[PATCH] D107766: [AggressiveInstCombine] Add `lshr` and `ashr` instructions to TruncInstCombine DAG

Fri Aug 13 06:22:10 PDT 2021

spatel added a comment.

In D107766#2941350 <https://reviews.llvm.org/D107766#2941350>, @xbolva00 wrote:

> AggressiveInstCombine runs only with -O3, right? Do we know how expensive it would be for -O2?

Yes - only at O3 <https://reviews.llvm.org/owners/package/3/> currently. That's mainly because nobody has bothered to see if it was worth fighting over to include at -O2.

That question is much easier to answer since we have compile-time-tracker. But I'm not sure how to answer the cost question directly - I think we can approximate it by just removing the pass from O3 <https://reviews.llvm.org/owners/package/3/> and checking the difference.

The result seems to be a consistent but very small cost (0.04% geomean here):
https://llvm-compile-time-tracker.com/?config=NewPM-O3&stat=instructions&remote=rotateright

Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D107766/new/

https://reviews.llvm.org/D107766