[libcxx-commits] [libcxx] [libc++][format] Adds print benchmarks. (PR #129765)

[Mark de Wever via libcxx-commits]

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@@ -0,0 +1,79 @@
+//===----------------------------------------------------------------------===//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// REQUIRES: std-at-least-c++23
+
+// This benchmark writes the print and benchmark data to stdout. In order to
+// preserve the benchmark output it needs to be stored in a file (using the
+// console format). Another issue with the benchmark is the time it takes to
+// write output to the real terminal. In order to avoid that overhead write the
+// output to a fast "terminal", like /dev/null. For example, the printf
+//   console    1546   ns
+//   /dev/null    70.9 ns
+// An example of a good test invocation.
+// BENCHMARK_OUT=benchmark.txt BENCHMARK_OUT_FORMAT=console <exe> >/dev/null
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mordante wrote:

That's indeed the case. This tests `std::print` which writes to `stdout`, which means part of the benchmark is benchmarking the terminal. Therefore this is needed. I'll have a look at it.

This patch was originally written a while ago for our non-lit benchmarking so I haven't investigated the lit invocation.

https://github.com/llvm/llvm-project/pull/129765