* tree-loop-distribution.c (const_with_all_bytes_same): New function.
	(generate_memset_builtin): Only handle integer_all_onesp as -1 val if
	TYPE_PRECISION is equal to mode bitsize.  Use const_with_all_bytes_same
	if possible to compute val.
	(classify_partition): Verify CONSTRUCTOR doesn't have any elts.
	For QImode integers don't require anything about precision.  Use
	const_with_all_bytes_same to find out if the constant doesn't have
	repeated bytes in it.

	* gcc.dg/pr56837.c: New test.
	* gcc.dg/tree-ssa/ldist-19.c: Don't check for
	"generated memset minus one".

From-SVN: r197568