X-Git-Url: http://git.hcoop.net/bpt/guile.git/blobdiff_plain/eebcacf41c4fe58ad8c9388d516a99f59212b223..26d148066f9cb20e395a7dc4fefdf2e2ef0b2fb0:/module/language/tree-il/peval.scm

diff --git a/module/language/tree-il/peval.scm b/module/language/tree-il/peval.scm
index 7f8575e58..fe637f0a5 100644
--- a/module/language/tree-il/peval.scm
+++ b/module/language/tree-il/peval.scm
@@ -1,6 +1,6 @@
 ;;; Tree-IL partial evaluator
 
-;; Copyright (C) 2011, 2012 Free Software Foundation, Inc.
+;; Copyright (C) 2011, 2012, 2013 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
@@ -19,6 +19,7 @@
 (define-module (language tree-il peval)
   #:use-module (language tree-il)
   #:use-module (language tree-il primitives)
+  #:use-module (language tree-il effects)
   #:use-module (ice-9 vlist)
   #:use-module (ice-9 match)
   #:use-module (srfi srfi-1)
@@ -108,9 +109,8 @@
     (($ <primitive-ref>) #t)
     (($ <module-ref>) #t)
     (($ <toplevel-ref>) #t)
-    (($ <application> _
-        ($ <primitive-ref> _ (? singly-valued-primitive?))) #t)
-    (($ <application> _ ($ <primitive-ref> _ 'values) (val)) #t)
+    (($ <primcall> _ (? singly-valued-primitive?)) #t)
+    (($ <primcall> _ 'values (val)) #t)
     (($ <lambda>) #t)
     (else #f)))
 
@@ -118,9 +118,7 @@
   "Discard all but the first value of X."
   (if (singly-valued-expression? x)
       x
-      (make-application (tree-il-src x)
-                        (make-primitive-ref #f 'values)
-                        (list x))))
+      (make-primcall (tree-il-src x) 'values (list x))))
 
 ;; Peval will do a one-pass analysis on the source program to determine
 ;; the set of assigned lexicals, and to identify unreferenced and
@@ -287,29 +285,38 @@
 ;; TODO: Record value size in operand structure?
 ;; 
 (define-record-type <operand>
-  (%make-operand var sym visit source visit-count residualize?
-                 copyable? residual-value constant-value)
+  (%make-operand var sym visit source visit-count use-count
+                 copyable? residual-value constant-value alias-value)
   operand?
   (var operand-var)
   (sym operand-sym)
   (visit %operand-visit)
   (source operand-source)
   (visit-count operand-visit-count set-operand-visit-count!)
-  (residualize? operand-residualize? set-operand-residualize?!)
+  (use-count operand-use-count set-operand-use-count!)
   (copyable? operand-copyable? set-operand-copyable?!)
   (residual-value operand-residual-value %set-operand-residual-value!)
-  (constant-value operand-constant-value set-operand-constant-value!))
+  (constant-value operand-constant-value set-operand-constant-value!)
+  (alias-value operand-alias-value set-operand-alias-value!))
 
-(define* (make-operand var sym #:optional source visit)
-  ;; Bind SYM to VAR, with value SOURCE.  Bound operands are considered
-  ;; copyable until we prove otherwise.  If we have a source expression,
-  ;; truncate it to one value.  Copy propagation does not work on
-  ;; multiply-valued expressions.
+(define* (make-operand var sym #:optional source visit alias)
+  ;; Bind SYM to VAR, with value SOURCE.  Unassigned bound operands are
+  ;; considered copyable until we prove otherwise.  If we have a source
+  ;; expression, truncate it to one value.  Copy propagation does not
+  ;; work on multiply-valued expressions.
   (let ((source (and=> source truncate-values)))
-    (%make-operand var sym visit source 0 #f (and source #t) #f #f)))
+    (%make-operand var sym visit source 0 0
+                   (and source (not (var-set? var))) #f #f
+                   (and (not (var-set? var)) alias))))
 
-(define (make-bound-operands vars syms sources visit)
-  (map (lambda (x y z) (make-operand x y z visit)) vars syms sources))
+(define* (make-bound-operands vars syms sources visit #:optional aliases)
+  (if aliases
+      (map (lambda (name sym source alias)
+             (make-operand name sym source visit alias))
+           vars syms sources aliases)
+      (map (lambda (name sym source)
+             (make-operand name sym source visit #f))
+           vars syms sources)))
 
 (define (make-unbound-operands vars syms)
   (map make-operand vars syms))
@@ -318,7 +325,7 @@
   (%set-operand-residual-value!
    op
    (match val
-    (($ <application> src ($ <primitive-ref> _ 'values) (first))
+    (($ <primcall> src 'values (first))
      ;; The continuation of a residualized binding does not need the
      ;; introduced `values' node, so undo the effects of truncation.
      first)
@@ -343,7 +350,12 @@
                 (if (or counter (and (not effort-limit) (not size-limit)))
                     ((%operand-visit op) (operand-source op) counter ctx)
                     (let/ec k
-                      (define (abort) (k #f))
+                      (define (abort)
+                        ;; If we abort when visiting the value in a
+                        ;; fresh context, we won't succeed in any future
+                        ;; attempt, so don't try to copy it again.
+                        (set-operand-copyable?! op #f)
+                        (k #f))
                       ((%operand-visit op)
                        (operand-source op) 
                        (make-top-counter effort-limit size-limit abort op)
@@ -386,18 +398,15 @@ top-level bindings from ENV and return the resulting expression."
 
