re PR tree-optimization/15991 (phi nodes with identical arguments still remain at...

re PR tree-optimization/15991 (phi nodes with identical arguments still remain at t50.tailc)

	PR tree-optimization/15991
	* tree-cfg.c (tree_block_label): Export.
	* tree-flow-inline.h (bsi_after_labels): New function.
	* tree-flow.h (bsi_after_labels, tree_block_label): Declare.
	* tree-ssa.c (propagate_into_addr): New function.
	(replace_immediate_uses): Handle propagation of pointer constants.
	(raise_value): Do not restrict propagation of pointer constants.
	* tree-ssanames.c (duplicate_ssa_name): New function.
	* tree.h (duplicate_ssa_name): Declare.

From-SVN: r83297