[bpt/guile.git] / test-suite / tests / peval.test

;;;; tree-il.test --- test suite for compiling tree-il   -*- scheme -*-
;;;; Andy Wingo <wingo@pobox.com> --- May 2009
;;;;
;;;; 	Copyright (C) 2009, 2010, 2011, 2012 Free Software Foundation, Inc.
;;;;
;;;; This library is free software; you can redistribute it and/or
;;;; modify it under the terms of the GNU Lesser General Public
;;;; License as published by the Free Software Foundation; either
;;;; version 3 of the License, or (at your option) any later version.
;;;;
;;;; This library is distributed in the hope that it will be useful,
;;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
;;;; Lesser General Public License for more details.
;;;;
;;;; You should have received a copy of the GNU Lesser General Public
;;;; License along with this library; if not, write to the Free Software
;;;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA

(define-module (test-suite tree-il)
  #:use-module (test-suite lib)
  #:use-module (system base compile)
  #:use-module (system base pmatch)
  #:use-module (system base message)
  #:use-module (language tree-il)
  #:use-module (language tree-il primitives)
  #:use-module (language glil)
  #:use-module (srfi srfi-13))

(define peval
  ;; The partial evaluator.
  (@@ (language tree-il optimize) peval))

(define-syntax pass-if-peval
  (syntax-rules (resolve-primitives)
    ((_ in pat)
     (pass-if-peval in pat
                    (compile 'in #:from 'scheme #:to 'tree-il)))
    ((_ resolve-primitives in pat)
     (pass-if-peval in pat
                    (expand-primitives!
                     (resolve-primitives!
                      (compile 'in #:from 'scheme #:to 'tree-il)
                      (current-module)))))
    ((_ in pat code)
     (pass-if 'in
       (let ((evaled (unparse-tree-il (peval code))))
         (pmatch evaled
           (pat #t)
           (_   (pk 'peval-mismatch)
                ((@ (ice-9 pretty-print) pretty-print)
                    'in)
                (newline)
                ((@ (ice-9 pretty-print) pretty-print)
                    evaled)
                (newline)
                ((@ (ice-9 pretty-print) pretty-print)
                    'pat)
                (newline)
                #f)))))))

\f
(with-test-prefix "partial evaluation"

  (pass-if-peval
    ;; First order, primitive.
    (let ((x 1) (y 2)) (+ x y))
    (const 3))

  (pass-if-peval
    ;; First order, thunk.
    (let ((x 1) (y 2))
      (let ((f (lambda () (+ x y))))
        (f)))
    (const 3))

  (pass-if-peval resolve-primitives
    ;; First order, let-values (requires primitive expansion for
    ;; `call-with-values'.)
    (let ((x 0))
      (call-with-values
          (lambda () (if (zero? x) (values 1 2) (values 3 4)))
        (lambda (a b)
          (+ a b))))
    (const 3))

  (pass-if-peval resolve-primitives
    ;; First order, multiple values.
    (let ((x 1) (y 2))
      (values x y))
    (apply (primitive values) (const 1) (const 2)))

  (pass-if-peval resolve-primitives
    ;; First order, multiple values truncated.
    (let ((x (values 1 'a)) (y 2))
      (values x y))
    (apply (primitive values) (const 1) (const 2)))

  (pass-if-peval resolve-primitives
    ;; First order, multiple values truncated.
    (or (values 1 2) 3)
    (const 1))

  (pass-if-peval
    ;; First order, coalesced, mutability preserved.
    (cons 0 (cons 1 (cons 2 (list 3 4 5))))
    (apply (primitive list)
           (const 0) (const 1) (const 2) (const 3) (const 4) (const 5)))

  (pass-if-peval
    ;; First order, coalesced, immutability preserved.
    (cons 0 (cons 1 (cons 2 '(3 4 5))))
    (apply (primitive cons) (const 0)
           (apply (primitive cons) (const 1)
                  (apply (primitive cons) (const 2)
                         (const (3 4 5))))))

