[libcxx-commits] [libcxx] Optimize std::print for Windows 8+ (PR #232993)

[Yexuan Xiao via libcxx-commits]

https://github.com/YexuanXiao updated https://github.com/llvm/llvm-project/pull/232993

>From 4eb0e80b623cbc4e2e719a53a1fbbdd47c2fe446 Mon Sep 17 00:00:00 2001
From: YexuanXiao <bizwen at nykz.org>
Date: Sat, 17 Oct 2026 08:52:42 +0800
Subject: [PATCH 1/3] Optimize std::print for Windows 8+

---
 libcxx/src/print.cpp | 38 ++++++++++++++++++++++++++++++++------
 1 file changed, 32 insertions(+), 6 deletions(-)

diff --git a/libcxx/src/print.cpp b/libcxx/src/print.cpp
index 2eb8a0f31488c4..c93a4841888884 100644
--- a/libcxx/src/print.cpp
+++ b/libcxx/src/print.cpp
@@ -19,7 +19,10 @@
 #  define WIN32_LEAN_AND_MEAN
 #  define NOMINMAX
 #  include <io.h>
+#  include <versionhelpers.h>
 #  include <windows.h>
+#  include <winioctl.h>
+#  include <winternl.h>
 #elif __has_include(<unistd.h>)
 #  include <unistd.h>
 #  if defined(_NEWLIB_VERSION)
@@ -36,19 +39,42 @@ _LIBCPP_BEGIN_NAMESPACE_STD
 _LIBCPP_BEGIN_EXPLICIT_ABI_ANNOTATIONS
 
 #ifdef _WIN32
+// Exported by ntdll.lib and can most efficiently query whether a HANDLE references a console.
+// Since the user mode header isn't provided, all needed declarations are declared manually.
+extern "C" NTSYSAPI NTSTATUS NTAPI NtQueryVolumeInformationFile(
+    HANDLE handle, PIO_STATUS_BLOCK ioStatus, PVOID information, ULONG length, ULONG informationClass);
 
-_LIBCPP_EXPORTED_FROM_ABI bool __is_windows_terminal(FILE* __stream) {
+// https://learn.microsoft.com/en-us/windows-hardware/drivers/ddi/wdm/ns-wdm-_file_fs_device_information
+struct FILE_FS_DEVICE_INFORMATION {
+  DEVICE_TYPE DeviceType;
+  ULONG Characteristics;
+};
+
+// https://learn.microsoft.com/en-us/windows/console/console-handles
+static bool __is_handle_terminal_win8_or_greater(HANDLE handle) {
+  // https://learn.microsoft.com/en-us/windows-hardware/drivers/ddi/wdm/ne-wdm-_fsinfoclass
+  constexpr ULONG FileFsDeviceInformation = 4;
+  IO_STATUS_BLOCK iosb;
+  FILE_FS_DEVICE_INFORMATION info;
+  const auto status = NtQueryVolumeInformationFile(handle, &iosb, &info, sizeof(info), FileFsDeviceInformation);
+  return (status >= 0) && (info.DeviceType == FILE_DEVICE_CONSOLE);
+}
+
+static bool __is_handle_terminal(HANDLE handle) {
   // Note the Standard does this in one call, but it's unclear whether
   // an invalid handle is allowed when calling GetConsoleMode.
-  //
-  // https://learn.microsoft.com/en-us/cpp/c-runtime-library/reference/get-osfhandle?view=msvc-170
   // https://learn.microsoft.com/en-us/windows/console/getconsolemode
+  unsigned long __mode;
+  return GetConsoleMode(reinterpret_cast<void*>(__handle), &__mode);
+}
+
+_LIBCPP_EXPORTED_FROM_ABI bool __is_windows_terminal(FILE* __stream) {
+  // https://learn.microsoft.com/en-us/cpp/c-runtime-library/reference/get-osfhandle?view=msvc-170
   intptr_t __handle = _get_osfhandle(fileno(__stream));
   if (__handle == -1)
     return false;
-
-  unsigned long __mode;
-  return GetConsoleMode(reinterpret_cast<void*>(__handle), &__mode);
+  static bool __win8_or_greater = IsWindows8OrGreater();
+  return __win8_or_greater ? __is_handle_terminal_win8_or_greater(__handle) : __is_handle_terminal(__handle);
 }
 
