forked from OSchip/llvm-project
1de1070559
The alias analysis in DAG Combine looks at the BaseAlign, the Offset and the Size of two accesses, and determines if they are known to access different parts of memory by the fact that they are different offsets from inside that "alignment window". It does not seem to account for accesses that are not a multiple of the size, and may overflow from one alignment window into another. For example in the test case we have a 19byte memset that is splits into a 16 byte neon store and an unaligned 4 byte store with a 15 byte offset. This 15byte offset (with a base align of 8) wraps around to the next alignment windows. When compared to an access that is a 16byte offset (of the same 4byte size and 8byte basealign), the two accesses are said not to alias. I've fixed this here by just ensuring that the offsets are a multiple of the size, ensuring that they don't overlap by wrapping. Fixes PR45035, which was exposed by the UseAA changes in the arm backend. Differential Revision: https://reviews.llvm.org/D75238 |
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README.txt
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