loop unswitching is sensitive to edge order

[Ben Elliston]

Zdenek Dvorak <rakdver@atrey.karlin.mff.cuni.cz> writes:

> > The following patch of yours seems to add some code that is sensitive
> > to the order of edges in the bb edge list.  Am I right?
> 
> I do not know, since I do not understand what you mean.  What problem
> do you see with the code?

My edges-in-vectors patch breaks when integrated with your patch.  I
was able to fix that breakage by modifying my code so that new
elements are inserted at the head of the vector and that vector order
is maintained when elements are removed (ie. it emulates the behaviour
of the existing pred and succ linked lists).

My understanding is that none of the code in GCC should depend on the
order of edges in their containers.  This is the first time I've
encountered such behaviour.

Ben