microsoft · Stephan T. Lavavej (StephanTLavavej) · Mar 16, 2026 · Mar 11, 2026 · Mar 11, 2026 · Mar 11, 2026
@@ -13,6 +13,10 @@ read the guidelines for submitting STL bug reports in `README.md`. If you are
 having problems with any component that is not the STL, instructions to get
 to the right place are there.
 
+Even if your project is using an older version of the MSVC Build Tools, please
+check the Latest production release (or better yet, the Preview release) before
+reporting bugs. This will save time by avoiding reports of already-fixed bugs.
+
 # Command-line test case
 ```
 C:\Temp>type repro.cpp

@@ -1,5 +1,19 @@
-<!--
-Before submitting a pull request, please ensure that:
+<!-- Before submitting a pull request, please ensure that:
+
+* Any AI-generated code has been clearly disclosed in your PR description.
+  We strongly discourage AI-generated changes to product code because the STL
+  is a highly unusual codebase with complex correctness and performance
+  requirements imposed by the Standard, and highly unusual code patterns that
+  don't look like typical codebases. Our intensive code review process
+  (to avoid bugs) is intentionally a bottleneck, so we ask that you be
+  considerate of the time and effort that we'll need to spend, by starting
+  with changes that you fully understand. Test code has weaker requirements,
+  so AI-generated changes for tests can be acceptable if properly disclosed.
+
+* Your PR description explains your intent behind the changes.
+  We discourage AI-generated PR descriptions because we can read the changes,
+  and we have access to the same AI tools that you have, so we can get
+  an AI-generated summary if we want.
 
 * Identifiers in product code changes are properly `_Ugly` as per
   https://eel.is/c++draft/lex.name#3.1 or there are no product code changes.

@@ -1,13 +1,13 @@
 # Copyright (c) Microsoft Corporation.
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-cmake_minimum_required(VERSION 4.2.1)
+cmake_minimum_required(VERSION 4.2.3)
 
 set(CMAKE_TRY_COMPILE_TARGET_TYPE STATIC_LIBRARY)
 project(msvc_standard_libraries LANGUAGES CXX)
 
-if(CMAKE_CXX_COMPILER_VERSION VERSION_LESS "19.51.36014")
-    message(FATAL_ERROR "The STL must be built with MSVC Compiler 19.51.36014 or later.")
+if(CMAKE_CXX_COMPILER_VERSION VERSION_LESS "19.51.36122")
+    message(FATAL_ERROR "The STL must be built with MSVC Compiler 19.51.36122 or later. Follow the README instructions.")
 endif()
 
 include(CheckCXXSourceCompiles)
@@ -18,7 +18,7 @@ int main() {}
 ]=] WINDOWS_SDK_VERSION_CHECK)
 
 if(NOT WINDOWS_SDK_VERSION_CHECK)
-    message(FATAL_ERROR "The STL must be built with the Windows 11 SDK (10.0.26100) or later. Make sure it's available by selecting it in the Individual Components tab of the VS Installer.")
+    message(FATAL_ERROR "The STL must be built with the Windows 11 SDK (10.0.26100) or later. Follow the README instructions.")
 endif()
 
 if(NOT DEFINED VCLIBS_TARGET_ARCHITECTURE)

@@ -142,7 +142,7 @@ Just try to follow these rules, so we can spend more time fixing bugs and implem
 # Visual Studio Installer Prerequisites
 
 * Install [VS 2026 Insiders][] and keep it up to date.
-  + **You must install Insiders for STL development.** *See Note 1 below.*
+  + **You must install the Insiders IDE and the Preview build tools for STL development.** *See Note 1 below.*
   + Select the "Desktop development with C++" workload.
   + Select the following components at a minimum:
     - "MSVC Build Tools for x64/x86 (Preview)"
@@ -155,8 +155,12 @@ Just try to follow these rules, so we can spend more time fixing bugs and implem
   + Select "Add python.exe to PATH" if you want to follow the instructions below that invoke `python`.
     Otherwise, you should be familiar with alternative methods.
 
-*Note 1:* The STL and the compiler ship together, and we frequently need the latest
-compiler fixes and features, so the last production release of the compiler is too old.
+*Note 1:* The STL and the compiler ship together, and we frequently need recently implemented
+compiler fixes and features, so the Latest build tools (i.e. latest production) are too old.
