backport: re PR middle-end/55481 (-O2 generates a wrong-code infinite loop in C+...

backport: re PR middle-end/55481 (-O2 generates a wrong-code infinite loop in C++Benchmark's simple_types_constant_folding int8 xor test)

2013-03-01  Richard Biener  <rguenther@suse.de>

	Backport from mainline
	2012-12-12  Zdenek Dvorak  <ook@ucw.cz>

	PR tree-optimization/55481
	* tree-ssa-loop-ivopts.c (rewrite_use_nonlinear_expr): Fall
	back to general rewriting if we cannot leave an original biv
	definition alone.

	* gcc.dg/torture/pr55481.c: New testcase.
	* gcc.dg/torture/pr56488.c: Likewise.

From-SVN: r196379