  ;; These two tests doesn't work any more because we changed the way we
  ;; deal with constants -- now the algorithm will see a construction as
  ;; being bound to the lexical, so it won't propagate it.  It can't
  ;; even propagate it in the case that it is only referenced once,
  ;; because:
  ;;
  ;;   (let ((x (cons 1 2))) (lambda () x))
  ;;
  ;; is not the same as
  ;;
  ;;   (lambda () (cons 1 2))
  ;;
  ;; Perhaps if we determined that not only was it only referenced once,
  ;; it was not closed over by a lambda, then we could propagate it, and
  ;; re-enable these two tests.
  ;;
  #;
  (pass-if-peval
   ;; First order, mutability preserved.
   (let loop ((i 3) (r '()))
     (if (zero? i)
         r
         (loop (1- i) (cons (cons i i) r))))
   (apply (primitive list)
          (apply (primitive cons) (const 1) (const 1))
          (apply (primitive cons) (const 2) (const 2))
          (apply (primitive cons) (const 3) (const 3))))
  ;;
  ;; See above.
  #;
  (pass-if-peval
   ;; First order, evaluated.
   (let loop ((i 7)
              (r '()))
     (if (<= i 0)
         (car r)
         (loop (1- i) (cons i r))))
   (const 1))

  ;; Instead here are tests for what happens for the above cases: they
  ;; unroll but they don't fold.
  (pass-if-peval
   (let loop ((i 3) (r '()))
     (if (zero? i)
         r
         (loop (1- i) (cons (cons i i) r))))
   (let (r) (_)
        ((apply (primitive list)
                (apply (primitive cons) (const 3) (const 3))))
        (let (r) (_)
             ((apply (primitive cons)
                     (apply (primitive cons) (const 2) (const 2))
                     (lexical r _)))
             (apply (primitive cons)
                    (apply (primitive cons) (const 1) (const 1))
                    (lexical r _)))))

  ;; See above.
  (pass-if-peval
   (let loop ((i 4)
              (r '()))
     (if (<= i 0)
         (car r)
         (loop (1- i) (cons i r))))
   (let (r) (_)
        ((apply (primitive list) (const 4)))
        (let (r) (_)
             ((apply (primitive cons)
                     (const 3)
                     (lexical r _)))
             (let (r) (_)
                  ((apply (primitive cons)
                          (const 2)
                          (lexical r _)))
                  (let (r) (_)
                       ((apply (primitive cons)
                               (const 1)
                               (lexical r _)))
                       (apply (primitive car)
                              (lexical r _)))))))

   ;; Static sums.
  (pass-if-peval
   (let loop ((l '(1 2 3 4)) (sum 0))
     (if (null? l)
         sum
         (loop (cdr l) (+ sum (car l)))))
   (const 10))

  (pass-if-peval resolve-primitives
   (let ((string->chars
          (lambda (s)
            (define (char-at n)
              (string-ref s n))
            (define (len)
              (string-length s))
            (let loop ((i 0))
              (if (< i (len))
                  (cons (char-at i)
                        (loop (1+ i)))
                  '())))))
     (string->chars "yo"))
   (apply (primitive list) (const #\y) (const #\o)))

  (pass-if-peval
    ;; Primitives in module-refs are resolved (the expansion of `pmatch'
    ;; below leads to calls to (@@ (system base pmatch) car) and
    ;; similar, which is what we want to be inlined.)
    (begin
      (use-modules (system base pmatch))
      (pmatch '(a b c d)
        ((a b . _)
         #t)))
    (begin
      (apply . _)
      (const #t)))

  (pass-if-peval
   ;; Mutability preserved.
   ((lambda (x y z) (list x y z)) 1 2 3)
   (apply (primitive list) (const 1) (const 2) (const 3)))

  (pass-if-peval
   ;; Don't propagate effect-free expressions that operate on mutable
   ;; objects.
   (let* ((x (list 1))
          (y (car x)))
     (set-car! x 0)
     y)
   (let (x) (_) ((apply (primitive list) (const 1)))
        (let (y) (_) ((apply (primitive car) (lexical x _)))
             (begin
               (apply (toplevel set-car!) (lexical x _) (const 0))
               (lexical y _)))))
  
