PR c/66618
	PR c/69960
c-family/
	* c-common.h (c_fully_fold): Add LVAL argument defaulted to false.
c/
	* c-parser.c (c_parser_omp_atomic): Pass true as LVAL to c_fully_fold
	where needed.
	* c-typeck.c (build_unary_op, build_modify_expr, build_asm_expr,
	handle_omp_array_sections): Likewise.
	(digest_init): Don't call decl_constant_value_for_optimization.
	* c-tree.h (decl_constant_value_for_optimization): Removed.
	* c-fold.c (c_fold_array_ref): New function.
	(c_fully_fold_internal): Add LVAL argument, propagate it through
	recursive calls.  For VAR_P call decl_constant_value and
	unshare if not LVAL and either optimizing or IN_INIT.  Remove
	decl_constant_value_for_optimization calls.  If IN_INIT and not LVAL,
	fold ARRAY_REF with STRING_CST and INTEGER_CST operands.
	(c_fully_fold): Add LVAL argument, pass it through to
	c_fully_fold_internal.
	(decl_constant_value_for_optimization): Removed.
cp/
	* cp-gimplify.c (c_fully_fold): Add LVAL argument, call
	cp_fold_maybe_rvalue instead of cp_fold_rvalue and pass it !LVAL.
testsuite/
	* gcc.dg/pr69960.c: New test.
	* gcc.dg/pr66618.c: New test.
	* gcc.dg/pr66618-2.c: New test.

From-SVN: r254930