From 43ba15ca389e99dc9825284daa6cb8562ac1d50c Mon Sep 17 00:00:00 2001
From: Matthew Flatt <mflatt@racket-lang.org>
Date: Thu, 18 Jul 2019 11:56:19 -0600
Subject: [PATCH] expander: fix performance problem with `datum->syntax`

In a pattern like

 (let loop ([l l])
   (define v (syntax-e l))
   (cond
     [(null? v) 'done]
     [else
      (loop (datum->syntax #f (cdr v)))]))

the running time was O(N^2) for a list of syntax objects of length N.
That pattern is relevant for traversals that use `syntax-case` like

 (let loop ([l l])
   (syntax-case l ()
     [(a . b) (loop #'b)]
     [() 'done]))

Avoid bad behavior by recording in an weak hash table certain pairs
that were previously been produced by `datum->syntax` internally so
that they can be used as-is.
---
 .../tests/racket/stress/datum-to-syntax.rkt   |  19 ++
 racket/src/expander/main.rkt                  |   2 +
 racket/src/expander/syntax/datum-map.rkt      |  28 ++-
 racket/src/expander/syntax/syntax.rkt         |  29 ++-
 racket/src/racket/src/startup.inc             | 225 ++++++++++++------
 5 files changed, 213 insertions(+), 90 deletions(-)
 create mode 100644 pkgs/racket-test/tests/racket/stress/datum-to-syntax.rkt

diff --git a/pkgs/racket-test/tests/racket/stress/datum-to-syntax.rkt b/pkgs/racket-test/tests/racket/stress/datum-to-syntax.rkt
new file mode 100644
index 0000000000..4e6ddd9f0d
--- /dev/null
+++ b/pkgs/racket-test/tests/racket/stress/datum-to-syntax.rkt
@@ -0,0 +1,19 @@
+#lang racket/base
+
+(define l (datum->syntax
+           #f
+           (for/list ([i 10000])
+             'x)))
+
+
+(let ([now (current-inexact-milliseconds)])
+  (let loop ([l l])
+    (define v (syntax-e l))
+    (cond
+      [(null? v) 'done]
+      [else
+       (loop (datum->syntax #f (cdr v)))]))
+  (define t (- (current-inexact-milliseconds) now))
+  (unless (t . < . 1000.0)
+    (error 'datum->syntax-stress "took too long: ~a" t)))
+
diff --git a/racket/src/expander/main.rkt b/racket/src/expander/main.rkt
index eb7d420485..5e81da2782 100644
--- a/racket/src/expander/main.rkt
+++ b/racket/src/expander/main.rkt
@@ -34,6 +34,7 @@
                   compiled-expression-recompile)
          (only-in racket/private/config find-main-config)
          (only-in "syntax/cache.rkt" cache-place-init!)
+         (only-in "syntax/syntax.rkt" syntax-place-init!)
          (only-in "syntax/scope.rkt" scope-place-init!)
          (only-in "eval/module-cache.rkt" module-cache-place-init!)
          (only-in "common/performance.rkt" performance-place-init!)
@@ -207,6 +208,7 @@
   (datum->syntax core-stx s))
 
 (define (expander-place-init!)
+  (syntax-place-init!)
   (scope-place-init!)
   (cache-place-init!)
   (core-place-init!)
diff --git a/racket/src/expander/syntax/datum-map.rkt b/racket/src/expander/syntax/datum-map.rkt
index 845b3cb0a1..f71fc17b49 100644
--- a/racket/src/expander/syntax/datum-map.rkt
+++ b/racket/src/expander/syntax/datum-map.rkt
@@ -11,7 +11,9 @@
 ;; 
 ;; `(f tail? d)` is called on each datum `d`, where `tail?`
 ;; indicates that the value is a pair/null in a `cdr` --- so that it
-;; doesn't need to be wrapped for `datum->syntax`, for example
+;; doesn't need to be wrapped for `datum->syntax`, for example;
+;; the `tail?` argument is actually #f or a fixnum for a lower bound
+;; on `cdr`s that have been taken
 ;;
 ;; `gf` is like `f`, but `gf` is used when the argument might be
 ;; syntax; if `gf` is provided, `f` can assume that its argument
@@ -21,28 +23,32 @@
 ;; hash table, and cycle checking is enabled; when a cycle is
 ;; discovered, the procedure attached to 'cycle-fail in the initial
 ;; table is called
+;;
+;; If a `known-pairs` argument is provided, then it should be an
+;; `eq?`-based hash table to map pairs that can be returned as-is
+;; in a `tail?` position
 
 ;; The inline version uses `f` only in an application position to
 ;; help avoid allocating a closure. It also covers only the most common
 ;; cases, defering to the general (not inlined) function for other cases.
-(define-inline (datum-map s f [gf f] [seen #f])
+(define-inline (datum-map s f [gf f] [seen #f] [known-pairs #f])
   (let loop ([tail? #f] [s s] [prev-depth 0])
     (define depth (fx+ 1 prev-depth)) ; avoid cycle-checking overhead for shallow cases
     (cond
      [(and seen (depth . fx> . 32))
-      (datum-map-slow tail? s  (lambda (tail? s) (gf tail? s)) seen)]
+      (datum-map-slow tail? s  (lambda (tail? s) (gf tail? s)) seen known-pairs)]
      [(null? s) (f tail? s)]
      [(pair? s)
       (f tail? (cons (loop #f (car s) depth)
-                     (loop #t (cdr s) depth)))]
+                     (loop 1 (cdr s) depth)))]
      [(symbol? s) (f #f s)]
      [(boolean? s) (f #f s)]
      [(number? s) (f #f s)]
      [(or (vector? s) (box? s) (prefab-struct-key s) (hash? s))
-      (datum-map-slow tail? s (lambda (tail? s) (gf tail? s)) seen)]
+      (datum-map-slow tail? s (lambda (tail? s) (gf tail? s)) seen known-pairs)]
      [else (gf #f s)])))
 
