[PATCH][libstdc++][testsuite] XFAIL tests relying on long double-to-string conversions on broken newlib

[Jonathan Wakely]

On 12/12/16 13:55 +0000, Kyrill Tkachov wrote:
>Hi all,
>
>I've been investigating the execution failures of:
>21_strings/basic_string/numeric_conversions/char/stod.cc
>21_strings/basic_string/numeric_conversions/wchar_t/stod.cc
>21_strings/basic_string/numeric_conversions/wchar_t/stold.cc
>27_io/basic_ostream/inserters_arithmetic/char/hexfloat.cc
>
>on aarch64-none-elf, a newlib target.
>The reason they are failing is because they are converting a long double to a string using to_string
>before trying to convert it back into a number.
>to_string ends up calling a vsnprintf from the C library (newlib in this case) with the %Lf format
>to convert from long double.
>Unfortunately the %Lf format is broken in newlib for platforms where long double is not the same as double.
>It gives bogus results because newlib doesn't implement the long double variant of frexp (frexpl) which is needed
>to implement printf properly. So it ends up using frexp even on long doubles. This gives wrong results which causes
>these tests to fail.
>
>So this patch marks them as XFAIL and adds an effective target check for broken newlib versions.
>
>With this patch these tests appear as XFAIL on aarch64-none-elf.
>
>Ok for trunk?

Yes OK, thanks.