c++: Mitigate -Wuseless-cast with classes [PR85043]

-Wuseless-cast (not part of -Wall/-Wextra) warns here:

  struct S { };
  void g (S&&);
  void f (S&& arg)
  {
    g (S(arg)); // warning: useless cast to type 'struct S'
  }

which is wrong: the code will not compile without the cast because
"arg" is an lvalue which cannot bind to S&&.

This patch disables the warning when an object that isn't a prvalue
is cast to a non-reference type.  Therefore we still warn about the
useless cast in "X(X{})".

	PR c++/85043

gcc/cp/ChangeLog:

	* typeck.cc (maybe_warn_about_useless_cast): Don't warn when
	a glvalue is cast to a non-reference type.

gcc/ChangeLog:

	* doc/invoke.texi: Update documentation of -Wuseless-cast.

gcc/testsuite/ChangeLog:

	* g++.dg/warn/Wuseless-cast.C: Remove dg-warning.
	* g++.dg/warn/Wuseless-cast3.C: New test.

0 files changed, 0 insertions, 0 deletions