re PR tree-optimization/90316 (large compile time increase in opt / alias stmt walking for Go example)

2019-05-07  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/90316
	* tree-ssa-pre.c (translate_vuse_through_block): When
	same_valid is NULL do not bother to search for a virtual
	PHI continuation.
	(phi_translate_1): When operands changed we cannot keep
	the same value-number so do not bother to ask whether
	that's possible from translate_vuse_through_block.

From-SVN: r270944