commit 23a85a3326efaf704b79a5f03319ca0ffd24eb74
author Clemens Hammacher <clemensh@chromium.org> Mon Jan 07 13:48:13 2019
committer Commit Bot <commit-bot@chromium.org> Mon Jan 07 14:23:39 2019
tree 1282bc0d56753439d3617291cc216c29413b8f90
parent 96671ab2e0c64c1c02b361d8c327bdea8655f8b1

[Liftoff] Avoid quadratic behaviour in stack transfers

We currently iterate the list of unexecuted register moves repeatedly,
always executing the moves whose destination register is not being used
as source register any more. This can lead to quadratic execution times
if only a small number of moves is processed in every iteration.

This CL refactors this such that we iterate the moves at most three
times: Once for executing moves which can be executed right away (fast
path) and for computing the source register use counts. A second time
to execute all remaining non-cyclic moves, and a third time to execute
cyclic moves.
During the second and third iteration, whenever we decrement the source
register use count, we check whether it drops to zero and execute the
respective move right away.

R=ahaas@chromium.org

Bug: v8:6600, v8:8423
Change-Id: I503328f5ae5f0208e35d53c71b4c289d75799892
Reviewed-on: https://chromium-review.googlesource.com/c/1397703
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58588}