   (define local-toplevel-env
     ;; The top-level environment of the module being compiled.
-    (match exp
-      (($ <toplevel-define> _ name)
-       (vhash-consq name #t env))
-      (($ <sequence> _ exps)
-       (fold (lambda (x r)
-               (match x
-                 (($ <toplevel-define> _ name)
-                  (vhash-consq name #t r))
-                 (_ r)))
-             env
-             exps))
-      (_ env)))
+    (let ()
+      (define (env-folder x env)
+        (match x
+          (($ <toplevel-define> _ name)
+           (vhash-consq name #t env))
+          (($ <seq> _ head tail)
+           (env-folder tail (env-folder head env)))
+          (_ env)))
+      (env-folder exp vlist-null)))
 
   (define (local-toplevel? name)
     (vhash-assq name local-toplevel-env))
@@ -417,11 +426,18 @@ top-level bindings from ENV and return the resulting expression."
   (define (fresh-gensyms vars)
     (map (lambda (var)
            (let ((new (gensym (string-append (symbol->string (var-name var))
-                                             "-"))))
+                                             " "))))
              (set! store (vhash-consq new var store))
              new))
          vars))
 
+  (define (fresh-temporaries ls)
+    (map (lambda (elt)
+           (let ((new (gensym "tmp ")))
+             (record-new-temporary! 'tmp new 1)
+             new))
+         ls))
+
   (define (assigned-lexical? sym)
     (var-set? (lookup-var sym)))
 
@@ -442,9 +458,18 @@ top-level bindings from ENV and return the resulting expression."
     (let ((x (vhash-assq new store)))
       (if x (cdr x) new)))
 
+  (define (record-operand-use op)
+    (set-operand-use-count! op (1+ (operand-use-count op))))
+
+  (define (unrecord-operand-uses op n)
+    (let ((count (- (operand-use-count op) n)))
+      (when (zero? count)
+        (set-operand-residual-value! op #f))
+      (set-operand-use-count! op count)))
+
   (define* (residualize-lexical op #:optional ctx val)
     (log 'residualize op)
-    (set-operand-residualize?! op #t)
+    (record-operand-use op)
     (if (memq ctx '(value values))
         (set-operand-residual-value! op val))
     (make-lexical-ref #f (var-name (operand-var op)) (operand-sym op)))
@@ -461,15 +486,13 @@ top-level bindings from ENV and return the resulting expression."
               (values #t results))))
         (lambda _
           (values #f '()))))
-
     (define (make-values src values)
       (match values
         ((single) single)               ; 1 value
         ((_ ...)                        ; 0, or 2 or more values
-         (make-application src (make-primitive-ref src 'values)
-                           values))))
+         (make-primcall src 'values values))))
     (define (residualize-call)
-      (make-application src (make-primitive-ref #f name) args))
+      (make-primcall src name args))
     (cond
      ((every const? args)
       (let-values (((success? values)
@@ -492,7 +515,7 @@ top-level bindings from ENV and return the resulting expression."
      (else
       (residualize-call))))
 
-  (define (inline-values exp src names gensyms body)
+  (define (inline-values src exp nmin nmax consumer)
     (let loop ((exp exp))
       (match exp
         ;; Some expression types are always singly-valued.
@@ -508,24 +531,22 @@ top-level bindings from ENV and return the resulting expression."
              ($ <toplevel-set>)         ; could return zero values in
              ($ <toplevel-define>)      ; the future
              ($ <module-set>)           ;
-             ($ <dynset>))              ; 
-         (and (= (length names) 1)
-              (make-let src names gensyms (list exp) body)))
-        (($ <application> src
-            ($ <primitive-ref> _ (? singly-valued-primitive? name)))
-         (and (= (length names) 1)
-              (make-let src names gensyms (list exp) body)))
+             ($ <dynset>)               ;
+             ($ <primcall> src (? singly-valued-primitive?)))
+         (and (<= nmin 1) (or (not nmax) (>= nmax 1))
+              (make-call src (make-lambda #f '() consumer) (list exp))))
 
         ;; Statically-known number of values.
-        (($ <application> src ($ <primitive-ref> _ 'values) vals)
-         (and (= (length names) (length vals))
-              (make-let src names gensyms vals body)))
+        (($ <primcall> src 'values vals)
+         (and (<= nmin (length vals)) (or (not nmax) (>= nmax (length vals)))
+              (make-call src (make-lambda #f '() consumer) vals)))
 
         ;; Not going to copy code into both branches.
         (($ <conditional>) #f)
 
         ;; Bail on other applications.
-        (($ <application>) #f)
+        (($ <call>) #f)
+        (($ <primcall>) #f)
 
         ;; Bail on prompt and abort.
         (($ <prompt>) #f)
@@ -551,66 +572,27 @@ top-level bindings from ENV and return the resulting expression."
                 (make-let-values src exp
                                  (make-lambda-case src2 req opt rest kw
                                                    inits gensyms body #f)))))
-        (($ <dynwind> src winder body unwinder)
+        (($ <dynwind> src winder pre body post unwinder)
          (let ((body (loop body)))
            (and body
-                (make-dynwind src winder body unwinder))))
+                (make-dynwind src winder pre body post unwinder))))
         (($ <dynlet> src fluids vals body)
          (let ((body (loop body)))
            (and body
                 (make-dynlet src fluids vals body))))
-        (($ <sequence> src exps)
-         (match exps
-           ((head ... tail)
-            (let ((tail (loop tail)))
-              (and tail
-                   (make-sequence src (append head (list tail)))))))))))
+        (($ <seq> src head tail)
+         (let ((tail (loop tail)))
+           (and tail (make-seq src head tail)))))))
+
+  (define compute-effects
+    (make-effects-analyzer assigned-lexical?))
 
   (define (constant-expression? x)
     ;; Return true if X is constant, for the purposes of copying or
     ;; elision---i.e., if it is known to have no effects, does not
     ;; allocate storage for a mutable object, and does not access
     ;; mutable data (like `car' or toplevel references).
-    (let loop ((x x))
-      (match x
-        (($ <void>) #t)
-        (($ <const>) #t)
-        (($ <lambda>) #t)
-        (($ <lambda-case> _ req opt rest kw inits syms body alternate)
-         (and (not (any assigned-lexical? syms))
-              (every loop inits) (loop body)
-              (or (not alternate) (loop alternate))))
-        (($ <lexical-ref> _ _ gensym)
-         (not (assigned-lexical? gensym)))
-        (($ <primitive-ref>) #t)
-        (($ <conditional> _ condition subsequent alternate)
-         (and (loop condition) (loop subsequent) (loop alternate)))
-        (($ <application> _ ($ <primitive-ref> _ 'values) exps)
-         (and (not (null? exps))
-              (every loop exps)))
-        (($ <application> _ ($ <primitive-ref> _ name) args)
-         (and (effect-free-primitive? name)
-              (not (constructor-primitive? name))
-              (not (accessor-primitive? name))
-              (types-check? name args)
-              (every loop args)))
-        (($ <application> _ ($ <lambda> _ _ body) args)
-         (and (loop body) (every loop args)))
-        (($ <sequence> _ exps)
-         (every loop exps))
-        (($ <let> _ _ syms vals body)
-         (and (not (any assigned-lexical? syms))
-              (every loop vals) (loop body)))
-        (($ <letrec> _ _ _ syms vals body)
-         (and (not (any assigned-lexical? syms))
-              (every loop vals) (loop body)))
-        (($ <fix> _ _ _ vals body)
-         (and (every loop vals) (loop body)))
-        (($ <let-values> _ exp body)
-         (and (loop exp) (loop body)))
-        (($ <prompt> _ tag body handler)
-         (and (loop tag) (loop body) (loop handler)))
-        (_ #f))))
+    (constant? (compute-effects x)))
 
