[PATCH v2 1/4] [gdb/cli] Skip string copy in source_cache::ensure

[Tom de Vries <tdevries@suse.de>]

In function source_cache::ensure we have:
...
 	      std::ostringstream output;
	      ...
	      contents = output.str();
...
The last line causes an unnecessary string copy.

C++20 allows us to skip it, like this:
...
	      contents = std::move (output).str();
...

Use the more efficient version if compiling with -std=c++20.

Tested on x86_64-linux.
---
 gdb/source-cache.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/gdb/source-cache.c b/gdb/source-cache.c
index 77b357cb42b..7ef54411c69 100644
--- a/gdb/source-cache.c
+++ b/gdb/source-cache.c
@@ -252,7 +252,11 @@ source_cache::ensure (struct symtab *s)
 	      std::istringstream input (contents);
 	      std::ostringstream output;
 	      highlighter->highlight (input, output, lang_name, fullname);
+#if __cplusplus >= 202002L
+	      contents = std::move (output).str();
+#else
 	      contents = output.str ();
+#endif
 	      already_styled = true;
 	    }
 	  catch (...)
-- 
2.35.3