ResolveInstanceMethond is called twice if there is no IMP added.

methodSignatureForSeletor
class_getInstanceMethod
class_getInstanceMethod

// No implementation found. Try method resolver once.

    if(resolver && ! triedResolver) { runtimeLock.unlock(); _class_resolveMethod(cls, sel, inst); runtimeLock.lock();// Don't cache the result; we don't hold the lock so it may have 
        // changed already. Re-do the search from scratch instead.
        triedResolver = YES;
        goto retry;
    }

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