 #  if _LIBCPP_HAS_WIDE_CHARACTERS

>From b470104af09770e24ee425b46fbfa961979c9494 Mon Sep 17 00:00:00 2001
From: YexuanXiao <bizwen at nykz.org>
Date: Sat, 17 Oct 2026 11:40:44 +0800
Subject: [PATCH 2/3] Fix viriable names

---
 libcxx/src/print.cpp | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/libcxx/src/print.cpp b/libcxx/src/print.cpp
index c93a4841888884..dc9640316ff82a 100644
--- a/libcxx/src/print.cpp
+++ b/libcxx/src/print.cpp
@@ -51,16 +51,16 @@ struct FILE_FS_DEVICE_INFORMATION {
 };
 
 // https://learn.microsoft.com/en-us/windows/console/console-handles
-static bool __is_handle_terminal_win8_or_greater(HANDLE handle) {
+static bool __is_handle_terminal_win8_or_greater(HANDLE __handle) {
   // https://learn.microsoft.com/en-us/windows-hardware/drivers/ddi/wdm/ne-wdm-_fsinfoclass
   constexpr ULONG FileFsDeviceInformation = 4;
   IO_STATUS_BLOCK iosb;
   FILE_FS_DEVICE_INFORMATION info;
-  const auto status = NtQueryVolumeInformationFile(handle, &iosb, &info, sizeof(info), FileFsDeviceInformation);
+  const auto status = NtQueryVolumeInformationFile(__handle, &iosb, &info, sizeof(info), FileFsDeviceInformation);
   return (status >= 0) && (info.DeviceType == FILE_DEVICE_CONSOLE);
 }
 
-static bool __is_handle_terminal(HANDLE handle) {
+static bool __is_handle_terminal(HANDLE __handle) {
   // Note the Standard does this in one call, but it's unclear whether
   // an invalid handle is allowed when calling GetConsoleMode.
   // https://learn.microsoft.com/en-us/windows/console/getconsolemode

>From 0096249d44580618ad103c7e214b4f562b352e27 Mon Sep 17 00:00:00 2001
From: YexuanXiao <bizwen at nykz.org>
Date: Sat, 17 Oct 2026 11:45:10 +0800
Subject: [PATCH 3/3] Underscore the variable name

---
 libcxx/src/print.cpp | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/libcxx/src/print.cpp b/libcxx/src/print.cpp
index dc9640316ff82a..e89effcc069a44 100644
--- a/libcxx/src/print.cpp
+++ b/libcxx/src/print.cpp
@@ -50,14 +50,16 @@ struct FILE_FS_DEVICE_INFORMATION {
   ULONG Characteristics;
 };
 
+// https://learn.microsoft.com/en-us/windows-hardware/drivers/ddi/wdm/ne-wdm-_fsinfoclass
+#  define FileFsDeviceInformation 4
+
 // https://learn.microsoft.com/en-us/windows/console/console-handles
 static bool __is_handle_terminal_win8_or_greater(HANDLE __handle) {
-  // https://learn.microsoft.com/en-us/windows-hardware/drivers/ddi/wdm/ne-wdm-_fsinfoclass
-  constexpr ULONG FileFsDeviceInformation = 4;
-  IO_STATUS_BLOCK iosb;
-  FILE_FS_DEVICE_INFORMATION info;
-  const auto status = NtQueryVolumeInformationFile(__handle, &iosb, &info, sizeof(info), FileFsDeviceInformation);
-  return (status >= 0) && (info.DeviceType == FILE_DEVICE_CONSOLE);
+  IO_STATUS_BLOCK __iosb;
+  FILE_FS_DEVICE_INFORMATION __info;
+  const auto __status =
+      NtQueryVolumeInformationFile(__handle, &__iosb, &__info, sizeof(__info), FileFsDeviceInformation);
+  return (__status >= 0) && (info.DeviceType == FILE_DEVICE_CONSOLE);
 }
 
 static bool __is_handle_terminal(HANDLE __handle) {