Re: [pushed] c++: allow NRV and non-NRV returns [PR58487]

[Hans-Peter Nilsson <hp@axis.com>]

> Date: Wed,  7 Jun 2023 18:06:15 -0400
> From: Jason Merrill via Gcc-patches <gcc-patches@gcc.gnu.org>

> Tested x86_64-pc-linux-gnu, applying to trunk.
> 
> -- 8< --
> 
> Now that we support NRV from an inner block, we can also support non-NRV
> returns from other blocks, since once the NRV is out of scope a later return
> expression can't possibly alias it.
> 
> This fixes 58487 and half-fixes 53637: now one of the returns is elided, but
> not the other.
> 
> Fixing the remaining xfails in these testcases will require a very different
> approach, probably involving a full tree/block walk from finalize_nrv, and
> check_return_expr only adding to a list of potential return variables.
> 
> 	PR c++/58487
> 	PR c++/53637
> 
> gcc/cp/ChangeLog:
> 
> 	* cp-tree.h (INIT_EXPR_NRV_P): New.
> 	* semantics.cc (finalize_nrv_r): Check it.
> 	* name-lookup.h (decl_in_scope_p): Declare.
> 	* name-lookup.cc (decl_in_scope_p): New.
> 	* typeck.cc (check_return_expr): Allow non-NRV
> 	returns if the NRV is no longer in scope.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/opt/nrv26.C: New test.
> 	* g++.dg/opt/nrv26a.C: New test.
> 	* g++.dg/opt/nrv27.C: New test.

This somehow caused 21 regressions for cris-elf in the c++
and libstdc++ testsuites.  I opened PR110185 to hold the
preprocessed g++.dg/cpp2a/spaceship-p1186.C.

brgds, H-P