[PATCH] D12596: Fix for bootstrap bug introduced in r244921

[Nemanja Ivanovic via llvm-commits]

nemanjai added a comment.

Hi Hal, sorry I was on vacation so I'm only getting to this now.
I agree that this code sequence in isolation is not better than what we had in the particular case. However, the direct move sequence is applicable in every situation whereas the old simpler sequence only occurred in the specific sequence you mentioned. Furthermore, if the loaded value is used for non-vector computations as well, it is still in the register we moved it from - although I have no idea if this actually happens or if LLVM infrastructure knows this.
Please advise whether I should:

1. Check this in as-is and move on
2. Add some info in the README about improving this sequence
3. Re-implement SCALAR_TO_VECTOR of v2i64 as custom lowering, detect this sequence and do not emit the direct move
4. Do something different - i.e. a peephole optimization or something along those lines

I am of the opinion that going with options 1 or 2 is fine as the new sequence is only marginally worse than what we had and it is a lot of work to get this small win.


Repository:
  rL LLVM

http://reviews.llvm.org/D12596