   (define (prune-bindings ops in-order? body counter ctx build-result)
     ;; This helper handles both `let' and `letrec'/`fix'.  In the latter
@@ -626,7 +608,8 @@ top-level bindings from ENV and return the resulting expression."
       ;; marked as needing residualization.  Here we hack around this
       ;; and treat all bindings as referenced if we are in operator
       ;; context.
-      (or (eq? ctx 'operator) (operand-residualize? op)))
+      (or (eq? ctx 'operator)
+          (not (zero? (operand-use-count op)))))
     
     ;; values := (op ...)
     ;; effects := (op ...)
@@ -646,7 +629,7 @@ top-level bindings from ENV and return the resulting expression."
                (if (null? effects)
                    body
                    (let ((effect-vals (map operand-residual-value effects)))
-                     (make-sequence #f (reverse (cons body effect-vals)))))))
+                     (list->seq #f (reverse (cons body effect-vals)))))))
           (if (null? values)
               body
               (let ((values (reverse values)))
@@ -714,6 +697,49 @@ top-level bindings from ENV and return the resulting expression."
        ((vhash-assq var env) => cdr)
        (else (error "unbound var" var))))
 
+    ;; Find a value referenced a specific number of times.  This is a hack
+    ;; that's used for propagating fresh data structures like rest lists and
+    ;; prompt tags.  Usually we wouldn't copy consed data, but we can do so in
+    ;; some special cases like `apply' or prompts if we can account
+    ;; for all of its uses.
+    ;;
+    ;; You don't want to use this in general because it introduces a slight
+    ;; nonlinearity by running peval again (though with a small effort and size
+    ;; counter).
+    ;;
+    (define (find-definition x n-aliases)
+      (cond
+       ((lexical-ref? x)
+        (cond
+         ((lookup (lexical-ref-gensym x))
+          => (lambda (op)
+               (let ((y (or (operand-residual-value op)
+                            (visit-operand op counter 'value 10 10)
+                            (operand-source op))))
+                 (cond
+                  ((and (lexical-ref? y)
+                        (= (lexical-refcount (lexical-ref-gensym x)) 1))
+                   ;; X is a simple alias for Y.  Recurse, regardless of
+                   ;; the number of aliases we were expecting.
+                   (find-definition y n-aliases))
+                  ((= (lexical-refcount (lexical-ref-gensym x)) n-aliases)
+                   ;; We found a definition that is aliased the right
+                   ;; number of times.  We still recurse in case it is a
+                   ;; lexical.
+                   (values (find-definition y 1)
+                           op))
+                  (else
+                   ;; We can't account for our aliases.
+                   (values #f #f))))))
+         (else
+          ;; A formal parameter.  Can't say anything about that.
+          (values #f #f))))
+       ((= n-aliases 1)
+        ;; Not a lexical: success, but only if we are looking for an
+        ;; unaliased value.
+        (values x #f))
+       (else (values #f #f))))
+
     (define (visit exp ctx)
       (loop exp env counter ctx))
 
