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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/245706">245706</a></dd>
<dt>Author</dt> <dd>sbarati@apple.com</dd>
<dt>Date</dt> <dd>2019-05-23 12:54:53 -0700 (Thu, 23 May 2019)</dd>
</dl>

<h3>Log Message</h3>
<pre>[WHLSL] Add a helper for in-place AST mutation
https://bugs.webkit.org/show_bug.cgi?id=198175

Reviewed by Myles Maxfield.

This makes WHLSL AST mutation code a bit easier to read and write.

Code that looked like:
```
static_assert(sizeof(AST::DereferenceExpression) <= sizeof(AST::DotExpression), "Dot expressions need to be able to become dereference expressions without updating backreferences");
void* location = &dotExpression;
dotExpression.~DotExpression();
auto* dereferenceExpression = new (location) AST::DereferenceExpression(WTFMove(origin), WTFMove(callExpression));
```

Can now be:
```
auto* dereferenceExpression = AST::replaceWith<AST::DereferenceExpression>(dotExpression, WTFMove(origin), WTFMove(callExpression));
```

* Modules/webgpu/WHLSL/AST/WHLSLNode.h:
(WebCore::WHLSL::AST::replaceWith):
* Modules/webgpu/WHLSL/WHLSLNameResolver.cpp:
(WebCore::WHLSL::NameResolver::visit):
* Modules/webgpu/WHLSL/WHLSLPropertyResolver.cpp:
(WebCore::WHLSL::PropertyResolver::visit):
(WebCore::WHLSL::PropertyResolver::simplifyRightValue):
(WebCore::WHLSL::LeftValueSimplifier::visit):</pre>

<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkSourceWebCoreChangeLog">trunk/Source/WebCore/ChangeLog</a></li>
<li><a href="#trunkSourceWebCoreModuleswebgpuWHLSLASTWHLSLNodeh">trunk/Source/WebCore/Modules/webgpu/WHLSL/AST/WHLSLNode.h</a></li>
<li><a href="#trunkSourceWebCoreModuleswebgpuWHLSLWHLSLNameResolvercpp">trunk/Source/WebCore/Modules/webgpu/WHLSL/WHLSLNameResolver.cpp</a></li>
<li><a href="#trunkSourceWebCoreModuleswebgpuWHLSLWHLSLPropertyResolvercpp">trunk/Source/WebCore/Modules/webgpu/WHLSL/WHLSLPropertyResolver.cpp</a></li>
</ul>

