[PATCH] D41603: [InstCombine] fold min/max tree with common operand (PR35717)

[Sanjay Patel via Phabricator via llvm-commits]

spatel created this revision.
spatel added reviewers: efriedma, hfinkel, majnemer.
Herald added a subscriber: mcrosier.

This might be over the edge of what we want from instcombine, but I'm not sure. There is precedence for factorization transforms in instcombine for FP ops with fast-math.

I think it would take more work to add this to reassociate because that's specialized for binops, and min/max are not binops (or even single instructions). Also, I don't have evidence that larger min/max trees than this exist in real code.

In the motivating example from https://bugs.llvm.org/show_bug.cgi?id=35717 , we have:

  int test(int xc, int xm, int xy) {
    int xk;
    if (xc < xm)
      xk = xc < xy ? xc : xy;
    else
      xk = xm < xy ? xm : xy;
    return xk;
  }

This patch is a preliminary step towards solving that case. We would still need to canonicalize the min/max to allow the fold for that example.

https://rise4fun.com/Alive/Qjne
https://rise4fun.com/Alive/3yg


https://reviews.llvm.org/D41603

Files:
  lib/Transforms/InstCombine/InstCombineSelect.cpp
  test/Transforms/InstCombine/minmax-fold.ll

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