@@ -746,6 +772,11 @@ top-level bindings from ENV and return the resulting expression."
           ((eq? ctx 'effect)
            (log 'lexical-for-effect gensym)
            (make-void #f))
+          ((operand-alias-value op)
+           ;; This is an unassigned operand that simply aliases some
+           ;; other operand.  Recurse to avoid residualizing the leaf
+           ;; binding.
+           => for-tail)
           ((eq? ctx 'call)
            ;; Don't propagate copies if we are residualizing a call.
            (log 'residualize-lexical-call gensym op)
@@ -833,28 +864,78 @@ top-level bindings from ENV and return the resulting expression."
              (let ((exp (for-effect exp)))
                (if (void? exp)
                    exp
-                   (make-sequence src (list exp (make-void #f)))))
+                   (make-seq src exp (make-void #f))))
              (begin
-               (set-operand-residualize?! op #t)
+               (record-operand-use op)
                (make-lexical-set src name (operand-sym op) (for-value exp))))))
+      (($ <let> src
+          (names ... rest)
+          (gensyms ... rest-sym)
+          (vals ... ($ <primcall> _ 'list rest-args))
+          ($ <primcall> asrc (or 'apply '@apply)
+             (proc args ...
+                   ($ <lexical-ref> _
+                      (? (cut eq? <> rest))
+                      (? (lambda (sym)
+                           (and (eq? sym rest-sym)
+                                (= (lexical-refcount sym) 1))))))))
+       (let* ((tmps (make-list (length rest-args) 'tmp))
+              (tmp-syms (fresh-temporaries tmps)))
+         (for-tail
+          (make-let src
+                    (append names tmps)
+                    (append gensyms tmp-syms)
+                    (append vals rest-args)
+                    (make-call
+                     asrc
+                     proc
+                     (append args
+                             (map (cut make-lexical-ref #f <> <>)
+                                  tmps tmp-syms)))))))
       (($ <let> src names gensyms vals body)
+       (define (compute-alias exp)
+         ;; It's very common for macros to introduce something like:
+         ;;
+         ;;   ((lambda (x y) ...) x-exp y-exp)
+         ;;
+         ;; In that case you might end up trying to inline something like:
+         ;;
+         ;;   (let ((x x-exp) (y y-exp)) ...)
+         ;;
+         ;; But if x-exp is itself a lexical-ref that aliases some much
+         ;; larger expression, perhaps it will fail to inline due to
+         ;; size.  However we don't want to introduce a useless alias
+         ;; (in this case, x).  So if the RHS of a let expression is a
+         ;; lexical-ref, we record that expression.  If we end up having
+         ;; to residualize X, then instead we residualize X-EXP, as long
+         ;; as it isn't assigned.
+         ;;
+         (match exp
+           (($ <lexical-ref> _ _ sym)
+            (let ((op (lookup sym)))
+              (and (not (var-set? (operand-var op)))
+                   (or (operand-alias-value op)
+                       exp))))
+           (_ #f)))
+
        (let* ((vars (map lookup-var gensyms))
               (new (fresh-gensyms vars))
               (ops (make-bound-operands vars new vals
                                         (lambda (exp counter ctx)
-                                          (loop exp env counter ctx))))
+                                          (loop exp env counter ctx))
+                                        (map compute-alias vals)))
               (env (fold extend-env env gensyms ops))
               (body (loop body env counter ctx)))
          (cond
           ((const? body)
-           (for-tail (make-sequence src (append vals (list body)))))
+           (for-tail (list->seq src (append vals (list body)))))
           ((and (lexical-ref? body)
                 (memq (lexical-ref-gensym body) new))
            (let ((sym (lexical-ref-gensym body))
                  (pairs (map cons new vals)))
              ;; (let ((x foo) (y bar) ...) x) => (begin bar ... foo)
              (for-tail
-              (make-sequence
+              (list->seq
                src
                (append (map cdr (alist-delete sym pairs eq?))
                        (list (assq-ref pairs sym)))))))
@@ -868,7 +949,9 @@ top-level bindings from ENV and return the resulting expression."
       (($ <letrec> src in-order? names gensyms vals body)
        ;; Note the difference from the `let' case: here we use letrec*
        ;; so that the `visit' procedure for the new operands closes over
-       ;; an environment that includes the operands.
+       ;; an environment that includes the operands.  Also we don't try
+       ;; to elide aliases, because we can't sensibly reduce something
+       ;; like (letrec ((a b) (b a)) a).
        (letrec* ((visit (lambda (exp counter ctx)
                           (loop exp env* counter ctx)))
                  (vars (map lookup-var gensyms))
@@ -904,47 +987,19 @@ top-level bindings from ENV and return the resulting expression."
        ;; reconstruct the let-values, pevaling the consumer.
        (let ((producer (for-values producer)))
          (or (match consumer
-               (($ <lambda-case> src req #f #f #f () gensyms body #f)
-                (cond
-                 ((inline-values producer src req gensyms body)
-                  => for-tail)
-                 (else #f)))
+               (($ <lambda-case> src req opt rest #f inits gensyms body #f)
+                (let* ((nmin (length req))
+                       (nmax (and (not rest) (+ nmin (if opt (length opt) 0)))))
+                  (cond
+                   ((inline-values lv-src producer nmin nmax consumer)
+                    => for-tail)
+                   (else #f))))
                (_ #f))
              (make-let-values lv-src producer (for-tail consumer)))))
-      (($ <dynwind> src winder body unwinder)
-       (let ((pre (for-value winder))
-             (body (for-tail body))
-             (post (for-value unwinder)))
-         (cond
-          ((not (constant-expression? pre))
-           (cond
-            ((not (constant-expression? post))
-             (let ((pre-sym (gensym "pre-")) (post-sym (gensym "post-")))
-               (record-new-temporary! 'pre pre-sym 1)
-               (record-new-temporary! 'post post-sym 1)
-               (make-let src '(pre post) (list pre-sym post-sym) (list pre post)
-                         (make-dynwind src
-                                       (make-lexical-ref #f 'pre pre-sym)
-                                       body
-                                       (make-lexical-ref #f 'post post-sym)))))
-            (else
-             (let ((pre-sym (gensym "pre-")))
-               (record-new-temporary! 'pre pre-sym 1)
-               (make-let src '(pre) (list pre-sym) (list pre)
-                         (make-dynwind src
-                                       (make-lexical-ref #f 'pre pre-sym)
-                                       body
-                                       post))))))
-          ((not (constant-expression? post))
-           (let ((post-sym (gensym "post-")))
-             (record-new-temporary! 'post post-sym 1)
-             (make-let src '(post) (list post-sym) (list post)
-                       (make-dynwind src
-                                     pre
-                                     body
-                                     (make-lexical-ref #f 'post post-sym)))))
-          (else
-           (make-dynwind src pre body post)))))
+      (($ <dynwind> src winder pre body post unwinder)
+       (make-dynwind src (for-value winder) (for-effect pre)
+                     (for-tail body)
+                     (for-effect post) (for-value unwinder)))
       (($ <dynlet> src fluids vals body)
        (make-dynlet src (map for-value fluids) (map for-value vals)
                     (for-tail body)))
@@ -953,12 +1008,7 @@ top-level bindings from ENV and return the resulting expression."
       (($ <dynset> src fluid exp)
        (make-dynset src (for-value fluid) (for-value exp)))
       (($ <toplevel-ref> src (? effect-free-primitive? name))
-       (if (local-toplevel? name)
-           exp
-           (let ((exp (resolve-primitives! exp cenv)))
-             (if (primitive-ref? exp)
-                 (for-tail exp)
-                 exp))))
+       exp)
       (($ <toplevel-ref>)
        ;; todo: open private local bindings.
        exp)
@@ -985,25 +1035,132 @@ top-level bindings from ENV and return the resulting expression."
          ((test) (make-const #f #t))
          (else exp)))
       (($ <conditional> src condition subsequent alternate)
-       (let ((condition (for-test condition)))
-         (if (const? condition)
-             (if (const-exp condition)
-                 (for-tail subsequent)
-                 (for-tail alternate))
-             (make-conditional src condition
-                               (for-tail subsequent)
-                               (for-tail alternate)))))
-      (($ <application> src
-          ($ <primitive-ref> _ '@call-with-values)
+       (define (call-with-failure-thunk exp proc)
+         (match exp
+           (($ <call> _ _ ()) (proc exp))
+           (($ <primcall> _ _ ()) (proc exp))
+           (($ <const>) (proc exp))
+           (($ <void>) (proc exp))
+           (($ <lexical-ref>) (proc exp))
+           (_
+            (let ((t (gensym "failure-")))
+              (record-new-temporary! 'failure t 2)
+              (make-let
+               src (list 'failure) (list t)
+               (list
+                (make-lambda
+                 #f '()
+                 (make-lambda-case #f '() #f #f #f '() '() exp #f)))
