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Summary: If a pointer is marked as dereferenceable_or_null(N), LLVM assumes it is either `null` or `dereferenceable(N)` or both. This change only introduces the attribute and adds a token test case for the `llvm-as` / `llvm-dis`. It does not hook up other parts of the optimizer to actually exploit the attribute -- those changes will come later. For pointers in address space 0, `dereferenceable(N)` is now exactly equivalent to `dereferenceable_or_null(N)` && `nonnull`. For other address spaces, `dereferenceable(N)` is potentially weaker than `dereferenceable_or_null(N)` && `nonnull` (since we could have a null `dereferenceable(N)` pointer). The motivating case for this change is Java (and other managed languages), where pointers are either `null` or dereferenceable up to some usually known-at-compile-time constant offset. Reviewers: rafael, hfinkel Reviewed By: hfinkel Subscribers: nicholas, llvm-commits Differential Revision: http://reviews.llvm.org/D8650 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@235132 91177308-0d34-0410-b5e6-96231b3b80d8
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