[PATCH] D24808: [AArch64] Avoid materializing 0.0 when generating FP CSEL

Tue Sep 27 14:35:14 PDT 2016

evandro added a comment.

In https://reviews.llvm.org/D24808#548901, @MatzeB wrote:

> Wouldn't this work with any constant? Should we consider it for the common DAGCombiner?

Thinking more about this suggestion, I think that this change improves code generation only if the comparison instruction has a form with an immediate operand encoding, which is very target dependent (e.g., AArch64).  Otherwise, if the target has to materialize the constant for the comparison, it can be used again by the selection (e.g., x86).

I couldn't find or devise an method to query such conditions generically and I'd appreciate suggestions.  If so, I believe that this change has to remain specific to AArch64 for this round.

Repository:
  rL LLVM

https://reviews.llvm.org/D24808