c++: Tweak for -Wpessimizing-move in templates [PR89780]
In my previous patches I've been extending our std::move warnings,
but this tweak actually dials it down a little bit. As reported in
bug 89780, it's questionable to warn about expressions in templates
that were type-dependent, but aren't anymore because we're instantiating
the template. As in,
template <typename T>
Dest withMove() {
T x;
return std::move(x);
}
template Dest withMove<Dest>(); // #1
template Dest withMove<Source>(); // #2
Saying that the std::move is pessimizing for #1 is not incorrect, but
it's not useful, because removing the std::move would then pessimize #2.
So the user can't really win. At the same time, disabling the warning
just because we're in a template would be going too far, I still want to
warn for
template <typename>
Dest withMove() {
Dest x;
return std::move(x);
}
because the std::move therein will be pessimizing for any instantiation.
So I'm using the suppress_warning machinery to that effect.
Problem: I had to add a new group to nowarn_spec_t, otherwise
suppressing the -Wpessimizing-move warning would disable a whole bunch
of other warnings, which we really don't want.
PR c++/89780
gcc/cp/ChangeLog:
* pt.cc (tsubst_copy_and_build) <case CALL_EXPR>: Maybe suppress
-Wpessimizing-move.
* typeck.cc (maybe_warn_pessimizing_move): Don't issue warnings
if they are suppressed.
(check_return_expr): Disable -Wpessimizing-move when returning
a dependent expression.
gcc/ChangeLog:
* diagnostic-spec.cc (nowarn_spec_t::nowarn_spec_t): Handle
OPT_Wpessimizing_move and OPT_Wredundant_move.
* diagnostic-spec.h (nowarn_spec_t): Add NW_REDUNDANT enumerator.
gcc/testsuite/ChangeLog:
* g++.dg/cpp0x/Wpessimizing-move3.C: Remove dg-warning.
* g++.dg/cpp0x/Wredundant-move2.C: Likewise.