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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/246075">246075</a></dd>
<dt>Author</dt> <dd>tzagallo@apple.com</dd>
<dt>Date</dt> <dd>2019-06-04 12:06:32 -0700 (Tue, 04 Jun 2019)</dd>
</dl>

<h3>Log Message</h3>
<pre>Argument elimination should check transitive dependents for interference
https://bugs.webkit.org/show_bug.cgi?id=198520
<rdar://problem/50863343>

Reviewed by Filip Pizlo.

JSTests:

* stress/argument-elimination-inline-rest-past-kill.js: Added.
(f2):
(f3):

Source/JavaScriptCore:

Consider the following program:

    a: CreateRest
    -->
        b: CreateRest
    <--
    c: Spread(@a)
    d: Spread(@b)
    e: NewArrayWithSpread(@a, @b)
    f: KillStack(locX)
    g: LoadVarargs(@e)

Suppose @b reads locX, then we cannot transform @e to PhantomNewArraySpread, since that would
move the stack access from @b into @g, and that stack location is no longer valid at that point.

We fix that by computing a set of all inline call frames that any argument elimination candidate
depends on and checking each of them for interference in `eliminateCandidatesThatInterfere`.

* dfg/DFGArgumentsEliminationPhase.cpp:</pre>

<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkJSTestsChangeLog">trunk/JSTests/ChangeLog</a></li>
<li><a href="#trunkSourceJavaScriptCoreChangeLog">trunk/Source/JavaScriptCore/ChangeLog</a></li>
<li><a href="#trunkSourceJavaScriptCoredfgDFGArgumentsEliminationPhasecpp">trunk/Source/JavaScriptCore/dfg/DFGArgumentsEliminationPhase.cpp</a></li>
</ul>

<h3>Added Paths</h3>
<ul>
<li><a href="#trunkJSTestsstressargumenteliminationinlinerestpastkilljs">trunk/JSTests/stress/argument-elimination-inline-rest-past-kill.js</a></li>
</ul>

