fix propagation of "multiple result" flag when optimizing `begin0'

collects/tests/racket/optimize.rktl

@@ -2450,6 +2450,17 @@
                               [read-accept-compiled #t])
                  (eval (read (open-input-bytes (get-output-bytes o2)))))
                exn:fail:read?))
+
+;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; make sure `begin0' propertly propagates "multiple results" flags
+
+(test '(1 2 3) (lambda ()
+                 (call-with-values
+                     (lambda () (begin0
+                                 (values 1 2 3)
+                                 (newline)))
+                   list)))
+
   
 ;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 

src/racket/src/optimize.c

@@ -3318,7 +3318,7 @@ case_lambda_shift(Scheme_Object *data, int delta, int after_depth)
 static Scheme_Object *
 begin0_optimize(Scheme_Object *obj, Optimize_Info *info, int context)
 {
-  int i, count, drop = 0, prev_size;
+  int i, count, drop = 0, prev_size, single_result = 0;
   Scheme_Sequence *s = (Scheme_Sequence *)obj;
   Scheme_Object *le;
 
@@ -3333,6 +3333,9 @@ begin0_optimize(Scheme_Object *obj, Optimize_Info *info, int context)
                                ? scheme_optimize_result_context(context)
                                : 0));
 
+    if (!i)
+      single_result = info->single_result;
+
     /* Inlining and constant propagation can expose
        omittable expressions. */
     if (i && scheme_omittable_expr(le, -1, -1, 0, info, NULL, -1, 0)) {
@@ -3367,8 +3370,8 @@ begin0_optimize(Scheme_Object *obj, Optimize_Info *info, int context)
     obj = (Scheme_Object *)s2;
   }
 
-  /* Optimization of expression 0 has already set single_result */
   info->preserves_marks = 1;
+  info->single_result = single_result;
 
   info->size += 1;