-(define (datum-map-slow tail? s f seen)
+(define (datum-map-slow tail? s f seen known-pairs)
   (let loop ([tail? tail?] [s s] [prev-seen seen])
     (define seen
       (cond
@@ -55,8 +61,14 @@
     (cond
      [(null? s) (f tail? s)]
      [(pair? s)
-      (f tail? (cons (loop #f (car s) seen)
-                     (loop #t (cdr s) seen)))]
+      (cond
+        [(and known-pairs
+              tail?
+              (hash-ref known-pairs s #f))
+         s]
+        [else
+         (f tail? (cons (loop #f (car s) seen)
+                        (loop (if tail? (fx+ 1 tail?) 1)  (cdr s) seen)))])]
      [(or (symbol? s) (boolean? s) (number? s))
       (f #f s)]
      [(vector? s)
diff --git a/racket/src/expander/syntax/syntax.rkt b/racket/src/expander/syntax/syntax.rkt
index 8610435ff3..b63a6e789f 100644
--- a/racket/src/expander/syntax/syntax.rkt
+++ b/racket/src/expander/syntax/syntax.rkt
@@ -1,5 +1,7 @@
 #lang racket/base
-(require "../compile/serialize-property.rkt"
+(require racket/private/place-local
+         racket/fixnum
+         "../compile/serialize-property.rkt"
          "../compile/serialize-state.rkt"
          "../common/set.rkt"
          "../common/inline.rkt"
@@ -30,7 +32,9 @@
  
  deserialize-syntax
  deserialize-datum->syntax
- current-arm-inspectors)
+ current-arm-inspectors
+
+ syntax-place-init!)
 
 (struct syntax ([content #:mutable] ; datum and nested syntax objects; mutated for lazy propagation
                 scopes  ; scopes that apply at all phases
@@ -186,6 +190,8 @@
 (define (syntax->datum s)
   (syntax-map s (lambda (tail? x) x) (lambda (s d) d) syntax-content))
 
+(define-place-local known-syntax-pairs (make-weak-hasheq))
+
 (define (datum->syntax stx-c s [stx-l #f] [stx-p #f])
   (cond
    [(syntax? s) s]
@@ -212,9 +218,16 @@
                    (weaker-inspector insp (syntax-inspector stx-c)))))
     (define result-s
       (non-syntax-map s
-                      (lambda (tail? x) (if tail? x (wrap x)))
+                      (lambda (tail? x) (cond
+                                          [tail?
+                                           (when (and (fx> tail? 32)
+                                                      (fx= 0 (fxand tail? (fx- tail? 1))))
+                                             (hash-set! known-syntax-pairs x #t))
+                                           x]
+                                          [else (wrap x)]))
                       (lambda (s) s)
-                      disallow-cycles))
+                      disallow-cycles
+                      known-syntax-pairs))
     (if (and stx-p (not (eq? (syntax-props stx-p) empty-props)))
         (struct-copy syntax result-s
                      [props (syntax-props stx-p)])
@@ -248,14 +261,15 @@
 ;;  when a syntax object is found, it is just passed to `s->` --- so there's
 ;;  no `d->s` or `s-e`, since they would not be called
 
-(define-inline (non-syntax-map s f [s-> (lambda (x) x)] [seen #f])
+(define-inline (non-syntax-map s f [s-> (lambda (x) x)] [seen #f] [known-pairs #f])
   (datum-map s
              f
              (lambda (tail? v)
                (cond
                 [(syntax? v) (s-> v)]
                 [else (f tail? v)]))
-             seen))
+             seen
+             known-pairs))
 
 (define disallow-cycles
   (hasheq 'cycle-fail
@@ -264,6 +278,9 @@
                                    "cannot create syntax from cyclic datum"
                                    "datum" s))))
 
+(define (syntax-place-init!)
+  (set! known-syntax-pairs (make-weak-hasheq)))
+
 ;; ----------------------------------------
 
