Changeset 183207 in webkit for trunk/Source/JavaScriptCore/bytecode/BytecodeLivenessAnalysis.cpp

Timestamp:

Apr 23, 2015, 1:47:31 PM (10 years ago)

Author:

[email protected]

Message:

DFG should insert Phantoms late using BytecodeKills and block-local OSR availability
​https://bugs.webkit.org/show_bug.cgi?id=143735

Reviewed by Geoffrey Garen.

We've always had bugs arising from the fact that we would MovHint something into a local,
and then fail to keep it alive. We would then try to keep things alive by putting Phantoms
on those Nodes that were MovHinted. But this became increasingly tricky. Given the
sophistication of the transformations we are doing today, this approach is just not sound
anymore.

This comprehensively fixes these bugs by having the DFG backend automatically insert
Phantoms just before codegen based on bytecode liveness. To make this practical, this also
makes it much faster to query bytecode liveness.

It's about as perf-neutral as it gets for a change that increases compiler work without
actually optimizing anything. Later changes will remove the old Phantom-preserving logic,
which should then speed us up. I can't really report concrete slow-down numbers because
they are low enough to basically be in the noise. For example, a 20-iteration run of
SunSpider yields "maybe 0.8% slower", whatever that means.

• CMakeLists.txt:
• JavaScriptCore.vcxproj/JavaScriptCore.vcxproj:
• JavaScriptCore.xcodeproj/project.pbxproj:
• bytecode/BytecodeLivenessAnalysis.cpp:

(JSC::BytecodeLivenessAnalysis::computeFullLiveness):

• bytecode/FullBytecodeLiveness.h:

(JSC::FullBytecodeLiveness::getLiveness):

• bytecode/VirtualRegister.h:

(JSC::VirtualRegister::operator+):
(JSC::VirtualRegister::operator-):

• dfg/DFGForAllKills.h:

(JSC::DFG::forAllLiveNodesAtTail):
(JSC::DFG::forAllKilledOperands):
(JSC::DFG::forAllKilledNodesAtNodeIndex):

• dfg/DFGGraph.cpp:

(JSC::DFG::Graph::isLiveInBytecode):
(JSC::DFG::Graph::localsLiveInBytecode):

• dfg/DFGGraph.h:

(JSC::DFG::Graph::forAllLocalsLiveInBytecode):
(JSC::DFG::Graph::forAllLiveInBytecode):

• dfg/DFGMayExit.cpp:

(JSC::DFG::mayExit):

• dfg/DFGMovHintRemovalPhase.cpp:
• dfg/DFGNodeType.h:
• dfg/DFGPhantomInsertionPhase.cpp: Added.

(JSC::DFG::performPhantomInsertion):

• dfg/DFGPhantomInsertionPhase.h: Added.
• dfg/DFGPlan.cpp:

(JSC::DFG::Plan::compileInThreadImpl):

• dfg/DFGScoreBoard.h:

(JSC::DFG::ScoreBoard::sortFree):
(JSC::DFG::ScoreBoard::assertClear):

• dfg/DFGVirtualRegisterAllocationPhase.cpp:

(JSC::DFG::VirtualRegisterAllocationPhase::run):

• ftl/FTLLowerDFGToLLVM.cpp:

(JSC::FTL::LowerDFGToLLVM::buildExitArguments):

• tests/stress/phantom-inadequacy.js: Added.

(bar):
(baz):
(foo):

File:

• trunk/Source/JavaScriptCore/bytecode/BytecodeLivenessAnalysis.cpp (modified) (2 diffs)

trunk/Source/JavaScriptCore/bytecode/BytecodeLivenessAnalysis.cpp

@@ -238 +238 @@
     FastBitVector out;
     
-    result.m_map.clear();
+    result.m_map.resize(m_codeBlock->instructions().size());
     
     for (unsigned i = m_basicBlocks.size(); i--;) {
@@ -250 +250 @@
             unsigned bytecodeOffset = block->bytecodeOffsets()[i];
             stepOverInstruction(m_codeBlock, m_basicBlocks, bytecodeOffset, out);
-            result.m_map.add(bytecodeOffset, out);
+            result.m_map[bytecodeOffset] = out;
         }
     }