  (pass-if-peval
   ;; Don't propagate effect-free expressions that operate on objects we
   ;; don't know about.
   (let ((y (car x)))
     (set-car! x 0)
     y)
   (let (y) (_) ((apply (primitive car) (toplevel x)))
        (begin
          (apply (toplevel set-car!) (toplevel x) (const 0))
          (lexical y _))))
  
  (pass-if-peval
   ;; Infinite recursion
   ((lambda (x) (x x)) (lambda (x) (x x)))
   (let (x) (_)
        ((lambda _
           (lambda-case
            (((x) _ _ _ _ _)
             (apply (lexical x _) (lexical x _))))))
        (apply (lexical x _) (lexical x _))))

  (pass-if-peval
    ;; First order, aliased primitive.
    (let* ((x *) (y (x 1 2))) y)
    (const 2))

  (pass-if-peval
    ;; First order, shadowed primitive.
    (begin
      (define (+ x y) (pk x y))
      (+ 1 2))
    (begin
      (define +
        (lambda (_)
          (lambda-case
           (((x y) #f #f #f () (_ _))
            (apply (toplevel pk) (lexical x _) (lexical y _))))))
      (apply (toplevel +) (const 1) (const 2))))

  (pass-if-peval
    ;; First-order, effects preserved.
    (let ((x 2))
      (do-something!)
      x)
    (begin
      (apply (toplevel do-something!))
      (const 2)))

  (pass-if-peval
    ;; First order, residual bindings removed.
    (let ((x 2) (y 3))
      (* (+ x y) z))
    (apply (primitive *) (const 5) (toplevel z)))

  (pass-if-peval
    ;; First order, with lambda.
    (define (foo x)
      (define (bar z) (* z z))
      (+ x (bar 3)))
    (define foo
      (lambda (_)
        (lambda-case
         (((x) #f #f #f () (_))
          (apply (primitive +) (lexical x _) (const 9)))))))

  (pass-if-peval
    ;; First order, with lambda inlined & specialized twice.
    (let ((f (lambda (x y)
               (+ (* x top) y)))
          (x 2)
          (y 3))
      (+ (* x (f x y))
         (f something x)))
    (apply (primitive +)
           (apply (primitive *)
                  (const 2)
                  (apply (primitive +)  ; (f 2 3)
                         (apply (primitive *)
                                (const 2)
                                (toplevel top))
                         (const 3)))
           (let (x) (_) ((toplevel something))                    ; (f something 2)
                ;; `something' is not const, so preserve order of
                ;; effects with a lexical binding.
                (apply (primitive +)
                       (apply (primitive *)
                              (lexical x _)
                              (toplevel top))
                       (const 2)))))
  
  (pass-if-peval
   ;; First order, with lambda inlined & specialized 3 times.
   (let ((f (lambda (x y) (if (> x 0) y x))))
     (+ (f -1 0)
        (f 1 0)
        (f -1 y)
        (f 2 y)
        (f z y)))
   (apply (primitive +)
          (const -1)                      ; (f -1 0)
          (const 0)                       ; (f 1 0)
          (begin (toplevel y) (const -1)) ; (f -1 y)
          (toplevel y)                    ; (f 2 y)
          (let (x y) (_ _) ((toplevel z) (toplevel y)) ; (f z y)
               (if (apply (primitive >) (lexical x _) (const 0))
                   (lexical y _)
                   (lexical x _)))))

  (pass-if-peval
    ;; First order, conditional.
    (let ((y 2))
      (lambda (x)
        (if (> y 0)
            (display x)
            'never-reached)))
    (lambda ()
      (lambda-case
       (((x) #f #f #f () (_))
        (apply (toplevel display) (lexical x _))))))