+               (proc (make-call #f (make-lexical-ref #f 'failure t)
+                                '())))))))
+       (define (simplify-conditional c)
+         (match c
+           ;; Swap the arms of (if (not FOO) A B), to simplify.
+           (($ <conditional> src ($ <primcall> _ 'not (pred))
+               subsequent alternate)
+            (simplify-conditional
+             (make-conditional src pred alternate subsequent)))
+           ;; Special cases for common tests in the predicates of chains
+           ;; of if expressions.
+           (($ <conditional> src
+               ($ <conditional> src* outer-test inner-test ($ <const> _ #f))
+               inner-subsequent
+               alternate)
+            (let lp ((alternate alternate))
+              (match alternate
+                ;; Lift a common repeated test out of a chain of if
+                ;; expressions.
+                (($ <conditional> _ (? (cut tree-il=? outer-test <>))
+                    other-subsequent alternate)
+                 (make-conditional
+                  src outer-test
+                  (simplify-conditional
+                   (make-conditional src* inner-test inner-subsequent
+                                     other-subsequent))
+                  alternate))
+                ;; Likewise, but punching through any surrounding
+                ;; failure continuations.
+                (($ <let> let-src (name) (sym) ((and thunk ($ <lambda>))) body)
+                 (make-let
+                  let-src (list name) (list sym) (list thunk)
+                  (lp body)))
+                ;; Otherwise, rotate AND tests to expose a simple
+                ;; condition in the front.  Although this may result in
+                ;; lexically binding failure thunks, the thunks will be
+                ;; compiled to labels allocation, so there's no actual
+                ;; code growth.
+                (_
+                 (call-with-failure-thunk
+                  alternate
+                  (lambda (failure)
+                    (make-conditional
+                     src outer-test
+                     (simplify-conditional
+                      (make-conditional src* inner-test inner-subsequent failure))
+                     failure)))))))
+           (_ c)))
+       (match (for-test condition)
+         (($ <const> _ val)
+          (if val
+              (for-tail subsequent)
+              (for-tail alternate)))
+         (c
+          (simplify-conditional
+           (make-conditional src c (for-tail subsequent)
+                             (for-tail alternate))))))
+      (($ <primcall> src '@call-with-values
           (producer
            ($ <lambda> _ _
               (and consumer
                    ;; No optional or kwargs.
                    ($ <lambda-case>
                       _ req #f rest #f () gensyms body #f)))))
-       (for-tail (make-let-values src (make-application src producer '())
+       (for-tail (make-let-values src (make-call src producer '())
                                   consumer)))
-      (($ <application> src ($ <primitive-ref> _ 'values) exps)
+      (($ <primcall> src 'dynamic-wind (w thunk u))
+       (for-tail
+        (cond
+         ((not (constant-expression? w))
+          (cond
+           ((not (constant-expression? u))
+            (let ((w-sym (gensym "w ")) (u-sym (gensym "u ")))
+              (record-new-temporary! 'w w-sym 2)
+              (record-new-temporary! 'u u-sym 2)
+              (make-let src '(w u) (list w-sym u-sym) (list w u)
+                        (make-dynwind
+                         src
+                         (make-lexical-ref #f 'w w-sym)
+                         (make-call #f (make-lexical-ref #f 'w w-sym) '())
+                         (make-call #f thunk '())
+                         (make-call #f (make-lexical-ref #f 'u u-sym) '())
+                         (make-lexical-ref #f 'u u-sym)))))
+           (else
+            (let ((w-sym (gensym "w ")))
+              (record-new-temporary! 'w w-sym 2)
+              (make-let src '(w) (list w-sym) (list w)
+                        (make-dynwind
+                         src
+                         (make-lexical-ref #f 'w w-sym)
+                         (make-call #f (make-lexical-ref #f 'w w-sym) '())
+                         (make-call #f thunk '())
+                         (make-call #f u '())
+                         u))))))
+         ((not (constant-expression? u))
+          (let ((u-sym (gensym "u ")))
+            (record-new-temporary! 'u u-sym 2)
+            (make-let src '(u) (list u-sym) (list u)
+                      (make-dynwind
+                       src
+                       w
+                       (make-call #f w '())
+                       (make-call #f thunk '())
+                       (make-call #f (make-lexical-ref #f 'u u-sym) '())
+                       (make-lexical-ref #f 'u u-sym)))))
+         (else
+          (make-dynwind src w (make-call #f w '()) (make-call #f thunk '())
+                        (make-call #f u '()) u)))))
+
+      (($ <primcall> src 'values exps)
        (cond
         ((null? exps)
          (if (eq? ctx 'effect)
@@ -1015,126 +1172,177 @@ top-level bindings from ENV and return the resulting expression."
                       ((value test effect) #t)
                       (else (null? (cdr vals))))
                     (every singly-valued-expression? vals))
-               (for-tail (make-sequence src (append (cdr vals) (list (car vals)))))
-               (make-application src (make-primitive-ref #f 'values) vals))))))
-      (($ <application> src orig-proc orig-args)
+               (for-tail (list->seq src (append (cdr vals) (list (car vals)))))
+               (make-primcall src 'values vals))))))
+
+      (($ <primcall> src (or 'apply '@apply) (proc args ... tail))
+       (let lp ((tail* (find-definition tail 1)) (speculative? #t))
+         (define (copyable? x)
+           ;; Inlining a result from find-definition effectively copies it,
+           ;; relying on the let-pruning to remove its original binding.  We
+           ;; shouldn't copy non-constant expressions.
+           (or (not speculative?) (constant-expression? x)))
+         (match tail*
+           (($ <const> _ (args* ...))
+            (let ((args* (map (cut make-const #f <>) args*)))
+              (for-tail (make-call src proc (append args args*)))))
+           (($ <primcall> _ 'cons
+               ((and head (? copyable?)) (and tail (? copyable?))))
+            (for-tail (make-primcall src '@apply
+                                     (cons proc
+                                           (append args (list head tail))))))
+           (($ <primcall> _ 'list
+               (and args* ((? copyable?) ...)))
+            (for-tail (make-call src proc (append args args*))))
+           (tail*
+            (if speculative?
+                (lp (for-value tail) #f)
+                (let ((args (append (map for-value args) (list tail*))))
+                  (make-primcall src '@apply
+                                 (cons (for-value proc) args))))))))
+
+      (($ <primcall> src (? constructor-primitive? name) args)
+       (cond
+        ((and (memq ctx '(effect test))
+              (match (cons name args)
+                ((or ('cons _ _)
+                     ('list . _)
+                     ('vector . _)
+                     ('make-prompt-tag)
+                     ('make-prompt-tag ($ <const> _ (? string?))))
+                 #t)
+                (_ #f)))
+         ;; Some expressions can be folded without visiting the
+         ;; arguments for value.
+         (let ((res (if (eq? ctx 'effect)
+                        (make-void #f)
+                        (make-const #f #t))))
+           (for-tail (list->seq src (append args (list res))))))
+        (else
+         (match (cons name (map for-value args))
+           (('cons x ($ <const> _ (? (cut eq? <> '()))))
+            (make-primcall src 'list (list x)))
+           (('cons x ($ <primcall> _ 'list elts))
+            (make-primcall src 'list (cons x elts)))
+           ((name . args)
+            (make-primcall src name args))))))
+
+      (($ <primcall> src (? accessor-primitive? name) args)
+       (match (cons name (map for-value args))
+         ;; FIXME: these for-tail recursions could take place outside
+         ;; an effort counter.
+         (('car ($ <primcall> src 'cons (head tail)))
+          (for-tail (make-seq src tail head)))
+         (('cdr ($ <primcall> src 'cons (head tail)))
+          (for-tail (make-seq src head tail)))
+         (('car ($ <primcall> src 'list (head . tail)))
+          (for-tail (list->seq src (append tail (list head)))))
+         (('cdr ($ <primcall> src 'list (head . tail)))
+          (for-tail (make-seq src head (make-primcall #f 'list tail))))
+                  
+         (('car ($ <const> src (head . tail)))
+          (for-tail (make-const src head)))
+         (('cdr ($ <const> src (head . tail)))
+          (for-tail (make-const src tail)))
+         (((or 'memq 'memv) k ($ <const> _ (elts ...)))
+          ;; FIXME: factor 
+          (case ctx
+            ((effect)
+             (for-tail
+              (make-seq src k (make-void #f))))
+            ((test)
+             (cond
+              ((const? k)
+               ;; A shortcut.  The `else' case would handle it, but
+               ;; this way is faster.
+               (let ((member (case name ((memq) memq) ((memv) memv))))
+                 (make-const #f (and (member (const-exp k) elts) #t))))
+              ((null? elts)
+               (for-tail
+                (make-seq src k (make-const #f #f))))
+              (else
