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no-alias with non-addr-taken globals: they cannot alias a captured pointer. If the non-global underlying object would have been a capture were it to alias the global, we can firmly conclude no-alias. It isn't reasonable for a transformation to introduce a capture in a way observable by an alias analysis. Consider, even if it were to temporarily capture one globals address into another global and then restore the other global afterward, there would be no way for the load in the alias query to observe that capture event correctly. If it observes it then the temporary capturing would have changed the meaning of the program, making it an invalid transformation. Even instrumentation passes or a pass which is synthesizing stores to global variables to expose race conditions in programs could not trigger this unless it queried the alias analysis infrastructure mid-transform, in which case it seems reasonable to return results from before the transform started. See the comments in the change for a more detailed outlining of the theory here. This should address the primary performance regression found when the non-conservatively-correct path of the alias query was disabled. Differential Revision: http://reviews.llvm.org/D11410 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@243405 91177308-0d34-0410-b5e6-96231b3b80d8
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