+Because the Insiders IDE supports having the Latest and Preview build tools installed simultaneously,
+you need to ensure that you're using the Preview build tools. If you build with the IDE, we've arranged for
+this to happen automatically. If you build with the Command Prompt, you need to pass `-vcvars_ver=preview`
+as explained below. For more info, read the [C++ Team Blog post][preview] that announced this release process.
 
 *Note 2:* The x64/x86 build tools are usually sufficient.
 You'll need the ARM64/ARM64EC build tools if you're working with architecture-sensitive code.
@@ -627,3 +631,4 @@ SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 [VS 2026 Insiders]: https://visualstudio.microsoft.com/insiders/
 [CXXFLAGS]: https://cmake.org/cmake/help/latest/envvar/CXXFLAGS.html
 [start-command]: https://learn.microsoft.com/windows-server/administration/windows-commands/start
+[preview]: https://devblogs.microsoft.com/cppblog/microsoft-c-msvc-build-tools-v14-51-preview-released-how-to-opt-in/
@@ -2,17 +2,6 @@
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 steps:
-- task: PowerShell@2
-  displayName: 'Setup TMP Directory'
-  inputs:
-    pwsh: true
-    targetType: inline
-    script: |
-      $PSNativeCommandUseErrorActionPreference = $true
-      if (Test-Path -LiteralPath "$(tmpDir)") {
-          Remove-Item -LiteralPath "$(tmpDir)" -Recurse -Force
-      }
-      mkdir "$(tmpDir)" -Force | Out-Null
 - checkout: self
   clean: true
   submodules: false
@@ -27,3 +16,7 @@ steps:
     script: |
       $PSNativeCommandUseErrorActionPreference = $true
       git clean --quiet -x -d -f -f
+      if (Test-Path -LiteralPath "$(tmpDir)") {
+          Remove-Item -LiteralPath "$(tmpDir)" -Recurse -Force
+      }
+      mkdir "$(tmpDir)" -Force | Out-Null
@@ -5,13 +5,13 @@
 
 variables:
 - name: x64SlowPoolName
-  value: 'Stl-2026-02-20T0952-x64-Pool'
+  value: 'Stl-2026-03-11T0936-x64-Fasv6-Pool'
   readonly: true
 - name: x64FastPoolName
-  value: 'Stl-2026-02-24T1452-x64-Fasv7-Pool'
+  value: 'Stl-2026-03-11T0936-x64-Fasv7-Pool'
   readonly: true
 - name: arm64PoolName
-  value: 'Stl-2026-02-20T0952-arm64-Pool'
+  value: 'Stl-2026-03-11T0936-arm64-Dpsv6-Pool'
   readonly: true
 - name: poolDemands
   value: 'EnableSpotVM -equals false'

@@ -48,7 +48,7 @@ if ($VMSku -ieq 'Fasv6') {
   $AvailableLocations = @('eastus2', 'northeurope') # Locations where CPP_STL_GitHub has quota for 1024 cores (32 VMs).
 }
 
-$AvailableLocationIdx = 5 # Increment for each new set of pools, to cycle through the available locations.
+$AvailableLocationIdx = 6 # Increment for each new set of pools, to cycle through the available locations.
 $Location = $AvailableLocations[$AvailableLocationIdx % $AvailableLocations.Length]
 
 if ($Arch -ieq 'x64') {

@@ -74,7 +74,7 @@ $PythonArgs = @('/quiet', 'InstallAllUsers=1', 'PrependPath=1', 'CompileAll=1',
 
 # https://developer.nvidia.com/cuda-toolkit
 if ($Provisioning_x64) {
-  $CudaUrl = 'https://developer.download.nvidia.com/compute/cuda/12.4.0/local_installers/cuda_12.4.0_551.61_windows.exe'
+  $CudaUrl = 'https://developer.download.nvidia.com/compute/cuda/13.2.0/local_installers/cuda_13.2.0_windows.exe'
 } else {
   $CudaUrl = 'CUDA is not installed for ARM64'
 }