+               (let ((t (gensym "t "))
+                     (eq (if (eq? name 'memq) 'eq? 'eqv?)))
+                 (record-new-temporary! 't t (length elts))
+                 (for-tail
+                  (make-let
+                   src (list 't) (list t) (list k)
+                   (let lp ((elts elts))
+                     (define test
+                       (make-primcall #f eq
+                                      (list (make-lexical-ref #f 't t)
+                                            (make-const #f (car elts)))))
+                     (if (null? (cdr elts))
+                         test
+                         (make-conditional src test
+                                           (make-const #f #t)
+                                           (lp (cdr elts)))))))))))
+            (else
+             (cond
+              ((const? k)
+               (let ((member (case name ((memq) memq) ((memv) memv))))
+                 (make-const #f (member (const-exp k) elts))))
+              ((null? elts)
+               (for-tail (make-seq src k (make-const #f #f))))
+              (else
+               (make-primcall src name (list k (make-const #f elts))))))))
+         ((name . args)
+          (fold-constants src name args ctx))))
+
+      (($ <primcall> src (? equality-primitive? name) (a b))
+       (let ((val-a (for-value a))
+             (val-b (for-value b)))
+         (log 'equality-primitive name val-a val-b)
+         (cond ((and (lexical-ref? val-a) (lexical-ref? val-b)
+                     (eq? (lexical-ref-gensym val-a)
+                          (lexical-ref-gensym val-b)))
+                (for-tail (make-const #f #t)))
+               (else
+                (fold-constants src name (list val-a val-b) ctx)))))
+      
+      (($ <primcall> src (? effect-free-primitive? name) args)
+       (fold-constants src name (map for-value args) ctx))
+
+      (($ <primcall> src name args)
+       (make-primcall src name (map for-value args)))
+
+      (($ <call> src orig-proc orig-args)
        ;; todo: augment the global env with specialized functions
-       (let ((proc (visit orig-proc 'operator)))
+       (let revisit-proc ((proc (visit orig-proc 'operator)))
          (match proc
-           (($ <primitive-ref> _ (? constructor-primitive? name))
-            (cond
-             ((and (memq ctx '(effect test))
-                   (match (cons name orig-args)
-                     ((or ('cons _ _)
-                          ('list . _)
-                          ('vector . _)
-                          ('make-prompt-tag)
-                          ('make-prompt-tag ($ <const> _ (? string?))))
-                      #t)
-                     (_ #f)))
-              ;; Some expressions can be folded without visiting the
-              ;; arguments for value.
-              (let ((res (if (eq? ctx 'effect)
-                             (make-void #f)
-                             (make-const #f #t))))
-                (for-tail (make-sequence src (append orig-args (list res))))))
-             (else
-              (match (cons name (map for-value orig-args))
-                (('cons head tail)
-                 (match tail
-                   (($ <const> src (? (cut eq? <> '())))
-                    (make-application src (make-primitive-ref #f 'list)
-                                      (list head)))
-                   (($ <application> src ($ <primitive-ref> _ 'list) elts)
-                    (make-application src (make-primitive-ref #f 'list)
-                                      (cons head elts)))
-                   (_ (make-application src proc (list head tail)))))
-                ((_ . args)
-                 (make-application src proc args))))))
-           (($ <primitive-ref> _ (? accessor-primitive? name))
-            (match (cons name (map for-value orig-args))
-              ;; FIXME: these for-tail recursions could take place outside
-              ;; an effort counter.
-              (('car ($ <application> src ($ <primitive-ref> _ 'cons) (head tail)))
-               (for-tail (make-sequence src (list tail head))))
-              (('cdr ($ <application> src ($ <primitive-ref> _ 'cons) (head tail)))
-               (for-tail (make-sequence src (list head tail))))
-              (('car ($ <application> src ($ <primitive-ref> _ 'list) (head . tail)))
-               (for-tail (make-sequence src (append tail (list head)))))
-              (('cdr ($ <application> src ($ <primitive-ref> _ 'list) (head . tail)))
-               (for-tail (make-sequence
-                          src
-                          (list head
-                                (make-application
-                                 src (make-primitive-ref #f 'list) tail)))))
-                  
-              (('car ($ <const> src (head . tail)))
-               (for-tail (make-const src head)))
-              (('cdr ($ <const> src (head . tail)))
-               (for-tail (make-const src tail)))
-              (((or 'memq 'memv) k ($ <const> _ (elts ...)))
-               ;; FIXME: factor 
-               (case ctx
-                 ((effect)
-                  (for-tail
-                   (make-sequence src (list k (make-void #f)))))
-                 ((test)
-                  (cond
-                   ((const? k)
-                    ;; A shortcut.  The `else' case would handle it, but
-                    ;; this way is faster.
-                    (let ((member (case name ((memq) memq) ((memv) memv))))
-                      (make-const #f (and (member (const-exp k) elts) #t))))
-                   ((null? elts)
-                    (for-tail
-                     (make-sequence src (list k (make-const #f #f)))))
-                   (else
-                    (let ((t (gensym "t-"))
-                          (eq (if (eq? name 'memq) 'eq? 'eqv?)))
-                      (record-new-temporary! 't t (length elts))
-                      (for-tail
-                       (make-let
-                        src (list 't) (list t) (list k)
-                        (let lp ((elts elts))
-                          (define test
-                            (make-application
-                             #f (make-primitive-ref #f eq)
-                             (list (make-lexical-ref #f 't t)
-                                   (make-const #f (car elts)))))
-                          (if (null? (cdr elts))
-                              test
-                              (make-conditional src test
-                                                (make-const #f #t)
-                                                (lp (cdr elts)))))))))))
-                 (else
-                  (cond
-                   ((const? k)
-                    (let ((member (case name ((memq) memq) ((memv) memv))))
-                      (make-const #f (member (const-exp k) elts))))
-                   ((null? elts)
-                    (for-tail (make-sequence src (list k (make-const #f #f)))))
-                   (else
-                    (make-application src proc (list k (make-const #f elts))))))))
-              ((_ . args)
-               (or (fold-constants src name args ctx)
-                   (make-application src proc args)))))
-           (($ <primitive-ref> _ (? effect-free-primitive? name))
-            (let ((args (map for-value orig-args)))
-              (or (fold-constants src name args ctx)
-                  (make-application src proc args))))
+           (($ <primitive-ref> _ name)
+            (for-tail (make-primcall src name orig-args)))
            (($ <lambda> _ _
-               ($ <lambda-case> _ req opt #f #f inits gensyms body #f))
-            ;; Simple case: no rest, no keyword arguments.
+               ($ <lambda-case> _ req opt rest #f inits gensyms body #f))
+            ;; Simple case: no keyword arguments.
             ;; todo: handle the more complex cases
             (let* ((nargs (length orig-args))
                    (nreq (length req))
                    (nopt (if opt (length opt) 0))
                    (key (source-expression proc)))
+              (define (inlined-call)
+                (make-let src
+                          (append req
+                                  (or opt '())
+                                  (if rest (list rest) '()))
+                          gensyms
+                          (if (> nargs (+ nreq nopt))
+                              (append (list-head orig-args (+ nreq nopt))
+                                      (list
+                                       (make-primcall
+                                        #f 'list
+                                        (drop orig-args (+ nreq nopt)))))
+                              (append orig-args
+                                      (drop inits (- nargs nreq))
+                                      (if rest
+                                          (list (make-const #f '()))
+                                          '())))
+                          body))
+
               (cond
-               ((or (< nargs nreq) (> nargs (+ nreq nopt)))
+               ((or (< nargs nreq) (and (not rest) (> nargs (+ nreq nopt))))
                 ;; An error, or effecting arguments.
-                (make-application src (for-call orig-proc)
-                                  (map for-value orig-args)))
+                (make-call src (for-call orig-proc) (map for-value orig-args)))
                ((or (and=> (find-counter key counter) counter-recursive?)
                     (lambda? orig-proc))
                 ;; A recursive call, or a lambda in the operator
@@ -1156,12 +1364,7 @@ top-level bindings from ENV and return the resulting expression."
                               (lp (counter-prev counter)))))))
 
