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[ic] Iterate polymorphic feedback backwards

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Reduce register pressure (and therefore spills) across the loop
iterating over the LoadIC polymorphic feedback array by starting at
length - 1 and iterating down to 0.

Might give a tiny recency boost too.

Change-Id: I1295a8136212c339b9d3974e2d49b3ecfe1ce543
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1687545
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62528}
This commit is contained in:
Leszek Swirski 2019-07-04 11:46:15 +02:00 committed by Commit Bot
parent 1f872cbc4c
commit cb0819200f
1 changed files with 8 additions and 7 deletions
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15
src/ic/accessor-assembler.cc
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@ -107,12 +107,12 @@ void AccessorAssembler::HandlePolymorphicCase(
// Load the {feedback} array length.
TNode<IntPtrT> length = LoadAndUntagWeakFixedArrayLength(feedback);
CSA_ASSERT(this, IntPtrLessThanOrEqual(IntPtrConstant(1), length));
CSA_ASSERT(this, IntPtrLessThanOrEqual(IntPtrConstant(kEntrySize), length));
// This is a hand-crafted loop that only compares against the {length}
// in the end, since we already know that we will have at least a single
// entry in the {feedback} array anyways.
TVARIABLE(IntPtrT, var_index, IntPtrConstant(0));
// This is a hand-crafted loop that iterates backwards and only compares
// against zero at the end, since we already know that we will have at least a
// single entry in the {feedback} array anyways.
TVARIABLE(IntPtrT, var_index, IntPtrSub(length, IntPtrConstant(kEntrySize)));
Label loop(this, &var_index), loop_next(this);
Goto(&loop);
BIND(&loop);
@ -131,8 +131,9 @@ void AccessorAssembler::HandlePolymorphicCase(
BIND(&loop_next);
var_index =
Signed(IntPtrAdd(var_index.value(), IntPtrConstant(kEntrySize)));
Branch(IntPtrLessThan(var_index.value(), length), &loop, if_miss);
Signed(IntPtrSub(var_index.value(), IntPtrConstant(kEntrySize)));
Branch(IntPtrGreaterThanOrEqual(var_index.value(), IntPtrConstant(0)),
&loop, if_miss);
}
}