</div>
<div id="patch">
<h3>Diff</h3>
<a id="trunkSourceWebCoreChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebCore/ChangeLog (245705 => 245706)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebCore/ChangeLog   2019-05-23 19:45:15 UTC (rev 245705)
+++ trunk/Source/WebCore/ChangeLog      2019-05-23 19:54:53 UTC (rev 245706)
</span><span class="lines">@@ -1,3 +1,34 @@
</span><ins>+2019-05-23  Saam barati  <sbarati@apple.com>
+
+        [WHLSL] Add a helper for in-place AST mutation
+        https://bugs.webkit.org/show_bug.cgi?id=198175
+
+        Reviewed by Myles Maxfield.
+
+        This makes WHLSL AST mutation code a bit easier to read and write.
+        
+        Code that looked like:
+        ```
+        static_assert(sizeof(AST::DereferenceExpression) <= sizeof(AST::DotExpression), "Dot expressions need to be able to become dereference expressions without updating backreferences");
+        void* location = &dotExpression;
+        dotExpression.~DotExpression();
+        auto* dereferenceExpression = new (location) AST::DereferenceExpression(WTFMove(origin), WTFMove(callExpression));
+        ```
+        
+        Can now be:
+        ```
+        auto* dereferenceExpression = AST::replaceWith<AST::DereferenceExpression>(dotExpression, WTFMove(origin), WTFMove(callExpression));
+        ```
+
+        * Modules/webgpu/WHLSL/AST/WHLSLNode.h:
+        (WebCore::WHLSL::AST::replaceWith):
+        * Modules/webgpu/WHLSL/WHLSLNameResolver.cpp:
+        (WebCore::WHLSL::NameResolver::visit):
+        * Modules/webgpu/WHLSL/WHLSLPropertyResolver.cpp:
+        (WebCore::WHLSL::PropertyResolver::visit):
+        (WebCore::WHLSL::PropertyResolver::simplifyRightValue):
+        (WebCore::WHLSL::LeftValueSimplifier::visit):
+
</ins><span class="cx"> 2019-05-23  Eric Carlson  <eric.carlson@apple.com>
</span><span class="cx"> 
</span><span class="cx">         [macOS,iOS] Add always-on logging for AVPlayerTimeControlStatus changes
</span></span></pre></div>
<a id="trunkSourceWebCoreModuleswebgpuWHLSLASTWHLSLNodeh"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebCore/Modules/webgpu/WHLSL/AST/WHLSLNode.h (245705 => 245706)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebCore/Modules/webgpu/WHLSL/AST/WHLSLNode.h        2019-05-23 19:45:15 UTC (rev 245705)
+++ trunk/Source/WebCore/Modules/webgpu/WHLSL/AST/WHLSLNode.h   2019-05-23 19:54:53 UTC (rev 245706)
</span><span class="lines">@@ -48,6 +48,15 @@
</span><span class="cx"> private:
</span><span class="cx"> };
</span><span class="cx"> 
</span><ins>+template <typename New, typename Old, typename ...Args>
+ALWAYS_INLINE New* replaceWith(Old& old, Args&&... args)
+{
+    static_assert(sizeof(New) <= sizeof(Old), "This is needed for the placement new below to not overwrite unowned memory.");
+    void* location = &old;
+    old.~Old();
+    return new (location) New(std::forward<Args>(args)...);
+}
+
</ins><span class="cx"> } // namespace AST
</span><span class="cx"> 
</span><span class="cx"> }
</span></span></pre></div>
<a id="trunkSourceWebCoreModuleswebgpuWHLSLWHLSLNameResolvercpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebCore/Modules/webgpu/WHLSL/WHLSLNameResolver.cpp (245705 => 245706)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebCore/Modules/webgpu/WHLSL/WHLSLNameResolver.cpp  2019-05-23 19:45:15 UTC (rev 245705)
+++ trunk/Source/WebCore/Modules/webgpu/WHLSL/WHLSLNameResolver.cpp     2019-05-23 19:54:53 UTC (rev 245706)
</span><span class="lines">@@ -194,12 +194,9 @@
</span><span class="cx">                 AST::EnumerationDefinition& enumerationDefinition = downcast<AST::EnumerationDefinition>(type);
</span><span class="cx">                 auto memberName = dotExpression.fieldName();
</span><span class="cx">                 if (auto* member = enumerationDefinition.memberByName(memberName)) {
</span><del>-                    static_assert(sizeof(AST::EnumerationMemberLiteral) <= sizeof(AST::DotExpression), "Dot expressions need to be able to become EnumerationMemberLiterals without updating backreferences");
</del><span class="cx">                     Lexer::Token origin = dotExpression.origin();
</span><del>-                    void* location = &dotExpression;
-                    dotExpression.~DotExpression();
</del><span class="cx">                     auto enumerationMemberLiteral = AST::EnumerationMemberLiteral::wrap(WTFMove(origin), WTFMove(baseName), WTFMove(memberName), enumerationDefinition, *member);
</span><del>-                    new (location) AST::EnumerationMemberLiteral(WTFMove(enumerationMemberLiteral));
