[PATCH] D128011: [SimplifyLibCalls] Transform memchr(STR, C, N) to chain of ORs

[Martin Sebor via Phabricator via llvm-commits]

msebor added a comment.

It seems important to put a limit on the length of the chain to avoid pathological expansion (that might come up in generated code, but not only there).  I expect the optimal maximum will vary across different targets but a suitably low minimum should be target-independent.  I don't have a good sense of what the ideal lower bound might be but I would hesitate to go over the proposed GCC limit of 8 unless the ORs could be assumed to collapse to something much simpler (like in `memchr-7.ll`).  Instrumenting the compiler and building a few projects might help dial it in.

Having said that, I don't think it's a guaranteed win to set the limit to zero (or to disable the subsequent folding) when optimizing for size.  But whatever the effect of `-Os` might be here, it should be exercised by the test suite if only to make the decision explicit.


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  https://reviews.llvm.org/D128011/new/

https://reviews.llvm.org/D128011