[libc++][format] Implements P3107R5 in <print>. #130500
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| ✅ With the latest revision this PR passed the C/C++ code formatter. |
mordante force-pushed the users/mordante/P3107R5-implementation branch 7 times, most recently from 3efe358 to 4bd6795 Compare 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
mordante force-pushed the users/mordante/P3107R5-implementation branch 2 times, most recently from 071b6c1 to 7ab2024 Compare mordante force-pushed the users/mordante/P3107R5-implementation branch from 7ab2024 to 4fcce8d Compare mordante added a commit to mordante/llvm-project that referenced this pull request Mar 14, 2025
This was discovered when using this name in llvm#130500.
mordante added a commit that referenced this pull request Mar 16, 2025
This was discovered when using this name in #130500.
mordante force-pushed the users/mordante/P3107R5-implementation branch from fb15f9b to 4b0bd31 Compare mordante force-pushed the users/mordante/P3107R5-implementation branch from 4b0bd31 to b190535 Compare 
ldionne reviewed Apr 1, 2025
| template <class = void> // TODO PRINT template or availability markup fires too eagerly (http://llvm.org/PR61563). | ||
| _LIBCPP_HIDE_FROM_ABI inline void | ||
| __vprint_nonunicode(FILE* __stream, string_view __fmt, format_args __args, bool __write_nl) { | ||
| _LIBCPP_HIDE_FROM_ABI inline void __flockfile(FILE* __stream) { |
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I think we should take the opportunity to introduce a proper "platform layer" for these functions. Something similar to what we do in libcxx/include/__thread/support.h or libcxx/include/__locale_dir/locale_base_api.h, or libcxx/include/__atomic/support.h. I think we might be able to grow this into something more generally useful for other parts of the library.
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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
std::printImplements parts of
Fixes: #105435