Title: [195744] trunk/Source/_javascript_Core
- Revision
- 195744
- Author
- [email protected]
- Date
- 2016-01-28 09:30:00 -0800 (Thu, 28 Jan 2016)
Log Message
LowerToAir::preferRightForResult() should resolve use count ties by selecting the child that is closest in an idom walk
https://bugs.webkit.org/show_bug.cgi?id=153583
Reviewed by Benjamin Poulain.
This undoes the AsmBench/n-body regression in r195654 while preserving that revision's
Kraken progression.
* b3/B3LowerToAir.cpp:
(JSC::B3::Air::LowerToAir::LowerToAir):
(JSC::B3::Air::LowerToAir::preferRightForResult):
Modified Paths
Diff
Modified: trunk/Source/_javascript_Core/ChangeLog (195743 => 195744)
--- trunk/Source/_javascript_Core/ChangeLog 2016-01-28 17:26:41 UTC (rev 195743)
+++ trunk/Source/_javascript_Core/ChangeLog 2016-01-28 17:30:00 UTC (rev 195744)
@@ -1,3 +1,17 @@
+2016-01-28 Filip Pizlo <[email protected]>
+
+ LowerToAir::preferRightForResult() should resolve use count ties by selecting the child that is closest in an idom walk
+ https://bugs.webkit.org/show_bug.cgi?id=153583
+
+ Reviewed by Benjamin Poulain.
+
+ This undoes the AsmBench/n-body regression in r195654 while preserving that revision's
+ Kraken progression.
+
+ * b3/B3LowerToAir.cpp:
+ (JSC::B3::Air::LowerToAir::LowerToAir):
+ (JSC::B3::Air::LowerToAir::preferRightForResult):
+
2016-01-28 Benjamin Poulain <[email protected]>
[JSC] B3 Tail Call with Varargs do not restore callee saved registers
Modified: trunk/Source/_javascript_Core/b3/B3LowerToAir.cpp (195743 => 195744)
--- trunk/Source/_javascript_Core/b3/B3LowerToAir.cpp 2016-01-28 17:26:41 UTC (rev 195743)
+++ trunk/Source/_javascript_Core/b3/B3LowerToAir.cpp 2016-01-28 17:30:00 UTC (rev 195744)
@@ -39,6 +39,7 @@
#include "B3CCallValue.h"
#include "B3CheckSpecial.h"
#include "B3Commutativity.h"
+#include "B3Dominators.h"
#include "B3IndexMap.h"
#include "B3IndexSet.h"
#include "B3MemoryValue.h"
@@ -75,6 +76,7 @@
, m_blockToBlock(procedure.size())
, m_useCounts(procedure)
, m_phiChildren(procedure)
+ , m_dominators(procedure.dominators())
, m_procedure(procedure)
, m_code(procedure.code())
{
@@ -592,18 +594,22 @@
if (leftIsPhiWithThis != rightIsPhiWithThis)
return rightIsPhiWithThis;
- bool leftResult = m_useCounts.numUsingInstructions(left) == 1;
- bool rightResult = m_useCounts.numUsingInstructions(right) == 1;
- if (leftResult && rightResult) {
- // If one operand is not in the block, it could be in a block dominating a loop
- // containing m_value.
- if (left->owner == m_value->owner)
- return false;
- if (right->owner == m_value->owner)
- return true;
- }
+ if (m_useCounts.numUsingInstructions(right) != 1)
+ return false;
+
+ if (m_useCounts.numUsingInstructions(left) != 1)
+ return true;
- return rightResult;
+ // The use count might be 1 if the variable is live around a loop. We can guarantee that we
+ // pick the the variable that is least likely to suffer this problem if we pick the one that
+ // is closest to us in an idom walk. By convention, we slightly bias this in favor of
+ // returning true.
+
+ // We cannot prefer right if right is further away in an idom walk.
+ if (m_dominators.strictlyDominates(right->owner, left->owner))
+ return false;
+
+ return true;
}
template<Air::Opcode opcode32, Air::Opcode opcode64, Air::Opcode opcodeDouble, Air::Opcode opcodeFloat, Commutativity commutativity = NotCommutative>
@@ -2297,6 +2303,7 @@
UseCounts m_useCounts;
PhiChildren m_phiChildren;
BlockWorklist m_fastWorklist;
+ Dominators& m_dominators;
Vector<Vector<Inst, 4>> m_insts;
Vector<Inst> m_prologue;
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