[COMMITTED] Dump should be read only. Do not trigger new lookups.

[Andrew MacLeod]

When we are dumping the rangers state, we tend to do it at the end when 
EVRP is shutting down.  The dumping routine is checking to see if the 
cache has an on-entry value or the edge generates a range before 
dumping, but when it does the actual dump, its calling range_on_edge 
which can go and do additional lookups. That late in the game, it can 
cause a trap in SCEV if a PHI node attempts to be rcalculated when a 
loop has been rewritten.

Instead, query the range_on_edge from the cache, which will only show 
information we know, and not cause additional lookups.

Bootstrap on x86_64-pc-linux-gnu with no regressions.  pushed.

Andrew

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