[PATCH] D149889: [TTI] Use users of GEP to guess access type in getGEPCost

[Nikita Popov via Phabricator via llvm-commits]

nikic added a comment.

You should be able to avoid the LICM changes by adjusting the code at https://github.com/llvm/llvm-project/blob/bfb7c99f3aeab09236adf1f684f7144f384c6dd7/llvm/lib/Transforms/Scalar/LICM.cpp#L1346-L1361 to only pass the users in the loop (and drop the separate user iteration that code does).

Something I'm concerned about here is that your default implementation is going to scan all users of the instruction, which means that the cost query is now O(n) instead of O(1). This is probably not acceptable for compile-time reasons. Can we get away with only inspecting a single user in that case and assume it is representative?

This change seems to cause some pretty large code size changes on x86 at least (https://llvm-compile-time-tracker.com/compare.php?from=b77265711b390a6905e8901694d75f4b3812c71a&to=113f1989fa7e469407942249b4086e3a28da2bf4&stat=size-text), so it seems like a pretty high impact change. I can't say whether those changes are good or bad though :)


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D149889/new/

https://reviews.llvm.org/D149889