[PATCH] D49097: [RegisterCoalescer] Another fix for subrange join unreachable

[Tim Renouf via Phabricator via llvm-commits]

tpr added a comment.

Surely that would be a problem if recalculating all the subranges, or the whole of live intervals, at the end of pass gives different results, because the idea of LLVM pass management is that semantically it doesn't matter if you recalculate stuff, and changing it incrementally is just a compile time optimization. Even if live intervals normally gets preserved through to register allocation, someone's backend might insert an extra pass that does not preserve live intervals, and that should not break everything.

So surely it ought to be possible to insert code to recalculate the live intervals at the end of RegisterCoalescing and assert if they end up (substantively) different, just to prove we've got the semantics right.

Anyway, notwithstanding all of the above, could someone review and hopefully approve the change as it please?


Repository:
  rL LLVM

https://reviews.llvm.org/D49097