[racket] Difference in speed accessing fields of a struct with

The JIT is able to recognize (the expansion of) simple `struct` forms
and specialize uses of the selectors that are bound by `struct`. Adding
a property in `struct` interferes with that specialization, currently.

At Mon, 23 Jun 2014 22:30:05 -0700, Eric Dobson wrote:
> I added gen:equal+hash to a struct type and noticed that accessing
> fields of the struct got slower, even though I never used equal? or
> hash functions. Is this expected? And if so what is the cause of it?
> 
> #lang racket
> 
> (struct foo (x) #:transparent)
> (struct bar (x) #:transparent
>         #:methods gen:equal+hash
>         [(define (equal-proc x y recur)
>            (recur (bar-x x) (bar-x y)))
>          (define (hash-proc x recur) (recur (bar-x x)))
>          (define (hash2-proc x recur) (recur (bar-x x)))])
> 
> 
> 
> 
> 
> 
> (define N 10000000)
> (define f (foo 3))
> (define b (bar 3))
> (for ((j 5))
>   (time
>     (for ((i (in-range N)))
>       (equal? (foo-x f) (foo-x f))))
>   (time
>     (for ((i (in-range N)))
>       (equal? (bar-x b) (bar-x b)))))
> 
> My timings showing a 10% slowdown.
> 
> cpu time: 296 real time: 296 gc time: 0
> 
> cpu time: 334 real time: 334 gc time: 0
> 
> cpu time: 297 real time: 297 gc time: 0
> 
> cpu time: 340 real time: 340 gc time: 0
> 
> cpu time: 303 real time: 302 gc time: 0
> 
> cpu time: 340 real time: 339 gc time: 0
> 
> cpu time: 292 real time: 292 gc time: 0
> 
> cpu time: 327 real time: 326 gc time: 0
> 
> cpu time: 291 real time: 291 gc time: 0
> 
> cpu time: 323 real time: 322 gc time: 0
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