -22,69 +22,46 @@
 
 #include "test_macros.h"
 
-int main(int, char**)
+template<class C>
+void test()
 {
     { // N3644 testing
-        typedef std::string C;
-        C::iterator ii1{}, ii2{};
-        C::iterator ii4 = ii1;
-        C::const_iterator cii{};
+        typename C::iterator ii1{}, ii2{};
+        typename C::iterator ii4 = ii1;
+        typename C::const_iterator cii{};
         assert ( ii1 == ii2 );
         assert ( ii1 == ii4 );
-        assert ( ii1 == cii );
-        assert ( !(ii1 != ii2 ));
-        assert ( !(ii1 != cii ));
-    }
 
-    { // N3644 testing
-        typedef std::wstring C;
-        C::iterator ii1{}, ii2{};
-        C::iterator ii4 = ii1;
-        C::const_iterator cii{};
-        assert ( ii1 == ii2 );
-        assert ( ii1 == ii4 );
-        assert ( ii1 == cii );
-        assert ( !(ii1 != ii2 ));
-        assert ( !(ii1 != cii ));
+        assert (!(ii1 != ii2 ));
+
+        assert ( (ii1 == cii ));
+        assert ( (cii == ii1 ));
+        assert (!(ii1 != cii ));
+        assert (!(cii != ii1 ));
+        assert (!(ii1 <  cii ));
+        assert (!(cii <  ii1 ));
+        assert ( (ii1 <= cii ));
+        assert ( (cii <= ii1 ));
+        assert (!(ii1 >  cii ));
+        assert (!(cii >  ii1 ));
+        assert ( (ii1 >= cii ));
+        assert ( (cii >= ii1 ));
+        assert (cii - ii1 == 0);
+        assert (ii1 - cii == 0);
     }
+}
+
+int main(int, char**)
+{
+    test<std::string>();
+    test<std::wstring>();
 
 #if defined(__cpp_lib_char8_t) && __cpp_lib_char8_t >= 201811L
-    {
-        typedef std::u8string C;
-        C::iterator ii1{}, ii2{};
-        C::iterator ii4 = ii1;
-        C::const_iterator cii{};
-        assert ( ii1 == ii2 );
-        assert ( ii1 == ii4 );
-        assert ( ii1 == cii );
-        assert ( !(ii1 != ii2 ));
-        assert ( !(ii1 != cii ));
-    }
+    test<std::u8string>();
 #endif
 
-    { // N3644 testing
-        typedef std::u16string C;
-        C::iterator ii1{}, ii2{};
-        C::iterator ii4 = ii1;
-        C::const_iterator cii{};
-        assert ( ii1 == ii2 );
-        assert ( ii1 == ii4 );
-        assert ( ii1 == cii );
-        assert ( !(ii1 != ii2 ));
-        assert ( !(ii1 != cii ));
-    }
-
-    { // N3644 testing
-        typedef std::u32string C;
-        C::iterator ii1{}, ii2{};
-        C::iterator ii4 = ii1;
-        C::const_iterator cii{};
-        assert ( ii1 == ii2 );
-        assert ( ii1 == ii4 );
-        assert ( ii1 == cii );
-        assert ( !(ii1 != ii2 ));
-        assert ( !(ii1 != cii ));
-    }
+    test<std::u16string>();
+    test<std::u32string>();
 
-  return 0;
+    return 0;
 }
diff --git a/libcxx/test/std/strings/basic.string/string.modifiers/string_assign/iterator.pass.cpp b/libcxx/test/std/strings/basic.string/string.modifiers/string_assign/iterator.pass.cpp
--- a/libcxx/test/std/strings/basic.string/string.modifiers/string_assign/iterator.pass.cpp
+++ b/libcxx/test/std/strings/basic.string/string.modifiers/string_assign/iterator.pass.cpp
@@ -6,6 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
+// XFAIL: LIBCXX-DEBUG-FIXME
+
 // <string>
 