@@ -1,7 +1,7 @@
 # Copyright (c) Microsoft Corporation.
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-cmake_minimum_required(VERSION 4.2.1)
+cmake_minimum_required(VERSION 4.2.3)
 project(msvc_standard_libraries_benchmarks LANGUAGES CXX)
 
 if(DEFINED STL_BINARY_DIR)

@@ -51,7 +51,7 @@ _NODISCARD constexpr int _Countl_zero_fallback(_Ty _Val) noexcept {
     return static_cast<int>(_Nx) - static_cast<int>(_Val);
 }
 
-#if !defined(_M_CEE_PURE) && !defined(__CUDACC__)
+#if !defined(_M_CEE_PURE)
 #define _HAS_COUNTL_ZERO_INTRINSICS 1
 #else // ^^^ intrinsics available / intrinsics unavailable vvv
 #define _HAS_COUNTL_ZERO_INTRINSICS 0
@@ -176,7 +176,7 @@ _NODISCARD constexpr int _Popcount_fallback(_Ty _Val) noexcept {
 }
 
 #if ((defined(_M_IX86) && !defined(_M_HYBRID_X86_ARM64)) || (defined(_M_X64) && !defined(_M_ARM64EC))) \
-    && !defined(_M_CEE_PURE) && !defined(__CUDACC__)
+    && !defined(_M_CEE_PURE)
 #define _HAS_TZCNT_BSF_INTRINSICS 1
 #else // ^^^ intrinsics available / intrinsics unavailable vvv
 #define _HAS_TZCNT_BSF_INTRINSICS 0
@@ -267,7 +267,7 @@ _NODISCARD int _Checked_x86_x64_countr_zero(const _Ty _Val) noexcept {
 
 #endif // _HAS_TZCNT_BSF_INTRINSICS
 
-#if (defined(_M_IX86) || defined(_M_X64) || defined(_M_ARM64)) && !defined(_M_CEE_PURE) && !defined(__CUDACC__)
+#if !defined(_M_CEE_PURE)
 #define _HAS_POPCNT_INTRINSICS 1
 #if defined(__AVX__) || defined(_M_ARM64) || defined(_M_ARM64EC)
 #define _POPCNT_INTRINSICS_ALWAYS_AVAILABLE 1
@@ -333,14 +333,14 @@ constexpr decltype(auto) _Select_countr_zero_impl(_Fn _Callback) {
 #ifndef __AVX2__
         const bool _Definitely_have_tzcnt = __isa_available >= _Stl_isa_available_avx2;
         if (!_Definitely_have_tzcnt) {
-            return _Callback([](_Ty _Val) _STATIC_CALL_OPERATOR { return _Countr_zero_bsf(_Val); });
+            return _Callback([](_Ty _Val) static { return _Countr_zero_bsf(_Val); });
         }
 #endif // ^^^ !defined(__AVX2__) ^^^
-        return _Callback([](_Ty _Val) _STATIC_CALL_OPERATOR { return _Countr_zero_tzcnt(_Val); });
+        return _Callback([](_Ty _Val) static { return _Countr_zero_tzcnt(_Val); });
     }
 #endif // ^^^ _HAS_TZCNT_BSF_INTRINSICS && _HAS_CXX20 ^^^
     // C++17 constexpr gcd() calls this function, so it should be constexpr unless we detect runtime evaluation.
-    return _Callback([](_Ty _Val) _STATIC_CALL_OPERATOR { return _Countr_zero_fallback(_Val); });
+    return _Callback([](_Ty _Val) static { return _Countr_zero_fallback(_Val); });
 }
 
 template <class _Ty>
@@ -385,13 +385,13 @@ _CONSTEXPR20 decltype(auto) _Select_popcount_impl(_Fn _Callback) {
 #if !_POPCNT_INTRINSICS_ALWAYS_AVAILABLE
         const bool _Definitely_have_popcnt = __isa_available >= _Stl_isa_available_sse42;
         if (!_Definitely_have_popcnt) {
-            return _Callback([](_Ty _Val) _STATIC_CALL_OPERATOR { return _Popcount_fallback(_Val); });
+            return _Callback([](_Ty _Val) static { return _Popcount_fallback(_Val); });
         }
 #endif // ^^^ !_POPCNT_INTRINSICS_ALWAYS_AVAILABLE ^^^
-        return _Callback([](_Ty _Val) _STATIC_CALL_OPERATOR { return _Unchecked_popcount(_Val); });
+        return _Callback([](_Ty _Val) static { return _Unchecked_popcount(_Val); });
     }
 #endif // ^^^ _HAS_POPCNT_INTRINSICS ^^^
-    return _Callback([](_Ty _Val) _STATIC_CALL_OPERATOR { return _Popcount_fallback(_Val); });
+    return _Callback([](_Ty _Val) static { return _Popcount_fallback(_Val); });
 }
 
 #undef _HAS_TZCNT_BSF_INTRINSICS

