[PATCH] PR libstdc++/90920 restore previous checks for empty ranges

[Jonathan Wakely]

On 20/06/19 00:00 +0100, Jonathan Wakely wrote:
>The change in r263433 broke the contract of the __rotate functions, by no
>longer accepting empty ranges. That means that callers which inlined the
>old version of std::rotate (without checks) that end up linking to a new
>definition of std::__rotate (also without checks) could perform a divide
>by zero and crash.
>
>This restores the old contract of the __rotate overloads.
>
>	PR libstdc++/90920 partially revert r263433
>	* include/bits/stl_algo.h (__rotate): Restore checks for empty ranges.
>	(rotate): Remove checks.
>	* testsuite/25_algorithms/rotate/90920.cc: New test.
>
>
>Tested x86_64-linux, committed to trunk.
>
>This needs to be backported to gcc-9-branch too.

Committed to gcc-9-branch. I will also add a notice to the
https://gcc.gnu.org/gcc-9/changes.html page.