The issue is with this pattern, assuming disjoint uses for all vregs:

phi: v1 = v0 ...
phi: v2 = v0 ...
phi: v3 = v0 ...
...
phi: vN = v0 ...

For every phi, BuildBundles proceeds as follows:
- Create a new bundle for the output
- Merge the input bundle into the output bundle

Since the bundle gets bigger at every iteration, the merges become more
and more expensive and consume Zone memory that is immediately thrown
away at the next iteration.

A simple fix is to check the size of the bundles before merging and
always copy the smallest one into the biggest. In the pattern above this
should always copy the single-range output bundle into the large input
bundle.

R=sigurds@chromium.org

Bug: v8:11237
Change-Id: I6ad9152035da698d94b02b5b41802545ba149307
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2584879Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Commit-Queue: Thibaud Michaud <thibaudm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71714}