                 (log 'inline-recurse key)
-                (loop (make-let src (append req (or opt '()))
-                                gensyms
-                                (append orig-args
-                                        (drop inits (- nargs nreq)))
-                                body)
-                  env counter ctx))
+                (loop (inlined-call) env counter ctx))
                (else
                 ;; An integration at the top-level, the first
                 ;; recursion of a recursive procedure, or a nested
@@ -1171,8 +1374,8 @@ top-level bindings from ENV and return the resulting expression."
                 (let/ec k
                   (define (abort)
                     (log 'inline-abort exp)
-                    (k (make-application src (for-call orig-proc)
-                                         (map for-value orig-args))))
+                    (k (make-call src (for-call orig-proc)
+                                  (map for-value orig-args))))
                   (define new-counter
                     (cond
                      ;; These first two cases will transfer effort
@@ -1192,12 +1395,7 @@ top-level bindings from ENV and return the resulting expression."
                       (make-top-counter effort-limit operand-size-limit
                                         abort key))))
                   (define result
-                    (loop (make-let src (append req (or opt '()))
-                                    gensyms
-                                    (append orig-args
-                                            (drop inits (- nargs nreq)))
-                                    body)
-                      env new-counter ctx))
+                    (loop (inlined-call) env new-counter ctx))
                       
