tree-optimization/112305 - SCEV cprop and conditional undefined overflow

tree-optimization/112305 - SCEV cprop and conditional undefined overflow

The following adjusts final value replacement to also rewrite the
replacement to defined overflow behavior if there's conditionally
evaluated stmts (with possibly undefined overflow), not only when
we "folded casts".  The patch hooks into expression_expensive for
this.

	PR tree-optimization/112305
	* tree-scalar-evolution.h (expression_expensive): Adjust.
	* tree-scalar-evolution.cc (expression_expensive): Record
	when we see a COND_EXPR.
	(final_value_replacement_loop): When the replacement contains
	a COND_EXPR, rewrite it to defined overflow.
	* tree-ssa-loop-ivopts.cc (may_eliminate_iv): Adjust.

	* gcc.dg/torture/pr112305.c: New testcase.