c++: don't mark void exprs as read [PR44677]

In Jakub's patch for PR44677 he added code to prevent mark_exp_read on
e.g. (void)++i from marking i as read, but it seems to me that we can
generalize that to avoid looking any farther into any void expression;
you can't read a void value, and an explicit cast will have already called
mark_exp_read on its operand in convert_to_void.

For testing I added an assert to catch places where we were trying to mark
void expressions as read, and fix a few that it found.  But there were
several other places (such as check_return_expr) where we could have a void
expression but always calling mark_exp_read makes sense, so I dropped the
assert from the final commit.

	PR c++/44677

gcc/cp/ChangeLog:

	* cp-gimplify.cc (cp_fold) [CLEANUP_POINT_EXPR]: Don't force rvalue.
	[COMPOUND_EXPR]: Likewise.
	* cvt.cc (convert_to_void): Call mark_exp_read later.
	* expr.cc (mark_use): Turn off read_p for any void argument.
	(mark_exp_read): Return early for void argument.

0 files changed, 0 insertions, 0 deletions