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

There is precedence for factorization transforms in instcombine for FP ops with fast-math. 
We also have similar logic in foldSPFofSPF().

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, but if we find that's true, we might
want to reorganize where/how we do this optimization.

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 solves that problem because we recognize more min/max patterns after rL321672

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

Differential Revision: https://reviews.llvm.org/D41603

llvm-svn: 321998

0 files changed, 0 insertions, 0 deletions