 // template<class InputIterator>
diff --git a/libcxx/test/std/strings/char.traits/char.traits.specializations/char.traits.specializations.char/copy.pass.cpp b/libcxx/test/std/strings/char.traits/char.traits.specializations/char.traits.specializations.char/copy.pass.cpp
--- a/libcxx/test/std/strings/char.traits/char.traits.specializations/char.traits.specializations.char/copy.pass.cpp
+++ b/libcxx/test/std/strings/char.traits/char.traits.specializations/char.traits.specializations.char/copy.pass.cpp
@@ -6,6 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
+// XFAIL: LIBCXX-DEBUG-FIXME
+
 // UNSUPPORTED: clang-8
 
 // <string>
diff --git a/libcxx/test/std/strings/char.traits/char.traits.specializations/char.traits.specializations.char16_t/copy.pass.cpp b/libcxx/test/std/strings/char.traits/char.traits.specializations/char.traits.specializations.char16_t/copy.pass.cpp
--- a/libcxx/test/std/strings/char.traits/char.traits.specializations/char.traits.specializations.char16_t/copy.pass.cpp
+++ b/libcxx/test/std/strings/char.traits/char.traits.specializations/char.traits.specializations.char16_t/copy.pass.cpp
@@ -6,6 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
+// XFAIL: LIBCXX-DEBUG-FIXME
+
 // <string>
 
 // template<> struct char_traits<char16_t>
diff --git a/libcxx/test/std/strings/char.traits/char.traits.specializations/char.traits.specializations.char32_t/copy.pass.cpp b/libcxx/test/std/strings/char.traits/char.traits.specializations/char.traits.specializations.char32_t/copy.pass.cpp
--- a/libcxx/test/std/strings/char.traits/char.traits.specializations/char.traits.specializations.char32_t/copy.pass.cpp
+++ b/libcxx/test/std/strings/char.traits/char.traits.specializations/char.traits.specializations.char32_t/copy.pass.cpp
@@ -6,6 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
+// XFAIL: LIBCXX-DEBUG-FIXME
+
 // <string>
 
 // template<> struct char_traits<char32_t>
diff --git a/libcxx/test/std/strings/char.traits/char.traits.specializations/char.traits.specializations.char8_t/copy.pass.cpp b/libcxx/test/std/strings/char.traits/char.traits.specializations/char.traits.specializations.char8_t/copy.pass.cpp
--- a/libcxx/test/std/strings/char.traits/char.traits.specializations/char.traits.specializations.char8_t/copy.pass.cpp
+++ b/libcxx/test/std/strings/char.traits/char.traits.specializations/char.traits.specializations.char8_t/copy.pass.cpp
@@ -9,6 +9,8 @@
 // UNSUPPORTED: c++03, c++11, c++14, c++17
 // UNSUPPORTED: clang-8
 
+// XFAIL: LIBCXX-DEBUG-FIXME
+
 // <string>
 
 // template<> struct char_traits<char8_t>
diff --git a/libcxx/test/std/strings/char.traits/char.traits.specializations/char.traits.specializations.wchar.t/copy.pass.cpp b/libcxx/test/std/strings/char.traits/char.traits.specializations/char.traits.specializations.wchar.t/copy.pass.cpp
--- a/libcxx/test/std/strings/char.traits/char.traits.specializations/char.traits.specializations.wchar.t/copy.pass.cpp
+++ b/libcxx/test/std/strings/char.traits/char.traits.specializations/char.traits.specializations.wchar.t/copy.pass.cpp
@@ -8,6 +8,8 @@
 
