Re: CPS Update

[William ML Leslie]

On 23 February 2013 18:49, Mark H Weaver <address@hidden> wrote:
> William ML Leslie <address@hidden> writes:
>> Recompiling every procedure that uses + when somebody binds it means
>> compiling a lot of code that probably isn't going to be used.  More
>> likely, if + has been inlined here, the compiler will have to emit a
>> guard that checks inlining assumptions as the start of the let body.
>
> I'm afraid this isn't good enough.  Even if one ignores the possibility
> of multiple threads, checks would have to be added not just at the start
> of each let body, but also upon return from every procedure that might
> rebind '+' or capture its continuation.  This includes all procedures
> accessed through toplevel/module bindings.

Not each let body, the let body in the example code.  Specifically, a
guard needs to be placed whenever code with undetermined effect
happens-before a 'call' to an inlined function.  That we are talking
about happens-before means the possibility of runtime invalidation of
code is limited not only by calls to functions of unknown effect, but
also by usages of the variable.

> Therefore, I repeat my initial assertion that this is a can of worms.

Except that most dynamic compilers for imperative languages already do
this (because it's a pretty common thing to need to do).

--
William Leslie