                   (if counter
                       ;; The nested inlining attempt succeeded.
@@ -1207,9 +1405,33 @@ top-level bindings from ENV and return the resulting expression."
 
                   (log 'inline-end result exp)
                   result)))))
+           (($ <let> _ _ _ vals _)
+            ;; Attempt to inline `let' in the operator position.
+            ;;
+            ;; We have to re-visit the proc in value mode, since the
+            ;; `let' bindings might have been introduced or renamed,
+            ;; whereas the lambda (if any) in operator position has not
+            ;; been renamed.
+            (if (or (and-map constant-expression? vals)
+                    (and-map constant-expression? orig-args))
+                ;; The arguments and the let-bound values commute.
+                (match (for-value orig-proc)
+                  (($ <let> lsrc names syms vals body)
+                   (log 'inline-let orig-proc)
+                   (for-tail
+                    (make-let lsrc names syms vals
+                              (make-call src body orig-args))))
+                  ;; It's possible for a `let' to go away after the
+                  ;; visit due to the fact that visiting a procedure in
+                  ;; value context will prune unused bindings, whereas
+                  ;; visiting in operator mode can't because it doesn't
+                  ;; traverse through lambdas.  In that case re-visit
+                  ;; the procedure.
+                  (proc (revisit-proc proc)))
+                (make-call src (for-call orig-proc)
+                           (map for-value orig-args))))
            (_
-            (make-application src (for-call orig-proc)
-                              (map for-value orig-args))))))
+            (make-call src (for-call orig-proc) (map for-value orig-args))))))
       (($ <lambda> src meta body)
        (case ctx
          ((effect) (make-void #f))
@@ -1217,14 +1439,13 @@ top-level bindings from ENV and return the resulting expression."
          ((operator) exp)
          (else (record-source-expression!
                 exp
-                (make-lambda src meta (for-values body))))))
+                (make-lambda src meta (and body (for-values body)))))))
       (($ <lambda-case> src req opt rest kw inits gensyms body alt)
        (define (lift-applied-lambda body gensyms)
          (and (not opt) rest (not kw)
               (match body
-                (($ <application> _
-                    ($ <primitive-ref> _ '@apply)
-                    (($ <lambda> _ _ lcase)
+                (($ <primcall> _ '@apply
+                    (($ <lambda> _ _ (and lcase ($ <lambda-case>)))
                      ($ <lexical-ref> _ _ sym)
                      ...))
                  (and (equal? sym gensyms)
@@ -1250,44 +1471,60 @@ top-level bindings from ENV and return the resulting expression."
                             new
                             body
                             (and alt (for-tail alt))))))
-      (($ <sequence> src exps)
-       (let lp ((exps exps) (effects '()))
-         (match exps
-           ((last)
-            (if (null? effects)
-                (for-tail last)
-                (make-sequence
-                 src
-                 (reverse (cons (for-tail last) effects)))))
-           ((head . rest)
-            (let ((head (for-effect head)))
-              (cond
-               ((sequence? head)
-                (lp (append (sequence-exps head) rest) effects))
-               ((void? head)
-                (lp rest effects))
-               (else
-                (lp rest (cons head effects)))))))))
+      (($ <seq> src head tail)
+       (let ((head (for-effect head))
+             (tail (for-tail tail)))
+         (if (void? head)
+             tail
+             (make-seq src
+                       (if (and (seq? head)
+                                (void? (seq-tail head)))
+                           (seq-head head)
+                           head)
+                       tail))))
       (($ <prompt> src tag body handler)
-       (define (singly-used-definition x)
+       (define (make-prompt-tag? x)
+         (match x
+           (($ <primcall> _ 'make-prompt-tag (or () ((? constant-expression?))))
+            #t)
+           (_ #f)))
+
+       (let ((tag (for-value tag))
+             (body (for-tail body)))
          (cond
-          ((and (lexical-ref? x)
-                ;; Only fetch definitions with single uses.
-                (= (lexical-refcount (lexical-ref-gensym x)) 1)
-                (lookup (lexical-ref-gensym x)))
-           => (lambda (x)
-                (singly-used-definition (visit-operand x counter 'value 10 10))))
-          (else x)))
-       (match (singly-used-definition tag)
-         (($ <application> _ ($ <primitive-ref> _ 'make-prompt-tag)
-             (or () ((? constant-expression?))))
-          ;; There is no way that an <abort> could know the tag
-          ;; for this <prompt>, so we can elide the <prompt>
-          ;; entirely.
-          (for-tail body))
-         (_
-          (make-prompt src (for-value tag) (for-tail body)
-                       (for-value handler)))))
+          ((find-definition tag 1)
+           (lambda (val op)
+             (make-prompt-tag? val))
+           => (lambda (val op)
+                ;; There is no way that an <abort> could know the tag
+                ;; for this <prompt>, so we can elide the <prompt>
+                ;; entirely.
+                (unrecord-operand-uses op 1)
+                body))
+          ((find-definition tag 2)
+           (lambda (val op)
+             (and (make-prompt-tag? val)
+                  (abort? body)
+                  (tree-il=? (abort-tag body) tag)))
+           => (lambda (val op)
+                ;; (let ((t (make-prompt-tag)))
+                ;;   (call-with-prompt t
+                ;;     (lambda () (abort-to-prompt t val ...))
+                ;;     (lambda (k arg ...) e ...)))
+                ;; => (let-values (((k arg ...) (values values val ...)))
+                ;;      e ...)
+                (unrecord-operand-uses op 2)
+                (for-tail
+                 (make-let-values
+                  src
+                  (make-primcall #f 'apply
+                                 `(,(make-primitive-ref #f 'values)
+                                   ,(make-primitive-ref #f 'values)
+                                   ,@(abort-args body)
+                                   ,(abort-tail body)))
+                  (for-value handler)))))
+          (else
+           (make-prompt src tag body (for-value handler))))))
       (($ <abort> src tag args tail)
        (make-abort src (for-value tag) (map for-value args)
                    (for-value tail))))))