Subject: bug#21899: closed (Re: bug#21899: let/ec continuations not distinct under compiler)

From: [email-masked] (GNU bug Tracking System)
Date: Fri, 24 Jun 2016 17:14:02 +0000

Your bug report

#21899: let/ec continuations not distinct under compiler

which was filed against the guile package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to [email-masked].

-- 
21899: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=21899
GNU Bug Tracking System
Contact [email-masked] with problems

Subject: Re: bug#21899: let/ec continuations not distinct under compiler
From: Andy Wingo <[email-masked]>
To: Zefram <[email-masked]>
Cc: [email-masked]
Date: Fri, 24 Jun 2016 19:13:01 +0200
List-Id: <debbugs-submit.debbugs.gnu.org>

On Fri 24 Jun 2016 19:00, Zefram <[email-masked]> writes:

> Andy Wingo wrote:
>>  ,opt (let* ((x (list 'a))
>>              (y (list 'a)))
>>         (list x y))
>>  ;; ->
>>  (let* ((x (list 'a)) (y x)) (list x y))
>
> Wow, that's a scary level of wrongitude.

Indeed :/

Fixed in git with this patch:

>From ea352d9e54793783a8272863748ea6d31b3f7295 Mon Sep 17 00:00:00 2001
From: Andy Wingo <[email-masked]>
Date: Fri, 24 Jun 2016 19:03:36 +0200
Subject: [PATCH] Fix bug that exposed `list' invocations to CSE

* module/language/tree-il/effects.scm (make-effects-analyzer):
  Fix analysis for list, cons, make-prompt-tage, and vector; &allocation
  is a `cause' effect.  Fixes #21899.
* test-suite/tests/cse.test ("cse"): Add test case.
---
 module/language/tree-il/effects.scm | 8 ++++----
 test-suite/tests/cse.test           | 9 +++++++++
 2 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/module/language/tree-il/effects.scm b/module/language/tree-il/effects.scm
index 1fe4aeb..6db4d47 100644
--- a/module/language/tree-il/effects.scm
+++ b/module/language/tree-il/effects.scm
@@ -278,16 +278,16 @@ of an expression."
           ;; Primitives that allocate memory.
           (($ <application> _ ($ <primitive-ref> _ 'cons) (x y))
            (logior (compute-effects x) (compute-effects y)
-                   &allocation))
+                   (cause &allocation)))
 
           (($ <application> _ ($ <primitive-ref> _ (or 'list 'vector)) args)
-           (logior (accumulate-effects args) &allocation))
+           (logior (accumulate-effects args) (cause &allocation)))
 
           (($ <application> _ ($ <primitive-ref> _ 'make-prompt-tag) ())
-           &allocation)
+           (cause &allocation))
 
           (($ <application> _ ($ <primitive-ref> _ 'make-prompt-tag) (arg))
-           (logior (compute-effects arg) &allocation))
+           (logior (compute-effects arg) (cause &allocation)))
 
           ;; Primitives that are normally effect-free, but which might
           ;; cause type checks, allocate memory, or access mutable
diff --git a/test-suite/tests/cse.test b/test-suite/tests/cse.test
index e0219e8..ca7dbc2 100644
--- a/test-suite/tests/cse.test
+++ b/test-suite/tests/cse.test
@@ -294,6 +294,15 @@
      (apply (primitive cons) (const 1) (const 2) (const 3))
      (const 4)))
 
+  ;; The (list 'a) does not propagate.
+  (pass-if-cse
+   (let* ((x (list 'a))
+          (y (list 'a)))
+     (list x y))
+   (let (x) (_) ((apply (primitive list) (const a)))
+        (let (y) (_) ((apply (primitive list) (const a)))
+             (apply (primitive list) (lexical x _) (lexical y _)))))
+
   (pass-if "http://bugs.gnu.org/12883"
     ;; In 2.0.6, compiling this code would trigger an out-of-bounds
     ;; vlist access in CSE's traversal of its "database".
-- 
2.8.3

Subject: let/ec continuations not distinct under compiler
From: Zefram <[email-masked]>
To: [email-masked]
Date: Fri, 13 Nov 2015 07:57:36 +0000
List-Id: <debbugs-submit.debbugs.gnu.org>

With guile 2.0.11:

scheme@(guile-user)> (use-modules (ice-9 control))
scheme@(guile-user)> (list 'a (let/ec ae (list 'b (let/ec be (be 2)))))
$1 = (a (b 2))
scheme@(guile-user)> (list 'a (let/ec ae (list 'b (let/ec be (ae 2)))))
$2 = (a (b 2))
scheme@(guile-user)> (list 'a (let/ec ae (list 'b (ae 2))))
$3 = (a 2)

The middle of these three cases is wrong: it attempts to invoke the outer
escape continuation, but only goes as far as the target of the inner one,
which it isn't using.  It therefore produces the same result as the first
case, which invokes the inner escape continuation.  It ought to behave
like the third case, which shows that the outer escape continuation can
be successfully invoked when the unused inner continuation is not present.

The problem only affects let/ec, *not* call/ec:

scheme@(guile-user)> (list 'a (call/ec (lambda (ae) (list 'b (call/ec (lambda (be) (be 2)))))))
$4 = (a (b 2))
scheme@(guile-user)> (list 'a (call/ec (lambda (ae) (list 'b (call/ec (lambda (be) (ae 2)))))))
$5 = (a 2)
scheme@(guile-user)> (list 'a (call/ec (lambda (ae) (list 'b (ae 2)))))
$6 = (a 2)

It also only happens when compiling, not when interpreting:

scheme@(guile-user)> ,o interp #t
scheme@(guile-user)> (list 'a (let/ec ae (list 'b (let/ec be (be 2)))))
$7 = (a (b 2))
scheme@(guile-user)> (list 'a (let/ec ae (list 'b (let/ec be (ae 2)))))
$8 = (a 2)
scheme@(guile-user)> (list 'a (let/ec ae (list 'b (ae 2))))
$9 = (a 2)

-zefram