peval: Recognize module-refs to primitives.

* module/language/tree-il/optimize.scm (peval): Handle module-refs to
  primitives.

* test-suite/tests/tree-il.test ("partial evaluation"): Add test, using
  `pmatch'.

module/language/tree-il/peval.scm

@@ -708,6 +708,15 @@ it does not handle <fix> and <let-values>, it should be called before
       (($ <toplevel-ref>)
        ;; todo: open private local bindings.
        exp)
+      (($ <module-ref> src module (? effect-free-primitive? name) #f)
+       (let ((module (false-if-exception
+                      (resolve-module module #:ensure #f))))
+         (if (module? module)
+             (let ((var (module-variable module name)))
+               (if (eq? var (module-variable the-scm-module name))
+                   (make-primitive-ref src name)
+                   exp))
+             exp)))
       (($ <module-ref>)
        exp)
       (($ <module-set> src mod name public? exp)

test-suite/tests/tree-il.test

@@ -761,6 +761,19 @@
          (loop (cdr l) (+ sum (car l)))))
    (const 10))
 
+  (pass-if-peval
+    ;; Primitives in module-refs are resolved (the expansion of `pmatch'
+    ;; below leads to calls to (@@ (system base pmatch) car) and
+    ;; similar, which is what we want to be inlined.)
+    (begin
+      (use-modules (system base pmatch))
+      (pmatch '(a b c d)
+        ((a b . _)
+         #t)))
+    (begin
+      (apply . _)
+      (const #t)))
+
   (pass-if-peval
    ;; Mutability preserved.
    ((lambda (x y z) (list x y z)) 1 2 3)