remove unnecessary Box when an argument is used before assigned (Juli…

…aLang#36245)

src/ast.scm

@@ -288,7 +288,7 @@
  (symbol? (cadr e))))
 
 (define (lam:args x) (cadr x))
-(define (lam:vars x) (llist-vars (lam:args x)))
+(define (lam:argnames x) (llist-vars (lam:args x)))
 (define (lam:vinfo x) (caddr x))
 (define (lam:body x) (cadddr x))
 (define (lam:sp x) (cadddr (lam:vinfo x)))

src/julia-syntax.scm

@@ -2556,7 +2556,7 @@
  (and (memq var (scope:locals scope)) 'local)
  (and (memq var (scope:globals scope))
  (if (and exclude-top-level-globals
- (null? (lam:vars (scope:lam scope)))
+ (null? (lam:args (scope:lam scope)))
  ;; don't inherit global decls from the outermost scope block
  ;; in a top-level expression.
  (or (not (scope:prev scope))
@@ -2636,13 +2636,13 @@
  '(false)
  '(true)))
  ((eq? (car e) 'lambda)
- (let* ((args (lam:vars e))
+ (let* ((args (lam:argnames e))
  (body (resolve-scopes- (lam:body e) (make-scope e args '() '() sp '() scope))))
  `(lambda ,(cadr e) ,(caddr e) ,body)))
  ((eq? (car e) 'scope-block)
  (let* ((blok (cadr e)) ;; body of scope-block expression
  (lam (scope:lam scope))
- (argnames (lam:vars lam))
+ (argnames (lam:argnames lam))
  (toplevel? (and (null? argnames) (eq? e (lam:body lam))))
  (current-locals (caddr lam)) ;; locals created so far in our lambda
  (globals (find-global-decls blok))
@@ -2755,7 +2755,7 @@
  ,(resolve-scopes- (cadddr e) scope (method-expr-static-parameters e))))
  (else
  (if (and (eq? (car e) '=) (symbol? (cadr e))
- scope (null? (lam:vars (scope:lam scope)))
+ scope (null? (lam:args (scope:lam scope)))
  (warn-var?! (cadr e) scope)
  (= *scopewarn-opt* 1))
  (let* ((v (cadr e))
@@ -2782,7 +2782,7 @@
 
 ;; names of arguments and local vars
 (define (lambda-all-vars e)
- (append (lam:vars e) (caddr e)))
+ (append (lam:argnames e) (caddr e)))
 
 ;; compute set of variables referenced in a lambda but not bound by it
 (define (free-vars- e tab)
@@ -3201,6 +3201,7 @@ f(x) = yt(x)
  ;; This does a basic-block-local dominance analysis to find variables that
  ;; are never used undef.
  (let ((vi (car (lam:vinfo lam)))
+ (args (lam:argnames lam))
  (unused (table)) ;; variables not (yet) used (read from) in the current block
  (live (table)) ;; variables that have been set in the current block
  (seen (table))) ;; all variables we've seen assignments to
@@ -3221,6 +3222,11 @@ f(x) = yt(x)
  (restore (table)))
  (define (mark-used var)
  ;; remove variable from the unused table
+ ;; Note arguments are only "used" for purposes of this analysis when
+ ;; they are captured, since they are never undefined.
+ (if (and (has? unused var) (not (memq var args)))
+ (del! unused var)))
+ (define (mark-captured var)
  (if (has? unused var)
  (del! unused var)))
  (define (assign! var)
@@ -3272,7 +3278,7 @@ f(x) = yt(x)
  (get-methods e (lam:body lam))
  (list e))))
  (for-each (lambda (ex)
- (for-each mark-used
+ (for-each mark-captured
  (map car (cadr (lam:vinfo (cadddr ex))))))
  all-methods)
  (assign! (cadr e))))

test/core.jl

@@ -5178,6 +5178,12 @@ end
 @test let_Box5()() == 46
 @test let_noBox()() == 21
 
+function _assigns_and_captures_arg(a)
+ a = a
+ return ()->a
+end
+@test !any(contains_Box, code_lowered(_assigns_and_captures_arg,(Any,))[1].code)
+
 module TestModuleAssignment
 using Test
 @eval $(GlobalRef(TestModuleAssignment, :x)) = 1