[Bug c++/99287] std::source_location::function_name breaks constexpr
cvs-commit at gcc dot gnu.org
gcc-bugzilla@gcc.gnu.org
Sat Mar 6 22:10:30 GMT 2021
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99287
--- Comment #7 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Patrick Palka <ppalka@gcc.gnu.org>:
https://gcc.gnu.org/g:d1bba463bd0d5692b7fa58ee37a61a55b2517456
commit r11-7546-gd1bba463bd0d5692b7fa58ee37a61a55b2517456
Author: Patrick Palka <ppalka@redhat.com>
Date: Sat Mar 6 17:09:07 2021 -0500
c++: Fix constexpr evaluation of pre-increment when !lval [PR99287]
Here, during cxx_eval_increment_expression (with lval=false) of
++__first where __first is &"mystr"[0], we correctly update __first
to &"mystr"[1] but we end up returning &"mystr"[0] + 1 instead of
&"mystr"[1]. This unreduced return value inhibits other pointer
arithmetic folding during later constexpr evaluation, which ultimately
causes the constexpr evaluation to fail.
It turns out the simplification of &"mystr"[0] + 1 to &"mystr"[1]
is performed by cxx_fold_pointer_plus_expression, not by fold_build2.
So we perform this simplification during constexpr evaluation of
the temporary MODIFY_EXPR (during which we assign to __first the
simplified value), but then we return 'mod' which has only been folded
via fold_build2 and hasn't gone through cxx_fold_pointer_plus_expression.
This patch fixes this by updating 'mod' with the result of the
MODIFY_EXPR evaluation appropriately, so that it captures any additional
folding of the expression when !lval. We now need to be wary of this
evaluation failing and returning e.g. the MODIFY_EXPR or NULL_TREE; it
seems checking *non_constant_p should cover our bases here and is
generally prudent.
gcc/cp/ChangeLog:
PR c++/99287
* constexpr.c (cxx_eval_increment_expression): Pass lval when
evaluating the MODIFY_EXPR, and update 'mod' with the result of
this evaluation. Check *non_constant_p afterwards. For prefix
ops, just return 'mod'.
gcc/testsuite/ChangeLog:
PR c++/99287
* g++.dg/cpp2a/constexpr-99287.C: New test.
Co-authored-by: Jakub Jelinek <jakub@redhat.com>
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