[libc++][format] Implements P3107R5 in <print>.

mordante · mordante · commit 4bd6795cb216 · 2025-03-11T20:21:50.000+01:00
The followup paper P3235R3 which is voted in as a DR changes the names foo_locking to foo_buffered. These changes have been applied in this patch. Before ------------------------------------------------------- Benchmark Time CPU Iterations ------------------------------------------------------- printf 71.3 ns 71.3 ns 9525175 print_string 226 ns 226 ns 3105850 print_stack 232 ns 232 ns 3026498 print_direct 530 ns 530 ns 1318447 After ------------------------------------------------------- Benchmark Time CPU Iterations ------------------------------------------------------- printf 70.6 ns 70.6 ns 9789585 print_string 222 ns 222 ns 3147678 print_stack 227 ns 227 ns 3084767 print_direct 474 ns 474 ns 1472786 Note: The performance of libc++'s std::print is still extemely slow compared to printf. Based on P3107R5 std::print should outperform printf. The main culprit is the call to isatty, which is resolved after implementing LWG4044 Confusing requirements for std::print on POSIX platforms Implements - P3107R5 - Permit an efficient implementation of ``std::print`` Implements parts of - P3235R3 std::print more types faster with less memory Fixes: #105435
diff --git a/libcxx/docs/ReleaseNotes/21.rst b/libcxx/docs/ReleaseNotes/21.rst
@@ -40,6 +40,7 @@ Implemented Papers
 
 - N4258: Cleaning-up noexcept in the Library (`Github <https://github.com/llvm/llvm-project/issues/99937>`__)
 - P1361R2: Integration of chrono with text formatting (`Github <https://github.com/llvm/llvm-project/issues/100014>`__)
+- P3107R5 - Permit an efficient implementation of ``std::print`` (`Github <https://github.com/llvm/llvm-project/issues/105435>`__)
 
 Improvements and New Features
 -----------------------------
diff --git a/libcxx/include/__format/buffer.h b/libcxx/include/__format/buffer.h
@@ -12,6 +12,7 @@
 
 #include <__algorithm/copy_n.h>
 #include <__algorithm/fill_n.h>
+#include <__algorithm/for_each.h>
 #include <__algorithm/max.h>
 #include <__algorithm/min.h>
 #include <__algorithm/ranges_copy.h>
@@ -34,11 +35,13 @@
 #include <__memory/construct_at.h>
 #include <__memory/destroy.h>
 #include <__memory/uninitialized_algorithms.h>
+#include <__system_error/system_error.h>
 #include <__type_traits/add_pointer.h>
 #include <__type_traits/conditional.h>
 #include <__utility/exception_guard.h>
 #include <__utility/move.h>
 #include <stdexcept>
+#include <stdio.h> // Uses the POSIX/Windows unlocked stream I/O
 #include <string_view>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
diff --git a/libcxx/include/print b/libcxx/include/print
diff --git a/libcxx/modules/std/print.inc b/libcxx/modules/std/print.inc
@@ -16,6 +16,7 @@ export namespace std {
   using std::vprint_nonunicode;
 #  if _LIBCPP_HAS_UNICODE
   using std::vprint_unicode;
+  using std::vprint_unicode_buffered;
 #  endif // _LIBCPP_HAS_UNICODE
 #endif   // _LIBCPP_STD_VER >= 23
 } // namespace std
diff --git a/libcxx/test/libcxx/system_reserved_names.gen.py b/libcxx/test/libcxx/system_reserved_names.gen.py
@@ -119,6 +119,11 @@
 #define __acquire SYSTEM_RESERVED_NAME
 #define __release SYSTEM_RESERVED_NAME
 