</del><ins>+                    AST::replaceWith<AST::EnumerationMemberLiteral>(dotExpression, WTFMove(enumerationMemberLiteral));
</ins><span class="cx">                     return;
</span><span class="cx">                 }
</span><span class="cx">                 setError();
</span></span></pre></div>
<a id="trunkSourceWebCoreModuleswebgpuWHLSLWHLSLPropertyResolvercpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebCore/Modules/webgpu/WHLSL/WHLSLPropertyResolver.cpp (245705 => 245706)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebCore/Modules/webgpu/WHLSL/WHLSLPropertyResolver.cpp      2019-05-23 19:45:15 UTC (rev 245705)
+++ trunk/Source/WebCore/Modules/webgpu/WHLSL/WHLSLPropertyResolver.cpp 2019-05-23 19:54:53 UTC (rev 245706)
</span><span class="lines">@@ -404,11 +404,8 @@
</span><span class="cx">     }
</span><span class="cx">     simplifyLeftValue(modifyResult->innerLeftValue);
</span><span class="cx"> 
</span><del>-    static_assert(sizeof(AST::CommaExpression) <= sizeof(AST::AssignmentExpression), "Assignment expressions need to be able to become comma expressions without updating backreferences");
</del><span class="cx">     Lexer::Token origin = assignmentExpression.origin();
</span><del>-    void* location = &assignmentExpression;
-    assignmentExpression.~AssignmentExpression();
-    auto* commaExpression = new (location) AST::CommaExpression(WTFMove(origin), WTFMove(modifyResult->expressions));
</del><ins>+    auto* commaExpression = AST::replaceWith<AST::CommaExpression>(assignmentExpression, WTFMove(origin), WTFMove(modifyResult->expressions));
</ins><span class="cx">     commaExpression->setType(WTFMove(type));
</span><span class="cx">     commaExpression->setTypeAnnotation(AST::RightValue());
</span><span class="cx"> 
</span><span class="lines">@@ -513,11 +510,8 @@
</span><span class="cx">         UniqueRef<AST::VariableDeclaration> oldVariableDeclaration = readModifyWriteExpression.takeOldValue();
</span><span class="cx">         UniqueRef<AST::VariableDeclaration> newVariableDeclaration = readModifyWriteExpression.takeNewValue();
</span><span class="cx"> 
</span><del>-        static_assert(sizeof(AST::CommaExpression) <= sizeof(AST::ReadModifyWriteExpression), "ReadModifyWrite expressions need to be able to become comma expressions without updating backreferences");
</del><span class="cx">         Lexer::Token origin = readModifyWriteExpression.origin();
</span><del>-        void* location = &readModifyWriteExpression;
-        readModifyWriteExpression.~ReadModifyWriteExpression();
-        auto* commaExpression = new (location) AST::CommaExpression(WTFMove(origin), WTFMove(expressions));
</del><ins>+        auto* commaExpression = AST::replaceWith<AST::CommaExpression>(readModifyWriteExpression, WTFMove(origin), WTFMove(expressions));
</ins><span class="cx">         commaExpression->setType(WTFMove(type));
</span><span class="cx">         commaExpression->setTypeAnnotation(AST::RightValue());
</span><span class="cx"> 
</span><span class="lines">@@ -580,11 +574,8 @@
</span><span class="cx">     UniqueRef<AST::VariableDeclaration> oldVariableDeclaration = readModifyWriteExpression.takeOldValue();
</span><span class="cx">     UniqueRef<AST::VariableDeclaration> newVariableDeclaration = readModifyWriteExpression.takeNewValue();
</span><span class="cx"> 
</span><del>-    static_assert(sizeof(AST::CommaExpression) <= sizeof(AST::ReadModifyWriteExpression), "ReadModifyWrite expressions need to be able to become comma expressions without updating backreferences");
</del><span class="cx">     Lexer::Token origin = readModifyWriteExpression.origin();
</span><del>-    void* location = &readModifyWriteExpression;
-    readModifyWriteExpression.~ReadModifyWriteExpression();
-    auto* commaExpression = new (location) AST::CommaExpression(WTFMove(origin), WTFMove(modifyResult->expressions));
</del><ins>+    auto* commaExpression = AST::replaceWith<AST::CommaExpression>(readModifyWriteExpression, WTFMove(origin), WTFMove(modifyResult->expressions));
</ins><span class="cx">     commaExpression->setType(WTFMove(type));
</span><span class="cx">     commaExpression->setTypeAnnotation(AST::RightValue());
</span><span class="cx"> 
</span><span class="lines">@@ -612,10 +603,7 @@
</span><span class="cx">             callExpression->setTypeAnnotation(AST::RightValue());
</span><span class="cx">             callExpression->setFunction(*anderFunction);
</span><span class="cx"> 
</span><del>-            static_assert(sizeof(AST::DereferenceExpression) <= sizeof(AST::DotExpression), "Dot expressions need to be able to become dereference expressions without updating backreferences");
