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<dl class="meta">
<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/175846">175846</a></dd>
<dt>Author</dt> <dd>akling@apple.com</dd>
<dt>Date</dt> <dd>2014-11-10 19:10:13 -0800 (Mon, 10 Nov 2014)</dd>
</dl>
<h3>Log Message</h3>
<pre>The JIT should cache property lookup misses.
<https://webkit.org/b/135578>
Source/JavaScriptCore:
Add support for inline caching of missed property lookups.
Previously this would banish us to C++ slow path.
It's implemented as a simple GetById cache that returns jsUndefined()
as long as the Structure chain check passes. There's no DFG exploitation
of this knowledge in this patch.
Test: js/regress/undefined-property-access.js (~5.5x speedup)
Reviewed by Filip Pizlo.
* bytecode/PolymorphicGetByIdList.h:
* bytecode/GetByIdStatus.cpp:
(JSC::GetByIdStatus::computeForStubInfo):
Add GetByIdAccess::SimpleMiss so we can communicate to the DFG that
the access has been cached.
* jit/Repatch.cpp:
(JSC::toString):
(JSC::kindFor):
(JSC::generateByIdStub):
(JSC::tryCacheGetByID):
(JSC::tryBuildGetByIDList):
Added a GetUndefined stub kind, just a simple "store jsUndefined()" snippet.
Use this to cache missed lookups, piggybacking mostly on the GetValue kind.
* runtime/PropertySlot.h:
(JSC::PropertySlot::isUnset):
Exposed the unset state so PropertySlot can communicate that lookup failed.
LayoutTests:
Add a JSRegress test for caching of property lookup misses.
There are three subtests:
1. Pure speed test.
2. Test for when a property previously cached as missing suddenly
appears on the object.
3. Same as (2), but it appears on the prototype.
The test runs ~5.5x faster with the optimization.
Reviewed by Filip Pizlo.
* js/regress/script-tests/undefined-property-access.js: Added.
(foo):
(bar):
(baz):
* js/regress/undefined-property-access-expected.txt: Added.
* js/regress/undefined-property-access.html: Added.</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkLayoutTestsChangeLog">trunk/LayoutTests/ChangeLog</a></li>
<li><a href="#trunkSourceJavaScriptCoreChangeLog">trunk/Source/JavaScriptCore/ChangeLog</a></li>
<li><a href="#trunkSourceJavaScriptCorebytecodeGetByIdStatuscpp">trunk/Source/JavaScriptCore/bytecode/GetByIdStatus.cpp</a></li>
<li><a href="#trunkSourceJavaScriptCorebytecodePolymorphicGetByIdListh">trunk/Source/JavaScriptCore/bytecode/PolymorphicGetByIdList.h</a></li>
<li><a href="#trunkSourceJavaScriptCorejitRepatchcpp">trunk/Source/JavaScriptCore/jit/Repatch.cpp</a></li>
<li><a href="#trunkSourceJavaScriptCoreruntimePropertySloth">trunk/Source/JavaScriptCore/runtime/PropertySlot.h</a></li>
</ul>
<h3>Added Paths</h3>
<ul>
<li><a href="#trunkLayoutTestsjsregressscripttestsundefinedpropertyaccessjs">trunk/LayoutTests/js/regress/script-tests/undefined-property-access.js</a></li>
<li><a href="#trunkLayoutTestsjsregressundefinedpropertyaccessexpectedtxt">trunk/LayoutTests/js/regress/undefined-property-access-expected.txt</a></li>
<li><a href="#trunkLayoutTestsjsregressundefinedpropertyaccesshtml">trunk/LayoutTests/js/regress/undefined-property-access.html</a></li>
</ul>
</div>
<div id="patch">
<h3>Diff</h3>
<a id="trunkLayoutTestsChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/LayoutTests/ChangeLog (175845 => 175846)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/LayoutTests/ChangeLog 2014-11-11 03:05:25 UTC (rev 175845)
+++ trunk/LayoutTests/ChangeLog 2014-11-11 03:10:13 UTC (rev 175846)
</span><span class="lines">@@ -1,3 +1,27 @@
</span><ins>+2014-11-10 Andreas Kling <akling@apple.com>
+
+ The JIT should cache property lookup misses.
+ <https://webkit.org/b/135578>
+
+ Add a JSRegress test for caching of property lookup misses.
+ There are three subtests:
+
+ 1. Pure speed test.
+ 2. Test for when a property previously cached as missing suddenly
+ appears on the object.
+ 3. Same as (2), but it appears on the prototype.
+
+ The test runs ~5.5x faster with the optimization.
+
+ Reviewed by Filip Pizlo.
