Make alloc policy realloc() easier to implement (bug 664353, r=luke).

js/src/jsalloc.h

@@ -52,6 +52,9 @@ namespace js {
  *      Responsible for OOM reporting on NULL return value.
  *  - void *realloc_(size_t)
  *      Responsible for OOM reporting on NULL return value.
+ *      The *used* bytes of the previous buffer is passed in
+ *      (rather than the old allocation size), in addition to
+ *      the *new* allocation size requested.
  *  - void free_(void *)
  *  - reportAllocOverflow()
  *      Called on overflow before the container returns NULL.
@@ -62,7 +65,7 @@ class SystemAllocPolicy
 {
   public:
     void *malloc_(size_t bytes) { return js_malloc(bytes); }
-    void *realloc_(void *p, size_t bytes) { return js_realloc(p, bytes); }
+    void *realloc_(void *p, size_t oldBytes, size_t bytes) { return js_realloc(p, bytes); }
     void free_(void *p) { js_free(p); }
     void reportAllocOverflow() const {}
 };
@@ -100,7 +103,7 @@ class ContextAllocPolicy
         return p;
     }
 
-    void *realloc_(void *p, size_t bytes) {
+    void *realloc_(void *p, size_t oldBytes, size_t bytes) {
         void *p2 = js_realloc(p, bytes);
         if (JS_UNLIKELY(!p2))
             p2 = onOutOfMemory(p2, bytes);

js/src/jsvector.h

@@ -158,7 +158,8 @@ struct VectorImpl<T, N, AP, true>
     static inline bool growTo(Vector<T,N,AP> &v, size_t newcap) {
         JS_ASSERT(!v.usingInlineStorage());
         size_t bytes = sizeof(T) * newcap;
-        T *newbuf = reinterpret_cast<T *>(v.realloc_(v.mBegin, bytes));
+        size_t oldBytes = sizeof(T) * v.mLength;
+        T *newbuf = reinterpret_cast<T *>(v.realloc_(v.mBegin, oldBytes, bytes));
         if (!newbuf)
             return false;
         v.mBegin = newbuf;

js/src/methodjit/MethodJIT.h

@@ -286,8 +286,8 @@ class CompilerAllocPolicy : public ContextAllocPolicy
     CompilerAllocPolicy(JSContext *cx, Compiler &compiler);
 
     void *malloc_(size_t bytes) { return checkAlloc(ContextAllocPolicy::malloc_(bytes)); }
-    void *realloc_(void *p, size_t bytes) {
-        return checkAlloc(ContextAllocPolicy::realloc_(p, bytes));
+    void *realloc_(void *p, size_t oldBytes, size_t bytes) {
+        return checkAlloc(ContextAllocPolicy::realloc_(p, oldBytes, bytes));
     }
 };