c++: improve constexpr prvalue folding [PR116416]

This patch improves upon r15-6052-g12de1942a0a673 by performing prvalue
folding with mce_false rather than mce_unknown when it's safe to do so
(i.e. ff_mce_false is set), so that we can also fold temporary initializers
that call is_constant_evaluated etc.

In passing I noticed constexpr-prvalue1.C could more precisely verify the
optimization happened by inspecting what the front end spits out instead
of inspecting the optimized assembly -- that there's no constructor call
doesn't necessarily imply the constructor has been completely folded away,
only that its body has been inlined.

	PR c++/116416

gcc/cp/ChangeLog:

	* constexpr.cc (maybe_constant_init_1): Generalize type of
	of manifestly_const_eval parameter from bool to mce_value.
	(maybe_constant_init): Define 3-parameter version taking a
	manifestly_const_eval instead of bool parameter.
	(cxx_constant_init): Adjust.
	* cp-gimplify.cc (cp_fold_r) <case TARGET_EXPR>: Pass mce_false
	to maybe_constant_init during prvalue folding if ff_mce_false is
	set.
	* cp-tree.h (maybe_constant_init): Declare new overload.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp1y/constexpr-prvalue1.C: Adjust to instead inspect
	the 'original' dump.
	* g++.dg/cpp1y/constexpr-prvalue1a.C: New test.

Reviewed-by: Jason Merrill <jason@redhat.com>

0 files changed, 0 insertions, 0 deletions