[PATCH] D52002: Switch optimization for known maximum switch values

[Hans Wennborg via Phabricator via llvm-commits]

hans added a comment.

I don't think storing the MaxSwitchValue in the switch instructions itself is the right approach. Generally LLVM doesn't store analysis results in the instructions.

I also don't think the right way to do this is necessarily to change the jump table lowering itself, instead I'd suggest doing it at the IR level:

if we detect that the value range for the switch variable is small enough that adding a few more cases to the switch would cover the range completely, add those cases and mark the default bb unreachable. Then let the lowering code deal with exploiting the unreachable default bb. There is room for improvement there, see "FIXME: Exploit unreachable default more aggressively" in visitSwitch() but we should do that anyway.

What do you think?


Repository:
  rL LLVM

https://reviews.llvm.org/D52002