Implement -fexpose-all-unfoldings, and fix a non-termination bug
The -fexpose-all-unfoldings flag arranges to put unfoldings for *everything* in the interface file. Of course, this makes the file a lot bigger, but it also makes it complete, and that's great for supercompilation; or indeed any whole-program work. Consequences: * Interface files need to record loop-breaker-hood. (Previously, loop breakers were never exposed, so that info wasn't necessary.) Hence a small interface file format change. * When inlining, must check loop-breaker-hood. (Previously, loop breakers didn't have an unfolding at all, so no need to check.) * Ditto in exprIsConApp_maybe. Roman actually tripped this bug, because a DFun, which had an unfolding, was also a loop breaker * TidyPgm.tidyIdInfo must be careful to preserve loop-breaker-hood So Id.idUnfolding checks for loop-breaker-hood and returns NoUnfolding if so. When you want the unfolding regardless of loop-breaker-hood, use Id.realIdUnfolding. I have not documented the flag yet, because it's experimental. Nor have I tested it thoroughly. But with the flag off (the normal case) everything should work.
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