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results when a loop is completely removed. This is very hard to manifest as a visible bug. You need to arrange for there to be a subsequent allocation of a 'Loop' object which gets the exact same address as the one which the unroll deleted, and you need the LoopAccessAnalysis results to be significant in the way that they're stale. And you need a million other things to align. But when it does, you get a deeply mysterious crash due to actually finding a stale analysis result. This fixes the issue and tests for it by directly checking we successfully invalidate things. I have not been able to get *any* test case to reliably trigger this. Changes to LLVM itself caused the only test case I ever had to cease to crash. I've looked pretty extensively at less brittle ways of fixing this and they are actually very, very hard to do. This is a somewhat strange and unusual case as we have a pass which is deleting an IR unit, but is not running within that IR unit's pass framework (which is what handles this cleanly for the normal loop unroll). And where there isn't a definitive way to clear *all* of the stale cache entries. And where the pass *is* updating the core analysis that provides the IR units! For example, we don't have any of these problems with Function analyses because it is easy to clear out function analyses when the functions themselves may have been deleted -- we clear an entire module's worth! But that is too heavy of a hammer down here in the LoopAnalysisManager layer. A better long-term solution IMO is to require that AnalysisManager's make their keys durable to this kind of thing. Specifically, when caching an analysis for one IR unit that is conceptually "owned" by a higher level IR unit, the AnalysisManager should incorporate this into its data structures so that we can reliably clear these results without having to teach each and every pass to do so manually as we do here. But that is a change for another day as it will be a fairly invasive change to the AnalysisManager infrastructure. Until then, this fortunately seems to be quite rare. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@310333 91177308-0d34-0410-b5e6-96231b3b80d8
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