**TL;DR:** This PR modifies a comparator. The comparator is used in a subsequent call to llvm::stable_sort. Sorting comparators should follow strict weak ordering - in particular, (x < x) should return false. This PR adds a fix to avoid an infinite loop when the inputs to the comparator are equal.
**Details**:
Sometimes when two equivalent tensors passed into the comparator, we encounter infinite looping (at aae2eaae2c/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp (L4049))
Although it seems like this comparator will never be called with two equivalent pointers, some sanitizers, e.g. https://chromium.googlesource.com/chromiumos/third_party/gcc/+/refs/heads/stabilize-zako-5712.88.B/libstdc++-v3/include/bits/stl_algo.h#360, will add checks for (x < x). When this sanitizer is used with the current implementation, it triggers a comparator check for (x < x) which runs into the infinite loop
Reviewed By: ABataev
Differential Revision: https://reviews.llvm.org/D155874
8fa02db8cf