 ;; When serializing syntax objects, let nested objects know the
diff --git a/racket/src/racket/src/startup.inc b/racket/src/racket/src/startup.inc
index b99e967733..d6c081253c 100644
--- a/racket/src/racket/src/startup.inc
+++ b/racket/src/racket/src/startup.inc
@@ -2755,7 +2755,7 @@ static const char *startup_source =
 "(define-values(end-atomic)(lambda()(begin(unsafe-end-atomic))))"
 "(define-values(start-breakable-atomic)(lambda()(begin(unsafe-start-breakable-atomic))))"
 "(define-values(end-breakable-atomic)(lambda()(begin(unsafe-end-breakable-atomic))))"
-"(define-values(cell.1$9)(unsafe-make-place-local #f))"
+"(define-values(cell.1$10)(unsafe-make-place-local #f))"
 "(define-values"
 "(entered-err-string-handler)"
 "(lambda(s_0 n_0)(begin(call-as-nonatomic(lambda()((error-value->string-handler) s_0 n_0))))))"
@@ -2772,7 +2772,7 @@ static const char *startup_source =
 "(if(if(procedure? f_0)(procedure-arity-includes? f_0 0) #f)"
 "(void)"
 "          (let-values () (raise-type-error 'call-as-atomic \"procedure (arity 0)\" f_0)))"
-"(if(eq?(unsafe-place-local-ref cell.1$9)(current-thread))"
+"(if(eq?(unsafe-place-local-ref cell.1$10)(current-thread))"
 "(let-values()"
 "(dynamic-wind"
 "(lambda()"
@@ -2791,7 +2791,7 @@ static const char *startup_source =
 "(call-with-continuation-prompt"
 "(lambda()"
 "(dynamic-wind"
-"(lambda()(begin(start-breakable-atomic)(unsafe-place-local-set! cell.1$9(current-thread))))"
+"(lambda()(begin(start-breakable-atomic)(unsafe-place-local-set! cell.1$10(current-thread))))"
 "(lambda()"
 "(begin"
 "(unsafe-place-local-set! cell.2$5(current-parameterization))"
@@ -2817,7 +2817,7 @@ static const char *startup_source =
 " f_0))))))))"
 "(lambda()"
 "(begin"
-"(unsafe-place-local-set! cell.1$9 #f)"
+"(unsafe-place-local-set! cell.1$10 #f)"
 "(unsafe-place-local-set! cell.2$5 #f)"
 "(unsafe-place-local-set! cell.3$2 #f)"
 "(end-breakable-atomic)))))"
@@ -2831,7 +2831,7 @@ static const char *startup_source =
 "(if(if(procedure? f_0)(procedure-arity-includes? f_0 0) #f)"
 "(void)"
 "          (let-values () (raise-type-error 'call-as-nonatomic \"procedure (arity 0)\" f_0)))"
-"(if(eq?(unsafe-place-local-ref cell.1$9)(current-thread))"
+"(if(eq?(unsafe-place-local-ref cell.1$10)(current-thread))"
 "(void)"
 "          (let-values () (error 'call-as-nonatomic \"not in atomic area for ~e\" f_0)))"
 "(let-values(((paramz_0)(unsafe-place-local-ref cell.2$5))"
@@ -2849,7 +2849,7 @@ static const char *startup_source =
 "(dynamic-wind"
 "(lambda()"
 "(begin"
-"(unsafe-place-local-set! cell.1$9 #f)"
+"(unsafe-place-local-set! cell.1$10 #f)"
 "(unsafe-place-local-set! cell.4$2 0)"
 "(end-breakable-atomic)"
 "((letrec-values(((loop_0)"
@@ -2877,7 +2877,7 @@ static const char *startup_source =
 " loop_0)"
 " extra-depth_0)"
 "(unsafe-place-local-set! cell.4$2 extra-depth_0)"
-"(unsafe-place-local-set! cell.1$9(current-thread)))))))))))))))"
+"(unsafe-place-local-set! cell.1$10(current-thread)))))))))))))))"
 "(define-values(prop:serialize serialize? serialize-ref)(make-struct-type-property 'serialize))"
 "(define-values"
 "(prop:serialize-fill! serialize-fill!? serialize-fill!-ref)"
@@ -2892,7 +2892,7 @@ static const char *startup_source =
 "(define-values"
 "(log-performance?)"
 "  (if (environment-variables-ref (current-environment-variables) #\"PLT_EXPANDER_TIMES\") #t #f))"
-"(define-values(cell.1$8)(unsafe-make-place-local #f))"
+"(define-values(cell.1$9)(unsafe-make-place-local #f))"
 "(define-values(cell.2$4)(unsafe-make-place-local(make-hasheq)))"
 "(define-values(performance-place-init!)(lambda()(begin(unsafe-place-local-set! cell.2$4(make-hasheq)))))"
 "(define-values"
@@ -2945,10 +2945,10 @@ static const char *startup_source =
 "(lambda path_0"
 "(begin"
 "(unsafe-place-local-set!"
-" cell.1$8"
+" cell.1$9"
 "(cons"
 "(region1.1"