 // UNSUPPORTED: clang-8
 
+// XFAIL: LIBCXX-DEBUG-FIXME
+
 // <string>
 
 // template<> struct char_traits<wchar_t>
diff --git a/libcxx/test/std/strings/string.view/string.view.ops/copy.pass.cpp b/libcxx/test/std/strings/string.view/string.view.ops/copy.pass.cpp
--- a/libcxx/test/std/strings/string.view/string.view.ops/copy.pass.cpp
+++ b/libcxx/test/std/strings/string.view/string.view.ops/copy.pass.cpp
@@ -6,6 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
+// XFAIL: LIBCXX-DEBUG-FIXME
+
 // XFAIL: gcc-10
 //     GCC's __builtin_strlen isn't constexpr yet
 
diff --git a/libcxx/utils/ci/buildkite-pipeline.yml b/libcxx/utils/ci/buildkite-pipeline.yml
--- a/libcxx/utils/ci/buildkite-pipeline.yml
+++ b/libcxx/utils/ci/buildkite-pipeline.yml
@@ -53,66 +53,6 @@
   #
   - wait
 
-  - label: "C++03"
-    command: "libcxx/utils/ci/run-buildbot generic-cxx03"
-    artifact_paths:
-      - "**/test-results.xml"
-      - "**/*.abilist"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "C++11"
-    command: "libcxx/utils/ci/run-buildbot generic-cxx11"
-    artifact_paths:
-      - "**/test-results.xml"
-      - "**/*.abilist"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "C++14"
-    command: "libcxx/utils/ci/run-buildbot generic-cxx14"
-    artifact_paths:
-      - "**/test-results.xml"
-      - "**/*.abilist"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "C++17"
-    command: "libcxx/utils/ci/run-buildbot generic-cxx17"
-    artifact_paths:
-      - "**/test-results.xml"
-      - "**/*.abilist"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "C++20"
-    command: "libcxx/utils/ci/run-buildbot generic-cxx20"
-    artifact_paths:
-      - "**/test-results.xml"
-      - "**/*.abilist"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
   - label: "C++2b"
     command: "libcxx/utils/ci/run-buildbot generic-cxx2b"
     artifact_paths:
@@ -125,337 +65,14 @@
         - exit_status: -1  # Agent was lost
           limit: 2
 