  (pass-if-peval
    ;; First order, recursive procedure.
    (letrec ((fibo (lambda (n)
                     (if (<= n 1)
                         n
                         (+ (fibo (- n 1))
                            (fibo (- n 2)))))))
      (fibo 4))
    (const 3))

  (pass-if-peval
   ;; Don't propagate toplevel references, as intervening expressions
   ;; could alter their bindings.
   (let ((x top))
     (foo)
     x)
   (let (x) (_) ((toplevel top))
        (begin
          (apply (toplevel foo))
          (lexical x _))))

  (pass-if-peval
    ;; Higher order.
    ((lambda (f x)
       (f (* (car x) (cadr x))))
     (lambda (x)
       (+ x 1))
     '(2 3))
    (const 7))

  (pass-if-peval
    ;; Higher order with optional argument (default value).
    ((lambda* (f x #:optional (y 0))
       (+ y (f (* (car x) (cadr x)))))
     (lambda (x)
       (+ x 1))
     '(2 3))
    (const 7))

  (pass-if-peval
    ;; Higher order with optional argument (caller-supplied value).
    ((lambda* (f x #:optional (y 0))
       (+ y (f (* (car x) (cadr x)))))
     (lambda (x)
       (+ x 1))
     '(2 3)
     35)
    (const 42))

  (pass-if-peval
    ;; Higher order with optional argument (side-effecting default
    ;; value).
    ((lambda* (f x #:optional (y (foo)))
       (+ y (f (* (car x) (cadr x)))))
     (lambda (x)
       (+ x 1))
     '(2 3))
    (let (y) (_) ((apply (toplevel foo)))
         (apply (primitive +) (lexical y _) (const 7))))

  (pass-if-peval
    ;; Higher order with optional argument (caller-supplied value).
    ((lambda* (f x #:optional (y (foo)))
       (+ y (f (* (car x) (cadr x)))))
     (lambda (x)
       (+ x 1))
     '(2 3)
     35)
    (const 42))

  (pass-if-peval
    ;; Higher order.
    ((lambda (f) (f x)) (lambda (x) x))
    (toplevel x))

  (pass-if-peval
    ;; Bug reported at
    ;; <https://lists.gnu.org/archive/html/bug-guile/2011-09/msg00019.html>.
    (let ((fold (lambda (f g) (f (g top)))))
      (fold 1+ (lambda (x) x)))
    (apply (primitive 1+) (toplevel top)))
  
  (pass-if-peval
    ;; Procedure not inlined when residual code contains recursive calls.
    ;; <http://debbugs.gnu.org/9542>
    (letrec ((fold (lambda (f x3 b null? car cdr)
                     (if (null? x3)
                         b
                         (f (car x3) (fold f (cdr x3) b null? car cdr))))))
      (fold * x 1 zero? (lambda (x1) x1) (lambda (x2) (- x2 1))))
    (letrec (fold) (_) (_)
            (apply (lexical fold _)
                   (primitive *)
                   (toplevel x)
                   (const 1)
                   (primitive zero?)
                   (lambda ()
                     (lambda-case
                      (((x1) #f #f #f () (_))
                       (lexical x1 _))))
                   (lambda ()
                     (lambda-case
                      (((x2) #f #f #f () (_))
                       (apply (primitive -) (lexical x2 _) (const 1))))))))

  (pass-if "inlined lambdas are alpha-renamed"
    ;; In this example, `make-adder' is inlined more than once; thus,
    ;; they should use different gensyms for their arguments, because
    ;; the various optimization passes assume uniquely-named variables.
    ;;
    ;; Bug reported at
    ;; <https://lists.gnu.org/archive/html/bug-guile/2011-09/msg00019.html> and
    ;; <https://lists.gnu.org/archive/html/bug-guile/2011-09/msg00029.html>.
    (pmatch (unparse-tree-il
             (peval (compile
                     '(let ((make-adder
                             (lambda (x) (lambda (y) (+ x y)))))
                        (cons (make-adder 1) (make-adder 2)))
                     #:to 'tree-il)))
      ((apply (primitive cons)
              (lambda ()
                (lambda-case
                 (((y) #f #f #f () (,gensym1))
                  (apply (primitive +)
                         (const 1)
                         (lexical y ,ref1)))))
              (lambda ()
                (lambda-case
                 (((y) #f #f #f () (,gensym2))
                  (apply (primitive +)
                         (const 2)
                         (lexical y ,ref2))))))
       (and (eq? gensym1 ref1)
            (eq? gensym2 ref2)
            (not (eq? gensym1 gensym2))))
      (_ #f)))