-"(if(unsafe-place-local-ref cell.1$8)"
+"(if(unsafe-place-local-ref cell.1$9)"
 "((letrec-values(((loop_0)"
 "(lambda(path_1 enclosing-path_0)"
 "(begin"
@@ -2964,22 +2964,22 @@ static const char *startup_source =
 "(if(pair? enclosing-path_0)(cdr enclosing-path_0) null))))))))"
 " loop_0)"
 " path_0"
-"(region-path(car(unsafe-place-local-ref cell.1$8))))"
+"(region-path(car(unsafe-place-local-ref cell.1$9))))"
 " path_0)"
 "(current-inexact-milliseconds)"
 "(current-memory-use 'cumulative)"
 " 0.0"
 " 0)"
-"(unsafe-place-local-ref cell.1$8))))))"
+"(unsafe-place-local-ref cell.1$9))))))"
 "(define-values"
 "(end-performance-region)"
 "(lambda()"
 "(begin"
 "(let-values(((now_0)(current-inexact-milliseconds)))"
 "(let-values(((now-memory_0)(current-memory-use 'cumulative)))"
-"(let-values(((r_0)(car(unsafe-place-local-ref cell.1$8))))"
+"(let-values(((r_0)(car(unsafe-place-local-ref cell.1$9))))"
 "(let-values((()"
-"(begin(unsafe-place-local-set! cell.1$8(cdr(unsafe-place-local-ref cell.1$8)))(values))))"
+"(begin(unsafe-place-local-set! cell.1$9(cdr(unsafe-place-local-ref cell.1$9)))(values))))"
 "(let-values(((full-delta_0)(- now_0(region-start r_0))))"
 "(let-values(((delta_0)(- full-delta_0(region-as-nested r_0))))"
 "(let-values(((full-delta-memory_0)(- now-memory_0(region-start-memory r_0))))"
@@ -3017,16 +3017,16 @@ static const char *startup_source =
 " loop_0)"
 "(unsafe-place-local-ref cell.2$4)"
 "(region-path r_0))"
-"(if(unsafe-place-local-ref cell.1$8)"
+"(if(unsafe-place-local-ref cell.1$9)"
 "(let-values()"
 "(begin"
 "(set-region-as-nested!"
-"(car(unsafe-place-local-ref cell.1$8))"
-"(+(region-as-nested(car(unsafe-place-local-ref cell.1$8))) full-delta_0))"
+"(car(unsafe-place-local-ref cell.1$9))"
+"(+(region-as-nested(car(unsafe-place-local-ref cell.1$9))) full-delta_0))"
 "(set-region-as-nested-memory!"
-"(car(unsafe-place-local-ref cell.1$8))"
+"(car(unsafe-place-local-ref cell.1$9))"
 "(+"
-"(region-as-nested-memory(car(unsafe-place-local-ref cell.1$8)))"
+"(region-as-nested-memory(car(unsafe-place-local-ref cell.1$9)))"
 " full-delta-memory_0))))"
 "(void))))))))))))))"
 "(call-with-values"
@@ -4784,9 +4784,9 @@ static const char *startup_source =
 "(make-self-module-path-index"
 "(let-values(((name25_0) name_0)((temp26_0)(if enclosing_0(1/module-path-index-resolve enclosing_0) #f)))"
 "(build-module-name16.1 unsafe-undefined name25_0 temp26_0))))))"
-"(define-values(cell.1$7)(unsafe-make-place-local(make-weak-hash)))"
+"(define-values(cell.1$8)(unsafe-make-place-local(make-weak-hash)))"
 "(define-values(generic-module-name) '|expanded module|)"
-"(define-values(module-path-place-init!)(lambda()(begin(unsafe-place-local-set! cell.1$7(make-weak-hash)))))"
+"(define-values(module-path-place-init!)(lambda()(begin(unsafe-place-local-set! cell.1$8(make-weak-hash)))))"
 "(define-values"
 "(make-generic-self-module-path-index)"
 "(lambda(self_0)"
@@ -4796,12 +4796,12 @@ static const char *startup_source =
 "(start-atomic)"
 "(begin0"
 "(let-values(((or-part_0)"
-"(let-values(((e_0)(hash-ref(unsafe-place-local-ref cell.1$7) r_0 #f)))"
+"(let-values(((e_0)(hash-ref(unsafe-place-local-ref cell.1$8) r_0 #f)))"
 "(if e_0(ephemeron-value e_0) #f))))"
 "(if or-part_0"
 " or-part_0"
 "(let-values(((mpi_0)(module-path-index2.1 #f #f r_0 #f)))"
-"(begin(hash-set!(unsafe-place-local-ref cell.1$7) r_0(make-ephemeron r_0 mpi_0)) mpi_0))))"
+"(begin(hash-set!(unsafe-place-local-ref cell.1$8) r_0(make-ephemeron r_0 mpi_0)) mpi_0))))"
 "(end-atomic)))))))"
 "(define-values"
 "(resolved-module-path-to-generic-resolved-module-path)"
@@ -5278,6 +5278,7 @@ static const char *startup_source =
 "(pop-syntax-context!)"
 "(lambda(state_0)"
 "(begin(let-values(((b_0)(serialize-state-syntax-context state_0)))(set-box! b_0(cdr(unbox b_0)))))))"
