re PR tree-optimization/29877 (out of SSA (TER) extends variable life of variable beyond original declared)

	PR tree-optimization/29877
	gcc/
	* tree-ssa-ter.c (is_replaceable_p): Deem assignments with
	a register variable on the RHS to not be replaceable.

	gcc/testsuite/
	* gcc.dg/pr16194.c: Skip test entirely if we don't know the
	name of a hard register for the target concerned.  Adjust dg-error
	directives to cope with new behaviour of TER.

From-SVN: r120571