backport: re PR testsuite/48809 (switch statement optimization error)

backport: re PR testsuite/48809 (switch statement optimization error)

	Backport from mainline
	2011-04-30  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/48809
	* tree-switch-conversion.c (build_arrays): Compute tidx in unsigned
	type.
	(gen_inbound_check): Don't compute index_expr - range_min in utype
	again, instead reuse SSA_NAME initialized in build_arrays.
	Remove two useless gsi_for_stmt calls.

	* gcc.c-torture/execute/pr48809.c: New test.

From-SVN: r173358