+" (define-values (not-an-fX.1) (lambda (who_0 v_0) (begin 'not-an-fX (raise-argument-error who_0 \"fixnum?\" v_0))))"
 "(define-values(root-tag)(unsafe-root-continuation-prompt-tag))"
 "(define-values(default-val.1$2) #f)"
 "(define-values"
@@ -5317,10 +5318,9 @@ static const char *startup_source =
 "(if(zero?(vector-length(car rk_2)))(all-fields-immutable?$1(cdr rk_2)) #f)"
 "(all-fields-immutable?$1 rk_2))))))))))))"
 "(define-values(all-fields-immutable?)(lambda(k_0)(begin(prefab-key-all-fields-immutable? k_0))))"
-" (define-values (not-an-fX.1) (lambda (who_0 v_0) (begin 'not-an-fX (raise-argument-error who_0 \"fixnum?\" v_0))))"
 "(define-values"
 "(datum-map-slow)"
-"(lambda(tail?_0 s_0 f_0 seen_0)"
+"(lambda(tail?_0 s_0 f_0 seen_0 known-pairs_0)"
 "(begin"
 "((letrec-values(((loop_0)"
 "(lambda(tail?_1 s_1 prev-seen_0)"
@@ -5337,7 +5337,14 @@ static const char *startup_source =
 "(let-values()(f_0 tail?_1 s_1))"
 "(if(pair? s_1)"
 "(let-values()"
-"(f_0 tail?_1(cons(loop_0 #f(car s_1) seen_1)(loop_0 #t(cdr s_1) seen_1))))"
+"(if(if known-pairs_0(if tail?_1(hash-ref known-pairs_0 s_1 #f) #f) #f)"
+"(let-values() s_1)"
+"(let-values()"
+"(f_0"
+" tail?_1"
+"(cons"
+"(loop_0 #f(car s_1) seen_1)"
+"(loop_0(if tail?_1(fx+ 1 tail?_1) 1)(cdr s_1) seen_1))))))"
 "(if(let-values(((or-part_0)(symbol? s_1)))"
 "(if or-part_0"
 " or-part_0"
@@ -5716,7 +5723,11 @@ static const char *startup_source =
 "                               \"value\""
 " v_1)))"
 " v_1)))))"
-"(let-values(((s_0) v_0)((f_0) check-preserve_0)((gf_0) check-preserve_0)((seen_0) disallow-cycles$1))"
+"(let-values(((s_0) v_0)"
+"((f_0) check-preserve_0)"
+"((gf_0) check-preserve_0)"
+"((seen_0) disallow-cycles$1)"
+"((known-pairs_0) #f))"
 "((letrec-values(((loop_0)"
 "(lambda(tail?_0 s_1 prev-depth_0)"
 "(begin"
@@ -5724,14 +5735,19 @@ static const char *startup_source =
 "(let-values(((depth_0)(fx+ 1 prev-depth_0)))"
 "(if(if seen_0(fx> depth_0 32) #f)"
 "(let-values()"
-"(datum-map-slow tail?_0 s_1(lambda(tail?_1 s_2)(gf_0 tail?_1 s_2)) seen_0))"
+"(datum-map-slow"
+" tail?_0"
+" s_1"
+"(lambda(tail?_1 s_2)(gf_0 tail?_1 s_2))"
+" seen_0"
+" known-pairs_0))"
 "(if(null? s_1)"
 "(let-values()(f_0 tail?_0 s_1))"
 "(if(pair? s_1)"
 "(let-values()"
 "(f_0"
 " tail?_0"
-"(cons(loop_0 #f(car s_1) depth_0)(loop_0 #t(cdr s_1) depth_0))))"
+"(cons(loop_0 #f(car s_1) depth_0)(loop_0 1(cdr s_1) depth_0))))"
 "(if(symbol? s_1)"
 "(let-values()(f_0 #f s_1))"
 "(if(boolean? s_1)"
@@ -5751,7 +5767,8 @@ static const char *startup_source =
 " tail?_0"
 " s_1"
 "(lambda(tail?_1 s_2)(gf_0 tail?_1 s_2))"
-" seen_0))"
+" seen_0"
+" known-pairs_0))"
 "(let-values()(gf_0 #f s_1))))))))))))))"
 " loop_0)"
 " #f"
@@ -5948,7 +5965,7 @@ static const char *startup_source =
 "(let-values((()(begin(ser-push!_0 'tag '#:syntax)(values))))"
 "(let-values(((this-state_0)"
 "(if(no-pair-syntax-in-cdr? content_0)"
-"(syntax-state17.1"
+"(syntax-state18.1"
 " #t"
 " context-triple_0"
 "(syntax-srcloc s_0))"
@@ -6075,7 +6092,8 @@ static const char *startup_source =
 "(if(syntax?$1 v_0)"
 "(let-values()(d->s_0 v_0(loop_0(s-e_0 v_0))))"
 "(let-values()(f_0 tail?_0 v_0))))))"
-"((seen_1) seen_0))"
+"((seen_1) seen_0)"
+"((known-pairs_0) #f))"
 "((letrec-values(((loop_1)"
 "(lambda(tail?_0 s_4 prev-depth_0)"
 "(begin"
@@ -6087,7 +6105,8 @@ static const char *startup_source =
 " tail?_0"
 " s_4"
 "(lambda(tail?_1 s_5)(gf_0 tail?_1 s_5))"
-" seen_1))"
+" seen_1"
+" known-pairs_0))"
 "(if(null? s_4)"
 "(let-values()(f_1 tail?_0 s_4))"
 "(if(pair? s_4)"
@@ -6096,7 +6115,7 @@ static const char *startup_source =
 " tail?_0"
 "(cons"
 "(loop_1 #f(car s_4) depth_0)"
-"(loop_1 #t(cdr s_4) depth_0))))"
+"(loop_1 1(cdr s_4) depth_0))))"
 "(if(symbol? s_4)"
 "(let-values()(f_1 #f s_4))"
 "(if(boolean? s_4)"
@@ -6119,7 +6138,8 @@ static const char *startup_source =
 " tail?_0"
 " s_4"
 "(lambda(tail?_1 s_5)(gf_0 tail?_1 s_5))"
