Re: [Sbcl-devel] [Sbcl-help] Function redefinition type error

[Nikodemus S. <nik...@ra...>]

On 21 March 2015 at 11:18, Nikodemus Siivola <nik...@ra...> wrote:
> ...while this *is* allowed, I'm pretty sure this is a regression as well.

Hah. Amusingly it looks like this is my handiwork. How time flies.

commit 12836ca105af62252aa0974c3f6992e60ce0ebf4
Author: Nikodemus Siivola <nik...@ra...>
Date:   Thu Oct 14 16:32:51 2010 +0000

    1.0.43.57: better handling of derived function types

     Fixes bug 657499, and improves the earlier fix of 655126.

     * Sort out TYPE vs. DEFINED-TYPE in FIND-GLOBAL-FUN:

      ** TYPE is the declarared type, OR the derived type iff
         *derive-function-types* is true, no ftype has been declared,
         we're not explicitly late-binding, and the function is not
         NOTINLINE.

      ** DEFINED-TYPE is the derived type, or FUNCTION if the function has
         been declared NOTINLINE or we're late-binding.

         Previously TYPE (which is what the rest of the system trusts
         implcitly) was the derived type for functions in the same file
         not declared NOTINLINE.

     * ASSERT-CALL-TYPE can now be used in "untrusted" cases as well:
       argument types are asserted as before, but instead of using
       DERIVE-NODE-TYPE to annotate the function LVAR with its type, we
       instead assert the return-type when appropriate.

     * VALIDATE-CALL-TYPE is now called with DEFINED-TYPE from
       IR1-OPTIMIZE-COMBINATION, not
       IR1-CONVERT-COMBINATION-CHECKING-TYPE: the DEFINED-TYPE may be used
       there in an untrusted call to ASSERT-CALL-TYPE.

       Also keep track of the leaves whose DEFINED-TYPE we have asserted,
       so that we won't do duplicate work. New slot in COMBINATION:
       TYPE-VALIDATED-FOR-LEAF is utilized for this.

     * LEAF-WHERE-FROM can now also be :DEFINED-HERE, meaning the
       definition originates in the file being compiled -- this
       information is used by VALIDATE-CALL-TYPE, and filled in by
       FIND-FREE-FUN and FIND-GLOBAL-FUN.

     * Adjust the tests for 655126 to account for full warnings
       in case *derive-function-types* and self-calls.

I didn't test if this is the commit that actually causes this to
happen, or if this is a later interaction with the above change -- but
this does look like a likely culprit.

I'd (I'll?) need to check that and think this more completely through
(including checking the bugs referenced above) before venturing a
further opinion.

...but on quick reflection I suspect my memory is just shot and this
is legit -- but at the same time from where I stand today, I would
turn down the default type propagation here a bit, and make stuff like
this require SPEED 2 or something, or maybe apply some selective
type-widening here: asserting something to be a singleton type without
an inlining or anything seems a bit rich.

...and we since we should be able to know that some other function in
the same compilation unit relies on the return type and this is an
incompatible redefinition, we should probably signal a full WARNING at
least for the redefinition. (Yeah, hair there in getting things
right.)

Cheers,

  -- nikodemus