Aggressive conversion of sext to zext blocks IndVarSimplify

IR & Optimizations
9

We should just have no-wrap flags for trunc and ext, i think:

  • trunc nsw == at most, only sign bits are lost during truncation, no non-sign bits are lost.
  • trunc nuw == no set bits are lost
  • zext nsw == arithmetic value does not change, we are actually padding with the sign bit, “this zext is an sext”.
  • zext nuw (implicit) == numeric value does not change, not really useful.
  • sext nsw (implicit) == arithmetic value does not change, not really useful.
  • sext nuw == numeric value does not change, we are actually padding with the zero bit, “this sext is an zext”.
[RFC] Add zext nneg flag