  (pass-if-peval
   ;; Unused letrec bindings are pruned.
   (letrec ((a (lambda () (b)))
            (b (lambda () (a)))
            (c (lambda (x) x)))
     (c 10))
   (const 10))

  (pass-if-peval
   ;; Unused letrec bindings are pruned.
   (letrec ((a (foo!))
            (b (lambda () (a)))
            (c (lambda (x) x)))
     (c 10))
   (begin (apply (toplevel foo!))
          (const 10)))

  (pass-if-peval
    ;; Higher order, mutually recursive procedures.
    (letrec ((even? (lambda (x)
                      (or (= 0 x)
                          (odd? (- x 1)))))
             (odd?  (lambda (x)
                      (not (even? x)))))
      (and (even? 4) (odd? 7)))
    (const #t))

  (pass-if-peval
    ;; Memv with constants.
    (memv 1 '(3 2 1))
    (const '(1)))

  (pass-if-peval
    ;; Memv with non-constant list.  It could fold but doesn't
    ;; currently.
    (memv 1 (list 3 2 1))
    (apply (primitive memv)
           (const 1)
           (apply (primitive list) (const 3) (const 2) (const 1))))

  (pass-if-peval
    ;; Memv with non-constant key, constant list, test context
    (case foo
      ((3 2 1) 'a)
      (else 'b))
    (let (key) (_) ((toplevel foo))
         (if (if (apply (primitive eqv?) (lexical key _) (const 3))
                 (const #t)
                 (if (apply (primitive eqv?) (lexical key _) (const 2))
                     (const #t)
                     (apply (primitive eqv?) (lexical key _) (const 1))))
             (const a)
             (const b))))

  (pass-if-peval
    ;; Memv with non-constant key, empty list, test context.  Currently
    ;; doesn't fold entirely.
    (case foo
      (() 'a)
      (else 'b))
    (begin (toplevel foo) (const b)))

  ;;
  ;; Below are cases where constant propagation should bail out.
  ;;

  (pass-if-peval
    ;; Non-constant lexical is not propagated.
    (let ((v (make-vector 6 #f)))
      (lambda (n)
        (vector-set! v n n)))
    (let (v) (_)
         ((apply (toplevel make-vector) (const 6) (const #f)))
         (lambda ()
           (lambda-case
            (((n) #f #f #f () (_))
             (apply (toplevel vector-set!)
                    (lexical v _) (lexical n _) (lexical n _)))))))

  (pass-if-peval
    ;; Mutable lexical is not propagated.
    (let ((v (vector 1 2 3)))
      (lambda ()
        v))
    (let (v) (_)
         ((apply (primitive vector) (const 1) (const 2) (const 3)))
         (lambda ()
           (lambda-case
            ((() #f #f #f () ())
             (lexical v _))))))

  (pass-if-peval
    ;; Lexical that is not provably pure is not inlined nor propagated.
    (let* ((x (if (> p q) (frob!) (display 'chbouib)))
           (y (* x 2)))
      (+ x x y))
    (let (x) (_) ((if (apply (primitive >) (toplevel p) (toplevel q))
                      (apply (toplevel frob!))
                      (apply (toplevel display) (const chbouib))))
         (let (y) (_) ((apply (primitive *) (lexical x _) (const 2)))
              (apply (primitive +)
                     (lexical x _) (lexical x _) (lexical y _)))))

