https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94772
--- Comment #3 from CVS Commits ---
The master branch has been updated by Patrick Palka :
https://gcc.gnu.org/g:64da1b761db248f4f0d2235a6055c025fbbc94eb
commit r10-7996-g64da1b761db248f4f0d2235a6055c025fbbc94eb
Author: Patrick Palka
Date: Mon Apr 27 17:06:35 2020 -0400
c++: Delegating constructor in constexpr init [PR94772]
In the first testcase below, the call to the target constructor foo{} from
foo's
delegating constructor is encoded as the INIT_EXPR
*(struct foo *) this = AGGR_INIT_EXPR <4, __ct_comp, D.2140, ...>;
During initialization of the variable 'bar', we prematurely set
TREE_READONLY on
bar's CONSTRUCTOR in two places before the outer delegating constructor has
returned: first, at the end of cxx_eval_call_expression after evaluating
the RHS
of the above INIT_EXPR, and second, at the end of cxx_eval_store_expression
after having finished evaluating the above INIT_EXPR. This then prevents
the
rest of the outer delegating constructor from mutating 'bar'.
This (hopefully minimally risky) patch makes cxx_eval_call_expression
refrain
from setting TREE_READONLY when evaluating the target constructor of a
delegating constructor. It also makes cxx_eval_store_expression refrain
from
setting TREE_READONLY when the object being initialized is "*this', on the
basis
that it should be the responsibility of the routine that set 'this' in the
first
place to set the object's TREE_READONLY appropriately.
gcc/cp/ChangeLog:
PR c++/94772
* constexpr.c (cxx_eval_call_expression): Don't set new_obj if
we're
evaluating the target constructor of a delegating constructor.
(cxx_eval_store_expression): Don't set TREE_READONLY if the LHS of
the
INIT_EXPR is '*this'.
gcc/testsuite/ChangeLog:
PR c++/94772
* g++.dg/cpp1y/constexpr-tracking-const23.C: New test.
* g++.dg/cpp1y/constexpr-tracking-const24.C: New test.
* g++.dg/cpp1y/constexpr-tracking-const25.C: New test.