+// Android and FreeBSD use this for __attribute__((__unused__))
+#if !defined(__FreeBSD__)  && !defined(__ANDROID__)
+#define __unused SYSTEM_RESERVED_NAME
+#endif
+
 // These names are not reserved, so the user can macro-define them.
 // These are intended to find improperly _Uglified template parameters.
 #define A SYSTEM_RESERVED_NAME
diff --git a/libcxx/test/libcxx/transitive_includes/cxx03.csv b/libcxx/test/libcxx/transitive_includes/cxx03.csv
@@ -122,15 +122,19 @@ atomic ratio
 atomic type_traits
 atomic version
 barrier atomic
+barrier cctype
 barrier climits
 barrier cmath
 barrier compare
 barrier concepts
 barrier cstddef
 barrier cstdint
+barrier cstdio
 barrier cstdlib
 barrier cstring
 barrier ctime
+barrier cwchar
+barrier cwctype
 barrier exception
 barrier initializer_list
 barrier iosfwd
@@ -2024,6 +2028,7 @@ stdexcept new
 stdexcept type_traits
 stdexcept typeinfo
 stdexcept version
+stop_token cstddef
 stop_token iosfwd
 stop_token version
 streambuf algorithm
diff --git a/libcxx/test/libcxx/transitive_includes/cxx11.csv b/libcxx/test/libcxx/transitive_includes/cxx11.csv
@@ -122,15 +122,19 @@ atomic ratio
 atomic type_traits
 atomic version
 barrier atomic
+barrier cctype
 barrier climits
 barrier cmath
 barrier compare
 barrier concepts
 barrier cstddef
 barrier cstdint
+barrier cstdio
 barrier cstdlib
 barrier cstring
 barrier ctime
+barrier cwchar
+barrier cwctype
 barrier exception
 barrier initializer_list
 barrier iosfwd
@@ -2024,6 +2028,7 @@ stdexcept new
 stdexcept type_traits
 stdexcept typeinfo
 stdexcept version
+stop_token cstddef
 stop_token iosfwd
 stop_token version
 streambuf algorithm
diff --git a/libcxx/test/libcxx/transitive_includes/cxx14.csv b/libcxx/test/libcxx/transitive_includes/cxx14.csv
@@ -125,15 +125,19 @@ atomic ratio
 atomic type_traits
 atomic version
 barrier atomic
+barrier cctype
 barrier climits
 barrier cmath
 barrier compare
 barrier concepts
 barrier cstddef
 barrier cstdint
+barrier cstdio
 barrier cstdlib
 barrier cstring
 barrier ctime
+barrier cwchar
+barrier cwctype
 barrier exception
 barrier initializer_list
 barrier iosfwd
@@ -2064,6 +2068,7 @@ stdexcept new
 stdexcept type_traits
 stdexcept typeinfo
 stdexcept version
+stop_token cstddef
 stop_token iosfwd
 stop_token version
 streambuf algorithm
diff --git a/libcxx/test/libcxx/transitive_includes/cxx17.csv b/libcxx/test/libcxx/transitive_includes/cxx17.csv
@@ -122,15 +122,19 @@ atomic ratio
 atomic type_traits
 atomic version
 barrier atomic
+barrier cctype
 barrier climits
 barrier cmath
 barrier compare
 barrier concepts
 barrier cstddef
 barrier cstdint
+barrier cstdio
 barrier cstdlib
 barrier cstring
 barrier ctime
+barrier cwchar
+barrier cwctype
 barrier exception
 barrier initializer_list
 barrier iosfwd
@@ -2077,6 +2081,7 @@ stdexcept new
 stdexcept type_traits
 stdexcept typeinfo
 stdexcept version
+stop_token cstddef
 stop_token iosfwd
 stop_token version
 streambuf algorithm
diff --git a/libcxx/test/libcxx/transitive_includes/cxx23.csv b/libcxx/test/libcxx/transitive_includes/cxx23.csv
@@ -556,7 +556,6 @@ istream ios
 istream iosfwd
 istream limits
 istream locale
-
 istream ratio
 istream stdexcept
 istream streambuf
@@ -765,6 +764,7 @@ queue deque
 queue initializer_list
 queue iosfwd
 queue limits
+queue optional
 queue stdexcept
 queue string
 queue string_view
@@ -831,6 +831,7 @@ regex deque
 regex initializer_list
 regex iosfwd
 regex limits
+regex optional
 regex stdexcept
 regex string
 regex string_view
@@ -1075,6 +1076,7 @@ thread iosfwd
 thread istream
 thread limits
 thread locale
+thread optional
 thread ratio
 thread sstream
 thread stdexcept
@@ -1146,6 +1148,7 @@ vector cwctype
 vector initializer_list
 vector iosfwd
 vector limits
+vector optional
 vector stdexcept
 vector string
 vector string_view
diff --git a/libcxx/test/libcxx/transitive_includes/cxx26.csv b/libcxx/test/libcxx/transitive_includes/cxx26.csv
@@ -763,6 +763,7 @@ queue deque
 queue initializer_list
 queue iosfwd
 queue limits
+queue optional
 queue stdexcept
 queue string
 queue string_view
@@ -829,6 +830,7 @@ regex deque
 regex initializer_list
 regex iosfwd
 regex limits
+regex optional
 regex stdexcept
 regex string
 regex string_view
@@ -1073,6 +1075,7 @@ thread iosfwd
 thread istream
 thread limits
 thread locale
+thread optional
 thread ratio
 thread sstream
 thread stdexcept
@@ -1144,6 +1147,7 @@ vector cwctype
 vector initializer_list
 vector iosfwd
 vector limits
+vector optional
 vector stdexcept
 vector string
 vector string_view
