re PR tree-optimization/79095 (spurious stringop-overflow warning)

re PR tree-optimization/79095 (spurious stringop-overflow warning)

	PR tree-optimization/79095
	* tree-vrp.c (extract_range_from_binary_expr_1): For EXACT_DIV_EXPR,
	if the numerator has the range ~[0,0] make the resultant range ~[0,0].
	(extract_range_from_binary_expr): For MINUS_EXPR with no derived range,
	if the operands are known to be not equal, then the resulting range
	is ~[0,0].
	(intersect_ranges): If the new range is ~[0,0] and the old range is
	wide, then prefer ~[0,0].
	* tree-vrp.c (overflow_comparison_p_1): New function.
	(overflow_comparison_p): New function.
	* tree-vrp.c (register_edge_assert_for_2): Register additional asserts
	if NAME is used in an overflow test.
	(vrp_evaluate_conditional_warnv_with_ops): If the ops represent an
	overflow check that can be expressed as an equality test, then adjust
	ops to be that equality test.

	PR tree-optimization/79095
	* g++.dg/pr79095-1.C: New test
	* g++.dg/pr79095-2.C: New test
	* g++.dg/pr79095-3.C: New test
	* g++.dg/pr79095-4.C: New test
	* g++.dg/pr79095-5.C: New test
	* gcc.c-torture/execute/arith-1.c: Update with more cases.
	* gcc.dg/tree-ssa/pr79095-1.c: New test.

From-SVN: r245434