fix optimizer imprecision for values

Without this repair,

 #lang racket/base
 (require 2htdp/abstraction)
 (for/list ((dropping-which-one (in-naturals)))
   1)

fails to compile with a "optimizer clock tracking has gone wrong"
error. A variant of this test (that doesn't depend on `2htdp`)
is now in the "optimize.rktl"; a simpler and more direct test
should be possible, but I wasn't able to construct one.

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

@@ -6390,6 +6390,37 @@
         (set! f f)
         ((car f))))
 
+;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; Regression test to check that `values` is
+;; handled correctly for estimating clock advances
+
+(module triggers-optimizer-clock-estimation racket/base
+  (require (for-syntax racket/base))
+  
+  (define (in-naturals0 n)
+    (in-naturals n))
+  
+  ;; restrict for/xyz to simple form and name it for/xyz0
+  (define-syntax (define-for stx)
+    (syntax-case stx ()
+      [(_ for/xyz0 for/xyz cleanup)
+       #'(define-syntax (for/xyz0 stx)
+           (syntax-case stx ()
+             [(_ ((clause0.x clause0.range)) body)
+              #`(cleanup
+                 (for/xyz ((clause0.x (string> clause0.range)))
+                          ;; the following line exists only so that coverage doesn't hilite x0 x ...
+                          clause0.x
+                          body))]))]))
+  
+  (define-for for/list0 for/list values)
+  
+  (define (string> s)
+    (if (string? s) (string->list s) s))
+  
+  (void
+   (for/list0 ((dropping-which-one (in-naturals0))) 1)))
+
 ;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
 (report-errs)

racket/src/racket/src/optimize.c

@@ -2815,6 +2815,8 @@ static int is_noncapturing_primitive(Scheme_Object *rator, int n)
     t = (((Scheme_Primitive_Proc *)rator)->pp.flags & SCHEME_PRIM_OTHER_TYPE_MASK);
     if (!n && (t == SCHEME_PRIM_TYPE_PARAMETER))
       return 1;
+    if (SAME_TYPE(rator, scheme_values_proc))
+      return 1;
   }
   
   return 0;
@@ -2827,6 +2829,8 @@ static int is_nonsaving_primitive(Scheme_Object *rator, int n)
     opt = ((Scheme_Prim_Proc_Header *)rator)->flags & SCHEME_PRIM_OPT_MASK;
     if (opt >= SCHEME_PRIM_OPT_IMMEDIATE)
       return 1;
+    if (SAME_TYPE(rator, scheme_values_proc))
+      return 1;
   }
 
   return 0;
@@ -6893,7 +6897,7 @@ void advance_clocks_for_optimized(Scheme_Object *o,
                                   Optimize_Info *info,
                                   int fuel)
 /* It's ok for this function to advance clocks *less* than
-   acurrately, but not more than acurrately */
+   accurately, but not more than accurately */
 {
   Scheme_Object *rator = NULL;
   int argc = 0;