https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86216
--- Comment #8 from Richard Biener <rguenth at gcc dot gnu.org> ---
The C FE does
/* Arrange for the SAVE_EXPR on the inside of the
MINUS_EXPR, which allows the -1 to get folded
with the +1 that happens when building TYPE_SIZE. */
if (size_varies)
size = save_expr (size);
while the C++ FE relies on variable_size() after building the whole
expression. Eliding the above optimization makes the IL more similar
but it still doesn't break.
