[PATCH] Make GVN more iterative

[Duncan P. N. Exon Smith]

> On 2014 Aug 11, at 15:25, Daniel Berlin <dberlin at dberlin.org> wrote:
> 
> We have cases where GVN is *really slow* (IE 29 seconds and 80% of
> compile time). Iterating it again is likely to make that worse.  Happy
> to give them to you (or test it with this patch)

A little off-topic, but I was looking for GVN testcases like this a
few months ago -- I'd appreciate if you could send them to me!