Revert "Revert of [turbofan] Splinter into one range.
(patchset #2 id:80001 of https://codereview.chromium.org/1391023007/ )"
This reverts commit 23a8837fcc.
Also added a CHECK in Merge to validate that splitting yields a different
range and thus advances the algorithm. Ran stress bots successfully. Likely my earlier change in Splintering addressed the stress test scenario
that was looping infinitely.
BUG=
Review URL: https://codereview.chromium.org/1406983004
Cr-Commit-Position: refs/heads/master@{#31430}
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}
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.
Review URL: https://codereview.chromium.org/1391023007
Cr-Commit-Position: refs/heads/master@{#31224}
A subset of the LiveRangeUnitTests (SplitInvalidPreStart,
InvalidSplitEnd, SplitInvalidPostEnd) fail or hang on AIX in release
mode.
These tests fork a child which is expected to crash in
register-allocator code after feeding in bad inputs.
In debug mode, they behave as expected due to hitting a debug assert.
In release mode, however, the tests rely only on the fact that
dereferencing a null pointer will cause a SEGFAULT. This is true on
most platforms, but not AIX. An AIX process has valid low memory
pages mapped for reading and will not fault. Thus, these tests fail
or hang because the child process survives the load from address zero
and either completes (with undefined results) or goes into an infinite
loop.
R=bmeurer@chromium.org, danno@chromium.org, michael_dawson@ca.ibm.com
BUG=
Review URL: https://codereview.chromium.org/1384733002
Cr-Commit-Position: refs/heads/master@{#31090}
A LiveRange is identified by 2 integers: the vreg() of its TopLevel,
which is the virtual register (operand) ID; and a relative_id(), which has
no meaning in the program, but is valuable in debugging or tracing
scenarios.
This change ensures that relative_id is unique even in cases of splinter
ranges and their children.
Review URL: https://codereview.chromium.org/1318493005
Cr-Commit-Position: refs/heads/master@{#30665}