-  - label: "MacOS C++20"
-    command: "libcxx/utils/ci/run-buildbot generic-cxx20"
+  - label: "Debug iterators"
+    command: "libcxx/utils/ci/run-buildbot generic-debug"
     artifact_paths:
       - "**/test-results.xml"
       - "**/*.abilist"
-    agents:
-      queue: "libcxx-builders-macos"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "GCC/C++20"
-    command: "libcxx/utils/ci/run-buildbot generic-gcc"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  #
-  # All other supported configurations of libc++.
-  #
-  - wait
-
-  - label: "-fno-exceptions"
-    command: "libcxx/utils/ci/run-buildbot generic-noexceptions"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "Static libraries"
-    command: "libcxx/utils/ci/run-buildbot generic-static"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "ASAN"
-    command: "libcxx/utils/ci/run-buildbot generic-asan"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "TSAN"
-    command: "libcxx/utils/ci/run-buildbot generic-tsan"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "UBSAN"
-    command: "libcxx/utils/ci/run-buildbot generic-ubsan"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "With LLVM's libunwind"
-    command: "libcxx/utils/ci/run-buildbot generic-with_llvm_unwinder"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "Single-threaded"
-    command: "libcxx/utils/ci/run-buildbot generic-singlethreaded"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "No debug mode"
-    command: "libcxx/utils/ci/run-buildbot generic-no-debug"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "No Filesystem"
-    command: "libcxx/utils/ci/run-buildbot generic-no-filesystem"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "No random device"
-    command: "libcxx/utils/ci/run-buildbot generic-no-random_device"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "No locale"
-    command: "libcxx/utils/ci/run-buildbot generic-no-localization"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "Benchmarks"
-    command: "libcxx/utils/ci/run-buildbot benchmarks"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "Documentation"
-    command: "libcxx/utils/ci/run-buildbot documentation"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "Legacy standalone build"
-    command: "libcxx/utils/ci/run-buildbot legacy-standalone"
-    artifact_paths:
-      - "**/test-results.xml"
     agents:
       queue: "libcxx-builders"
     retry:
       automatic:
         - exit_status: -1  # Agent was lost
           limit: 2
-
-  - label: "Unified standalone build"
-    command: "libcxx/utils/ci/run-buildbot unified-standalone"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "Runtimes build"
-    command: "libcxx/utils/ci/run-buildbot runtimes-build"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "Windows"
-    # TODO: The CI runner doesn't have bash in the path currently. Once it
-    # has that, remove the absolute path and just call 'bash' here.
-    command: "\"\\Program Files\\Git\\usr\\bin\\bash\" libcxx/utils/ci/run-buildbot generic-win"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "windows"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  # Build with the configuration we use to generate libc++.dylib on Apple platforms
-  - label: "Apple system"
-    command: "libcxx/utils/ci/run-buildbot x86_64-apple-system"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders-macos"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "Apple system -fno-exceptions"
-    command: "libcxx/utils/ci/run-buildbot x86_64-apple-system-noexceptions"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders-macos"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  # Test back-deployment to older Apple platforms
-  - label: "Apple back-deployment macosx10.9"
-    command: "libcxx/utils/ci/run-buildbot x86_64-apple-system-backdeployment-10.9"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders-macos10.15" # TODO: For now, we're running the back-deployment tests for 10.9 on 10.15, because we don't have proper 10.9 machines
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "Apple back-deployment macosx10.15"
-    command: "libcxx/utils/ci/run-buildbot x86_64-apple-system-backdeployment-10.15"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders-macos10.15"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "AArch64"
-    command: "libcxx/utils/ci/run-buildbot aarch64"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders-linaro-arm"
-      arch: "aarch64"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "AArch64 -fno-exceptions"
-    command: "libcxx/utils/ci/run-buildbot aarch64-noexceptions"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders-linaro-arm"
-      arch: "aarch64"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "Armv8"
-    command: "libcxx/utils/ci/run-buildbot armv8"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders-linaro-arm"
-      arch: "armv8l"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "Armv8 -fno-exceptions"
-    command: "libcxx/utils/ci/run-buildbot armv8-noexceptions"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders-linaro-arm"
-      arch: "armv8l"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "Armv7"
-    command: "libcxx/utils/ci/run-buildbot armv7"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders-linaro-arm"
-      arch: "armv8l" # Compiling for v7, running on v8 hardware
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "Armv7 -fno-exceptions"
-    command: "libcxx/utils/ci/run-buildbot armv7-noexceptions"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders-linaro-arm"
-      arch: "armv8l" # Compiling for v7, running on v8 hardware
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
diff --git a/libcxx/utils/ci/run-buildbot b/libcxx/utils/ci/run-buildbot
--- a/libcxx/utils/ci/run-buildbot
+++ b/libcxx/utils/ci/run-buildbot
@@ -514,6 +514,11 @@
     echo "+++ Running the libc++ tests"
     ${NINJA} -vC "${BUILD_DIR}" check-cxx
 ;;
+generic-debug)
+    clean
+    generate-cmake -C "${MONOREPO_ROOT}/libcxx/cmake/caches/Generic-debug.cmake"
+    check-cxx-cxxabi
+;;
 *)
     echo "${BUILDER} is not a known configuration"
     exit 1
diff --git a/libcxx/utils/libcxx/test/config.py b/libcxx/utils/libcxx/test/config.py
--- a/libcxx/utils/libcxx/test/config.py
+++ b/libcxx/utils/libcxx/test/config.py
@@ -481,6 +481,7 @@
             self.lit_config.fatal('Invalid value for debug_level "%s".'
                                   % debug_level)
         self.cxx.compile_flags += ['-D_LIBCPP_DEBUG=%s' % debug_level]
+        self.config.available_features.add('debug_level_%s' % debug_level)
 
     def configure_sanitizer(self):
         san = self.get_lit_conf('use_sanitizer', '').strip()