Reviewers: Benedikt Meurer, Jarin (OOO),
Description:
[turbofan] Optimize Splinter by remembering where it left
off.
Splintering relies on DetachAt, which in turn relies on
FirstSearchIntervalForPosition to find the first UseInterval
to split, given a position. The later API (Find...) has an
optimization for linear traversals. Splintering traverses
linearly (block by block), so we leverage the same
optimization by moving current_interval_ forward.
(Also added an unrelated TODO.)
BUG=
Please review this at https://codereview.chromium.org/1322623007/
Base URL: https://chromium.googlesource.com/v8/v8.git@master
Affected files (+10, -0 lines):
M src/compiler/register-allocator.cc
Index: src/compiler/register-allocator.cc
diff --git a/src/compiler/register-allocator.cc
b/src/compiler/register-allocator.cc
index
f6c339234abb4d8a143d4858134e16fa272d5dac..563c9a276d8d0da93cf1b7b0791f86566e22029b
100644
--- a/src/compiler/register-allocator.cc
+++ b/src/compiler/register-allocator.cc
@@ -825,6 +825,12 @@ void TopLevelLiveRange::Splinter(LifetimePosition
start, LifetimePosition end,
result->set_spill_type(spill_type());
if (start <= Start()) {
+ // TODO(mtrofin): here, the TopLevel part is in the deferred range, so
we
+ // may want to continue processing the splinter. However, if the value
is
+ // defined in a cold block, and then used in a hot block, it follows
that
+ // it should terminate on the RHS of a phi, defined on the hot path. We
+ // should check this, however, this may not be the place, because we
don't
+ // have access to the instruction sequence.
DCHECK(end < End());
DetachAt(end, result, zone);
next_ = nullptr;
@@ -844,6 +850,10 @@ void TopLevelLiveRange::Splinter(LifetimePosition
start, LifetimePosition end,
next_ = end_part.next_;
last_interval_->set_next(end_part.first_interval_);
+ // The next splinter will happen either at or after the current
interval.
+ // We can optimize DetachAt by setting current_interval_ accordingly,
+ // which will then be picked up by FirstSearchIntervalForPosition.
+ current_interval_ = last_interval_;
last_interval_ = end_part.last_interval_;
--
--
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