  (pass-if-peval
    ;; Non-constant arguments not propagated to lambdas.
    ((lambda (x y z)
       (vector-set! x 0 0)
       (set-car! y 0)
       (set-cdr! z '()))
     (vector 1 2 3)
     (make-list 10)
     (list 1 2 3))
    (let (x y z) (_ _ _)
         ((apply (primitive vector) (const 1) (const 2) (const 3))
          (apply (toplevel make-list) (const 10))
          (apply (primitive list) (const 1) (const 2) (const 3)))
         (begin
           (apply (toplevel vector-set!)
                  (lexical x _) (const 0) (const 0))
           (apply (toplevel set-car!)
                  (lexical y _) (const 0))
           (apply (toplevel set-cdr!)
                  (lexical z _) (const ())))))

  (pass-if-peval
   (let ((foo top-foo) (bar top-bar))
     (let* ((g (lambda (x y) (+ x y)))
            (f (lambda (g x) (g x x))))
       (+ (f g foo) (f g bar))))
   (let (foo bar) (_ _) ((toplevel top-foo) (toplevel top-bar))
        (apply (primitive +)
               (apply (primitive +) (lexical foo _) (lexical foo _))
               (apply (primitive +) (lexical bar _) (lexical bar _)))))

  (pass-if-peval
    ;; Fresh objects are not turned into constants, nor are constants
    ;; turned into fresh objects.
    (let* ((c '(2 3))
           (x (cons 1 c))
           (y (cons 0 x)))
      y)
    (let (x) (_) ((apply (primitive cons) (const 1) (const (2 3))))
         (apply (primitive cons) (const 0) (lexical x _))))

  (pass-if-peval
    ;; Bindings mutated.
    (let ((x 2))
      (set! x 3)
      x)
    (let (x) (_) ((const 2))
         (begin
           (set! (lexical x _) (const 3))
           (lexical x _))))

  (pass-if-peval
    ;; Bindings mutated.
    (letrec ((x 0)
             (f (lambda ()
                  (set! x (+ 1 x))
                  x)))
      (frob f) ; may mutate `x'
      x)
    (letrec (x) (_) ((const 0))
            (begin
              (apply (toplevel frob) (lambda _ _))
              (lexical x _))))

  (pass-if-peval
    ;; Bindings mutated.
    (letrec ((f (lambda (x)
                  (set! f (lambda (_) x))
                  x)))
      (f 2))
    (letrec _ . _))

  (pass-if-peval
    ;; Bindings possibly mutated.
    (let ((x (make-foo)))
      (frob! x) ; may mutate `x'
      x)
    (let (x) (_) ((apply (toplevel make-foo)))
         (begin
           (apply (toplevel frob!) (lexical x _))
           (lexical x _))))

  (pass-if-peval
    ;; Inlining stops at recursive calls with dynamic arguments.
    (let loop ((x x))
      (if (< x 0) x (loop (1- x))))
    (letrec (loop) (_) ((lambda (_)
                          (lambda-case
                           (((x) #f #f #f () (_))
                            (if _ _
                                (apply (lexical loop _)
                                       (apply (primitive 1-)
                                              (lexical x _))))))))
            (apply (lexical loop _) (toplevel x))))

  (pass-if-peval
    ;; Recursion on the 2nd argument is fully evaluated.
    (let ((x (top)))
      (let loop ((x x) (y 10))
        (if (> y 0)
            (loop x (1- y))
            (foo x y))))
    (let (x) (_) ((apply (toplevel top)))
         (apply (toplevel foo) (lexical x _) (const 0))))

  (pass-if-peval
    ;; Inlining aborted when residual code contains recursive calls.
    ;;
    ;; <http://debbugs.gnu.org/9542>
    (let loop ((x x) (y 0))
      (if (> y 0)
          (loop (1- x) (1- y))
          (if (< x 0)
              x
              (loop (1+ x) (1+ y)))))
    (letrec (loop) (_) ((lambda (_)
                          (lambda-case
                           (((x y) #f #f #f () (_ _))
                            (if (apply (primitive >)
                                       (lexical y _) (const 0))
                                _ _)))))
            (apply (lexical loop _) (toplevel x) (const 0))))