</div>
<div id="patch">
<h3>Diff</h3>
<a id="trunkJSTestsChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/JSTests/ChangeLog (246074 => 246075)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/JSTests/ChangeLog  2019-06-04 19:00:12 UTC (rev 246074)
+++ trunk/JSTests/ChangeLog     2019-06-04 19:06:32 UTC (rev 246075)
</span><span class="lines">@@ -1,5 +1,17 @@
</span><span class="cx"> 2019-06-04  Tadeu Zagallo  <tzagallo@apple.com>
</span><span class="cx"> 
</span><ins>+        Argument elimination should check transitive dependents for interference
+        https://bugs.webkit.org/show_bug.cgi?id=198520
+        <rdar://problem/50863343>
+
+        Reviewed by Filip Pizlo.
+
+        * stress/argument-elimination-inline-rest-past-kill.js: Added.
+        (f2):
+        (f3):
+
+2019-06-04  Tadeu Zagallo  <tzagallo@apple.com>
+
</ins><span class="cx">         Argument elimination should check for negative indices in GetByVal
</span><span class="cx">         https://bugs.webkit.org/show_bug.cgi?id=198302
</span><span class="cx">         <rdar://problem/51188095>
</span></span></pre></div>
<a id="trunkJSTestsstressargumenteliminationinlinerestpastkilljs"></a>
<div class="addfile"><h4>Added: trunk/JSTests/stress/argument-elimination-inline-rest-past-kill.js (0 => 246075)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/JSTests/stress/argument-elimination-inline-rest-past-kill.js                               (rev 0)
+++ trunk/JSTests/stress/argument-elimination-inline-rest-past-kill.js  2019-06-04 19:06:32 UTC (rev 246075)
</span><span class="lines">@@ -0,0 +1,16 @@
</span><ins>+//@ requireOptions("--forceEagerCompilation=1")
+function f2(...a1) {
+    return a1;
+}
+
+function f3(...a2) {
+    let v1 = f2([]);
+    return f2(...a2, ...v1);
+}
+noInline(f3);
+
+for (let i = 0; i < 1e5; i++) {
+    var v3 = f3();
+    if (!Array.isArray(v3[v3.length - 1]))
+        throw new Error('Should be an array');
+}
</ins></span></pre></div>
<a id="trunkSourceJavaScriptCoreChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/ChangeLog (246074 => 246075)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/ChangeLog    2019-06-04 19:00:12 UTC (rev 246074)
+++ trunk/Source/JavaScriptCore/ChangeLog       2019-06-04 19:06:32 UTC (rev 246075)
</span><span class="lines">@@ -1,3 +1,31 @@
</span><ins>+2019-06-04  Tadeu Zagallo  <tzagallo@apple.com>
+
+        Argument elimination should check transitive dependents for interference
+        https://bugs.webkit.org/show_bug.cgi?id=198520
+        <rdar://problem/50863343>
+
+        Reviewed by Filip Pizlo.
+
+        Consider the following program:
+
+            a: CreateRest
+            -->
+                b: CreateRest
+            <--
+            c: Spread(@a)
+            d: Spread(@b)
+            e: NewArrayWithSpread(@a, @b)
+            f: KillStack(locX)
+            g: LoadVarargs(@e)
+
+        Suppose @b reads locX, then we cannot transform @e to PhantomNewArraySpread, since that would
+        move the stack access from @b into @g, and that stack location is no longer valid at that point.
+
+        We fix that by computing a set of all inline call frames that any argument elimination candidate
+        depends on and checking each of them for interference in `eliminateCandidatesThatInterfere`.
+
+        * dfg/DFGArgumentsEliminationPhase.cpp:
+
</ins><span class="cx"> 2019-06-04  Yusuke Suzuki  <ysuzuki@apple.com>
</span><span class="cx"> 
</span><span class="cx">         [JSC] InferredValue should not be a JSCell
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoredfgDFGArgumentsEliminationPhasecpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/dfg/DFGArgumentsEliminationPhase.cpp (246074 => 246075)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/dfg/DFGArgumentsEliminationPhase.cpp 2019-06-04 19:00:12 UTC (rev 246074)
+++ trunk/Source/JavaScriptCore/dfg/DFGArgumentsEliminationPhase.cpp    2019-06-04 19:06:32 UTC (rev 246075)
</span><span class="lines">@@ -502,6 +502,33 @@
</span><span class="cx">             }
</span><span class="cx">         }
</span><span class="cx">         
</span><ins>+        using InlineCallFrames = HashSet<InlineCallFrame*, WTF::DefaultHash<InlineCallFrame*>::Hash, WTF::NullableHashTraits<InlineCallFrame*>>;
+        using InlineCallFramesForCanditates = HashMap<Node*, InlineCallFrames>;
+        InlineCallFramesForCanditates inlineCallFramesForCandidate;
+        auto forEachDependentNode = recursableLambda([&](auto self, Node* node, const auto& functor) -> void {
+            functor(node);
+
+            if (node->op() == Spread) {
+                self(node->child1().node(), functor);
+                return;
+            }
+
+            if (node->op() == NewArrayWithSpread) {
+                BitVector* bitVector = node->bitVector();
+                for (unsigned i = node->numChildren(); i--; ) {
+                    if (bitVector->get(i))
+                        self(m_graph.varArgChild(node, i).node(), functor);
+                }
+                return;
+            }
+        });
+        for (Node* candidate : m_candidates) {
+            auto& set = inlineCallFramesForCandidate.add(candidate, InlineCallFrames()).iterator->value;
+            forEachDependentNode(candidate, [&](Node* dependent) {
+                set.add(dependent->origin.semantic.inlineCallFrame());
+            });
+        }
+
</ins><span class="cx">         for (BasicBlock* block : m_graph.blocksInNaturalOrder()) {
</span><span class="cx">             // Stop if we've already removed all candidates.
</span><span class="cx">             if (m_candidates.isEmpty())
</span><span class="lines">@@ -524,83 +551,85 @@
</span><span class="cx">                     if (!m_candidates.contains(candidate))
</span><span class="cx">                         return;
</span><span class="cx">                     
</span><del>-                    // Check if this block has any clobbers that affect this candidate. This is a fairly
-                    // fast check.
-                    bool isClobberedByBlock = false;
-                    Operands<bool>& clobberedByThisBlock = clobberedByBlock[block];
-                    
-                    if (InlineCallFrame* inlineCallFrame = candidate->origin.semantic.inlineCallFrame()) {
-                        if (inlineCallFrame->isVarargs()) {
-                            isClobberedByBlock |= clobberedByThisBlock.operand(
-                                inlineCallFrame->stackOffset + CallFrameSlot::argumentCount);
-                        }
</del><ins>+                    for (InlineCallFrame* inlineCallFrame : inlineCallFramesForCandidate.get(candidate)) {
+                        // Check if this block has any clobbers that affect this candidate. This is a fairly
+                        // fast check.
+                        bool isClobberedByBlock = false;
+                        Operands<bool>& clobberedByThisBlock = clobberedByBlock[block];
</ins><span class="cx">                         
</span><del>-                        if (!isClobberedByBlock || inlineCallFrame->isClosureCall) {
-                            isClobberedByBlock |= clobberedByThisBlock.operand(
-                                inlineCallFrame->stackOffset + CallFrameSlot::callee);
-                        }
-                        
-                        if (!isClobberedByBlock) {
-                            for (unsigned i = 0; i < inlineCallFrame->argumentCountIncludingThis - 1; ++i) {
-                                VirtualRegister reg =
-                                    VirtualRegister(inlineCallFrame->stackOffset) +
