re PR rtl-optimization/51821 (64bit > 32bit conversion produces incorrect results with optimizations)

	PR rtl-optimization/51821
	* recog.c (peep2_find_free_register): Determine clobbered registers
	from insn pattern.

testsuite/ChangeLog:

	PR rtl-optimization/51821
	* gcc.dg/pr51821.c: New test.

From-SVN: r183194