-" seen_1))"
+" seen_1"
+" known-pairs_0))"
 "(let-values()(gf_0 #f s_4))))))))))))))"
 " loop_1)"
 " #f"
@@ -6127,6 +6147,7 @@ static const char *startup_source =
 " 0))))))"
 " loop_0)"
 " s_1)))))"
+"(define-values(cell.1$7)(unsafe-make-place-local(make-weak-hasheq)))"
 "(define-values"
 "(datum->syntax$1)"
 "(let-values(((datum->syntax6_0)"
@@ -6182,9 +6203,27 @@ static const char *startup_source =
 "(let-values(((s_1) s_0)"
 "((f_0)"
 "(lambda(tail?_0 x_0)"
-"(begin 'f(if tail?_0 x_0(wrap_0 x_0)))))"
+"(begin"
+" 'f"
+"(if tail?_0"
+"(let-values()"
+"(begin"
+"(if(if(fx> tail?_0 32)"
+"(fx="
+" 0"
+"(fxand tail?_0(fx- tail?_0 1)))"
+" #f)"
+"(let-values()"
+"(hash-set!"
+"(unsafe-place-local-ref cell.1$7)"
+" x_0"
+" #t))"
+"(void))"
+" x_0))"
+"(let-values()(wrap_0 x_0))))))"
 "((s->_0)(lambda(s_1)(begin 's-> s_1)))"
-"((seen_0) disallow-cycles))"
+"((seen_0) disallow-cycles)"
+"((known-pairs_0)(unsafe-place-local-ref cell.1$7)))"
 "(let-values(((s_2) s_1)"
 "((f_1) f_0)"
 "((gf_0)"
@@ -6194,7 +6233,8 @@ static const char *startup_source =
 "(if(syntax?$1 v_0)"
 "(let-values()(s->_0 v_0))"
 "(let-values()(f_0 tail?_0 v_0))))))"
-"((seen_1) seen_0))"
+"((seen_1) seen_0)"
+"((known-pairs_1) known-pairs_0))"
 "((letrec-values(((loop_0)"
 "(lambda(tail?_0 s_3 prev-depth_0)"
 "(begin"
@@ -6208,7 +6248,8 @@ static const char *startup_source =
 " s_3"
 "(lambda(tail?_1 s_4)"
 "(gf_0 tail?_1 s_4))"
-" seen_1))"
+" seen_1"
+" known-pairs_1))"
 "(if(null? s_3)"
 "(let-values()(f_1 tail?_0 s_3))"
 "(if(pair? s_3)"
@@ -6218,7 +6259,7 @@ static const char *startup_source =
 "(cons"
 "(loop_0 #f(car s_3) depth_0)"
 "(loop_0"
-" #t"
+" 1"
 "(cdr s_3)"
 " depth_0))))"
 "(if(symbol? s_3)"
@@ -6250,7 +6291,8 @@ static const char *startup_source =
 " s_3"
 "(lambda(tail?_1 s_4)"
 "(gf_0 tail?_1 s_4))"
-" seen_1))"
+" seen_1"
+" known-pairs_1))"
 "(let-values()"
 "(gf_0"
 " #f"
@@ -6262,7 +6304,7 @@ static const char *startup_source =
 "(if(if stx-p_0(not(eq?(syntax-props stx-p_0) empty-props)) #f)"
 "(let-values(((the-struct_0) result-s_0))"
 "(if(syntax?$1 the-struct_0)"
-"(let-values(((props19_0)(syntax-props stx-p_0)))"
+"(let-values(((props20_0)(syntax-props stx-p_0)))"
 "(syntax1.1"
 "(syntax-content the-struct_0)"
 "(syntax-scopes the-struct_0)"
@@ -6270,7 +6312,7 @@ static const char *startup_source =
 "(syntax-scope-propagations+tamper the-struct_0)"
 "(syntax-mpi-shifts the-struct_0)"
 "(syntax-srcloc the-struct_0)"
-" props19_0"
+" props20_0"
 "(syntax-inspector the-struct_0)))"
 "                                              (raise-argument-error 'struct-copy \"syntax?\" the-struct_0)))"
 " result-s_0)))))))))))))))"
@@ -6283,9 +6325,10 @@ static const char *startup_source =
 "(hasheq"
 " 'cycle-fail"
 "   (lambda (s_0) (raise-arguments-error 'datum->syntax \"cannot create syntax from cyclic datum\" \"datum\" s_0))))"
+"(define-values(syntax-place-init!)(lambda()(begin(unsafe-place-local-set! cell.1$7(make-weak-hasheq)))))"
 "(define-values"
 "(struct:syntax-state"
-" syntax-state17.1"
+" syntax-state18.1"
 " syntax-state?"
 " syntax-state-all-sharing?"
 " syntax-state-context-triple"
@@ -7807,13 +7850,15 @@ static const char *startup_source =
 "(syntax-props the-struct_0)"
 "(syntax-inspector the-struct_0)))"
 "                                  (raise-argument-error 'struct-copy \"syntax?\" the-struct_0)))))))))"
-"((seen_0) #f))"
+"((seen_0) #f)"
+"((known-pairs_0) #f))"
 "(let-values(((s_1) s_0)"
 "((f_1) f_0)"
 "((gf_0)"
 "(lambda(tail?_0 v_0)"
 "(begin 'gf(if(syntax?$1 v_0)(let-values()(s->_0 v_0))(let-values()(f_0 tail?_0 v_0))))))"
-"((seen_1) seen_0))"
+"((seen_1) seen_0)"
+"((known-pairs_1) known-pairs_0))"
 "((letrec-values(((loop_0)"
 "(lambda(tail?_0 s_2 prev-depth_0)"
 "(begin"
@@ -7821,14 +7866,19 @@ static const char *startup_source =
