JavaScriptCore-7601.1.46.3.tar.gz

[apple/javascriptcore.git] / bytecode / ComplexGetStatus.h

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+/*
+ * Copyright (C) 2014 Apple Inc. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
+ * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
+ */
+
+#ifndef ComplexGetStatus_h
+#define ComplexGetStatus_h
+
+#include "IntendedStructureChain.h"
+#include "JSCJSValue.h"
+#include "PropertyOffset.h"
+
+namespace JSC {
+
+class CodeBlock;
+class StructureChain;
+
+// This class is useful for figuring out how to inline a cached get-like access. We
+// say "get-like" because this is appropriate for loading the GetterSetter object in
+// a put_by_id that hits a setter. Notably, this doesn't figure out how to call
+// accessors, or even whether they should be called. What it gives us, is a way of
+// determining how to load the value from the requested property (identified by a
+// StringImpl* uid) from an object of the given structure in the given CodeBlock,
+// assuming that such an access had already been cached by Repatch (and so Repatch had
+// already done a bunch of safety checks). This doesn't reexecute any checks that
+// Repatch would have executed, and for prototype chain accesses, it doesn't ask the
+// objects in the prototype chain whether their getOwnPropertySlot would attempt to
+// intercept the access - so this really is only appropriate if you already know that
+// one of the JITOperations had OK'd this for caching and that Repatch concurred.
+//
+// The typical use pattern is something like:
+//
+//     ComplexGetStatus status = ComplexGetStatus::computeFor(...);
+//     switch (status.kind()) {
+//     case ComplexGetStatus::ShouldSkip:
+//         // Handle the case where this kind of access is possibly safe but wouldn't
+//         // pass the required safety checks. For example, if an IC gives us a list of
+//         // accesses and one of them is ShouldSkip, then we should pretend as if it
+//         // wasn't even there.
+//         break;
+//     case ComplexGetStatus::TakesSlowPath:
+//         // This kind of access is not safe to inline. Bail out of any attempst to
+//         // inline.
+//         break;
+//     case ComplexGetStatus::Inlineable:
+//         // The good stuff goes here. If it's Inlineable then the other properties of
+//         // the 'status' object will tell you everything you need to know about how
+//         // to execute the get-like operation.
+//         break;
+//     }
+
+class ComplexGetStatus {
+public:
+    enum Kind {
+        ShouldSkip,
+        TakesSlowPath,
+        Inlineable
+    };
+    
+    ComplexGetStatus()
+        : m_kind(ShouldSkip)
+        , m_offset(invalidOffset)
+        , m_attributes(UINT_MAX)
+    {
+    }
+    
+    static ComplexGetStatus skip()
+    {
+        return ComplexGetStatus();
+    }
+    
+    static ComplexGetStatus takesSlowPath()
+    {
+        ComplexGetStatus result;
+        result.m_kind = TakesSlowPath;
+        return result;
+    }
+    
+    static ComplexGetStatus computeFor(
+        CodeBlock* profiledBlock, Structure* headStructure, StructureChain* chain,
+        unsigned chainCount, UniquedStringImpl* uid);
+    
+    Kind kind() const { return m_kind; }
+    unsigned attributes() const { return m_attributes; }
+    JSValue specificValue() const { return m_specificValue; }
+    PropertyOffset offset() const { return m_offset; }
+    IntendedStructureChain* chain() const { return m_chain.get(); }
+    
+private:
+    Kind m_kind;
+    PropertyOffset m_offset;
+    unsigned m_attributes;
+    JSValue m_specificValue;
+    RefPtr<IntendedStructureChain> m_chain;
+};
+
+} // namespace JSC
+
+#endif // ComplexGetStatus_h
+