@@ -318,8 +318,8 @@ _EXPORT_STD enum class range_format { disabled, map, set, sequence, string, debu
 
 template <class _Ty>
 struct _Invalid_format_kind {
-    static_assert(_Always_false<_Ty>, "A program that instantiates the primary template of format_kind is ill-formed. "
-                                      "(N4981 [format.range.fmtkind]/1)");
+    static_assert(false, "A program that instantiates the primary template of format_kind is ill-formed. "
+                         "(N4981 [format.range.fmtkind]/1)");
 };
 
 _EXPORT_STD template <class _Ty>

@@ -36,7 +36,7 @@ _STL_DISABLE_CLANG_WARNINGS
 
 _STD_BEGIN
 
-#if defined(_M_X64) && !defined(_M_ARM64EC) && !defined(_M_CEE_PURE) && !defined(__CUDACC__)
+#if defined(_M_X64) && !defined(_M_ARM64EC) && !defined(_M_CEE_PURE)
 #define _STL_128_INTRINSICS 1
 #ifdef __clang__ // clang doesn't have _udiv128 / _div128
 #define _STL_128_DIV_INTRINSICS 0

@@ -289,11 +289,7 @@ struct _Iter_traits_category4<false> {
 
 template <class _It>
 concept _Cpp17_random_delta =
-#if defined(__CUDACC__) && !defined(__clang__) // TRANSITION, fixed in CUDA 12.5
-    totally_ordered<_It> && requires(_It __i, typename incrementable_traits<_It>::difference_type __n) {
-#else // ^^^ workaround / no workaround vvv
     totally_ordered<_It> && requires(_It __i, incrementable_traits<_It>::difference_type __n) {
-#endif // ^^^ no workaround ^^^
         { __i += __n } -> same_as<_It&>;
         { __i -= __n } -> same_as<_It&>;
         { __i + __n } -> same_as<_It>;
@@ -506,6 +502,9 @@ struct iterator_traits<_Ty*> : _Iterator_traits_pointer_base<_Ty> {}; // get tra
 
 template <class _Ty>
 constexpr bool _Integer_like = _Is_nonbool_integral<_Ty>;
+
+template <class _Ty>
+constexpr bool _Signed_integer_like = _Integer_like<_Ty> && is_signed_v<_Ty>;
 #endif // ^^^ !_HAS_CXX20 ^^^
 
 _INLINE_VAR constexpr auto _Meta_npos = ~size_t{0};

@@ -621,8 +621,7 @@ namespace ranges {
         public:
             template <viewable_range _Rng>
                 requires (_Choice<_Rng>._Strategy != _St::_None)
-            _NODISCARD _STATIC_CALL_OPERATOR constexpr auto operator()(_Rng&& _Range) _CONST_CALL_OPERATOR
-                noexcept(_Choice<_Rng>._No_throw) {
+            _NODISCARD static constexpr auto operator()(_Rng&& _Range) noexcept(_Choice<_Rng>._No_throw) {
                 constexpr _St _Strat = _Choice<_Rng>._Strategy;
 
                 if constexpr (_Strat == _St::_View) {
@@ -1046,7 +1045,7 @@ namespace ranges {
     namespace views {
         struct _Transform_fn {
             template <viewable_range _Rng, class _Fn>
-            _NODISCARD _STATIC_CALL_OPERATOR constexpr auto operator()(_Rng&& _Range, _Fn _Fun) _CONST_CALL_OPERATOR
+            _NODISCARD static constexpr auto operator()(_Rng&& _Range, _Fn _Fun)
                 noexcept(noexcept(transform_view(_STD forward<_Rng>(_Range), _STD move(_Fun))))
                 requires requires { transform_view(static_cast<_Rng &&>(_Range), _STD move(_Fun)); }
             {
@@ -1055,7 +1054,7 @@ namespace ranges {
 
             template <class _Fn>
                 requires constructible_from<decay_t<_Fn>, _Fn>
-            _NODISCARD _STATIC_CALL_OPERATOR constexpr auto operator()(_Fn&& _Fun) _CONST_CALL_OPERATOR
+            _NODISCARD static constexpr auto operator()(_Fn&& _Fun)
                 noexcept(is_nothrow_constructible_v<decay_t<_Fn>, _Fn>) {
                 return _Range_closure<_Transform_fn, decay_t<_Fn>>{_STD forward<_Fn>(_Fun)};
             }
@@ -1146,7 +1145,7 @@ namespace ranges {
