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

2019-05-06  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/90316
	* tree-ssa-alias.c (maybe_skip_until): Pass in target BB,
	compute target on demand.
	(get_continuation_for_phi): Remove code walking stmts to
	get to a target virtual operand which could end up being
	quadratic.

From-SVN: r270902