+
+ * js/regress/script-tests/undefined-property-access.js: Added.
+ (foo):
+ (bar):
+ (baz):
+ * js/regress/undefined-property-access-expected.txt: Added.
+ * js/regress/undefined-property-access.html: Added.
+
</ins><span class="cx"> 2014-11-10 Myles C. Maxfield <mmaxfield@apple.com>
</span><span class="cx">
</span><span class="cx"> Test that complext and fast text codepaths measure the same width
</span></span></pre></div>
<a id="trunkLayoutTestsjsregressscripttestsundefinedpropertyaccessjs"></a>
<div class="addfile"><h4>Added: trunk/LayoutTests/js/regress/script-tests/undefined-property-access.js (0 => 175846)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/LayoutTests/js/regress/script-tests/undefined-property-access.js (rev 0)
+++ trunk/LayoutTests/js/regress/script-tests/undefined-property-access.js 2014-11-11 03:10:13 UTC (rev 175846)
</span><span class="lines">@@ -0,0 +1,48 @@
</span><ins>+var someGlobal;
+
+// This is a simple speed test. It should go fast.
+
+function foo() {
+ var myObject = {};
+ for (var i = 0; i < 10000000; ++i) {
+ someGlobal = myObject.undefinedProperty;
+ }
+ return someGlobal;
+}
+result = foo();
+if (result != undefined)
+ throw "Bad result: " + result;
+
+// This test checks that a cached property lookup miss doesn't continue to fire when the property suddenly appears on the object.
+
+function bar() {
+ var myObject = {};
+ for (var i = 0; i < 100000000; ++i) {
+ someGlobal = myObject.someProperty;
+ if (i == 50000000)
+ myObject.someProperty = 1;
+ }
+ return someGlobal;
+}
+var result = bar();
+if (result != 1)
+ throw "Bad result: " + result;
+someGlobal = undefined;
+
+// This test checks that a cached property lookup miss doesn't continue to fire when the property suddenly appears on the object's prototype.
+
+function baz() {
+ var myPrototype = {}
+ var myObject = {};
+ myObject.__proto__ = myPrototype;
+ for (var i = 0; i < 100000000; ++i) {
+ someGlobal = myObject.someProperty;
+ if (i == 50000000)
+ myPrototype.someProperty = 2;
+ }
+ return someGlobal;
+}
+var result = baz();
+if (result != 2)
+ throw "Bad result: " + result;
+
</ins></span></pre></div>
<a id="trunkLayoutTestsjsregressundefinedpropertyaccessexpectedtxt"></a>
<div class="addfile"><h4>Added: trunk/LayoutTests/js/regress/undefined-property-access-expected.txt (0 => 175846)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/LayoutTests/js/regress/undefined-property-access-expected.txt (rev 0)
+++ trunk/LayoutTests/js/regress/undefined-property-access-expected.txt 2014-11-11 03:10:13 UTC (rev 175846)
</span><span class="lines">@@ -0,0 +1,10 @@
</span><ins>+JSRegress/undefined-property-access
+
+On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".
+
+
+PASS no exception thrown
+PASS successfullyParsed is true
+
+TEST COMPLETE
+
</ins></span></pre></div>
<a id="trunkLayoutTestsjsregressundefinedpropertyaccesshtml"></a>
<div class="addfile"><h4>Added: trunk/LayoutTests/js/regress/undefined-property-access.html (0 => 175846)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/LayoutTests/js/regress/undefined-property-access.html (rev 0)
+++ trunk/LayoutTests/js/regress/undefined-property-access.html 2014-11-11 03:10:13 UTC (rev 175846)
</span><span class="lines">@@ -0,0 +1,12 @@
</span><ins>+<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML//EN">
+<html>
+<head>
+<script src="../../resources/js-test-pre.js"></script>
+</head>
+<body>
+<script src="../../resources/regress-pre.js"></script>
+<script src="script-tests/undefined-property-access.js"></script>
+<script src="../../resources/regress-post.js"></script>
+<script src="../../resources/js-test-post.js"></script>
+</body>
+</html>
</ins></span></pre></div>
<a id="trunkSourceJavaScriptCoreChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/ChangeLog (175845 => 175846)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/ChangeLog 2014-11-11 03:05:25 UTC (rev 175845)
+++ trunk/Source/JavaScriptCore/ChangeLog 2014-11-11 03:10:13 UTC (rev 175846)
</span><span class="lines">@@ -1,3 +1,41 @@
</span><ins>+2014-11-10 Andreas Kling <akling@apple.com>
+
+ The JIT should cache property lookup misses.