-            void* location = &dotExpression;
-            dotExpression.~DotExpression();
-            auto* dereferenceExpression = new (location) AST::DereferenceExpression(WTFMove(origin), WTFMove(callExpression));
</del><ins>+            auto* dereferenceExpression = AST::replaceWith<AST::DereferenceExpression>(dotExpression, WTFMove(origin), WTFMove(callExpression));
</ins><span class="cx">             dereferenceExpression->setType(downcast<AST::PointerType>(anderFunction->type()).elementType().clone());
</span><span class="cx">             dereferenceExpression->setTypeAnnotation(AST::LeftValue { downcast<AST::PointerType>(anderFunction->type()).addressSpace() });
</span><span class="cx">             return true;
</span><span class="lines">@@ -655,13 +643,10 @@
</span><span class="cx">         dereferenceExpression->setType(downcast<AST::PointerType>(anderFunction->type()).elementType().clone());
</span><span class="cx">         dereferenceExpression->setTypeAnnotation(AST::LeftValue { AST::AddressSpace::Thread });
</span><span class="cx"> 
</span><del>-        static_assert(sizeof(AST::CommaExpression) <= sizeof(AST::DotExpression), "Dot expressions need to be able to become comma expressions without updating backreferences");
-        void* location = &dotExpression;
-        dotExpression.~DotExpression();
</del><span class="cx">         Vector<UniqueRef<AST::Expression>> expressions;
</span><span class="cx">         expressions.append(WTFMove(assignmentExpression));
</span><span class="cx">         expressions.append(WTFMove(dereferenceExpression));
</span><del>-        auto* commaExpression = new (location) AST::CommaExpression(WTFMove(origin), WTFMove(expressions));
</del><ins>+        auto* commaExpression = AST::replaceWith<AST::CommaExpression>(dotExpression, WTFMove(origin), WTFMove(expressions));
</ins><span class="cx">         commaExpression->setType(downcast<AST::PointerType>(anderFunction->type()).elementType().clone());
</span><span class="cx">         commaExpression->setTypeAnnotation(AST::LeftValue { AST::AddressSpace::Thread });
</span><span class="cx"> 
</span><span class="lines">@@ -669,14 +654,11 @@
</span><span class="cx">         return true;
</span><span class="cx">     }
</span><span class="cx"> 
</span><del>-    static_assert(sizeof(AST::CallExpression) <= sizeof(AST::DotExpression), "Dot expressions need to be able to become call expressions without updating backreferences");
</del><span class="cx">     ASSERT(dotExpression.getterFunction());
</span><span class="cx">     auto& getterFunction = *dotExpression.getterFunction();
</span><span class="cx">     Vector<UniqueRef<AST::Expression>> arguments;
</span><span class="cx">     arguments.append(dotExpression.takeBase());
</span><del>-    void* location = &dotExpression;
-    dotExpression.~DotExpression();
-    auto* callExpression = new (location) AST::CallExpression(WTFMove(origin), String(getterFunction.name()), WTFMove(arguments));
</del><ins>+    auto* callExpression = AST::replaceWith<AST::CallExpression>(dotExpression, WTFMove(origin), String(getterFunction.name()), WTFMove(arguments));
</ins><span class="cx">     callExpression->setFunction(getterFunction);
</span><span class="cx">     callExpression->setType(getterFunction.type().clone());
</span><span class="cx">     callExpression->setTypeAnnotation(AST::RightValue());
</span><span class="lines">@@ -712,10 +694,7 @@
</span><span class="cx">     callExpression->setTypeAnnotation(AST::RightValue());
</span><span class="cx">     callExpression->setFunction(*anderFunction);
</span><span class="cx"> 
</span><del>-    static_assert(sizeof(AST::DereferenceExpression) <= sizeof(AST::DotExpression), "Dot expressions need to be able to become dereference expressions without updating backreferences");
-    void* location = &dotExpression;
-    dotExpression.~DotExpression();
-    auto* dereferenceExpression = new (location) AST::DereferenceExpression(WTFMove(origin), WTFMove(callExpression));
</del><ins>+    auto* dereferenceExpression = AST::replaceWith<AST::DereferenceExpression>(dotExpression, WTFMove(origin), WTFMove(callExpression));
</ins><span class="cx">     dereferenceExpression->setType(downcast<AST::PointerType>(anderFunction->type()).elementType().clone());
</span><span class="cx">     dereferenceExpression->setTypeAnnotation(AST::LeftValue { downcast<AST::PointerType>(anderFunction->type()).addressSpace() });
</span><span class="cx"> }
</span></span></pre>
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