Bug 909989 - Part 1: Implement DataPtr to refer to objects in runtimeData_. (r=nbp)

js/src/jit/CodeGenerator.cpp

@@ -95,7 +95,7 @@ class OutOfLineUpdateCache :
 bool
 CodeGeneratorShared::addCache(LInstruction *lir, size_t cacheIndex)
 {
-    IonCache *cache = reinterpret_cast<IonCache *>(&runtimeData_[cacheIndex]);
+    DataPtr<IonCache> cache(this, cacheIndex);
     MInstruction *mir = lir->mirRaw()->toInstruction();
     if (mir->resumePoint())
         cache->setScriptedLocation(mir->block()->info().script(),
@@ -119,7 +119,7 @@ CodeGeneratorShared::addCache(LInstruction *lir, size_t cacheIndex)
 bool
 CodeGenerator::visitOutOfLineCache(OutOfLineUpdateCache *ool)
 {
-    IonCache *cache = reinterpret_cast<IonCache *>(&runtimeData_[ool->getCacheIndex()]);
+    DataPtr<IonCache> cache(this, ool->getCacheIndex());
 
     // Register the location of the OOL path in the IC.
     cache->setFallbackLabel(masm.labelForPatch());

js/src/jit/shared/CodeGenerator-shared.h

@@ -205,6 +205,33 @@ class CodeGeneratorShared : public LInstructionVisitor
     void verifyOsiPointRegs(LSafepoint *safepoint);
 #endif
 
+  public:
+
+    // When appending to runtimeData_, the vector might realloc, leaving pointers
+    // int the origianl vector stale and unusable. DataPtr acts like a pointer,
+    // but allows safety in the face of potentially realloc'ing vector appends.
+    friend class DataPtr;
+    template <typename T>
+    class DataPtr
+    {
+        CodeGeneratorShared *cg_;
+        size_t index_;
+
+        T *lookup() {
+            return reinterpret_cast<T *>(&cg_->runtimeData_[index_]);
+        }
+      public:
+        DataPtr(CodeGeneratorShared *cg, size_t index)
+          : cg_(cg), index_(index) { }
+
+        T * operator ->() {
+            return lookup();
+        }
+        T * operator *() {
+            return lookup();
+        }
+    };
+
   protected:
 
     size_t allocateData(size_t size) {