+ <https://webkit.org/b/135578>
+
+ Add support for inline caching of missed property lookups.
+ Previously this would banish us to C++ slow path.
+
+ It's implemented as a simple GetById cache that returns jsUndefined()
+ as long as the Structure chain check passes. There's no DFG exploitation
+ of this knowledge in this patch.
+
+ Test: js/regress/undefined-property-access.js (~5.5x speedup)
+
+ Reviewed by Filip Pizlo.
+
+ * bytecode/PolymorphicGetByIdList.h:
+ * bytecode/GetByIdStatus.cpp:
+ (JSC::GetByIdStatus::computeForStubInfo):
+
+ Add GetByIdAccess::SimpleMiss so we can communicate to the DFG that
+ the access has been cached.
+
+ * jit/Repatch.cpp:
+ (JSC::toString):
+ (JSC::kindFor):
+ (JSC::generateByIdStub):
+ (JSC::tryCacheGetByID):
+ (JSC::tryBuildGetByIDList):
+
+ Added a GetUndefined stub kind, just a simple "store jsUndefined()" snippet.
+ Use this to cache missed lookups, piggybacking mostly on the GetValue kind.
+
+ * runtime/PropertySlot.h:
+ (JSC::PropertySlot::isUnset):
+
+ Exposed the unset state so PropertySlot can communicate that lookup failed.
+
</ins><span class="cx"> 2014-11-10 Michael Saboff <msaboff@apple.com>
</span><span class="cx">
</span><span class="cx"> Add scope operand to op_create_lexical_environment
</span></span></pre></div>
<a id="trunkSourceJavaScriptCorebytecodeGetByIdStatuscpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/bytecode/GetByIdStatus.cpp (175845 => 175846)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/bytecode/GetByIdStatus.cpp 2014-11-11 03:05:25 UTC (rev 175845)
+++ trunk/Source/JavaScriptCore/bytecode/GetByIdStatus.cpp 2014-11-11 03:10:13 UTC (rev 175846)
</span><span class="lines">@@ -189,6 +189,7 @@
</span><span class="cx"> locker, profiledBlock, *stub->m_callLinkInfo, callExitSiteData));
</span><span class="cx"> break;
</span><span class="cx"> }
</span><ins>+ case GetByIdAccess::SimpleMiss:
</ins><span class="cx"> case GetByIdAccess::CustomGetter:
</span><span class="cx"> case GetByIdAccess::WatchedStub:{
</span><span class="cx"> // FIXME: It would be totally sweet to support this at some point in the future.
</span></span></pre></div>
<a id="trunkSourceJavaScriptCorebytecodePolymorphicGetByIdListh"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/bytecode/PolymorphicGetByIdList.h (175845 => 175846)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/bytecode/PolymorphicGetByIdList.h 2014-11-11 03:05:25 UTC (rev 175845)
+++ trunk/Source/JavaScriptCore/bytecode/PolymorphicGetByIdList.h 2014-11-11 03:10:13 UTC (rev 175846)
</span><span class="lines">@@ -47,7 +47,8 @@
</span><span class="cx"> SimpleStub, // This is a stub.
</span><span class="cx"> WatchedStub,
</span><span class="cx"> Getter,
</span><del>- CustomGetter
</del><ins>+ CustomGetter,
+ SimpleMiss,
</ins><span class="cx"> };
</span><span class="cx">
</span><span class="cx"> GetByIdAccess()
</span></span></pre></div>
<a id="trunkSourceJavaScriptCorejitRepatchcpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/jit/Repatch.cpp (175845 => 175846)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/jit/Repatch.cpp 2014-11-11 03:05:25 UTC (rev 175845)
+++ trunk/Source/JavaScriptCore/jit/Repatch.cpp 2014-11-11 03:10:13 UTC (rev 175846)
</span><span class="lines">@@ -228,6 +228,7 @@
</span><span class="cx">
</span><span class="cx"> enum ByIdStubKind {
</span><span class="cx"> GetValue,
</span><ins>+ GetUndefined,
</ins><span class="cx"> CallGetter,
</span><span class="cx"> CallCustomGetter,
</span><span class="cx"> CallSetter,
</span><span class="lines">@@ -239,6 +240,8 @@
</span><span class="cx"> switch (kind) {
</span><span class="cx"> case GetValue:
</span><span class="cx"> return "GetValue";
</span><ins>+ case GetUndefined:
+ return "GetUndefined";
</ins><span class="cx"> case CallGetter:
</span><span class="cx"> return "CallGetter";
</span><span class="cx"> case CallCustomGetter:
</span><span class="lines">@@ -257,6 +260,8 @@
</span><span class="cx"> {
</span><span class="cx"> if (slot.isCacheableValue())
</span><span class="cx"> return GetValue;
</span><ins>+ if (slot.isUnset())
+ return GetUndefined;
</ins><span class="cx"> if (slot.isCacheableCustom())
</span><span class="cx"> return CallCustomGetter;
</span><span class="cx"> RELEASE_ASSERT(slot.isCacheableGetter());
</span><span class="lines">@@ -301,7 +306,7 @@
</span><span class="cx"> static_cast<GPRReg>(stubInfo.patch.valueGPR));
</span><span class="cx"> GPRReg scratchGPR = TempRegisterSet(stubInfo.patch.usedRegisters).getFreeGPR();
</span><span class="cx"> bool needToRestoreScratch = scratchGPR == InvalidGPRReg;
</span><del>- RELEASE_ASSERT(!needToRestoreScratch || kind == GetValue);
</del><ins>+ RELEASE_ASSERT(!needToRestoreScratch || (kind == GetValue || kind == GetUndefined));
</ins><span class="cx">
</span><span class="cx"> CCallHelpers stubJit(&exec->vm(), exec->codeBlock());
</span><span class="cx"> if (needToRestoreScratch) {
</span><span class="lines">@@ -361,24 +366,28 @@
</span><span class="cx"> }
</span><span class="cx">
</span><span class="cx"> currStructure->startWatchingPropertyForReplacements(*vm, offset);
</span><del>- GPRReg baseForAccessGPR;
- if (chain) {
- // We could have clobbered scratchGPR earlier, so we have to reload from baseGPR to get the target.
- if (loadTargetFromProxy)
- stubJit.loadPtr(MacroAssembler::Address(baseGPR, JSProxy::targetOffset()), baseForGetGPR);
- stubJit.move(MacroAssembler::TrustedImmPtr(protoObject), scratchGPR);
- baseForAccessGPR = scratchGPR;
- } else {
- // For proxy objects, we need to do all the Structure checks before moving the baseGPR into
- // baseForGetGPR because if we fail any of the checks then we would have the wrong value in baseGPR
- // on the slow path.
- if (loadTargetFromProxy)
- stubJit.move(scratchGPR, baseForGetGPR);
- baseForAccessGPR = baseForGetGPR;
</del><ins>+ GPRReg baseForAccessGPR = InvalidGPRReg;
+ if (kind != GetUndefined) {
+ if (chain) {
+ // We could have clobbered scratchGPR earlier, so we have to reload from baseGPR to get the target.
+ if (loadTargetFromProxy)
+ stubJit.loadPtr(MacroAssembler::Address(baseGPR, JSProxy::targetOffset()), baseForGetGPR);
+ stubJit.move(MacroAssembler::TrustedImmPtr(protoObject), scratchGPR);
+ baseForAccessGPR = scratchGPR;
+ } else {
+ // For proxy objects, we need to do all the Structure checks before moving the baseGPR into
+ // baseForGetGPR because if we fail any of the checks then we would have the wrong value in baseGPR
+ // on the slow path.
+ if (loadTargetFromProxy)
+ stubJit.move(scratchGPR, baseForGetGPR);
+ baseForAccessGPR = baseForGetGPR;
+ }
</ins><span class="cx"> }
</span><span class="cx">
</span><span class="cx"> GPRReg loadedValueGPR = InvalidGPRReg;
</span><del>- if (kind != CallCustomGetter && kind != CallCustomSetter) {
</del><ins>+ if (kind == GetUndefined)
+ stubJit.moveTrustedValue(jsUndefined(), valueRegs);
+ else if (kind != CallCustomGetter && kind != CallCustomSetter) {
</ins><span class="cx"> if (kind == GetValue)
</span><span class="cx"> loadedValueGPR = valueRegs.payloadGPR();
</span><span class="cx"> else
</span><span class="lines">@@ -412,7 +421,7 @@
</span><span class="cx"> std::unique_ptr<CallLinkInfo> callLinkInfo;
</span><span class="cx">
</span><span class="cx"> MacroAssembler::Jump success, fail;
</span><del>- if (kind != GetValue) {
</del><ins>+ if (kind != GetValue && kind != GetUndefined) {
</ins><span class="cx"> // Need to make sure that whenever this call is made in the future, we remember the
</span><span class="cx"> // place that we made it from. It just so happens to be the place that we are at
</span><span class="cx"> // right now!
</span><span class="lines">@@ -733,10 +742,12 @@
</span><span class="cx"> // FIXME: Cache property access for immediates.
