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InsertBinop tries to find an appropriate instruction instead of creating a new instruction. When it checks whether instruction is the same as we need to create it ignores nuw/nsw/exact flags. It leads to invalid behavior when poison instruction can be used when it was not expected. Specifically, for example Expander expands the SCEV built for instruction %a = add i32 %v, 1 It is possible that InsertBinop can find an instruction % b = add nuw nsw i32 %v, 1 and will use it instead of version w/o nuw nsw. It is incorrect. The patch conservatively ignores all instructions with any of poison flags installed. Reviewers: sanjoy, mkazantsev, sebpop, jbhateja Reviewed By: sanjoy Subscribers: llvm-commits Differential Revision: https://reviews.llvm.org/D41576 llvm-svn: 321475
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