 "(let-values(((depth_0)(fx+ 1 prev-depth_0)))"
 "(if(if seen_1(fx> depth_0 32) #f)"
 "(let-values()"
-"(datum-map-slow tail?_0 s_2(lambda(tail?_1 s_3)(gf_0 tail?_1 s_3)) seen_1))"
+"(datum-map-slow"
+" tail?_0"
+" s_2"
+"(lambda(tail?_1 s_3)(gf_0 tail?_1 s_3))"
+" seen_1"
+" known-pairs_1))"
 "(if(null? s_2)"
 "(let-values()(f_1 tail?_0 s_2))"
 "(if(pair? s_2)"
 "(let-values()"
 "(f_1"
 " tail?_0"
-"(cons(loop_0 #f(car s_2) depth_0)(loop_0 #t(cdr s_2) depth_0))))"
+"(cons(loop_0 #f(car s_2) depth_0)(loop_0 1(cdr s_2) depth_0))))"
 "(if(symbol? s_2)"
 "(let-values()(f_1 #f s_2))"
 "(if(boolean? s_2)"
@@ -7848,7 +7898,8 @@ static const char *startup_source =
 " tail?_0"
 " s_2"
 "(lambda(tail?_1 s_3)(gf_0 tail?_1 s_3))"
-" seen_1))"
+" seen_1"
+" known-pairs_1))"
 "(let-values()(gf_0 #f s_2))))))))))))))"
 " loop_0)"
 " #f"
@@ -9055,7 +9106,8 @@ static const char *startup_source =
 "(syntax-props the-struct_0)"
 "(syntax-inspector the-struct_0)))"
 "                                                  (raise-argument-error 'struct-copy \"syntax?\" the-struct_0))))))))"
-"((seen_0) #f))"
+"((seen_0) #f)"
+"((known-pairs_0) #f))"
 "(let-values(((s_2) s_1)"
 "((f_1) f_0)"
 "((gf_0)"
@@ -9065,7 +9117,8 @@ static const char *startup_source =
 "(if(syntax?$1 v_0)"
 "(let-values()(s->_0 v_0))"
 "(let-values()(f_0 tail?_0 v_0))))))"
-"((seen_1) seen_0))"
+"((seen_1) seen_0)"
+"((known-pairs_1) known-pairs_0))"
 "((letrec-values(((loop_0)"
 "(lambda(tail?_0 s_3 prev-depth_0)"
 "(begin"
@@ -9077,7 +9130,8 @@ static const char *startup_source =
 " tail?_0"
 " s_3"
 "(lambda(tail?_1 s_4)(gf_0 tail?_1 s_4))"
-" seen_1))"
+" seen_1"
+" known-pairs_1))"
 "(if(null? s_3)"
 "(let-values()(f_1 tail?_0 s_3))"
 "(if(pair? s_3)"
@@ -9086,7 +9140,7 @@ static const char *startup_source =
 " tail?_0"
 "(cons"
 "(loop_0 #f(car s_3) depth_0)"
-"(loop_0 #t(cdr s_3) depth_0))))"
+"(loop_0 1(cdr s_3) depth_0))))"
 "(if(symbol? s_3)"
 "(let-values()(f_1 #f s_3))"
 "(if(boolean? s_3)"
@@ -9107,7 +9161,8 @@ static const char *startup_source =
 " tail?_0"
 " s_3"
 "(lambda(tail?_1 s_4)(gf_0 tail?_1 s_4))"
-" seen_1))"
+" seen_1"
+" known-pairs_1))"
 "(let-values()(gf_0 #f s_3))))))))))))))"
 " loop_0)"
 " #f"
@@ -9431,7 +9486,8 @@ static const char *startup_source =
 "(if(syntax?$1 v_0)"
 "(let-values()(d->s_0 v_0(loop_0(s-e_0 v_0))))"
 "(let-values()(f_0 tail?_0 v_0))))))"
-"((seen_1) seen_0))"
+"((seen_1) seen_0)"
+"((known-pairs_0) #f))"
 "((letrec-values(((loop_1)"
 "(lambda(tail?_0 s_4 prev-depth_0)"
 "(begin"
@@ -9443,7 +9499,8 @@ static const char *startup_source =
 " tail?_0"
 " s_4"
 "(lambda(tail?_1 s_5)(gf_0 tail?_1 s_5))"
-" seen_1))"
+" seen_1"
+" known-pairs_0))"
 "(if(null? s_4)"
 "(let-values()(f_1 tail?_0 s_4))"
 "(if(pair? s_4)"
@@ -9452,7 +9509,7 @@ static const char *startup_source =
 " tail?_0"
 "(cons"
 "(loop_1 #f(car s_4) depth_0)"
-"(loop_1 #t(cdr s_4) depth_0))))"
+"(loop_1 1(cdr s_4) depth_0))))"
 "(if(symbol? s_4)"
 "(let-values()(f_1 #f s_4))"
 "(if(boolean? s_4)"
@@ -9476,7 +9533,8 @@ static const char *startup_source =
 " tail?_0"
 " s_4"
 "(lambda(tail?_1 s_5)(gf_0 tail?_1 s_5))"
-" seen_1))"
+" seen_1"
+" known-pairs_0))"
 "(let-values()(gf_0 #f s_4))))))))))))))"
 " loop_1)"
 " #f"
@@ -10042,7 +10100,8 @@ static const char *startup_source =
 "(if(syntax?$1 v_0)"
 "(let-values()(d->s_0 v_0(loop_0(s-e_0 v_0))))"
 "(let-values()(f_0 tail?_0 v_0))))))"
-"((seen_1) seen_0))"
+"((seen_1) seen_0)"
+"((known-pairs_0) #f))"
 "((letrec-values(((loop_1)"
 "(lambda(tail?_0 s_4 prev-depth_0)"
 "(begin"
@@ -10054,7 +10113,8 @@ static const char *startup_source =
 " tail?_0"
 " s_4"
 "(lambda(tail?_1 s_5)(gf_0 tail?_1 s_5))"
-" seen_1))"
+" seen_1"
+" known-pairs_0))"
 "(if(null? s_4)"
 "(let-values()(f_1 tail?_0 s_4))"
 "(if(pair? s_4)"
@@ -10063,7 +10123,7 @@ static const char *startup_source =