</span><span class="cx"> if (!baseValue.isCell())
</span><span class="cx"> return GiveUpOnCache;
</span><ins>+
+ if (!slot.isCacheable() && !slot.isUnset())
+ return GiveUpOnCache;
+
</ins><span class="cx"> JSCell* baseCell = baseValue.asCell();
</span><span class="cx"> Structure* structure = baseCell->structure();
</span><del>- if (!slot.isCacheable())
- return GiveUpOnCache;
</del><span class="cx">
</span><span class="cx"> InlineCacheAction action = actionForCell(*vm, baseCell);
</span><span class="cx"> if (action != AttemptToCache)
</span><span class="lines">@@ -783,7 +794,7 @@
</span><span class="cx"> static InlineCacheAction tryBuildGetByIDList(ExecState* exec, JSValue baseValue, const Identifier& ident, const PropertySlot& slot, StructureStubInfo& stubInfo)
</span><span class="cx"> {
</span><span class="cx"> if (!baseValue.isCell()
</span><del>- || !slot.isCacheable())
</del><ins>+ || (!slot.isCacheable() && !slot.isUnset()))
</ins><span class="cx"> return GiveUpOnCache;
</span><span class="cx">
</span><span class="cx"> JSCell* baseCell = baseValue.asCell();
</span><span class="lines">@@ -808,20 +819,23 @@
</span><span class="cx"> // We cannot do as much inline caching if the registers were not flushed prior to this GetById. In particular,
</span><span class="cx"> // non-Value cached properties require planting calls, which requires registers to have been flushed. Thus,
</span><span class="cx"> // if registers were not flushed, don't do non-Value caching.
</span><del>- if (!slot.isCacheableValue())
</del><ins>+ if (!slot.isCacheableValue() && !slot.isUnset())
</ins><span class="cx"> return GiveUpOnCache;
</span><span class="cx"> }
</span><del>-
- PropertyOffset offset = slot.cachedOffset();
</del><ins>+
+ PropertyOffset offset = slot.isUnset() ? invalidOffset : slot.cachedOffset();
</ins><span class="cx"> StructureChain* prototypeChain = 0;
</span><span class="cx"> size_t count = 0;
</span><span class="cx">
</span><del>- if (slot.slotBase() != baseValue) {
</del><ins>+ if (slot.isUnset() || slot.slotBase() != baseValue) {
</ins><span class="cx"> if (typeInfo.prohibitsPropertyCaching() || structure->isDictionary())
</span><span class="cx"> return GiveUpOnCache;
</span><del>-
- count = normalizePrototypeChainForChainAccess(
- exec, baseValue, slot.slotBase(), ident, offset);
</del><ins>+
+ if (slot.isUnset())
+ count = normalizePrototypeChain(exec, baseCell);
+ else
+ count = normalizePrototypeChainForChainAccess(
+ exec, baseValue, slot.slotBase(), ident, offset);
</ins><span class="cx"> if (count == InvalidPrototypeChain)
</span><span class="cx"> return GiveUpOnCache;
</span><span class="cx"> prototypeChain = structure->prototypeChain(exec);
</span><span class="lines">@@ -843,6 +857,8 @@
</span><span class="cx"> GetByIdAccess::AccessType accessType;
</span><span class="cx"> if (slot.isCacheableValue())
</span><span class="cx"> accessType = slot.watchpointSet() ? GetByIdAccess::WatchedStub : GetByIdAccess::SimpleStub;
</span><ins>+ else if (slot.isUnset())
+ accessType = GetByIdAccess::SimpleMiss;
</ins><span class="cx"> else if (slot.isCacheableGetter())
</span><span class="cx"> accessType = GetByIdAccess::Getter;
</span><span class="cx"> else
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoreruntimePropertySloth"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/runtime/PropertySlot.h (175845 => 175846)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/runtime/PropertySlot.h 2014-11-11 03:05:25 UTC (rev 175845)
+++ trunk/Source/JavaScriptCore/runtime/PropertySlot.h 2014-11-11 03:10:13 UTC (rev 175846)
</span><span class="lines">@@ -78,6 +78,7 @@
</span><span class="cx"> JSValue getValue(ExecState*, unsigned propertyName) const;
</span><span class="cx">
</span><span class="cx"> bool isCacheable() const { return m_cacheability == CachingAllowed && m_offset != invalidOffset; }
</span><ins>+ bool isUnset() const { return m_propertyType == TypeUnset; }
</ins><span class="cx"> bool isValue() const { return m_propertyType == TypeValue; }
</span><span class="cx"> bool isAccessor() const { return m_propertyType == TypeGetter; }
</span><span class="cx"> bool isCustom() const { return m_propertyType == TypeCustom; }
</span></span></pre>
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