PR c/58943
	* c-typeck.c (build_modify_expr): For lhs op= rhs, if rhs has side
	effects, preevaluate rhs using SAVE_EXPR first.

	* c-omp.c (c_finish_omp_atomic): Set in_late_binary_op around
	build_modify_expr with non-NOP_EXPR opcode.  Handle return from it
	being COMPOUND_EXPR.
	(c_finish_omp_for): Handle incr being COMPOUND_EXPR with first
	operand a SAVE_EXPR and second MODIFY_EXPR.

	* gcc.c-torture/execute/pr58943.c: New test.
	* gcc.dg/tree-ssa/ssa-fre-33.c (main): Avoid using += in the test.

From-SVN: r206620