We previously only optimized cases like

  Parent <- Decompression <- Compression <- Child

to

  Parent <- Child

This CL also adds the complementary optimization, namely, it reduces

  Parent <- Compression <- Decompression <- Child

as above.

Such a cases became apparent after a recent extension of CSA load elimination (see https://chromium-review.googlesource.com/c/v8/v8/+/1660626), breaking a load elimination test case and thus the pointer compression build.

R=jarin@chromium.org, solanes@chromium.org

Change-Id: Ic730d05175f214e7055f94704141744ca44fefe5
Bug: v8:9353
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1664070
Commit-Queue: Georg Schmid <gsps@google.com>
Reviewed-by: Michael Stanton <mvstanton@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62246}