                                      "the default-constructed object. (N5014 [range.utility.conv.to]/2.1.5)");
             }
         } else if constexpr (input_range<range_reference_t<_Rng>>) {
-            const auto _Xform = [](auto&& _Elem) _STATIC_CALL_OPERATOR {
+            const auto _Xform = [](auto&& _Elem) static {
                 return _RANGES to<range_value_t<_Container>>(_STD forward<decltype(_Elem)>(_Elem));
             };
             return _RANGES to<_Container>(views::transform(ref_view{_Range}, _Xform), _STD forward<_Types>(_Args)...);
@@ -1166,8 +1165,7 @@ namespace ranges {
         _STL_INTERNAL_STATIC_ASSERT(!view<_Container>);
 
         template <input_range _Rng, class... _Types>
-        _NODISCARD _STATIC_CALL_OPERATOR constexpr auto operator()(
-            _Rng&& _Range, _Types&&... _Args) _CONST_CALL_OPERATOR
+        _NODISCARD static constexpr auto operator()(_Rng&& _Range, _Types&&... _Args)
             requires requires { _RANGES to<_Container>(_STD forward<_Rng>(_Range), _STD forward<_Types>(_Args)...); }
         {
             return _RANGES to<_Container>(_STD forward<_Rng>(_Range), _STD forward<_Types>(_Args)...);
@@ -1222,8 +1220,7 @@ namespace ranges {
     struct _To_template_fn {
         template <input_range _Rng, class... _Types,
             class _Deduced = remove_pointer_t<decltype(_To_helper<_Container, _Rng, _Types...>())>>
-        _NODISCARD _STATIC_CALL_OPERATOR constexpr auto operator()(
-            _Rng&& _Range, _Types&&... _Args) _CONST_CALL_OPERATOR {
+        _NODISCARD static constexpr auto operator()(_Rng&& _Range, _Types&&... _Args) {
             return _RANGES to<_Deduced>(_STD forward<_Rng>(_Range), _STD forward<_Types>(_Args)...);
         }
     };

@@ -271,7 +271,7 @@ class _NO_SPECIALIZATIONS_CITING("N5014 [format.arg]/2") basic_format_arg {
         }
     };
 
-#if defined(__clang__) || defined(__CUDACC__) // TRANSITION, LLVM-81774 (Clang), VSO-2411436 (needed by CUDA 12.8.1)
+#if defined(__clang__) || defined(__CUDACC__) // TRANSITION, LLVM-81774, DevCom-10863472 (still needed by CUDA 13.2)
     basic_format_arg() noexcept : _Active_state(_Basic_format_arg_type::_None), _No_state() {}
 #else // ^^^ workaround / no workaround vvv
     basic_format_arg() noexcept = default;

@@ -101,28 +101,28 @@ struct _Tzdb_deleter;
 
 template <>
 struct _Tzdb_deleter<__std_tzdb_time_zones_info> {
-    _STATIC_CALL_OPERATOR void operator()(__std_tzdb_time_zones_info* _Info) _CONST_CALL_OPERATOR noexcept {
+    static void operator()(__std_tzdb_time_zones_info* _Info) noexcept {
         __std_tzdb_delete_time_zones(_Info);
     }
 };
 
 template <>
 struct _Tzdb_deleter<__std_tzdb_current_zone_info> {
-    _STATIC_CALL_OPERATOR void operator()(__std_tzdb_current_zone_info* _Info) _CONST_CALL_OPERATOR noexcept {
+    static void operator()(__std_tzdb_current_zone_info* _Info) noexcept {
         __std_tzdb_delete_current_zone(_Info);
     }
 };
 
 template <>
 struct _Tzdb_deleter<__std_tzdb_sys_info> {
-    _STATIC_CALL_OPERATOR void operator()(__std_tzdb_sys_info* _Info) _CONST_CALL_OPERATOR noexcept {
+    static void operator()(__std_tzdb_sys_info* _Info) noexcept {
         __std_tzdb_delete_sys_info(_Info);
     }
 };
 
 template <>
 struct _Tzdb_deleter<__std_tzdb_leap_info[]> {
-    _STATIC_CALL_OPERATOR void operator()(__std_tzdb_leap_info* _Info) _CONST_CALL_OPERATOR noexcept {
+    static void operator()(__std_tzdb_leap_info* _Info) noexcept {
         __std_tzdb_delete_leap_seconds(_Info);
     }
 };