X-Git-Url: http://git.hcoop.net/bpt/guile.git/blobdiff_plain/cc8afa2b361635953dfba7f10e4193b1f243a50f..9ddf06dceee3a2bf5480a3e261ec01aaa91a1f67:/module/language/tree-il/peval.scm

diff --git a/module/language/tree-il/peval.scm b/module/language/tree-il/peval.scm
index a6bb954e2..da3f4a82c 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 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)
@@ -287,29 +288,38 @@
 ;; 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))
@@ -343,7 +353,12 @@
                 (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)
@@ -422,6 +437,13 @@ top-level bindings from ENV and return the resulting expression."
              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 +464,18 @@ 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)))
@@ -492,7 +523,7 @@ 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.
@@ -508,18 +539,16 @@ 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>)               ;
+             ($ <application> src
+                ($ <primitive-ref> _ (? singly-valued-primitive?))))
+         (and (<= nmin 1) (or (not nmax) (>= nmax 1))
+              (make-application 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)))
+         (and (<= nmin (length vals)) (or (not nmax) (>= nmax (length vals)))
+              (make-application src (make-lambda #f '() consumer) vals)))
 
         ;; Not going to copy code into both branches.
         (($ <conditional>) #f)
@@ -566,51 +595,15 @@ top-level bindings from ENV and return the resulting expression."
               (and tail
                    (make-sequence src (append head (list 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 +619,8 @@ 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 ...)
@@ -714,6 +708,49 @@ 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 +783,11 @@ 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)
@@ -835,14 +877,65 @@ top-level bindings from ENV and return the resulting expression."
                    exp
                    (make-sequence src (list 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 ... ($ <application> _ ($ <primitive-ref> _ 'list) rest-args))
+          ($ <application> asrc
+             ($ <primitive-ref> _ (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-application
+                     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
@@ -868,7 +961,9 @@ 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))
@@ -904,11 +999,13 @@ 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)
@@ -919,7 +1016,7 @@ top-level bindings from ENV and return the resulting expression."
           ((not (constant-expression? pre))
            (cond
             ((not (constant-expression? post))
-             (let ((pre-sym (gensym "pre ")) (post-sym (gensym "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)
@@ -928,7 +1025,7 @@ top-level bindings from ENV and return the resulting expression."
                                        body
                                        (make-lexical-ref #f 'post post-sym)))))
             (else
-             (let ((pre-sym (gensym "pre ")))
+             (let ((pre-sym (gensym "pre-")))
                (record-new-temporary! 'pre pre-sym 1)
                (make-let src '(pre) (list pre-sym) (list pre)
                          (make-dynwind src
@@ -936,7 +1033,7 @@ top-level bindings from ENV and return the resulting expression."
                                        body
                                        post))))))
           ((not (constant-expression? post))
-           (let ((post-sym (gensym "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
@@ -985,14 +1082,79 @@ 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)))))
+       (define (call-with-failure-thunk exp proc)
+         (match exp
+           (($ <application> _ _ ()) (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-application #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
+               ($ <application> _ ($ <primitive-ref> _ '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))))))
       (($ <application> src
           ($ <primitive-ref> _ '@call-with-values)
           (producer
@@ -1011,13 +1173,41 @@ top-level bindings from ENV and return the resulting expression."
              exp))
         (else
          (let ((vals (map for-value exps)))
-           (if (and (memq ctx '(value test effect))
+           (if (and (case ctx
+                      ((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 (and apply ($ <primitive-ref> _ (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-application src proc (append args args*)))))
+           (($ <application> _ ($ <primitive-ref> _ 'cons)
+               ((and head (? copyable?)) (and tail (? copyable?))))
+            (for-tail (make-application src apply
+                                        (cons proc
+                                              (append args (list head tail))))))
+           (($ <application> _ ($ <primitive-ref> _ 'list)
+               (and args* ((? copyable?) ...)))
+            (for-tail (make-application src proc (append args args*))))
+           (tail*
+            (if speculative?
+                (lp (for-value tail) #f)
+                (let ((args (append (map for-value args) (list tail*))))
+                  (make-application src apply
+                                    (cons (for-value proc) args))))))))
       (($ <application> 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
@@ -1087,7 +1277,7 @@ top-level bindings from ENV and return the resulting expression."
                     (for-tail
                      (make-sequence src (list k (make-const #f #f)))))
                    (else
-                    (let ((t (gensym "t "))
+                    (let ((t (gensym "t-"))
                           (eq (if (eq? name 'memq) 'eq? 'eqv?)))
                       (record-new-temporary! 't t (length elts))
                       (for-tail
@@ -1121,15 +1311,35 @@ top-level bindings from ENV and return the resulting expression."
               (or (fold-constants src name args ctx)
                   (make-application src proc 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-application)
+                (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-application
+                                        #f
+                                        (make-primitive-ref #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)))
@@ -1154,12 +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-application) env counter ctx))
                (else
                 ;; An integration at the top-level, the first
                 ;; recursion of a recursive procedure, or a nested
@@ -1190,12 +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-application) env new-counter ctx))
                       
                   (if counter
                       ;; The nested inlining attempt succeeded.
@@ -1205,6 +1405,31 @@ 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-application 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-application src (for-call orig-proc)
+                                  (map for-value orig-args))))
            (_
             (make-application src (for-call orig-proc)
                               (map for-value orig-args))))))
@@ -1217,21 +1442,37 @@ top-level bindings from ENV and return the resulting expression."
                 exp
                 (make-lambda src meta (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)
+                     ($ <lexical-ref> _ _ sym)
+                     ...))
+                 (and (equal? sym gensyms)
+                      (not (lambda-case-alternate lcase))
+                      lcase))
+                (_ #f))))
        (let* ((vars (map lookup-var gensyms))
               (new (fresh-gensyms vars))
               (env (fold extend-env env gensyms
                          (make-unbound-operands vars new)))
               (new-sym (lambda (old)
-                         (operand-sym (cdr (vhash-assq old env))))))
-         (make-lambda-case src req opt rest
-                           (match kw
-                             ((aok? (kw name old) ...)
-                              (cons aok? (map list kw name (map new-sym old))))
-                             (_ #f))
-                           (map (cut loop <> env counter 'value) inits)
-                           new
-                           (loop body env counter ctx)
-                           (and alt (for-tail alt)))))
+                         (operand-sym (cdr (vhash-assq old env)))))
+              (body (loop body env counter ctx)))
+         (or
+          ;; (lambda args (apply (lambda ...) args)) => (lambda ...)
+          (lift-applied-lambda body new)
+          (make-lambda-case src req opt rest
+                            (match kw
+                              ((aok? (kw name old) ...)
+                               (cons aok? (map list kw name (map new-sym old))))
+                              (_ #f))
+                            (map (cut loop <> env counter 'value) inits)
+                            new
+                            body
+                            (and alt (for-tail alt))))))
       (($ <sequence> src exps)
        (let lp ((exps exps) (effects '()))
          (match exps
@@ -1251,25 +1492,49 @@ top-level bindings from ENV and return the resulting expression."
                (else
                 (lp rest (cons head effects)))))))))
       (($ <prompt> src tag body handler)
-       (define (singly-used-definition x)
+       (define (make-prompt-tag? x)
+         (match x
+           (($ <application> _ ($ <primitive-ref> _ '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-application #f (make-primitive-ref #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))))))