[PATCH] Detect loops in find_comparison_args

[Andrew Jenner]

Hi Paolo,

On 5/21/2012 10:12 AM, Paolo Bonzini wrote:
> That's pretty heavy-weight.  Perhaps you can try the usual algorithm of
> looking at x->next and x->next->next?

That would only detect cycles of length 1 and 2 though. While that would 
cover all the testcases we currently know about, I wanted to eliminate 
the entire pattern of hangs. Otherwise it's only a question of time 
until someone hits a cycle of length >= 3.

We could use less memory at the expense of CPU time by using the 
tortoise and hare algorithm, but that would make the code much more 
complicated.

Andrew