Reason for revert:
Weird endless loop in TopLevelLiveRange::Merge() due to always splitting first and not making progress. See comments, unfortunately no useable repro.
Original issue's description:
> [turbofan] Splinter into one range.
>
> Before this CL, we created one live range per successive set of
> deferred blocks. For scenarios with many such blocks, this creates
> an upfront pressure for the register allocator to deal with many ranges.
> Linear sorts ranges, which is a super-linear operation.
>
> The change places all deferred intervals into one range, meaning that,
> at most, there will be twice as many live ranges as the original set. In
> pathological cases (benchmarks/Compile/slow_nbody1.js), this change
> halves the compilation time. We see some improvements elsewhere,
> notably SQLite at ~4-5%.
>
> We may be able to avoid the subsequent merge. Its cost is the
> additional ranges it may need to create. The sole reason for the merge
> phase is to provide an unchanged view of the world to the subsequent
> phases. With the at-most-one splinter model, we may be able to teach
> the other phases about splintering - should we find perf hindrances
> due to merging.
>
> Committed: https://crrev.com/efdcd20267870276c5824f1ccf4e171ac378f7ae
> Cr-Commit-Position: refs/heads/master@{#31224}
TBR=jarin@chromium.org,mtrofin@google.com,mtrofin@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
Review URL: https://codereview.chromium.org/1403163003
Cr-Commit-Position: refs/heads/master@{#31300}
23a8837fcc