  (pass-if-peval
    ;; Infinite recursion: `peval' gives up and leaves it as is.
    (letrec ((f (lambda (x) (g (1- x))))
             (g (lambda (x) (h (1+ x))))
             (h (lambda (x) (f x))))
      (f 0))
    (letrec _ . _))

  (pass-if-peval
    ;; Infinite recursion: all the arguments to `loop' are static, but
    ;; unrolling it would lead `peval' to enter an infinite loop.
    (let loop ((x 0))
      (and (< x top)
           (loop (1+ x))))
    (letrec (loop) (_) ((lambda . _))
            (apply (lexical loop _) (const 0))))

  (pass-if-peval
    ;; This test checks that the `start' binding is indeed residualized.
    ;; See the `referenced?' procedure in peval's `prune-bindings'.
    (let ((pos 0))
      (let ((here (let ((start pos)) (lambda () start))))
        (set! pos 1) ;; Cause references to `pos' to residualize.
        (here)))
    (let (pos) (_) ((const 0))
         (let (here) (_) (_)
              (begin
                (set! (lexical pos _) (const 1))
                (apply (lexical here _))))))
  
  (pass-if-peval
   ;; FIXME: should this one residualize the binding?
   (letrec ((a a))
     1)
   (const 1))

  (pass-if-peval
   ;; This is a fun one for peval to handle.
   (letrec ((a a))
     a)
   (letrec (a) (_) ((lexical a _))
           (lexical a _)))

  (pass-if-peval
   ;; Another interesting recursive case.
   (letrec ((a b) (b a))
     a)
   (letrec (a) (_) ((lexical a _))
           (lexical a _)))

  (pass-if-peval
   ;; Another pruning case, that `a' is residualized.
   (letrec ((a (lambda () (a)))
            (b (lambda () (a)))
            (c (lambda (x) x)))
     (let ((d (foo b)))
       (c d)))

   ;; "b c a" is the current order that we get with unordered letrec,
   ;; but it's not important to this test, so if it changes, just adapt
   ;; the test.
   (letrec (b c a) (_ _ _)
     ((lambda _
        (lambda-case
         ((() #f #f #f () ())
          (apply (lexical a _)))))
      (lambda _
        (lambda-case
         (((x) #f #f #f () (_))
          (lexical x _))))
      (lambda _
        (lambda-case
         ((() #f #f #f () ())
          (apply (lexical a _))))))
     (let (d)
       (_)
       ((apply (toplevel foo) (lexical b _)))
       (apply (lexical c _)
              (lexical d _)))))

  (pass-if-peval
   ;; In this case, we can prune the bindings.  `a' ends up being copied
   ;; because it is only referenced once in the source program.  Oh
   ;; well.
   (letrec* ((a (lambda (x) (top x)))
             (b (lambda () a)))
     (foo (b) (b)))
   (apply (toplevel foo)
          (lambda _
            (lambda-case
             (((x) #f #f #f () (_))
              (apply (toplevel top) (lexical x _)))))
          (lambda _
            (lambda-case
             (((x) #f #f #f () (_))
              (apply (toplevel top) (lexical x _)))))))
  
  (pass-if-peval
   ;; Constant folding: cons of #nil does not make list
   (cons 1 #nil)
   (apply (primitive cons) (const 1) (const '#nil)))
  
  (pass-if-peval
    ;; Constant folding: cons
   (begin (cons 1 2) #f)
   (const #f))
  
  (pass-if-peval
    ;; Constant folding: cons
   (begin (cons (foo) 2) #f)
   (begin (apply (toplevel foo)) (const #f)))
  
  (pass-if-peval
    ;; Constant folding: cons
   (if (cons 0 0) 1 2)
   (const 1))
  
  (pass-if-peval
   ;; Constant folding: car+cons
   (car (cons 1 0))
   (const 1))
  