 " tail?_0"
 "(cons"
 "(loop_1 #f(car s_4) depth_0)"
-"(loop_1 #t(cdr s_4) depth_0))))"
+"(loop_1 1(cdr s_4) depth_0))))"
 "(if(symbol? s_4)"
 "(let-values()(f_1 #f s_4))"
 "(if(boolean? s_4)"
@@ -10090,7 +10150,8 @@ static const char *startup_source =
 " s_4"
 "(lambda(tail?_1 s_5)"
 "(gf_0 tail?_1 s_5))"
-" seen_1))"
+" seen_1"
+" known-pairs_0))"
 "(let-values()"
 "(gf_0 #f s_4))))))))))))))"
 " loop_1)"
@@ -10257,7 +10318,8 @@ static const char *startup_source =
 "(if(syntax?$1 v_0)"
 "(let-values()(d->s_0 v_0(loop_0(s-e_0 v_0))))"
 "(let-values()(f_0 tail?_0 v_0))))))"
-"((seen_1) seen_0))"
+"((seen_1) seen_0)"
+"((known-pairs_0) #f))"
 "((letrec-values(((loop_1)"
 "(lambda(tail?_0 s_4 prev-depth_0)"
 "(begin"
@@ -10269,7 +10331,8 @@ static const char *startup_source =
 " tail?_0"
 " s_4"
 "(lambda(tail?_1 s_5)(gf_0 tail?_1 s_5))"
-" seen_1))"
+" seen_1"
+" known-pairs_0))"
 "(if(null? s_4)"
 "(let-values()(f_1 tail?_0 s_4))"
 "(if(pair? s_4)"
@@ -10278,7 +10341,7 @@ static const char *startup_source =
 " tail?_0"
 "(cons"
 "(loop_1 #f(car s_4) depth_0)"
-"(loop_1 #t(cdr s_4) depth_0))))"
+"(loop_1 1(cdr s_4) depth_0))))"
 "(if(symbol? s_4)"
 "(let-values()(f_1 #f s_4))"
 "(if(boolean? s_4)"
@@ -10305,7 +10368,8 @@ static const char *startup_source =
 " s_4"
 "(lambda(tail?_1 s_5)"
 "(gf_0 tail?_1 s_5))"
-" seen_1))"
+" seen_1"
+" known-pairs_0))"
 "(let-values()"
 "(gf_0 #f s_4))))))))))))))"
 " loop_1)"
@@ -16353,7 +16417,8 @@ static const char *startup_source =
 "(begin"
 " 's->"
 "(loop_0 s_2(syntax-taint-mode-property s_2)))))"
-"((seen_0) #f))"
+"((seen_0) #f)"
+"((known-pairs_0) #f))"
 "(let-values(((s_3) s_2)"
 "((f_1) f_0)"
 "((gf_0)"
@@ -16363,7 +16428,8 @@ static const char *startup_source =
 "(if(syntax?$1 v_0)"
 "(let-values()(s->_0 v_0))"
 "(let-values()(f_0 tail?_0 v_0))))))"
-"((seen_1) seen_0))"
+"((seen_1) seen_0)"
+"((known-pairs_1) known-pairs_0))"
 "((letrec-values(((loop_1)"
 "(lambda(tail?_0 s_4 prev-depth_0)"
 "(begin"
@@ -16377,7 +16443,8 @@ static const char *startup_source =
 " s_4"
 "(lambda(tail?_1 s_5)"
 "(gf_0 tail?_1 s_5))"
-" seen_1))"
+" seen_1"
+" known-pairs_1))"
 "(if(null? s_4)"
 "(let-values()(f_1 tail?_0 s_4))"
 "(if(pair? s_4)"
@@ -16387,7 +16454,7 @@ static const char *startup_source =
 "(cons"
 "(loop_1 #f(car s_4) depth_0)"
 "(loop_1"
-" #t"
+" 1"
 "(cdr s_4)"
 " depth_0))))"
 "(if(symbol? s_4)"
@@ -16419,7 +16486,8 @@ static const char *startup_source =
 " s_4"
 "(lambda(tail?_1 s_5)"
 "(gf_0 tail?_1 s_5))"
-" seen_1))"
+" seen_1"
+" known-pairs_1))"
 "(let-values()"
 "(gf_0"
 " #f"
@@ -16465,7 +16533,8 @@ static const char *startup_source =
 "(loop_0"
 " s_2"
 "(syntax-taint-mode-property s_2)))))"
-"((seen_0) #f))"
+"((seen_0) #f)"
+"((known-pairs_0) #f))"
 "(let-values(((s_3) s_2)"
 "((f_1) f_0)"
 "((gf_0)"
@@ -16475,7 +16544,8 @@ static const char *startup_source =
 "(if(syntax?$1 v_0)"
 "(let-values()(s->_0 v_0))"
 "(let-values()(f_0 tail?_0 v_0))))))"
-"((seen_1) seen_0))"
+"((seen_1) seen_0)"
+"((known-pairs_1) known-pairs_0))"
 "((letrec-values(((loop_1)"
 "(lambda(tail?_0 s_4 prev-depth_0)"
 "(begin"
@@ -16489,7 +16559,8 @@ static const char *startup_source =
 " s_4"
 "(lambda(tail?_1 s_5)"
 "(gf_0 tail?_1 s_5))"
-" seen_1))"
+" seen_1"
+" known-pairs_1))"
 "(if(null? s_4)"
 "(let-values()"
 "(f_1 tail?_0 s_4))"
@@ -16503,7 +16574,7 @@ static const char *startup_source =
 "(car s_4)"
 " depth_0)"
 "(loop_1"
-" #t"
+" 1"
 "(cdr s_4)"
 " depth_0))))"
 "(if(symbol? s_4)"
@@ -16541,7 +16612,8 @@ static const char *startup_source =
 "(gf_0"
 " tail?_1"
 " s_5))"
-" seen_1))"
+" seen_1"
+" known-pairs_1))"
 "(let-values()"
 "(gf_0"
 " #f"
@@ -83784,6 +83856,7 @@ static const char *startup_source =
 "(lambda()"
 "(begin"
 "(begin"
+"(syntax-place-init!)"
 "(scope-place-init!)"
 "(cache-place-init!)"
 "(core-place-init!)"