cs: fix schemify bug with imported mutated variable

Closes racket#3998

Author: mflatt

pkgs/racket-test-core/tests/racket/optimize.rktl

@@ -7147,6 +7147,25 @@
 
 (test '(1 2) dynamic-require ''check-inline-of-set!-expression 'result)
 
+;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; Regression test for schemify cross-module inlining
+
+(module modifies-its-exported-variable racket/base
+  (provide (all-defined-out))
+  (define X '())
+  (define (change-X!)
+    (set! X (cons 'shouldnt-be X))))
+
+(module uses-imported-variable-before-modify racket/base
+  (require 'modifies-its-exported-variable)
+  (provide old-X)
+  (define old-X
+    (let ([copy-of-X X])
+      (change-X!)
+      copy-of-X)))
+
+(test '() dynamic-require ''uses-imported-variable-before-modify 'old-X)
+
 ;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
 (report-errs)

racket/src/cs/schemified/schemify.scm

@@ -14242,7 +14242,9 @@
                                        c2_0)))
                                  (if defn8_0
                                    a-known-constant
-                                   (known-copy rhs_0))))))))
+                                   (if (hash-ref imports12_0 u-rhs_0 #f)
+                                     a-known-constant
+                                     (known-copy rhs_0)))))))))
                      (if (parameter-result?
                           rhs_0
                           prim-knowns11_0

racket/src/schemify/infer-known.rkt

@@ -80,6 +80,9 @@
                   (known-copy rhs)]
                  [else known]))]
          [defn a-known-constant]
+         [(hash-ref imports u-rhs #f)
+          ;; imported, but nothing known about it => could be mutable
+          a-known-constant]
          [else (known-copy rhs)])]
       [(parameter-result? rhs prim-knowns knowns mutated)
        (known-procedure 3)]