-                                    CallFrame::argumentOffset(i);
-                                if (clobberedByThisBlock.operand(reg)) {
</del><ins>+                        if (inlineCallFrame) {
+                            if (inlineCallFrame->isVarargs()) {
+                                isClobberedByBlock |= clobberedByThisBlock.operand(
+                                    inlineCallFrame->stackOffset + CallFrameSlot::argumentCount);
+                            }
+
+                            if (!isClobberedByBlock || inlineCallFrame->isClosureCall) {
+                                isClobberedByBlock |= clobberedByThisBlock.operand(
+                                    inlineCallFrame->stackOffset + CallFrameSlot::callee);
+                            }
+
+                            if (!isClobberedByBlock) {
+                                for (unsigned i = 0; i < inlineCallFrame->argumentCountIncludingThis - 1; ++i) {
+                                    VirtualRegister reg =
+                                        VirtualRegister(inlineCallFrame->stackOffset) +
+                                        CallFrame::argumentOffset(i);
+                                    if (clobberedByThisBlock.operand(reg)) {
+                                        isClobberedByBlock = true;
+                                        break;
+                                    }
+                                }
+                            }
+                        } else {
+                            // We don't include the ArgumentCount or Callee in this case because we can be
+                            // damn sure that this won't be clobbered.
+                            for (unsigned i = 1; i < static_cast<unsigned>(codeBlock()->numParameters()); ++i) {
+                                if (clobberedByThisBlock.argument(i)) {
</ins><span class="cx">                                     isClobberedByBlock = true;
</span><span class="cx">                                     break;
</span><span class="cx">                                 }
</span><span class="cx">                             }
</span><span class="cx">                         }
</span><del>-                    } else {
-                        // We don't include the ArgumentCount or Callee in this case because we can be
-                        // damn sure that this won't be clobbered.
-                        for (unsigned i = 1; i < static_cast<unsigned>(codeBlock()->numParameters()); ++i) {
-                            if (clobberedByThisBlock.argument(i)) {
-                                isClobberedByBlock = true;
-                                break;
-                            }
-                        }
-                    }
-                    
-                    if (!isClobberedByBlock)
-                        return;
-                    
-                    // Check if we can immediately eliminate this candidate. If the block has a clobber
-                    // for this arguments allocation, and we'd have to examine every node in the block,
-                    // then we can just eliminate the candidate.
-                    if (nodeIndex == block->size() && candidate->owner != block) {
-                        if (DFGArgumentsEliminationPhaseInternal::verbose)
-                            dataLog("eliminating candidate: ", candidate, " because it is clobbered by: ", block->at(nodeIndex), "\n");
-                        transitivelyRemoveCandidate(candidate);
-                        return;
-                    }
-                    
-                    // This loop considers all nodes up to the nodeIndex, excluding the nodeIndex.
-                    while (nodeIndex--) {
-                        Node* node = block->at(nodeIndex);
-                        if (node == candidate)
-                            break;
</del><span class="cx">                         
</span><del>-                        bool found = false;
-                        clobberize(
-                            m_graph, node, NoOpClobberize(),
-                            [&] (AbstractHeap heap) {
-                                if (heap.kind() == Stack && !heap.payload().isTop()) {
-                                    if (argumentsInvolveStackSlot(candidate, VirtualRegister(heap.payload().value32())))
-                                        found = true;
-                                    return;
-                                }
-                                if (heap.overlaps(Stack))
-                                    found = true;
-                            },
-                            NoOpClobberize());
</del><ins>+                        if (!isClobberedByBlock)
+                            continue;
</ins><span class="cx">                         
</span><del>-                        if (found) {
</del><ins>+                        // Check if we can immediately eliminate this candidate. If the block has a clobber
+                        // for this arguments allocation, and we'd have to examine every node in the block,
+                        // then we can just eliminate the candidate.
+                        if (nodeIndex == block->size() && candidate->owner != block) {
</ins><span class="cx">                             if (DFGArgumentsEliminationPhaseInternal::verbose)
</span><del>-                                dataLog("eliminating candidate: ", candidate, " because it is clobbered by ", block->at(nodeIndex), "\n");
</del><ins>+                                dataLog("eliminating candidate: ", candidate, " because it is clobbered by: ", block->at(nodeIndex), "\n");
</ins><span class="cx">                             transitivelyRemoveCandidate(candidate);
</span><span class="cx">                             return;
</span><span class="cx">                         }
</span><ins>+
+                        // This loop considers all nodes up to the nodeIndex, excluding the nodeIndex.
+                        while (nodeIndex--) {
+                            Node* node = block->at(nodeIndex);
+                            if (node == candidate)
+                                break;
+
+                            bool found = false;
+                            clobberize(
+                                m_graph, node, NoOpClobberize(),
+                                [&] (AbstractHeap heap) {
+                                    if (heap.kind() == Stack && !heap.payload().isTop()) {
+                                        if (argumentsInvolveStackSlot(inlineCallFrame, VirtualRegister(heap.payload().value32())))
+                                            found = true;
+                                        return;
+                                    }
+                                    if (heap.overlaps(Stack))
+                                        found = true;
+                                },
+                                NoOpClobberize());
+
+                            if (found) {
+                                if (DFGArgumentsEliminationPhaseInternal::verbose)
+                                    dataLog("eliminating candidate: ", candidate, " because it is clobbered by ", block->at(nodeIndex), "\n");
+                                transitivelyRemoveCandidate(candidate);
+                                return;
+                            }
+                        }
</ins><span class="cx">                     }
</span><span class="cx">                 });
</span><span class="cx">         }
</span></span></pre>
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