  (pass-if-peval
   ;; Constant folding: cdr+cons
   (cdr (cons 1 0))
   (const 0))
  
  (pass-if-peval
   ;; Constant folding: car+cons, impure
   (car (cons 1 (bar)))
   (begin (apply (toplevel bar)) (const 1)))
  
  (pass-if-peval
   ;; Constant folding: cdr+cons, impure
   (cdr (cons (bar) 0))
   (begin (apply (toplevel bar)) (const 0)))
  
  (pass-if-peval
   ;; Constant folding: car+list
   (car (list 1 0))
   (const 1))
  
  (pass-if-peval
   ;; Constant folding: cdr+list
   (cdr (list 1 0))
   (apply (primitive list) (const 0)))
  
  (pass-if-peval
   ;; Constant folding: car+list, impure
   (car (list 1 (bar)))
   (begin (apply (toplevel bar)) (const 1)))
  
  (pass-if-peval
   ;; Constant folding: cdr+list, impure
   (cdr (list (bar) 0))
   (begin (apply (toplevel bar)) (apply (primitive list) (const 0))))
  
  (pass-if-peval
   resolve-primitives
   ;; Non-constant guards get lexical bindings.
   (dynamic-wind foo (lambda () bar) baz)
   (let (pre post) (_ _) ((toplevel foo) (toplevel baz))
        (dynwind (lexical pre _) (toplevel bar) (lexical post _))))
  
  (pass-if-peval
   resolve-primitives
   ;; Constant guards don't need lexical bindings.
   (dynamic-wind (lambda () foo) (lambda () bar) (lambda () baz))
   (dynwind
    (lambda ()
      (lambda-case
       ((() #f #f #f () ()) (toplevel foo))))
    (toplevel bar)
    (lambda ()
      (lambda-case
       ((() #f #f #f () ()) (toplevel baz))))))
  
  (pass-if-peval
   resolve-primitives
   ;; Prompt is removed if tag is unreferenced
   (let ((tag (make-prompt-tag)))
     (call-with-prompt tag
                       (lambda () 1)
                       (lambda args args)))
   (const 1))
  
  (pass-if-peval
   resolve-primitives
   ;; Prompt is removed if tag is unreferenced, with explicit stem
   (let ((tag (make-prompt-tag "foo")))
     (call-with-prompt tag
                       (lambda () 1)
                       (lambda args args)))
   (const 1))

  ;; Handler lambda inlined
  (pass-if-peval
   resolve-primitives
   (call-with-prompt tag
                     (lambda () 1)
                     (lambda (k x) x))
   (prompt (toplevel tag)
           (const 1)
           (lambda-case
            (((k x) #f #f #f () (_ _))
             (lexical x _)))))

  ;; Handler toplevel not inlined
  (pass-if-peval
   resolve-primitives
   (call-with-prompt tag
                     (lambda () 1)
                     handler)
   (let (handler) (_) ((toplevel handler))
        (prompt (toplevel tag)
                (const 1)
                (lambda-case
                 ((() #f args #f () (_))
                  (apply (primitive @apply)
                         (lexical handler _)
                         (lexical args _)))))))

  (pass-if-peval
   resolve-primitives
   ;; `while' without `break' or `continue' has no prompts and gets its
   ;; condition folded.  Unfortunately the outer `lp' does not yet get
   ;; elided.
   (while #t #t)
   (letrec (lp) (_)
           ((lambda _
              (lambda-case
               ((() #f #f #f () ())
                (letrec (loop) (_)
                        ((lambda _
                           (lambda-case
                            ((() #f #f #f () ())
                             (apply (lexical loop _))))))
                        (apply (lexical loop _)))))))
           (apply (lexical lp _))))

  (pass-if-peval
   resolve-primitives
   (lambda (a . rest)
     (apply (lambda (x y) (+ x y))
            a rest))
   (lambda _
     (lambda-case
      (((x y) #f #f #f () (_ _))
       _))))

  (pass-if-peval resolve-primitives
    (car '(1 2))
    (const 1)))